Sunday, July 15, 2007

Crank Basics -IV


The crankshaft goes down to the magnaflux shop bare. That’s so they can peer down into the Woodruff keyways and the bottom of the groove for the circlip and, most important on a Chinese crankshaft, into the groove between the pulley hub and the #4 main bearing. That’s because on Chinese crankshafts this groove has square corners, whereas it’s a smoothly radiused curve on real crankshafts. The snap-ring groove on Chinese crankshafts also wanders around a bit.

If you look closely (click on the picture), Fig 1 will give you some idea of what I’m talking about. That’s a Chinese stroker on the left (of course :-) and a stock Germany crankshaft on the right. But the scary bit is the square corners in the groove behind the pulley hub (Fig 2). Square corners act as stress concentration points and standard manufacturing practice, especially with hardened, high-alloy steels, is to avoid them. Figure 3 is a close-up of the German crank for comparison

- - - - - - - - - - - - -

After the crank comes back from the NDT shop, assuming it’s usable, the next step is to have it balanced. Which isn’t to say it isn't already balanced. But proper balancing calls for the crankshaft to be spun-up with with all of its attachments. That means we have to assemble the crankshaft, except for bearings, from the prop hub right through to the dynamo’s rotor, torque everything to spec and deliver it to the balance shop.

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The first step in assembling the crankshaft is to install the large Woodruff key then the cam’s driver-gear, a spacer, the distributor’s bevel gear and the snap-ring that prevents the world from coming to an end.

The steel driver gear and brass bevel gear are a shrink fit to the crankshaft, meaning we have to heat them. The spec calls them to be heated to 80 C. or about 176 F. Everyone gets them hotter of course, assuming that if a little heat is good, a lot of heat is better. It’s not, but there you are.


Figure 4 shows a very plebeian method of properly heating your gears. Put about three inches of water in the big can, the gears in the small can, then spoon in enough lard to cover the gears. (The curiously bent wire is how you retrieve them.) Put the can full of gears into the water and put the big can on a stove and bring the water to a boil. Let it simmer for about twenty minutes then carry the whole shebang over to the bench holding the crankshaft, fish out the cam gear, slide it on (bevel toward the flywheel, please) and seat it with a few carefully aimed blows using a brass drift. Slide on the spacer then fish out the scroll gear and slide it on. Get rid of your tin cans & boiling water and install the snap-ring.

I donno why the thought of using lard makes so many people laugh. If you got something against pigs you can use salad oil. Or motor oil. The idea of the water is that it has a high specific heat – it will keep the parts hot while you carry them back & forth. Plus you can do all your heating with a ‘hobo’ stove and two charcoal briquets... or a camp-fire, if it comes down to it. The key is that you need a pretty good heat sink, because the minute you remove the gears from the heat they start to cool off. The shade-tree types solve the problem by heating the gear to the point where the steel changes color... along with its physical properties.

You don’t have to ruin your cam gear by overheating the poor thing. It slips on just fine if heated to the specified temperature, assuming it’s actually at that temperature when you slide the thing on.

When I start assembling a crankshaft I put the gears atop a big hunk of aluminum (Fig 5), pop them into a little oven I’ve got out in the shop and set the dial to ‘200' (which is as low as it goes). When I’m ready for the gears I drape a welding glove over them, carry the block over to the bench and install them. The block of aluminum will keep the gears hot for about ten minutes.

No aluminum? Then use steel.

No metal at all? So use a brick, fer crysakes. And if you don’t have a brick, use a pie-pan filled with sand. Or rocks. Or whatever else that can serve as a thermal mass.

And about here you’ll see that lard (or whatever oil you prefer) and a coffee can of boiling water isn’t quite as funny as it seems.

Once you’ve got your gears installed you can assemble whatever else goes on your particular crankshaft. Figures 6 & 7 is the crank for an engine that drives the prop off the flywheel end. The rotor for a permanent-magnet type dynamo is attached to the pulley hub. Everything is indexed; there’s only one way for it all to go together. It will be spun up as an assembly, resulting in a smoother-running, more durable and more efficient engine.












(The spruce lath is to keep it from rolling away. The prop flange and hub are from Great Planes. The cam gear has been treated with a solid-film lubricant.)

