Tuesday, February 27, 2007

AV - Manually starting the VW Engine





> > Please explain to me the adjustments/mods to be made to my 2.0l Type 4
> stock distributor to facilitate easy hand propping. The engine will
> drive from the flywheel end.
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There are four key factors involved here. (Although I may add more later :-)

1. Engine Assembly
2. Ignition Timing
3. Propeller Orientation
4. Type of Ignition System

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1. Engine Assembly

There are two areas of critical concern, the first is cam selection, the second is accurate assembly of the engine, especially with regard to your valve train geometry.

With regard to the cam, most VW engine converted for flight are hot-rod engines -- something you'd expect to find in a dune-buggy rather than an airplane. And as a dune-buggy engine, they are fitted with dune-buggy cams, meaning the torque band has been shifted toward the upper end of the rpm range. This is accomplished by grinding a lot of overlap into the cam and extending the duration, two features never found in a direct-drive aircraft engine. What you want is the stock cam, which happens to have a torque band suitable for slinging a propeller of useful diameter. (There are a few other cams that are suitable. They were used in VW's industrial engines or in VW's converted to serve as orchard blowers.)

With regard to engine assmebly, there's no way I can cover the subject via email. I'm working on a manual that does the job fairly well but it's already over 200 pages in length and I've only just gotten to the heads :-) But as a general rule, you need to ensure that your cam is correctly indexed to the crankshaft. Simply lining up the dots is only an assembly-line approximation, usually accurate to withing +/- 2 degrees or so. You not only want it dead-on, for a low rpm, high-torque engine you generally want to retard the stock setting by 4 degrees. This task is typically referred to as 'dialing in the cam' and requires the ability to rotate the camshaft very slightly relative to the cam gear when the cam gear is locked in place and the engine is precisely at TDC. (How do you manage that? You reach in through the opening provided for the oil pump.)

I covered this procedure in some detail for the Type I engine in an illustrated article that appeared in VW Trends magazine a couple of years ago but the basic procedure will be found in any tome covering professionally built high-output engines.

Once the lower-end is dialed in you focus on accurate valve-train geometry, which is a fancy way to say you ensure minimum lost motion in transferring the movement of the cam to the depression of the valve. This matter is worthy of your attention because it's not uncommon to see loses as great as 25% in this area. (That is, an anticipated 10mm of movement at the valve reduced to as little as 7.5mm due to improper assembly of the valve train components.) The point most fail to appreciate here is that faulty valve train geometry effectively alters the engine's mechanical timing. It isn't uncommon to see a casually assembled stock engine give away as much as 15% of its normal output. (Indeed, it is more the rule than the exception.)

The key point here is that an improperly assembled engine can effect your valve timing, and improper valve timing can make an engine very difficult to hand-prop.

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2. Ignition Timing

Don't waste your time here unless you've already confirmed that the engine is properly assembled, because for every degree you're off relative to the crankshaft/camshaft combination, you'll be off by 2 degrees in your ignition timing.

But assuming a properly assembled engine, to ensure easy starting you want to set your static timing somewhere between three and five degrees BEFORE top-dead-center. The closer to TDC, the easier the thing will start... but the farther the timing will need to advance when you open the throttle.

This assumes you are using an ignition system which allows the firing point to advance as the rpm increases (ie, a centrifugal- advance mechanism). You'll not find this in a magneto and only half of it in a stock, late-model Bosch distributor (ie, the 'composite type,' having both vacuum- and centrifugal-advance). The Bosch -009 distributor will serve but you should know that it was never installed on any VW vehicle. It is in fact a generic after-market replacement for the dozen or so centrifugal distributors used on the early Transporter, and for at least that number that were found on VW industrial engines. But it is beloved of dune-buggy types because it is inexpensive and can be adjusted to give as much as 30 degrees of advance. (Typical is 17 to 19 degrees.)

You will want at least 28 degrees total ignition advance, assuming you want to spin your prop at least 2700 rpm. To increase the advance range you simply fiddle with the stops on the advance plate and bob-weights -- a good mechanic can show you how. But proceed with caution. If you file away a tad too much metal you'll find it hard to replace :-) (To increase the advance rate you reduce the mass of the bob-weights and use springs of lighter tension. But that's only needed on dune-buggies, dragsters and the like.)

I hope you can see the quandry here: To make the engine easy to start the static firing point must be near (or even slightly AFTER) top-dead-center. But for the engine to run fast enough to be useful, the firing point must be advanced to about 28 crankshaft degrees BEFORE top-dead-center. If your distributor can only provide twenty degrees of advance (fairly common for a -009 straight out of the box) then your static firing point will have to be at 8 degrees BTDC, which will make the engine slightly hard to hand-prop. Move the static firing point nearer TDC and you automatically limit your peak rpm. (Need I mention proper engine assembly again? I hope not. But just in case... understanding that the relationship between ignition timing and rpm should offer a hint as to why many sloppily assembled engines never live up to their potential.)

Luckily for me I won't have to figure it out since you are the Mechanic-in-Charge :-)

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3. Propeller Orientation

You've probably never owned a Model-T Ford but if you had, you would know that there was a certain feel -- a kind of 'springiness' -- in the crank as the piston approached TDC. You would feel for that (with the ignition off) as you charged the cylinders. Then with the ignition ON (and SPARK set to fully retarded), you'd flip the crank past the springy point and the engine would clatter into life. (The Model T's cam didn't have any overlap at all, limiting its maximum rpm to about 1800... and making it superbly easy to start.)

The T4 engine isn't a Model-T but when it comes to manually starting, your prop is still a crank.

With the prop mounted on the clutch end of the crankshaft it's going to rotate clockwise relative to the pilot (Volksplane assumed). That means you want TDC to occur at about 9 o'clock when you're standing in front of the plane facing the prop. The firing point is going to be a few degrees up from the 9 o'clock position, allowing you a 'swing' of nearly 90 degrees. That is, with the cylinders charged you'll bring your 'signature' blade to about the 12 o'clock position then turn on the ignition, then put your hand flat on the blade out near the tip (do not allow your fingers to curl around the edge of the blade) and flip it down toward the 9 o'clock position -- using a motion that carrys your hand and arm out and away from the arc of the propeller.

(All of which assumes you've got the tail-wheel chained to a fence- post and the slack pulled out... 'cause if you don't, it'll chase you :-)

So why 'Prop Orientation'? Because you need to know when a cylinder is coming up on TDC. And you need to know that relative to the blades of the prop.

VW engine fires once every 180 degrees. If you have a two-bladed prop you'd think it doesn't much matter how the thing is bolted on but it turns out, you do, and aligning one blade to #1 cyl is generally best. (Of course, that means the same blade is also aligned to #3 but I'll get to that in a minute.)

With a four-cylinder, horizontally opposed engine what you don't want is to have your signature cylinder in the same sequence on the same bank.

Clear as mud, right?

Go look at the VW's firing sequence: 1 - 4 - 3 - 2.

(Ed.Note: Cylinders 1 & 2 share the right-hand bank when facing the pulley-hub; cylinders 3 & 4 on on the left-hand bank.)

That means you don't want to have it fire on #2. Nor on #4. Because the next cylinder will be on the same bank... and the odds are, that cylinder won't have a full charge... because you just fired it's paired cylinder. What you do want is for the thing to initially fire on #1. Or #3. Because the next cylinder will be on the opposite bank. And -- trust me here -- the odds of the engine starting and continuing to run are about 100% better when the second cylinder to fire is on the opposite bank.

So mark one of your blades; the one that is going to fire on #1. Or on #3.

Now, you may have a problem with the 'clock'-related alignment if your prop-hub is drilled so a pair of holes aligns with the throws of the crankshaft. Because if you look at your prop, the usual arrangement is to have one of the prop's bolting holes aligned with the center of the blade. In theory, this should work okay -- and a lot of props are installed that way. (If your holes are so aligned, go aheady and try it.) But with a wooden prop you'll generally find the VW runs smoothest when the prop is not aligned with the crankshaft throws. And that presents something of a problem because you've only got six holes -- only three orientations -- to play with and only one of them is good for hand-propping... and it seems to have nodal points. (This is for the Type I engine. I don't think the T4 engine is any different.)

One solution is to use a prop extension in which the bolting holes are offset by thirty degrees. This gives you a bit more latitude. Or your prop, pitch, engine mount and crankshaft may present an entirely different torsional system than the T1 engine, which is what most of my experience is based upon.

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4. Type of Ignition System (Finally!)

Hand-propped, even with an impulse coupling, a magneto puts out a weak spark. That means you'll need to use a narrow spark plug gap and a modest compression ratio, typically 7.5:1 or less, and those things can combine to make the engine notoriously hard to hand-prop. Not when everything is new and fresh but after it accumulates a few hours. Your plug-gap widens in use, as does the distributor air-gap, and the compression ratio falls as the engine accumulates wear.

At starting-speeds the stock Kittering-type ignition system (ie, as found in most vehicles up to about the 1995 model year) is vastly superior to a magneto. That's because the Kettering system delivers its maximum spark energy at the lowest engine speed. Makes things easy to start. But once its running, the spark energy drops steadily as the rpm increases, thanks to the declining amount of time the coil has to build up its 'charge.' (It isn't really a charge, it's just a magnetic field. But it's output is proportional to its strength and its strength is proportional to the amount of time so while it isn't electrically correct to say 'charge' it generally gets the idea across.)

A lot of folks -- especially the ones trying to sell you stuff -- will tell you that replacing the points with a transistor will give you a hotter spark. It won't. You've still got a Kettering ignition system and the output is still a function of the coil's current over time. But such systems do have a better wear factor and tend to give you a better spark because of it. That is, in the stock system your spark energy will decline as the points accumulate wear. Eliminate the points, you eliminate the wear, allowing you to enjoy maximum spark-energy the system can produce for a longer period of time.

Most modern-day ignition systems are some form of the Kettering System. The only ones that are truly different are Capacitance Discharge Systems, in which the points (or other trigger) discharge a capacitor through the coil. The advantage here is that the capacitor is charged with an invertor that may operate at voltages as high as 400, allowing it to re-charge the capacitor rapidly enough to allow the system to provide as much as 40,000 volts of spark energy up to speeds as great as 12,000 rpm.

Most of which is as useless as tits on a boar when it comes to flying Volkswagens :-)

But the bottom line is that that higher spark energy ensures more reliable starting. So if you're running points, replace them more often than you would in a car. And consider replacing them entirely, substituting some form of solid-state switch. Just be sure to not use any form of optical sensor. The VW distributor is not sealed and so long as you retain the distributor function (ie, the wires, rotor and cap) the central graphite button guarantees the optical sensor will eventually become obscured by oil vapor and carbon particles.

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There's a few thousand things I haven't mentioned but the above should be enough to get you started. (Little play on words there, I suppose :-)

-R.S.Hoover

Ed.Note: In general, the factors discussed above must be taken into account when configuring any Otto Cycle engine for manual starting. In many cases Continental A-series engines with a reputation for being difficult to start need only to have the propeller re-oriented to make them start on the first flip. This is especially important with a 'Cub' on floats, where the engine must be started with one hand whilst balancing atop the starboard-side float.

Wednesday, February 21, 2007

Flying On The Cheap -- DOORSKINS

Flying On The Cheap – Doorskins

A 'door skin' is a 3' x 7' sheet of 1/8" Luan plywood. It differs from a regular four-by-eight sheet of eighth-inch luan ply because door skins are USUALLY fabricated using waterproof glue.

The simple test for waterproof glue is to boil a sample of the plywood. The regular stuff comes apart almost as soon as you drop the coupons in the water whereas the waterproof stuff can be boiled and dried several times before it starts coming apart.

Door skins tend to cost about 10% more than the regular stuff, partly because of the different glue but also because each sheet will have one perfect face. Typical example of the cost difference (as of 18 March 2006) is $6.98 for a doorskin (ie, 21 square feet) vs $9.79 for a 4x8 sheet of 1/8" luan (ie, 32 square feet). (Dixieline Lumber, Escondido, California)

The box stores tend to NOT carry door skins; most of their clerks won't even know what you're talking about but will try very hard to sell you whatever they do happen to carry.

Door skins have flown in Fly Babys, Volksplanes and a number of similar designs, albeit without benefit of clergy. When properly glued, carefully varnished and religiously maintained, the common door skin has proven to be a trust-worthy material for those of us who are flying on the cheap.

-R.S.Hoover

Sunday, February 11, 2007

BLOW-BY


BLOW-BY and BAND-AIDS

Basics

The cylinders of Otto-cycle engines do not form a perfect seal. The piston rings provide a near perfect seal only during the Power Cycle when the pressure of the combustion process is above a given level. Depending on the fit of the parts and their state of wear, gases and finely divided liquids may cross the piston/ring/cylinder interface in either direction.

Gasses that escape past the piston rings or valves FROM the combustion chamber TO the sump or valve gallery is referred to as ‘blow-by.’ Some amount of blow-by is present in all Otto-cycle IC engines as a by-product of normal operation. The amount of blow-by is determined by a host of factors including but not limited to the number of piston rings, temperature differential across the system of piston, rings and cylinder, the fit of the parts, the, presence of valve stem seals, and the engine’s operating parameters, with more blow-by seen at elevated temperatures and high rpms.

Unless the valves are fitted with suitable stem seals, the intake manifold, exhaust manifold and combustion chamber is NOT isolated from the valve gallery. Blow-by that appears in the valve gallery tends to be extremely hot, easily capable of eroding valve guides and carburizing oil.

The crankcase of all Otto-cycle engines is vented to the atmosphere and meant to operate at atmospheric pressure.

Like all other fluids, the flow of gasses responds to a difference in pressure.

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General

A basic goal of modern engine design is to eliminate blow-by at normal operating temperatures and engine speed. This goal may be attained through the use of shaft- and stem-seals, ‘Total-Seal’ type piston rings, additional piston rings and controlling the normal operating temperatures to within a narrow range.

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All of That and a VW Too

The above should give you some idea why the tree-huggers go zoo when they see an old Volkswagen chugging down the road. (Or flying overhead, too.) The VW engine was designed in the 1930's. It’s crankcase ventilation system consists of pumping the air in around the pulley hub and using a road-draft tube to suck it out, along with whatever it happens to pick up such as water vapor, oil vapor and combustion products.

As Volkswagenwerk AG bored & stroked the basic engine, the spew became worse; so bad they were eventually forced to close the road-draft tube with a flapper valve and use the carburetor as the source of suction needed to provide the pressure differential that ensured a proper flow of ventilation through the crankcase. But unlike modern crankcase ventilation systems, the inlet remained unfiltered and always open.

California’s effort to require Positive Crankcase Ventilation (PCV) on early bugs and buses came to an embarrassed halt after reputable testing laboratories showed the bureaucrat’s solution of add-on valves, hoses and temperature sensors more than DOUBLED the engine’s emissions.

All modern engines are fitted with shaft seals and any air entering the crankcase is filtered. Volkswagen owners who liked to play in the sand quickly discovered the practicality of such features and began fitting their engines with shaft seals, commonly called a ‘sand seal.’

Sealing the inlet to the VW’s crankcase ventilation system dictates the need for an alternative inlet, ideally one that is provided with a filter. After-market retailers provided a number of such devices in which the inlet function was transferred to the valve covers. The stock outlet was left in place. Unfortunately, the purpose of these after-market devices was generally misunderstood by VW owners, most of whom depend almost entirely upon Conventional Wisdom for their automotive information. Most VW owners as well as the ‘technical’ editors of VW-specific magazines ASSUMED the inlet fixtures were a new kind of OUTLET, disabled the stock outlet and ended up even worse off than they were before.

Since the customer is always right, the after-market suppliers merely shrugged their shoulders and began providing a number of shinier and more complex crankcase ventilation fixtures, all of which were eagerly purchased by mechanically naive owners, praised in the magazines and featured at the car shows and then installed incorrectly. Life is strange :-) In the mean time, real mechanics built their own inlet systems or installed a properly plumbed after-market device (there were several good ones) and got on with the race. Most everybody else began blowing smoke in a major way.

(Remember the joke about the idiot carpenter who threw away half the nails he took from his pouch because the point was on the wrong end? Remember how his boss explained that he shouldn’t throw them away because they were for the opposite wall? Keep it in mind as you read the following :-)

The usual cause for disabling the inlet to the VW engine’s crankcase ventilation system was the installation of a sand seal. On flying Volkswagens the most common cause was the installation of the Long-Taper sleeve-type propeller hub developed by Bob Huggins in the early 1960's.

The usual cause for disabling the outlet of the VW engine’s crankcase ventilation system was the installation of an after-market air-cleaner or dual carbs, in each case having no provision for the outlet hose. For flying Volkswagens the most common reason for destroying the crankcase ventilation system is because most people didn’t even know the Volkswagen HAS a crankcase ventilation system (!) (Must be for the other wall, right? :-)

The punch line is that once the crankcase ventilation system had been disabled Volkswagens began blowing their oil overboard. The cause of such behavior differs slightly between rolling and flying Volkswagens but the end result is the same. And of course, since the PERCEIVED problem was ‘blowing oil overboard’ the obvious solution was some kind of vapor separator; an oil recovery system. Which as you’ve probably guessed, the after-market retailers were quick to provide, along with boxes of nails for the Opposite Wall :-)

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Wheat/Chaff, Men/Boys, Fact/Fiction, Oil/Vapor

One of the funniest lectures I ever heard in my entire life was a VW ‘expert’ telling a bunch of people that if your 1600cc engine was turning 4600 rpm, then it was producing exactly 53 horsepower. No exceptions. God Has Spoken.

Here’s the Real World version: The amount of power produced by your engine at ANY rpm is a function of it’s volumetric efficiency, which to save time you make think of as the position of the throttle. Throttle wide open? Then the cylinder is going to draw in a larger charge than if the throttle were barely cracked. Volumetric Efficiency defines the ratio between the maximum possible charge (100%) and how much the cylinder actually manages to suck in. The actual amount is sometimes referred to as the Effective Volumetric Efficiency or EVE. (I’ll get to ADAM, Seth and the boys in a minute :-)

(Have trouble getting a grip on this concept? Think about rolling down the road, lightly loaded, no wind, doing a steady 30 mph. (Do this on a chassis dyno, it will tell you that you’re putting out between seven and ten horsepower.) Then a Hill comes along (dreaded object for any VW owner). If you want to keep doing 30 mph you gotta keep pushing down on the accelerator pedal. If the hill is steep enough you’ll soon find the pedal flat to the floor. Your temperatures are starting to head for the red. The throttle is WIDE OPEN and you are only doing 30 mph. The engine’s rpm has NOT changed... but the engine is producing the maximum amount of power for those conditions. How much is that in horsepower? I donno... 25, thirty... around there. Truth is, horsepower isn’t what you should be concerned with; you should be looking at your head temps and your manifold pressure. But one thing I can guarantee you: If you just sit there, foot flat to the floor, watching your speed decay, you’re going to trash the engine. (And yes, Virginia, you can do exactly the same thing in your airyplane :-)

EVE for the air cooled Volkswagen ranges from about 10% at an idle to about 60%. (And that may help you understand why I’ve spent so many years trying to improve the volumetric efficiency of this particular power plant.)

You need to understand this because the problem of blowing oil is related to Maximum Output. The tricky bit is that Maximum Output may occur at less than 3,000 rpm in a flying Volkswagen but over 6,000 rpm in one with wheels. And if you really believe in equal power for equal rpm, in horsepower instead of thrust and the Tooth Faiery instead of slipping the kid a buck, you may as well toss this aside right now because nothing that follows will make any sense to you.

Maximum torque occurs at the point of peak volumetric efficiency. You may consider the former as the product of the latter. Peak volumetric efficiency occurs when the chamber is filled as full as possible under the existing circumstances, you light the fire and are rewarded with a specific impulse of the greatest possible magnitude and duration; lotta fuel means lotta fire; fire means heat; heat means pressure and the leg-bone is connected to the knee-bone.

Still with me? If so, you will see that the VW on wheels is blowing oil because of the high rpm, peaking temps and so forth. He’s a long, long ways away from his maximum volumetric efficiency but has managed to reach maximum output relative to rpm. The flying VW is rev-limited by the prop but the engine has reached its maximum output relative to that particular rpm. His volumetric efficiency is higher, as is his blow-by. And at that point his engine temps are liable to be well ABOVE anything you’ll ever see in a vehicle. (Why? Because John Thorpe is dead. The most popular of the flying Volkswagens are nothing more dune buggy engines with a fan on the nose, except they lack the dune buggy’s cooling system. The configuration of those engines as well as the public statements of the people selling them makes it painfully clear that they don’t know very much about aircraft engines, either in building them or cooling them, which John Thorpe did and taught to the rest of us.)