-R.S.Hoover

Saturday, July 14, 2007

Crank Basics - III



(Be sure to read Crank Basics I & II)

Crankshafts from China, supposedly forged, supposedly of SAE 4340 steel, having been coming into the marketplace for some time now at prices ranging from under $200 to over $400. Same cartons with the same cranks inside them but from different retailers.




Inside the box you'll find the crankshaft wrapped like a mummy. The plastic wrap and cardboard box is its only protection against the rock & roll of an ocean crossing, to say nothing of the hazards of UPS, should you order one. (Stock, replacement crankshafts from Europe are shipped a molded styrofoam block.)



The plastic wrapping is in the form of a sheet. The crank is first rolled in a bundle of the stuff, the ends neatly wrapped in upon the crank, then thirty feet of the stuff is spun out like a pig's intestine to make a plastic rope, which is bound around the mummy.

Your first chore is to unwrap the mummy without dropping the thing on your toe. Unwrap because cutting this stuff is not only a thankless task, it leaves a hell of a mess. So try unwrapping before reaching for your sword.

Once unwrapped the mummy turns out to be a fully machined, counter-weighted Volkswagen crankshaft fitted with eight dowel pins in the Porsche/SPG pattern.

Using a new gland nut as a gauge, you should check the threaded bore in the flywheel-end of the crank. Ditto for the pulley hub, using a clean pulley-hub bolt. Use new Woodruff keys to gauge the keyways milled into the nose of the crank. Finally, use a snap-ring to test the width of the snap-ring groove.

As a point of interest the crankshaft shown in the photos weighs almost exactly 21 pounds whereas a stock crank weighs about 16-3/4. Longer rods and bigger jugs also weigh more than their stock cousins but the weight difference between bone-stock and the largest big-bore stroker is rarely more than ten pounds.

After cursory checks of the threads, keyways and weight, suspend the crankshaft and perform the ringing test for cracks. (Just give it a light tap with a small hammer. It should ring like a bell, where a cracked crank gives a dull clank.) Using a good light and a magnifier, if necessary, give the crankshaft a close visual inspection paying particular attention to the radius of the corners and the lips of the oiling holes. A simple radius gauge filed out shim brass will prove handy here. (The specs for radius and dimension are printed on the form mentioned below.)




In the Chugger's Group files archive, in the crankshaft folder inside the Engine file, you'll find a Crankshaft Check Form. Print a copy, add the date, the serial number of the engine and any details about your micrometer that may be germane. As with all professionally built engines, the blueprint check-list will become a part of the engine's documentation package, along with a copy of the crankshaft's bill of sale, balancer's report and magnaflux report. The package need not be elaborate but it must be complete.

A set of standard bearings will serve as a quick check for main bearing journals 1, 3 and four.

With bearings 1 and 4 installed on the crankshaft you can use one of the crankcase halves to support the crank while you measure the run-out at the #2 bearing. The alternative is a good surface plate and vee-blocks.

To mike your crank you'll need to make a minimum of two measurements per journal and record the results. Provide yourself with good light and sufficient time; this isn't something you want to rush through. (The magnifying glass is because I often forget my eyes are nearly seventy years old :-)

Once you've miked the crankshaft, stand it on its nose using a spare pulley then bag the thing. A large zip-loc bag can be tightened around the nose of the crank to provide a dust-free environment suitable for a few day's storage. For any longer period the journals need to be protected with grease.

If you're satisfied with the crank's dimensions the next steps are to have it magnafluxed and balanced.

-------------------------------------------------------

The crankshaft shown in the photos was a bit of a disappointment. Main journals 2 and 3 miked 2.1642", which is the low end of acceptable specs, while #1 miked 2.1640" -- two tenths below spec. Assuming it magnafluxes okay it can be used but the bearing clearances are going to be more than I like. It will definitely be happier with 40W rather than 30.

The final step before cleaning & use is to attach everything that will rotate in the same plane as the crankshaft and deliver it up to a competent balancer.