What it boils down to is a pair of engines lacking a proper crankcase ventilation system. One of the engines is maxed out for rpm, hotter than it should be, thrashing most of its liquid oil into hot vapor. It’s got some blow-by but it ain’t all that serious because the effective volumetric efficiency is right down near the bottom of the scale, not because the throttle is closed but because of the inertial mass of the fuel/air charge; at high rpms the cylinder doesn’t have enough TIME to suck in a big charge.

The other engine is maxed out for torque, running way over in the red, producing enormous quantities of blow-by, the combination of which has thrashed most of its liquid oil into hot vapor.

So now you want to separate the oil from the vapor.

Good luck :-)

You CAN separate oil vapor from air and I’ll describe the usual methods in a minute but the whole idea behind everything written up to this point was to help you understand that you’re buying a dead horse. Vapor separation AT THIS LEVEL is dealing with the symptom rather than the problem. What you should be doing is addressing the root problem, which is to PREVENT the vaporization of your oil. But the fact you’re here to begin with is good evidence that you are not mechanically adept; that you’ve probably bought an engine that came with the problems BUILT IN. And if you are not mechanically adept, when it comes to engines you are literally at the mercy of others; a victim-in-waiting with legions of slick hucksters eager to screw you out of your last buck. And your very life, in many cases.

‘Nuff of that; you won’t believe it until it happens, by which time it will be too late. So let’s go sort the wheat from the chaff. Or whatever.

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Oil vapor is a generic term applied to everything from smoke to rain. True vapor, which is like smoke, responds best to condensation; chill it, the stuff turns back into liquid oil. Oil that has been divided into minuscule particles is still liquid oil. It may be hot and it may respond to cooling but so long as it is ALREADY a liquid the best strategy is to use its greater mass to cause it to coalesce into a FILM of liquid oil that you may then collect using gravity, centrifugal force, wipers (!!) or whateverthell you got.

So whatcha got? Can you drive a centrifugal separator? Prolly not.

If what you got is a bug, bus or airplane, the tactics you can apply to the problem are limited. When Porsche ran into this problem in the late 1950's (i.e., high revs resulting in excessive oil loss through vaporization) they added MORE OIL. Then they bit the bullet and put a vapor separator on the front of the blower housing. Hot weather, they still blew a lot of oil overboard but so long as they won their share of races nobody gave a shit. (You gotta be a Real Man to drive a sports car, right? :-)

The separator Porsche used was the column-type, similar to the one shown in the drawing (OIL_SEPARATOR_01). (As with most of the other drawings it is in .dc file format; download the free demo software to view it.) Mounting the separator on the front of the blower housing kept the thing reasonably cool. As the particulate oil collected on the baffles, it cooled and served as a cool-surfaced collector for the vaporized oil. End result was to reduce the oil loss by about 75%.

The outlet of the vapor separator must go to an area of low pressure relative to the inlet. On a carbureted engine the most logical low-pressure source is above the carburetor. If the vehicle is moving at a fairly high speed you can use a road draft tube; at higher speeds you can rig a venturi in the slip stream.

The oil separator should have the largest possible exterior surface in order to facilitate cooling of the captured oil. Fins would be a good idea. In an airplane you should consider an air blast tube.

Vapor separation occurs at ever level within the system. The plumbing runs to the inlet ports should have a constant downward angle toward the source. I’ve found half-inch or larger 3003 tubing to be the best stuff for the inlet plumbing runs. Hose makes suitable connectors and flex fittings. The liquid oil return line should use regular hose fittings.

The diameter of the column is up to the builder, as is the number of baffles. To fabricate the thing I simply cut a series of angled slots in opposite sides of the tubing. The baffles are trimmed to match the contour of the tube then welded in place.

The idea here is to force the vapor to turn a lot of corners. Oil, either as a true vapor or a suspended particle, has a mass several MILLION times that of a molecule of air. The air doesn’t even notice the corners, other than to spend a bit more time getting from Inlet to Outlet. The oil however sees the baffles as virtual dead-ends and can’t help but hit the wall. And that’s what you want. Once the oil hits the wall, you got it. Gravity takes over, the oil heads downhill, finds the liquid oil outlet and ends up back in the sump. You want to maintain an adequate head on the return line. Remember, this whole mess got started because the sump was allowed to get above atmospheric pressure. If you keep an adequate head on the return line there may be enough pressure in the sump to prevent the return of the liquid oil.

The effectiveness of the vapor separator is a function of its internal surface area, the number of baffles, the pressure differential and the temperature. To get more length you may have to lay the thing down. The tricky bit here is that if you place it too close to horizontal you will defeat the purpose of the baffles, turning them into oil traps. The thing will fill up with liquid oil, reducing the interior volume and you’ll commence blowing oil overboard again. So think it out, especially if the thing is going airborne. Not only must it be functional, it must be able to withstand whatever acceleration you plan to impose on your butt. (Hint: Go for at least eight g’s; you can do that much on a bad landing without even trying :-)

Like most other crankcase ventilation systems the one found on the early air cooled engines is a superb bit of engineering. (Indeed, just about everything on the basic VW engine reflects the results of evolutionary refinement during the production of twenty-two MILLION engines over more than half a century of use. ) The ratio of inlet to outlet accurately reflects accepted standards for such systems and is very similar to the equation applied to aircraft engine cooling systems. When you modify such a system, or when you add a vapor separator, you must pay the keenest attention to maintaining an adequate pressure differential across the system or device. The basic rule is to keep the outlet larger and at a lower pressure than the inlet. Temperature, the length of your plumbing runs, and a host of other factors will effect the outcome, as does where and how the thing is mounted. The point here is that what works for me may not for thee. Tinker with it. You’re the Mechanic in Charge.

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Couple of concluding remarks for the Instant Experts:

The use of a synthetic lubricant addresses only the heat-related side of the equation, in that synthetics typically have a higher boiling temperature. Excessive blow-by, itself an artifact of elevated temperature, and any rpm above an idle (when the engine is hot) is more than enough to give you a oil ‘vapor’ consisting of finely divided particles.

We’re talking fog here, okay? Ever seen a real pea-souper? According to NOAA the densest fog on the American continent is the so-called ‘Tule Fog’ that occurs in the Central Valley of California. And fog is water vapor, right? So how dense is dense? About 900 particles per cubic centimeter. (How bigz a centimeter? About... that big.)

So that’s water. And naturally occurring fog. (You can make a denser suspension using ultrasonics. Very tricky, kinda like cold steam.)

So what about OIL? Well... according to the U.S.Army’s kemical corpse, using simple procedures and light oils you can produce colloidal suspensions as dense as 4000 particles per cc. How? Same way you do with your VW engine: Just heat & stir :-)

So what’s the major factor, heat or rpm?

Heat. Oh, there’s a strong linkage but if you solve the heat problem a lot of the down-stream effects simply don’t occur.

But my 2180 ALWAYS RUNS COOL.

More happy horseshit. If you’ve followed the instrumentation procedures advocated by Great Plains or John Monnet you’re measuring the temperature of the CRANKCASE rather than the oil it contains, and the temperature of the SPARK PLUG rather than the cylinder head.

Volkswagen knew what it was doing when it instrumented its industrial engines and measured CHT for its EFI systems. Measured at the spark plug your ‘cht’ could be as much as 150* F too low, compared to the measurement point recommended (and used) by Volkswagen, which is a specially cast lug on later model heads although they provided a Service Note explaining how to attach the CHT sensor to the lower exhaust stud on early model heads.

Same problem with the oil temp. If you just screw the sensor into a hole in the side of the crankcase, that’s the temperature you’re going to get. Volkswagen poked the sensor into the core of the stream of oil being sucked into the oil pump. On average, it reads nearly 100* F more than the temperature of the crankcase. And of course, the interior temps of the valve gallery runs about 100 degrees hotter than the average oil temperature.

This is another case of nails for the opposite wall. Wanna sell a kid a junker? Just diddle the speedo so it reads about ten miles per hour faster.

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Bottom Line Time

Blowing oil? Then find out why. There are three main reasons: Excessive blow-by at the rings. Excessive blow-by at the EXHAUST VALVE STEM. Improper sizing of the inlet-to-outlet ratio of your crankcase ventilation system.

A leak-down test will detect the first cause. The wiggle test will detect the second. Direct inspection will detect the third, assuming you know what you’re looking for, which is the TOTAL RESTRICTION offered by the outlet of the ventilation system. You could be running hose that is 3/4" in diameter, which should be more than enough. But if that hose is too long or if it has too many bends, the sum of its restrictions may cause the engine to ‘see’ only a tiny outlet.

Tiny outlet, the velocity goes up. When the velocity goes up so does its energy density, meaning it’s now strong enough to suspend & transport oil droplets of significant size, meaning you’re going to be blowing oil despite having a big hose.

The stock VW crankcase comes with a very effective oil separator built-in. Pull the dynamo tower and you’re looking at it. You can improve its effectiveness by stuffing the space under the dynamo tower with coarse metal mesh, such as a bronze or copper ‘Chore Girl’ pot scrubber. Not real handy as an oil-filler port since all new oil has to filter its way down through an inch of pot-scrubber but it works a treat at keeping the blow-by dry.

In the attached drawings the top of the column is often made to accept a removable valve-cover vent, like you see on an old Chevrolet Six. The cap contains a wire ‘filter’ that can be washed.

-30-

Tuesday, January 23, 2007

TULZ - Part Eleven

TULZ – Part Eleven

CLICK!

You jump in, pump the accelerator pedal a few times, even though you know it sez to only press it down once. (More is better, right?) You turn the key and… CLICK.

The moment of Truth has arrived.

If you're late for class or work or whatever, when you hear the Big CLICK! the wiser course is to IMMEDIATELY fall back on your alternative means of transportation. And if you ain't got one perhaps you should think about that.

Your second alternative is to push-start it. But there's more involved here than just starting the engine. First, you gotta know HOW to push- start it. Second, you gotta be fairly sure the problem is not a dead battery. Did the warning lights come on? That means you got juice but it doesn't tell you how much. Got headlights? Then the battery is probably okay and you're Go for the Push-Start Follies. But before you start pushing, think. Wherez your tools? The odds are, it's not going to start after you get to wherever it is you're going, either. The Big Click is fair evidence you've got repairs ahead of you. If the vehicle is already home with your tools, hoof it.

A push-start may get you to where you're going. Or it may not. What if it dies in traffic? And if it doesn't you're still going to have to push it again to get home so that means you need to park it someplace where push- starting is practical. Can you be sure of finding such a place?

Remember the Unholy Trinity of maintenance? You need the tools, the skills and a place to work. If you KNOW your ride needs fixen, taking it AWAY from your tools with the notion of getting around to the work later is stacking the odds against you.

So you're at work or school or whatever and you gotta get home because that's where all your tulz are, and the battery is up and the thing was running okay the last time it ran and you're parked in a place that will allow you to do a push-start, go ahead. But you need to know HOW to do a push-start.

PUSH-START, HOW-TO

Brake is OFF. Lean into it, get it rolling, jump in, turning on the key and putting it into FIRST GEAR at the same time as you pop the clutch. That is, let the clutch out SUDDENLY then push it right back in. When multiplied by the gearing, a walking pace is fast enough to cause the engine to rotate one or more full revolutions, which means at least TWO cylinders will have a chance to fire. If the engine is in a good state of tune, that's all it takes.

Once it fires, baby it; keep the thing running until it warms up and idles sweet, because you don't want it dying on you in traffic.

THINK ABOUT IT

Odds are, if you've never push-started your vehicle, it won't start the first time you try it. Push-starting by yourself calls for a fair degree of strength and coordination. The lesson here is pretty simple: The best time to learn how to do a push-start when you DON'T need it; when your ride is running. So go PRACTICE. Find yourself an empty parking lot and TEACH YOURSELF how to get your vehicle running without using the starter. Back in Part Eight I suggested you teach yourself how to drive without using the clutch. Learning how to start your engine without using the starter falls into the same category of Get Home skills.

When push-starting your ride here's some tricks that will help. Pump your tires up. That will make it roll a lot easier. Get your engine in perfect tune. Set the static firing point closer to TDC or even a couple of degrees AFTER top dead center. You can't drive it with that setting but it will start and idle a lot easier. And if you have a dynamic timing light it's a simple matter to reset the timing once you get it running. Don't leave the key on too long. You need the choke for it to start and the choke is electric. If you leave the key on and the choke will eventually move to the off position even if the engine isn't running.

FIXING THE BIG CLICK

The CLICK itself is your main clue. It tells you power is getting to the solenoid. At that point the decision tree branches. Either the contact bar in the solenoid is worn or corroded or otherwise damaged so that it is not capable of doing its job (which is to connect the battery to the starter) or the solenoid isn't getting enough power to press the contact bar closed. There are some variations on this theme but they have different signatures. For example, CLICK! Whirrrr… means the pinion isn't engaging the flywheel whereas CLICK! Groannn… means the pinion is binding or the engine is seized or one of half a dozen other things.

The above should make it pretty clear that diagnosis is based on a complete understanding of how the system operates. It should also serve to illustrate that diagnosis reflects a decision tree.

If you'll examine the workshop manual for any modern vehicle you find it is largely devoted to depictions of the diagnostic decision tree in schematic format. You'll also see that virtually no space is given to telling you HOW to do the mechanical aspects of the repair. Instead, they tell you how to do the various diagnostic tests. When it comes down to R&R, the removal & repair (or replacement) of the component, the manuals assume you know how. Indeed, the WRENCHING is the easy part. The hard part is knowing what to wrench and you can only learn that by starting with the basics and working your way up, which is why I suggested you begin with a lawnmower engine. But that's too much trouble, right? Especially when you can jump on the Internet and take a poll as to why your wheel just fell off. Unfortunately mediocrity can never rise above itself. A majority of unskilled mechanics will always give you an unskilled answer. (For every two hundred people who read this, only one will understand. So be it. Right now we're trying to get your bug started so let's get on with it :-)

The Big Click sez the problem is either in the solenoid or that insufficient power is getting to the solenoid. We can test for the latter by using a jumper cable from the battery lead to the spade lug on the solenoid, thereby eliminating about twenty feet of wiring and the possibility of a bad ignition switch. But let me tell you right now this is a very dangerous test. It should only be done when the vehicle is supported on jackstands. Why? Because the engine is liable to start. And if it does, it's liable to run over your ass.

So leave the key OFF. That will prevent power from going to the ignition circuit. Better yet, pull the HV lead out of the coil. Then do the test. If you don't know which lead goes to the battery, use your manual to figure it out. And if your solenoid is the later model with the two spade lugs, figure out which one goes to the ignition switch.

Back in Part Four I suggested you make up some test leads, including some with spade-lug connectors. This is a good time to use one. Detach the starter-switch lead from the solenoid and replace it with a jumper having a female spade-lug connector on one end and an alligator clip on the other. To complete the circuit, TOUCH (do NOT clip) the alligator clip to the battery cable connector. Do NOT touch the copper stud nor the nut. The arc is enough to damage the threads of the stud and will bugger the nut when you try to remove it.

IF the jumper test causes the starter to engage and to crank the engine then the problem is in the wiring or the ignition switch, with the higher probability for the latter. There is an interesting history to this particular problem.

The starter solenoid needs about ten amperes to pull-in but only about an amp to hold-in. This is not uncommon and is a characteristic of solenoids. Your ignition coil is also a solenoid-wound inductor and it too has a high inrush current. Unfortunately, the VW ignition switch is only good for about eight amps (!) whereas the inrush current when you try to start the engine EXCEEDS the safe current carrying capacity of the switch meaning it's going to go bad, sooner or later. Bosch recognized this and came up with a simple fix, a pilot relay that mounts on the solenoid. The Bosch part number is WR-1 and the whole thing only costs a few bucks.

What the pilot relay does is to use about a quarter of an amp to connect the solenoid directly to the battery, eliminating the need to run that momentary jolt of ten amps through the ignition switch. Well designed and easy to install, the pilot relay will eliminate a host of starter problems on Volkswagens, especially on the Transporter which has longer wiring runs and therefore more loses.

Unfortunately, 'way back when, Muir and other experts told all the kiddies to use a Ford contactor as a pilot relay. The joke here is that the Ford contactor pulls almost as much current as the Bosch solenoid!

A pilot relay is a good idea. Bosch dealers sell them as do a few VW dealers. Berg recently rediscovered them after years of selling the Ford contactor. Or you can make your own. A horn or headlight relay works fine and the installation procedure has been posted to the Internet on numerous occasions. Check the various archives.

If the jumper test didn't help then you've narrowed the problem down to the solenoid. Fortunately, the fix is pretty simple. Start by removing the battery from the vehicle, then remove the starter, dismantle the solenoid and file the contactor and contacts smooth. You'll need to unsolder a couple of leads to dismantle the solenoid. Use a bit of Solder Wick to get the solder out of the holes. When you reassemble the solenoid be VERY SURE to use RTV or other WATERPROOF sealant.

The 'Idiot' book covers starter problems rather well and certainly justifies your study. But DON'T use that ohsokewl trick of shorting the terminals with a screwdriver. Yeah, it works. It also damages the terminals as well as the screwdriver.

Next time you go to replace the battery cable you discover the threads on the solenoid are buggered all to hell; the nut won't come off (or it shears the copper stud). You can't get a die onto them, even if you had the proper die [which you don't] and you can't remove the old cable. You have to remove the entire starter and chase the damaged threads with a sixty-degree vee-file [see a set of Swiss pattern-maker's files]. That is, assuming the threads aren't buggered too badly. But if you've done that ohsokewl Idiot Trick more than a couple of times, forget; you'll have to buy a new solenoid. Swell idea, eh?

In the same vein, DON'T go pounding on the solenoid with a hammer. Yeah, this also works. And damages the solenoid in the process.

The usual reason for a solenoid to stick is due to rust on the plunger. The proper fix is to remove the starter, dismantle the solenoid and DEAL WITH THE RUST. If you just pound on the thing you might jar the plunger loose… and you might not. The odds are about 50-50. And of course, you'll only hear about the successful tries.

A basic tenet of a good mechanic is to do no greater harm. The 'Idiot' book is larded with procedures that damage the vehicle. Once you've buggered an axle nut or starter stud don't expect to find a mechanic to save your bacon. Competent mechanics usually refuse to work on a vehicle that shows obvious signs of abuse since they can be held liable for future failures even if they didn't work on that particular component. It isn't fair and it certainly isn't logical but when our nation's President, who happens to be an attorney, doesn't know the difference between a blowjob and a hand shake, it's easy to see how such bullshit comes about. Idiot book indeed. (Ed.Note [2006]: The current Prez is an even dimmer bulb :-) Indeed, we Americans have the best government money can buy.)

THE BIG NO-CLICK

You jump in your ride, turn the key and… You turn the key and… eh? Nothing. Well, mebbe something. Mebbe the indicator lights came on. Or mebbe not.

The Big Click is pretty easy to diagnose but the Big No-Click can be a worse headache because of the lack of data. No click means no juice getting to the solenoid… mebbe.

No click and no indicator lights is pretty good evidence you're not getting any juice. The first thing you need to find out is if you got any juice to get. Try your headlights. Bright? Normal? Then you can probably rule out the battery. But no lights doesn't mean the opposite, it simply means no juice is getting to the lights; the battery could be just fine. So you start from Ground Zero and begin climbing the diagnostic decision tree.

Ground Zero is your battery and cables. And one of those cables is the ground strap on the nose of the tranny.

The Main Electrical Buss runs from the starter to the battery. That's why it's there; the battery's primary purpose is to start the engine. All else, from your ignition system and electric lights to your bitchin' sound system came along later. (Early cars used magnetos and were started with a crank. If you wanted to drive at night there were acetylene lamps, some of which were brighter than any headlight you've ever seen. And if you wanted a bitchin' sound system you hired the band :-) When it comes to the battery and cables there really isn't much to diagnose. The terminals must be clean, tight and free of corrosion. The cable must be undamaged with no sign of corrosion at the fittings. The grommets isolating the cable from the chassis must be in good condition.

If your electrical system fails this very basic inspection, deal with it! Neutralize any rust you find and put down an anti-corrosion pad under the battery. Clean the terminals down to bright metal, put anti-corrosion pads under the terminals and install new cables with suitably fitted terminals. Once everything is tight, give them a spritz of anti-corrosion spray (I use that purple stuff). Where the ground lead is bolted to the chassis, eliminate any rust or corrosion then put a light coating of copper-based anti-sieze where the fitting will be bolted down. Thereafter your only maintenance is periodic inspection and cleaning.

The Distribution Buss is a heavy red wire that runs from the battery cable-solenoid junction to the fuse block via the headlight switch. The ignition, starter solenoid and indicator lamps are not fused and pick their power directly from the headlight switch via the ignition switch.

You can track the path of the circuits using your timing light. In most cases of the Big No-Click the fault will be in the headlight switch or the ignition switch and the repair is to replace the switch. But in some cases you can track the active circuit all the way back to the solenoid only to discover it is bad. (This is where Muir brings out his hammers. Resist the impulse.)