-R.S.Hoover

(Ed. Note: In case you were wondering, this is not the same crankshaft as shown in Crank Basics - II.
These crankshafts are often advertised as being balanced and magnafluxed, made from high-alloy steel and so forth. Yet none of the two dozen or so I've examined have shown any of the marks characteristic of balanicng. )

Monday, July 9, 2007

Crankcase Ventilation

The Volkswagen engine holds exactly 2.5 liters of oil, which ain't much. Modify the engine for full-flow oil filtration you could count on the extra quart or so but back in the Good Ol' Days, whenever that was, you could blow better than a quart an hour when you were flying low through the sage brush. It wasn't uncommon to catch & pass your competition when they pulled up to pour another quart down the spout. And for them to do the same to you a few miles later. No big deal, since everyone had the same handicap.

Except for Charlie. He flew out of San Quintin running sixth overall and managed to pass everyone in front of him by the time he reached Catavina. He was better than ten minutes up when he blew through San Ignacio and would of won for sure if he hadn't tried to plow a cow north of Villa Insurgentes.

So what was Charlie's secret? He'd stuffed his dynamo tower with copper 'Chore Girl' pot scrubbers. They created a near-perfect labyrinth separator. No blown oil meant no stops to top-up.

Every crankcase has to breathe. You gotta provide some place for air to flow in and someplace for it to flow out. If your engine's running hot a lot of oil vapor will be mixed with the out-flow. If you don't do something about it, you'll blow it overboard. Which is less of a problem running the Baja than it is flying from here to there. Running the Baja, you can pull over & park.

On the Volkswagen engine the crankcase ventilation inlet is the annular gap around the pulley hub, which was machined with an Archimedes Screw to pump air -- and oil -- into the engine. Running off pavement you've gotta seal it up or you'll suck a lot of sand & grit into the sump. The outlet is via the dynamo tower, which usta have a road-draft tube that extended below the engine so your forward motion would produce a slight negative pressure at the outlet. (Later engines plumbed the outlet to the air cleaner, using the carb to provide the negative pressure that ensured good ventilation flow.

Once you'd installed a sand seal you had to provide a new ventilation inlet to the crankcase. Most guys plumbed a filtered line to their valve covers.

Since flying Volkswagens don't have dynamo towers you see all sorts of methods used to deal with crankcase effluvium; a lot of guys don't use any kind of oil separator. But then, a lot of guys still don't believe in oil filters, mom's apple pie or that Cheney is pulling the strings :-)

My approach was to try and use what's already there, such as the little shelf just below where the dynamo tower attaches, as shown in Fig. 1. The shelf is pierced with an opening over against the wall of the crankcase. (See Fig. 2 ).


To keep the mesh in place you'll need to tap a couple of 8-24 holes along the parting line and install a couple of drilled-head bolts to serve as a fence. (Fig. 3)

You want the mesh to pretty much fill the D-shaped hole for the dynamo tower but not to bulge above it. (Fig. 4) That will allow you to use an inexpensive oil pump cover as your outlet. Nor do you want it hanging out the bottom. This is the cam-gear gallery and the last thing you need is to have your mesh get sucked into the gear train.

If you shop around you can generally find a cast aluminum oil pump cover for a full-flow oil filtration set-up. These come with a threaded outlet.

As an oil pump cover, cast aluminum is about as durabile as a politician's promise. Enormously popular of course, at least to the Kiddie Trade. But as soon as youngsters see how rapidly an aluminum cover can wear they go for a cast-iron pump cover, which is why you can often find cast aluminum covers on sale. The two shown in Fig. 5 are idential, purchased for about $5 each. The one on the left is as-received, the one on the right has been bead-blasted then treated with a thermal dispersant. (Tech Line's 'TLTD').

On the flip side of the pump covers (Fig. 6) you can see the location of the outlet hole. Also note that one of the pump covers has been treated with a solid lubricant coating. (Another Tech Line product, although I don't recall it's name at the moment.) Coated in this fashion the pump cover holds up about as well as an anodized cover and can serve as a repair part. But it also makes a dandy crankcase ventilation outlet :-)


Since dynamo tower studs are closer together than oil-pump studs you'll have to open up the bolt holes in the pump cover. (See Fig. 7) You won't need the gasket nor the deflector plate. On my engines I run the outlet down to the carb-heat box, where the carb provides the required negative pressure.