Now you got a major problem because you can't repair the winding of a Bosch solenoid, you've got to replace it. Unfortunately, a new solenoid, assuming you can find one, will cost over a hundred dollars. So you start hitting the junkies, trying to find a replacement starter which, by custom, comes with the solenoid attached. (In the mid-1950's I push-started my bug for a YEAR because I couldn't afford a replacement starter only to discover the problem was the solenoid. Live & lurn :-)

The electrical routing above is valid for about eighteen million Volkswagens. I don't have a lot of experience with later models but the same principles of diagnosis will apply. See your manual for your particular vehicle's wiring diagram, which you should study until you can draw it from memory. And if that sounds a bit much, it's not. There are common elements to all automotive electrical systems. Once you've learned one it will serve as the foundation on which to learn others

PREVENTION vs CURE

Your electrical system is one of the easiest parts of the vehicle to maintain. It has very few moving parts and its operation is governed by only a few basic principles. Once you've mastered them the system has no secrets.

Certain types of electrical system problems having to do with the AGE of your ride are becoming more common. They involve the grounding circuit. Using the steel body of the vehicle as one side of the electrical circuit is common automotive practice and typically causes no problems. But after a quarter-century or so the dissimilar metal junction between the electrical connector and the steel body can create a barrier having a high resistance. This is especially critical with regard to your headlights and tail lights.

Owners of vehicles having a six-volt electrical system often convert to twelve-volts because their headlights have dimmed down to a yellow glow. It comes as quite a surprise to find their new 12v system doesn't do any better. The truth is, a six-volt headlight is just as bright as a 12v headlight. The problem is not a lack of voltage but an excess of resistance, typically in the grounding circuit. Repair usually requires no more than dismantling and cleaning.

Add this to your warbag: Never pound on a battery's terminals. You'll break the seal between the terminal and the case and the electrolyte will wick through the crack. Always use acid neutralizing pads, the big kind for under the battery and the small circular jobbies under the battery terminals. NEVER slosh your battery with a mixture of water & baking soda. It will get inside the battery (see above; cracks worth in both directions) and ruin the end cells. If your cables are corroded, replace them. When replacing a cable ream the terminal to a perfect fit on the battery posts. Add the little tool for this job to your electrical kit. Batteries are heavy and inherently dangerous. Get yourself a battery carrier and use it. Keep it in your electrical kit. Ditto for the little can of anti-corrosion spray. Make it a habit to REMOVE THE BATTERY any time you work on the vehicle. Not only does this prevent accidents, it gives you a chance to inspect the battery. When the battery is out of the vehicle, put a board or piece of cardboard across it; you don't want anything to short across the posts. (I know a kid who lost a finger when his wedding ring completed the circuit across a fully charged battery.)

-Bob Hoover
-22 May 2K

Saturday, January 6, 2007

Dialing in Your Cam


DIALING IN YOUR CAM

You’ve worked all summer to get the bread to build a bitchin 1776 engine. It’s got big jugs, dual carbs, a hot cam and valves the size of dinner plates. You and your buds pull an all-nighter to get it buttoned up in time for school. It fires right up with a lopey idle that sounds way kewl. But punch it, it’s a total POS. Nobody knows why. The timing is dead on and the dizzy checked out. Ditto for the carbs. All your buds agree it should run good but it don’t. A call to the local guru is no help, ‘Bring it in, lemme lookatit.’ At a hundred bucks a glance. But at least it runs, sorta, so you drive it. Maybe it will heal or something.

First day of school Mrs. Wilson who teaches Home Ec and drives that bone stock ‘67 she’s had since high school blows you off pulling out of the parking lot. She wasn’t even trying to dust you. But she did. Bad. The real killer is that your buds saw it happen.

Before you buy a Toyota or transfer to another school let me ask you a couple of questions. Did you dial in your cam? Did you set up your valve train geometry? Have you got any idea in the blue eyed world what I’m even talking about?

“Actually, I’m more into computers ...”

Okay, then think of your cam as the engine’s BIOS. It tells your valves when to open, how far and for how long. The crankshaft is the Master Clock, with Top Dead Center of #1 cylinder as the zero point. Dialing in your cam loads the program at the right address. With the engine above, put your foot down, it should take off like Mad Max blowing nitrous. But only if the crank and cam are in sync.

So didja? Did you dial in your cam? Because even in a stock engine, stack-up errors can put your cam timing out by as much as 4.5 degrees, more than enough to turn your tiger into a turkey.

STACK-UP ERRORS

The Volkswagen was the world’s second economy car ( first was the Ford Model ‘T’). Its low cost of production is reflected by the spec of its parts, which are pretty loose. Some engines came out of the factory sorta sloppy and some sorta tight but the wide tolerances guarantee almost any engine would run. That’s why you don’t dial in the cam doing a rebuild. If you don’t change the cam gear, odds are the rebuilt will run about as well as the original. But when you use non-stock parts, or even a high percentage of rebuilt parts, the odds run the other way.

When you build a high performance engine from a collection of after-market parts, for the duration of the job you better not be into anything but engines. You’re the Mechanic-in-Charge. The chore of making sure things fit falls on you. And one of those chores is dialing in your cam. So didja?

No, don’t tell me. Mrs. Wilson already did.

GAUGING THE CRANKCASE

Building a good engine starts with the crankcase, each of which is just a tiny bit different from every other because of normal variations in tooling wear and production tolerances. The differences are tiny but they’re important. Ignore them and it’s like building a house on a foundation that’s off level by just a tiny bit. The higher you go, the worse it gets. By the time you put the roof on, the thing is leaning like a drunk. One of those tiny differences is the distance between the centerline of the crankshaft and the centerline of the camshaft. It’s not a bunch but if you ignore it, by the time you get out to the valves your high performance engine isn’t.

Because of that difference Volkswagen used nine sizes of cam gear, from +4, through 0, to -4. (The size is stamped on the back of the gear. It reflects a change of .01mm on the diametrical pitch.) About 95% of factory-built engines use cam gears near the zero size, with a nominal range of about +2 to -2. Align boring, which Volkswagen used to do on all their rebuilt engines, dictates the need for the other sizes. How well the gear fits determines how rapidly it wears. Good fit, slow wear. Good fit also means good performance since the fit effects your cam timing and valve train geometry. So that’s where you begin.

Immediately after checking the fit of the main bearings to the crankshaft and case, the driver gear is installed on the crank and the crankcase is gauged to discover what size cam gear is needed. One of the most practical ways to do this to is to obtain three stock cams for use as gauges. With a +2, a 0 and a -2, it takes only a few minutes to figure out the right size cam gear for any crankcase. All you have to do is install your gauge-cams in your crankcase and check their lash against your crank. Here’s how to do it.

CHECK YOUR GEAR LASH

Install the crankshaft into the crankcase half, take your cam and roll the gears into mesh. Don’t worry about the dots, you’re just checking the lash, not assembling an engine.

With the crankcase open, use a pulley or crank on the nose of the crankshaft to smoothly rotate the crankshaft in its normal direction (ie, clockwise when facing the pulley). Do not allow any axial motion of the crankshaft during this test. Using a thrust hub is a good idea. Do several revolutions to insure the two shafts are properly bedded and the gears fully meshed. This test is normally done early in the assembly of the engine, before the connecting rods are mated to the crank.

Spec for cam gear mesh is .000" to .002.” The zero clearance reflects the fact that thermal expansion causes the two shafts to move farther apart at operating temperatures.

To check the mesh, hold the crankshaft stationary, rest your palm on the cam gear and rock it gently back & forth. One of three things is going to happen. You may not feel any motion at all, as if it were bedded in concrete. Or you’ll feel a little motion, usually accompanied by a faint clink-clink as you rock it back & forth. Or you’re going to feel a lot of motion, along with a loud CLUNK-CLUNK .

CLUNK is bad. You’re using the wrong size cam gear; its got too much clearance. Don’t take my word for it, check it. Set up your dial indicator to rest on the bottom-most tooth, right next to the parting line of the crank case. Use a pointed pallet on your dial indicator and set it up to bear on the corner of the gear tooth. Now rock the cam gear back & forth like you did before. (Remember to keep the crank from moving.) If you see more than two thou of movement, you need a larger gear.

If you felt some motion but not enough to give you a clink, the lash is probably okay. But it’s smart to check it out. Set up a dial indicator and measure the lash.

If you didn’t feel any motion the lash may be okay. Or it may be too tight. Try rotating the crankshaft backwards. Here again, do not allow any axial motion of the crankshaft during this test – keep it pressed firmly against the thrust face of the #1 bearing. The handy way to do this is to make yourself a thrust hub. That’s a fancy name for a junked flywheel, cut down to about 6". [See Tools You Can Make] The unhandy way is to use hand pressure. Of course, when you get to dialing in the cam you’ll need to grow a third hand.

If reversing the crankshaft lifts the cam out of its bearings, the gears are jamming, the mesh is too tight. You need a smaller cam gear. But if it rotates smoothly and the cam stays in its bearings, you’re okay.

When gauging your case you start with a 0 (zero) gear. Too tight? Then try your -2. If that’s too loose, you need a -1. Too tight, you need a -3. (Only 13 engines out of 10,000 use a -4.)

The same procedure works the other way. If the 0 is too lose you go up two sizes.

In fully half the engines you’ll build it takes only two trials to nail down which size you need. That’s because over 95% of all VW engines use a cam gear between a +2 and a -2.. A majority of new cases, about 65%, use a +1, 0, or -1. After being align-bored a case may need to go up one size but a +3 case is uncommon, +4 rarer than lips on a chicken. There’s no mystery to any of this, it’s simple statistics.

FINDING A GEAR THAT FITS

For the engine builder without a drawer full of spare cams, finding a gear that fits can be a conundrum. Here’s why. Let’s assume you have a gear on your cam. You check the lash using the procedure above and discover you’ve got either too much clearance or not enough. You need to buy a new gear. But with only one gears-worth of data, you can’t say which size you need. Like all conundrums the gear size question has no satisfactory answer.

What to do? Best bet is to get your case gauged by somebody who knows what they’re doing. If there’s a good VW engine man in your area and you show up with a clean case, the driver on the crank and all the bearings properly fitted, he may be willing to gauge the crankcase for you. It can be done on the bench; no need for the engine fixture.. And it doesn’t take long, if he’s got the right tools, or even if he’s got known-good stock gears to use as gauges. But if you show up with just a box of unblueprinted parts, forget it. There’s at least a couple hours labor to get a batch of raw parts to the point where you can accurately gauge the fit of the cam gear.

PRECISION GUESSWORK

If you can’t gauge your crankcase, get your hands on any cam gear of known size. Do the lash check and use your one cam’s-worth of data to approximate a better fit. Follow me through, here. This isn’t as crazy as it sounds.

Cam gear size reflects a Gaussian distribution curve. Statistically that means 95.44% of all stock engines used a cam gear between +2 and -2. We also know that a little bit too much clearance is better than not enough. Armed with that information, let’s play the odds.

Let’s say the gear you have jams. That sez you need a smaller gear. Read the number on the gear. If it is +2, +3 or +4, find yourself a 0 (zero). If it is a +1 or 0 (zero), go find a -1. If it is a -1 or -2, go find either a -3 or -4. If it is a -3, ignore it; the mismatch should be no more than 1/100mm. If your cam gear is a -4 and it is jammed, your crankcase has been improperly align bored because there isn’t any more sizes left. ( I’ve heard there are actually eleven sizes of cam gear, +5 through -5, but I’ve never seen a 5 and can’t say they actually exist.)

Now let’s look at the possibility your cam gear has too much lash. This is an easier problem to solve because we have more data. The fact it is too loose tells us we need a larger gear. By measuring the amount of that looseness – the excess lash – we can estimate what size will be a better fit.

First off, expand your acceptance spec to .004". If your gear measures less than .004" lash, go ahead and use it. It’s sloppy but it’ll run. If it measures .004 to .008, go up two sizes. If more than .008, go up three sizes.

You can’t build a good engine with guess work but an educated guess, making full use of what information you have is better than pretending your gear lash doesn’t matter.

When you know what size gear you need, give Clyde Berg a call, see if he can help you out. His dad used to keep a pretty good stock of different size gears on hand for his cam customers. Or do like I do and head for the junkyard. Because the cam runs at half the speed of the crank, the cam may be junk but the gear is usually well within spec. Simply drill out the rivets, throw away the cam and you’ve got yourself a usable gear.

HOW NOT TO SAVE MONEY

To keep down the cost a lot of guys use a reground cam. Not one of the good ones, the other kind, with the gear already attached. You know the ones I mean, you’ve seen them at swap meets and in the J. C. Whitney catalog.

Such a cam is not a good choice because its gear is probably the wrong size for your engine.

Since you may need any one of nine different gears, most cam grinders ship their wiggle sticks without any gear at all. The flange is drilled & tapped (usually for M8x1.0) to accept cap screws. As the Mechanic-in-Charge it’s your responsibility to install the proper gear. But nowadays the trick is finding the proper gear.

ONE SIZE FITS ALL – NOT!

So you buy a hot cam for your dream machine. Now you need a cam gear. You drop by the local VW store and sure enough, there’s a batch of cam gears hanging on the wall.

Odds are, they won’t fit either.

In preparing this article I examined more than thirty after-market gears obtained from a number of retailers here in southern California. Most of the gears were from Taiwan, some from Germany. All of the after-market cam gears I examined were not marked as to size. Of the Taiwanese gears I checked, all were about a +3. This may be an example of Oriental humor since a +3 is too big for 98% of all crankcases. ( To find out what size they are you have to set them up in an engine and compare their lash to gears of known size or measure their diametrical pitch. But unless you want to tool up for it and do them in batches, it’s impossible to justify the time it takes to determine the size of an unmarked gear, so long as gears of known size, even used ones, are available at junkyard prices. )

The people selling those oversized, unmarked gears worked pretty hard to convince me gear lash is no big deal. I was told that after-market gears only come in one size because it’s made of cast aluminum, much softer stuff than the magnesium alloy used for stock gears, and will wear itself in.

I got the same story at different places, often delivered in a scornful tone of voice. Oversize gears wear themselves in. Everyone knows that. So what about undersize gears? They don’t matter, according to a clerk about twenty years old who claimed to have run one for the last five years (!) in his 250 hp daily driver. Gives him more power, he sez.

Sure it does. (Can I get fries with that?)

Allow me to offer a bit of advice based on more than forty years of VW engine building experience. What an oversized gear does is wear itself out and quickly, too, along with your engine. The first time you fire it up, jammed against the steel driver gear the softer aluminum wears at a furious rate, generating spoonfuls of metal flakes to contaminate your bearings. That’s where most of that non-magnetic metallic sludge comes from in lo-buck rebuilds. By the time the engine reaches its normal operating temperature and thermal expansion draws the gears apart, it’s too late, the thing will be worn beyond spec.

You’re the Mechanic-in-Charge. Deciding which gear to use is up to you. But before you buy in to the one-size-fits-all philosophy, keep in mind that philosophy is saying Volkswagen, with nine sizes of cam gear in more than twenty-two million engines was wrong. Personally, I found most after-market cam gears to be shoddy goods due to their poor fit with the camshaft flange. Notable exceptions were gears of German manufacture which usually come drilled only for 6mm rivets. (Old stuff. Box said ‘W. Germany.’) They were a uniformly tight fit on the flange of the camshaft and although unmarked, ran about +1 in size. Opening up and counterboring the rivet holes to accept cap screws is a simple task.

If gauging the case says that a +3 is just the size you need, one of those cast aluminum jobbies from Taiwan may be justified. But a word of caution: Take your cam with you and do a trial fit before you buy. The flange of the camshaft must fit tightly into the socket on the cam gear. The fit of the flange to the socket is what provides axial alignment between the camshaft and its gear. Although it’s rather hard to believe, most of the after-market gears I’ve examined simply did not fit, the spigot was too large, too small or the bolting holes were misaligned.

Once your cam has been blessed with a gear that fits we can determine the indexing error between the cam and the crank. To do that we’ll do a partial assembly of the engine and set up our degree wheel. But first we need to find TDC.

WHERE IS TDC?

One Tuesday afternoon in 1873 Nicholas Otto invented the four stroke engine. On Thursday he dropped his TDC, it rolled under a bench and got lost. Mechanics have been looking for TDC ever since.

All piston engines have a TDC but there’s two Top Dead Centers in the Otto cycle and two ways of defining it. The TDC we’re interested in is the one on the compression stroke (the other is on the exhaust stroke). When setting the compression ratio or adjusting volumetric balance we define TDC in terms of deck height. But for cam timing, TDC is defined in terms of crankshaft rotation. Any way you cut it, before you dial in your cam you gotta find your TDC. So let’s do that.

At this point I’ll assume you’re using a cam gear having the proper mesh, the cam bearings are fully bedded in their saddles and the cam’s end-float is within spec. I’ll also assume you’ve set your crankshaft end-play and are using a thrust hub.

In the following procedure when I mention rotating the crankshaft, always turn it in the normal (ie, clockwise) direction unless told to do otherwise. The angle of the cam gear teeth combined with the end-float of the two shafts generates a surprising amount of slop any time the direction of rotation is reversed. When you need to back up and try again, always go back at least a quarter turn of the crankshaft. This insures you’ve taken up the slop. When asked to rotate the crankshaft to a specific point, do so with a smooth continuous motion. Don’t jiggle the thing back & forth. Jiggling about introduces slop into your readings and you’ll never get the same numbers twice in a row.

Install a pair of modified cam followers on the #1 cylinder (See Tools You Can Make). Install the #1 connecting rod and torque the cap to spec. Close the case, install the six large (M12) nuts with washers and torque to 24 ft-lbs in a ‘W’ pattern, checking for free rotation of the crankshaft as the torquing progresses. When torqued to spec the crank should turn freely with finger pressure. Install the #1 piston, without rings, onto the #1 con rod. Inspect the cylinder sealing surface on the case and cylinders then install the head studs. Install #1 & #2 cylinder barrels with their spacers, if any. Install the deck plate, washers, spacers and nuts (See Tools You Can Make) then torque to spec for your particular studs (ie, M8 = 18 ft-lb, M10 = 30 ft-lb).

TDC - DIAL INDICATOR METHOD

Once the deck plate is in position you may install your dial indicator, timing wheel and timing wheel pointer. (See Tools You Can Make.)

The markings on your timing wheel will put you in the vicinity of TDC and your dial indicator will tell you when you’ve arrived. Use the lifters to identify which TDC you’re on. At TDC on the compression stroke both of your valves will be closed, meaning the lifters will be down. Rock the crank through at least ninety degrees of arc at least half a dozen times to confirm the reading of your dial indicator. Once you’re satisfied you’ve found TDC, position the degree wheel pointer precisely upon the TDC mark.

TDC - STOP-BOLT METHOD

Finding TDC with a dial indicator works fine with most engines based on VW components but as the stroke increases so too does piston dwell at the point of reversal. If you’ve got good equipment – and young eyes – the dial indicator method will work for any engine although the probable error will increase with the stroke.

The stop-bolt method of determining TDC eliminates the dial indicator and any dwell-induced error. You insert a bolt in the torque plate so as to stop the upward travel of the piston before it reaches TDC. You put a piece of masking tape or a white stickum on your degree wheel centered on the as-marked TDC and extending to either side. Rotate the crank until the piston is stopped by the bolt. Do this gently so as not to mar the top of the piston. Keeping tension on the crank, make a mark on the tape precisely aligned with whatever pointer you’ve rigged. Reverse the rotation of the crank until the piston again is stopped by the bolt. Make a second mark on the tape, again precisely aligned with your pointer.

TDC is exactly half-way between the two marks.

A lot of guys go astray by trying to use the stop-bolt method without marking their degree wheel. Instead, they record the stopped position in degrees, such as -3 going one direction and +4 going the other. Then they go crazy and subtract three from four and declare TDC to be at the +1 degree mark. Which is close but not nearly close enough. The correct answer is the difference divided by two, or half a degree.

To keep from going crazy, when using the stop-bolt method ignore the degree wheel markings. Make your own marks, measure the distance between them and divide it by two. The result is TDC with an accuracy of about half a degree.

INDEXING THE DEGREE WHEEL

The whole idea behind finding TDC is to index our degree wheel. The reason we need to index the wheel is because every engine is slightly different. When dialing in the cam we find TDC with as much precision as possible, move our pointer to align with the degree wheel’s TDC mark and tighten it down. Some guys get confused on this issue because they think cam timing and ignition timing are the same thing or that TDC is represented by the centerline of the crankcase. The centerline is just a handy reference used in conjunction with the stock pulley to locate the approximate position of the static timing point for the ignition system. Ignition timing is akin to horseshoes, where close enough is usually good enough. Cam timing is the fixed relationship between the cam and the crank. With cam timing, you’ve either got it right or you lose.