Although I originally used copper 'Chore Girl' scrubbers for this application I found they corroded pretty easily. For the last fifteen years or so I've been using stainless steel pot scrubbers, found in the paint department of the local Home Depot. Unfortunately, they are larger and springier than the copper jobbies which makes installing one like trying to shove a watermelon up a monkey's ass.

Over the past fifty years or so when converting a VW engine for flight I've found it best to keep things simple. I'm not an engineer and don't pretend to be one. But there's heaps of sound engineering out there, much of it embodied in components that are commonly available. Before resorting to something I have to buy and bolt on, I try to see if there's some feature already on the engine that can resolve the problem by simply configuring it differently. Such as the providing adequate crankcase ventilation without blowing all your oil overboard.

By devoting a bit of thought to the various problems involved in converting a car engine for use in an airplane I've managed to come up with reliable, inexpensive solutions, most of which can be easily duplicated by fellow home-builders. This approach is wildly unpopular, of course. Not because the engine's don't work but because Americans seem to have gotten out of the habit of thinking for themselves.


-R.S.Hoover

Wednesday, July 4, 2007

AV - Chugger's Progress - III


The ribs of a fabric covered wing are interesting things, their role in the lore of flight often as confused as the plot of a Russian novel. The ribs themselves are nothing more than sticks of softwood. Sitka Spruce is the preferred material because it offers an excellent ratio of weight to strength but it has become so expensive that most of the people who would like to fly can no longer afford to do so.

The shape of the rib is blocked out in a jig which holds the sticks in place while gussets are secured to the joints with glue and tiny nails. The nails are so small they are usually positioned with forceps or needle-nosed pliers before being driving into place with a small hammer.

This method of construction, using glue and nails to secure some kind of stringer to some form of plywood, dates from the earliest days of aviation and is known to provide light, strong and durable structures. But cults devoted to the particulars of this method have sprang upand their partisanship often obscures the basic goal. The Wood Cult insists the only stuff suitable is Sitka Spruce, the Plywood Cult says only a particular type of plywood can be used and there are similar cults for the nails, how to install them, remove them and so on. And we haven't even gotten to the Glue Cults.

In modern-day America flying is all about money. If you have a lot of it you can fly; if you don't, you can't. Low-cost alternative materials and methods are out there but to determine their suitability for airplane construction you're pretty much forced to emulate the Wright brothers and conduct your own experiments. But even that is discouraged. After all, there's no need to experiment now that we have all those helpful, friendly Cults. Of course, if you can't afford to follow the cultist's advice, why, then you simply can't afford to fly.

I don't agree with that. I'm not an engineer but I do quite a bit of experimenting in which I compare inexpensive materials against cultist-approved stuff. In doing so I've learned there's no such thing as a Bad Experiment. Things often fail in unexpected ways but there is knowledge to be gained from such failures since they tell you 'Don't Go There.' In fact, most of my experiments are failures in that the Cheap Stuff rarely equals the performance of the Expensive Stuff, with the rib shown in the opening photo being a good example. Although it will bear the same weight as an identical rib fabricated from Sitka Spruce and aviation-grade plywood it weighs more than twice as much, a clear Failure according to cultist criteria.

Of course, in a more practical vein, that horribly heavy Cheap Stuff rib, weighing-in at a massive 3.88 ounces cost less than fifty cents, whereas it's more elegant Cultist Approved cousin, at a svelte 1.8 ounces, cost more than $5. Or to look at it another way, the plane would gain three and a quarter pounds while the builder would save over $100.

Oddly enough, when it comes to Flying on the Cheap, cost isn't the only factor. See all those tiny nails? It takes about half an hour to assemble such a rib, regardless of the materials you use. Rich or poor, when building an airplane your time has no value but poor people tend to have less leisure time than rich people. Even if I could come up with inexpensive alternative materials the sixty-eight million or so Americans who earn less than the median $28k per year generally don't have the luxury of enough spare time to build an airplane. That meant methods of saving time as well as money are a valid area for experimentation. As a result of those experiments I have largely replaced aircraft nails and tiny hammers with other fasteners and different methods.