Perhaps it would help resolve the parting line confusion if we started with a degree wheel that had no marks at all and covered up the parting line with tape. When the piston is at TDC so too is the degree wheel. You may position your pointer anywhere on the edge of the pulley, pencil in a mark and call it TDC. Or you may chose to put the degree marks on the engine and place the pointer on the wheel, which is what Volkswagen did with the Type IV engine.

HOW TO SPEAK CAMLOBIAN

To dial in your cam you have to be able to read its specs; to understand a cam card. To do that you need to speak Camlobian.

At first glance Camlobian seems crazier than a hoot owl in heat. It is not. What’s crazy is the description of the Otto cycle as taught in Auto Shop 101, where the two revolutions of the crankshaft are neatly divided into four distinct strokes during which the valves pop open and snap closed precisely (and instantly) at TDC and BDC. Real engines don’t work like that. And never did. Those pretty pictures in all those text books are as phoney as Washington chopping down the cherry tree. Or cam gears that wear themselves in.

The fuel/air charge has mass and mass has inertia, as do all components in your valve train. It takes time and energy to overcome inertia. You must initiate the opening of a valve well before such opening is needed and start closing them well ahead of when it must be fully closed. That’s why the intake valve in a real engine starts to open during the exhaust stroke and the exhaust valve opens rather early on in the power stroke. At one point, the two valves are even open at the same time.

Camlobian reflects the reality of Otto cycle engines by ignoring the four strokes and focusing on intake and exhaust events. It does this by combining the 2:1 relationship between the crank and cam into quadrants of crankshaft rotation during which particular intake and exhaust events normally occur. The quadrants are identified relative to Before (B) and After (A) Top Dead Center (TDC) or Bottom Dead Center (BDC) and are named according; BTDC, ATDC, BBDC and ABDC. (Not to worry. I put all this poop on the degree wheel I’ve included with this article.)

What this form of notation does is convert each cam event into a logical data set, unique from every other. For example, the intake valve opens (IO) in the BTDC quadrant of the exhaust stroke. Since each quadrant represents 180° of cam rotation, so long as we’re speaking of automotive Otto cycle engines a particular event will always occur in its particular quadrant. Having opened in the BTDC quadrant the intake valve must close (IC) at some point during the ABDC quadrant of the compression stroke. In a similar fashion, the exhaust opens (EO) during the BBDC quadrant of the power stroke which means it must close (EC) in the ATDC quadrant of the intake stroke. (And yes, there are some exceptions. Most occur with cams for supercharged engines, where you will occasionally see a quadrant number larger than 90 or less than zero. The basic definitions remain unchanged.)

Now comes the neat part.

Having established those conventions, speakers of camlobian needn’t bother to mention either quadrant or stroke. ‘The intake valves opens 18 degrees before Top Dead Center on the Exhaust Stroke‘ becomes simply ‘IO 18.’ Some cam cards are even more terse, such as ‘I 18-50, E 14-54,’ wherein 18 is the opening point, 50 the close. Since by convention the intake valve is listed first, a cam’s timing may even be defined by the ultra cryptic ‘18-50/14-54.’

Although Camlobian is a culturally rich tongue I’ve cited only a few basic phrases, enough for you to understand a cam card. For dialing in a cam, for each lobe, we’re only interested in three of its many events. We want to know when it opens (O), when it closes (C) and when it peaks (P). To adjust our valve train geometry, normally done in conjunction with dialing in the cam, we also need the maximum lift and the half-height point but that will have to wait for another article. And perhaps another language.

.050" SPECS vs ADVERTISED SPECS

Because there are several ways to grind a cam and some marvelously ingenious methods of selling them, cam grinders have agreed to use the 0.050" lift point as a common standard for determining when various events occur. This is called the checking clearance.

You must read cam ads very carefully. The advertised specifications often use something other than the .050 checking clearance as their base point and may even refer to valve lift rather than cam lift, coyly neglecting to define rocker ratio. Such deceptive practices are used by some folks to sell stock sticks as full-race flame throwers.

CLOCKING THE CAM

For obvious reasons a dial indicator is commonly called a clock. Or perhaps not so obvious in these digital days. (Early clocks only had one hand.) To a machinist, automotive or otherwise, a clock is a dial indicator. To clock the cam means to measure it’s lift, and determine its timing relative to the crankshaft.

The trail of tasks which have lead you to his point -- adjusting the lash of the cam gear, finding TDC and indexing your degree wheel -- have laid the foundation for the accuracy of the measurements you are about to make. If you think you could have done any of the preceding tasks better, go back and do them over because dialing in your cam is a classic case of GIGO – the output will reflect any inaccuracies in the input.

Your cam should have come with a data sheet, probably in Camlobian, listing when the valves open and close. Clocking the cam will tell us when these events occur in this particular engine. It’s important to understand that normal dimensional variations in the manufacturing process combined with your method of measurement and the imprecision of your tools guarantees you will see some error in the cam’s timing. Your purpose is to find out how much. If it’s less than one degree you may decide to accept it. If it is more than five degrees at the crank you might want to try another cam. But in a majority of cases the error will be a couple of degrees, plus or minus, and you will elect to reduce it as much as possible by adjusting the relationship of the cam to the crank using one of the methods I’ll describe in a minute.

By convention we do the intake first so begin by setting up your dial indicator to read off the modified tappet installed on #1 cylinder. (See Tools You Can Make for a holding fixture.) In all cases, on the VW engine the intake valves are those in the middle of the engine; the exhaust valves are the ones on the corners.

Slowly rotate the crankshaft through several revolutions while watching the dial indicator. You will see a prolonged period where the indicator makes no movement then rises, rather rapidly, to some peak value before dropping back. The prolonged period of no movement is when the tappet is riding on the heel of the cam. We need to find the middle of the heel. To do so, note when the peak reading occurs and mark that point on your degree wheel. Rotating the crankshaft one complete turn from the peak should put you in the middle of the heel for that lobe. Zero your clock at that point. (Simply loosen the lock and rotate the dial until the zero-mark is aligned with the needle then re-tighten the lock. If your indicator is properly mounted it will remain steady as a rock while being zero’d. If not, it needs a better mount.)

Once the indicator has been zeroed it may be used as a measuring device. Slowly rotate the crankshaft to measure maximum cam lift. Count the turns or use the turn indicator to keep track, remembering that the first revolution is the ‘zero’ turn. That is, if the needle passes through zero four times before coming to rest on 29 the dimension measured is .329" Record both the lift and the timing.

Once you’ve zero’d on the heel and found max lift, return to the middle of the heel, rotate the crankshaft until the cam follower has risen exactly .050". Record the reading from the degree wheel as IO (ie, Intake Opens) and reset the dial indicator to zero at this point. This is the .050" checking clearance point. Once your clock is zero’d, rotate the crank in the normal direction until you return to zero. Record the reading from the degree wheel at this point as IC (ie, Intake Closes). (By convention, I’ve used .050 for the checking clearance. Use whatever checking clearance is specified for your cam. Cams from metric countries typically use 1mm (~0.040"). )

With the indicator zero still set at the .050 checking point, find the peak lift and record it as IP (ie, Intake Peak). It should occur at the same point as before but the max lift will be less because we’ve reset our dial indicator to zero at the .050 lift point..

Divide the Intake Peak reading just recorded by two. This is the 50% Lift Point. Write it down. Now go find it! Go back to zero and rotate the crank until the clock reads 50% of max lift. Record when this occurs by reading the degree wheel. We’ll need this information when we adjust your valve train geometry.

Move the dial indicator over to the exhaust tappet for #1 cylinder and repeat the above tests. Record your findings. If you’re using a split lift cam, such as a stock VW stick, be very careful to record the 50% lift point for the exhaust.

WHICH WAY? HOW FAR?

Once you’ve found TDC, indexed your degree wheel and clocked your cam, the data you’ve collected tells you if the cam is properly indexed to the crankshaft. It won’t be. When clocking a cam the question is never if there is any error but how much and in what direction.

Did that come across? The reason we’ve gone through all this is to find out how big an indexing error we’re dealing with. Once you know what the error is, you can decide if it’s significant. As a general rule for street engines, an error of one degree or less, plus or minus, is not considered significant. Unless you like to build really good engines. In which case your standard of excellence will vary from zero error to some fraction of a degree.

When you build your own engine you’re not punching a time clock. There’s no foreman breathing down your neck. You don’t have a ten-engines-a-day nut to crack like the sweat shops cranking out those shoddy lo-buck rebuilts. When you build your own engine there is only you and the tools and the parts. There is absolutely no reason for you to settle for less than the very best you are capable of doing.

PULLING IT ALL TOGETHER

I’m building a low rpm, high torque engine to run on natural gas. After gauging the case, finding a suitable cam gear ( a +1) and modifying it to accept cap screws, I did a pre-assembly and started clocking the cam, a Schneider 248-F. After clocking it a couple of times my notes read:

IO = 2 IC = 38 EO = 38 EC = 2

Unfortunately the cam tag read: ‘4-36, 40-0' Translated, that meant

IO = 4 IC = 36 EO = 40 EC = 0

The numbers say the cam matches its specs, which is good, but they also say there is an indexing error of 2 degrees (retarded) measured at the crankshaft. To dial in the cam it needs one degree of advance.

Did that come across? Your crankshaft rotates twice in the time your camshaft rotates once. When the crankshaft rotates 720 degrees, the cam shaft rotates only 360. Two degrees of rotation at the crankshaft translates into one degree of rotation at the cam shaft.

Once we know how much the cam needs to be adjusted we have to figure out which direction it should be rotated. The gearing between the crankshaft and the cam causes the cam to rotate in opposite directions. Since the crankshaft rotates clockwise, to advance the cam we need to rotate it to the left or anti-clockwise. To retard it we would move it to the right. Always keep in mind that any adjustment is applied to the camshaft and not the gear. The gear remains fixed, relative to the crankshaft.

Once we know how much the cam needs to be rotated and in which direction, we need to know how far that amount of rotation is in dimensional terms. To figure it out we simply have ourselves a piece of pie. Or rather, π. (See the drawing.)

The radius of the bolting circle on the flange of the cam is about an inch and an eighth, something like 2.244" on the diameter. One degree on a diameter of 2.244" is about .019". That tells us how far we need to rotate the cam, which is fine if you happen to be a cap screw. For humans, a handier measure is to use the outer diameter of the cam’s bolting flange, the thing that sockets into the recess on the back of the cam gear. One degree on the diameter of the flange is about .024.” If we scribe a line across the cam’s flange and the gear, we can gauge degrees of rotation by measuring the displacement between the scribed lines and dividing by 0.024."

DIALING IN YOUR CAM

The term dialing in the cam comes from watching the needle of your dial indicator ooze toward zero as you make the adjustment. Given everything you’ve done to arrive at this point, the dialing-in procedure is anticlimactic, a hoo-hum no-brainer. Simply bring the degree wheel to whatever set-point you’re using, loosen the cam gear’s cap screws, lock the crank in position and rotate the cam until your dial indicator reads zero. For example, let’s say we’re using IO as our set point. Our clock has been zeroed at the .050 checking clearance. With the degree wheel set to IO, the dial indicator should read zero. It doesn’t but that’s okay; that’s why we’re here. Simply lock the crankshaft at the set point (IO in this case), loosen the cap screws and rotate the cam while watching the dial. When the needle touches zero the cam is at IO. And so is the crank. And that’s what we want. Tighten down the cap screws and move on to setting up your valve train geometry.

The main objective of this article is this one procedure, so allow me to go over it again. All of your work up to this point has been to cause the position of the needle on the dial indicator to reflect the difference between the indexing of the crank and the indexing of the cam. At this point you don’t care what that difference is, you’ve already measured it and determined it’s within your range of adjustability. The crankshaft is locked in position but the camshaft is not. The dial indicator, which is pointing at a figure other than zero, is riding on the cam. So you reach in through the oil pump hole with a tool and twist the camshaft – in whatever direction – until the needle reads zero.

If your cam was accurately fitted, dial indicator firmly mounted, TDC accurately determined and the degree wheel accurately indexed, zeroing your clock will dial in your cam to better than one-quarter of a degree. No myths, no math, no science and no expensive tools.

What makes this procedure a no-brainer is being able to adjust the cam when it’s inside the crankcase and its gear is locked in mesh with the crankshaft. The ability to do this -- the secret of turning a tough job into a five-minute no-brainer -- depends on two factors. The first is some provision that allows the cam to be rotated relative to its gear without removing the cam from the crankcase. There are a number of ways to accomplish this and I’ve described two of them below. The second factor is that the flange of the cam must be a tight fit in the spigot on the gear. If it’s not, when you loosen the fasteners and rotate the cam, any slop will be transferred to the gear. In effect, you’ve just shoved the gear to one side. The axis of the gear’s rotation is now different from that of the cam. That means the cam gear’s rate of rotation will not be uniform. This leads to a whole shopping list of problems including accelerated wear and poor performance.

DIAL-IN ADJUSTABILITY

In my opinion, the best method of achieving dial-in adjustability is by machining the bolting hole and its counterbore on an arc. (See the drawing.) Since this cuts away a good deal of the cam gear, stepped steel washers are used under the cap screws. The steel washers, commonly called cam buttons are symmetrical. Thanks to the use of cam buttons, this method is strong enough for all but the most powerful engines, plus it offers the convenience of being able to dial in the cam while it’s in the crankcase.

Gene Berg used to sell a good dial-in cam gear. And in any size you needed, so long as it was for one of his cams. If you don’t want to make one up yourself, give Clyde a call, see if he still has some.

If you prefer to roll your own by modifying a stock gear (which is what I do) you’ll probably find the easiest way is to use a rotary table and a milling machine, but other methods will work. I saw a guy in Baja doing a nice job on a cam gear using a router with the cam gear mounted in a wooden fixture. You wouldn’t think it would work but it did a pretty good job. I guess when you don’t have a shop full of tools you have to be a little smarter than the average bear.

THE FAT HOLE METHOD

Another way to achieve dial-in adjustability is by simply starting out with a fat hole for your fasteners. An M8 cap screw has a diameter of only 7.8mm, which means it has .004" of clearance in a 5/16" hole. Open up the hole to 11/32" and you end up with .0358" of clearance for a .308" bolt. You may now adjust the cam by nearly a full degree, plus or minus. That’s enough to reduce a two degree index error at the crank to under half a degree, good enough for most work.

Everyone who understands the need to dial in their cam has used the fat hole method at one time or another. Unfortunately, some engine builders use only this method, opening up the bolt holes to a whopping .375". Used with a small washer, that gives them about sixty-thou of slop, a full +/- three degrees at the crank, enough to dial in almost any cam. But counterboring weakens the cam gear and opening up the bolt hole makes matter worse. The risk here is that, having successfully used the fat hole method to build engines needing only a small amount of adjustment, they eventually try hogging out a huge hole and pushing the cap screw clear over to one side. Now it’s going it fail. And take the engine with it.

NON-DIAL-IN METHODS OF ADJUSTABILITY

The following methods of adjusting the cam gear require removing the cam from the engine to do the adjustment. After adjusting the gear always repeat the clocking procedure. Indeed, when dialing in a cam, regardless of the method used, it’s a good idea to verify the timing. Dialing in a cam is surprisingly easy once you learn how. Dialing it in wrong is even easier and there’s no training required.

CAM BUTTON METHOD

First off, they aren’t buttons they’re stepped steel washers. Eccentric steel washers, in this case. (See the drawings.) How they came to be used is pretty obvious once you’ve dialed in a few cams using the fat hole method. It has to do with the fact that counterboring weakens the cam gear and with how fat a hole can you go. The answer is not fat enough, without causing the gear to fail. But let’s say you hog out a 7/16" hole in the middle of your 3/4" counterbore. To provide support for the cap screw and prevent failure of the cam gear, you make up a stepped washer as shown in the drawing.

If you make up the washer so the pilot – the stepped portion -- is concentric to the bolt hole, your cam will be indexed straight up, without advance or retard. You may then install the cam and clock it. If clocking the cam sez you need to move it two degrees, you go over to the lathe and make up three new buttons with the hole offset by forty thou. That may sound like a major chore but trust me here, making eccentric buttons is a trivial task, assuming you have access to a lathe and know how to twirl the knobs. An 8th grader in metal shop class can crank out half a dozen engine’s worth of cam buttons before the bell rings.

Once you know how much adjustment you need and have the buttons in hand it’s usually quicker to tear down the engine rather than try to work through the oil pump bore. Yeah I know; some guys say it takes them only a few minutes. Your mileage may vary.

FILE TO FIT

Yup. Just like it sez. Start with a stock cam of the correct size, counterbore to 3/4", open it up to 5/16", install on the camshaft, assemble the case and clock the cam. When you know how much and which way it needs to move, tear it down and go at the bolt holes with a chain saw file, moving the hole in the direction you want the cam to move .020" for each degree.

If you don’t have a lathe or a box full of cam buttons, so long as the required adjustment is no more than 4 degrees at the crank, filing the gear to fit is the lo-buck winner. Four degrees at the crank is two at the cam so you move the hole forty-thou; about 1mm. If you go more than forty-thou you’ll have to use a smaller washer under your cap screw and things are liable to break.

Filing to fit isn’t the smartest solution. Buttons are stronger and more accurate. But moving the bolt holes with a file is the cheapest solution and when you’re young you can’t always afford to be smart.

WOODRUFF KEY METHOD

When you’re forced to use a pre-assembled cam/gear combo the use of an offset Woodruff key is your most practical means of making any adjustment to the timing. Volkswagen used to offer offset Woodruff keys as a special order item. They came in about five sizes and cost the same as the straight key, except you had to wait for it.

A big joke back then was to ask a new parts guy for Woodruff with a minus two degree offset and watch him go flipping through his book. This was a real knee slapper, on the same order as a left-handed monkey wrench. (Offset Woodruff keys don’t come as plus or minus... you simply install it with the overhang on the right-hand side of the slot to retard the cam, on the left to advance it. In other words, as with the monkey wrench, you simply turned the thing over.)

Offset keys were catalogued by degrees at the cam which could lead to confusion since American mechanics normally dial in the cam relative to crankshaft degrees. No problem, just divide your crankshaft-based index error by two. Of course, it’s even less of a problem nowadays since such parts are no longer available.

An automotive machinist can make any kind of Woodruff key you want, with any amount of offset up to a maximum of about 10 degrees (ie, an offset approximately half the width of the key). But expect to pay a good price for it. It might cost a bit less if he starts with standard #1210 Woodruff key, the closest match to the metric size used in your engine, but he can only give you about 4 degrees because that’s all the width he has to work with, a #1210 being 3/8" wide. And it’s still going to cost you something because it’s a fairly tricky bit of work to set up. Fortunately, an adjustment range of +/- 4 degrees is usually more than enough to cover the usual range of cam timing.

If you need an offset Woodruff key, give the machinist the driver gear and a new key and tell him how much offset you need in crankshaft degrees. He’ll use the stock parts to figure out the dimensions of the new key. As a point of interest, the bore of the driver gear is about 1.645" which tells you one degree is about .01435" at the Woodruff key (ie, 1.645 times pi, divided by 360 equals one degree). The amount of the overhang is equal to the number of degrees you want to change the timing times .0144". I’ve also included a drawing of the stock Woodruff key but don’t take the dimensions as gospel; measure it for yourself.

AFTER-MARKET ADJUSTABLE CAM GEARS

If you want to try an adjustable after-market cam gear I strongly suggest you keep your money in your jeans until you’ve inspected the part. Take your cam with you and try it in the spigot. You want a good tight fit. Then make sure the buttons fit the counterbore & hole in the cam. Finally, bolt it to your cam to insure the holes are properly aligned.

MAKING IT GOOD

Okay, so you got the cam dialed in to within a gnat’s a**. What’s going to keep it there?

After setting your cam timing, dismantle the engine, remove the cam, put it face down on the bench and make a couple of witness marks where the flange of the camshaft nests into the recess on the back of the cam gear. Make these distinctive from any other marks and make a note of their location in your documentation package. If you need to dismantle the cam from the gear, the marks will insure it goes back together properly.

Examine the cam-gear cap screws. Are they drilled for safety wire? Have you got one of those little drill blocks? Can you even use safety wire on the fasteners? (If you can, you should.)

Remove the cap screws one at a time. Clean them with MEK. Using a Q-tip, clean the threaded bore in the cam shaft. Reassemble using high strength Loctite and lockwashers. Torque to 10 ft-lb. When you’ve cleaned, Loctited and torqued all three, retorque to 14 ft-lbs. If possible, install safety wire.

-30-

(Ed.Note: This article was published in 2001 the Nov. and Dec. issues of 'VW Trends' magazine and was supported by about two dozen illustrations.)
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