I recently described using a pneumatic brad-driver in a post to this blog that was meant to offer a bit of comic relief about the Evils of Experimentation. ( http://www.itwtr.com/2007/05/av-n666rh.html ) I was surprised by the vehemence of some of the messages it produced.

Didn’t I know that aircraft nails are always 20 gauge? (about .025"). Pneumatically driven brads are always 18 gauge or larger. Didn't I realize that a brad that size would split a cap-strip of Sitka Spruce to flinders?

Fig 1 will give you some idea as to what all the fuss is about. The 20 gauge aircraft nails are above the pocket-ruler. Below it is an assortment of 18 gauge brads, which are rectangular in cross-section and about .035" x .048". That's a fairly massive spike to drive into a quarter-inch cap-strip.

I’ve been experimenting to find out how large the stringer or cap-strip has to be to prevent splitting. But not when driven into $7.95 Sitka Spruce, which is actually rather forgiving when it comes to nails. I was more interested in learning what happens when you use pneumatically-driven fasteners in the far more brash $1.98 Douglas Fir and even lowly .89 cent Western Hemlock ( the stuff Bernard Pietenpol used for his spars ).

The fact the brads are rectangular caused me to wonder what would happen if I took the grain of the wood into account. So I made a test-spar -- just a pair of stringers with a shear web of luan ply -- and then broke it under controlled conditions. (That's the spar mentioned in the earlier article.)

My mention of foamy glue, meaning polyurethane, caused the Glue Cult to point out that it was not certified for use in aircraft and suggested I try T-88, which was ‘stronger.’ The fact T-88 is also uncertified somehow escaped their notice, as did the cost and availability. In fact, most of my experiments are with Weldwood ‘Plastic Resin,’ which does happen to be a certified adhesive. But the point missed by the Glue Cultists is that all modern adhesives have a higher shear strength than any of the softwoods normally used in aircraft. While there are many reasons to use a good epoxy, strength isn’t one of them.

The tricky bit with a water-mix glue such as Plastic Resin is that that it requires a significant amount of pressure due to the water causing the wood to expand. Polyurethane glues require a similar amount of pressure because the glue itself expands whilst curing. When properly clamped and cured each of those adhesives is stronger than the wood and while ‘Plastic Resin’ is far less expensive, polyurethane is more convenient to use, especially when doing spare-time experiments.

Some of my experiments were to determine how many brads are needed to achieve the required amount of pressure, along with what type of brad was best for different combinations of plywood & stringers, and how small the stringer could be before the orientation of the brad was significant.

Even the pneumatic brad-driver caught a bit of hell from the Cultists. Nails were meant to be driven by hand; pneumatic tools were evil incarnate, the airplane would fall apart and famine and plague would surely follow. Clamps are apparently okay. Ditto for wedges. But nobody used pneumatic brad-drivers. (Splits the wood, you know.)

Oddly enough, no one mentioned nailing strips, a standard method when applying plywood skins. Which caused me to wonder if the people who took the time to write were merely expressing Conventional Wisdom – stuff they’d heard was bad, rather than stuff based on their own experience.

Another fact offered by the Cultists was that aircraft nails were always removed. Because of the weight, according to one; because they work out of the wood, according to another. And of course, they always rust.

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Perhaps the most important thing I've learned from my experiments is to ignore the Cultists. I'm sure their interest is well-meant but I'm equally sure it is misguided. The goal is not to build an unsafe airplane but an inexpensive one.

As a point of interest I've found most of the information offered by the cultists, while originally based on a kernel of truth, to be incorrect for most modern-day materials. For example, pneumatically driven brads come in sizes even smaller than aircraft nails and are available in stainless steel as well as bronze. And they are less expensive than aircraft nails. (My grandfather called them cigar box nails.)

Below you'll find a couple of photos of a test-piece assembled from hemlock, luan plywood (ie, doorskins) and 23 gauge pneumatically-driven brads 5/8" long. When driven atop a steel plate the brad neatly bends itself over and locks into the wood in a manner remarkably similar to the copper brads used on a clinker-built hull. On this end of the piece the spacing was rather random but for stringers up to 3/8" wide the glue-line exceeded the strength of the wood when fastened with one brad every two inches.

Chugger's fuselage is little more than a tapered box, plated with plywood forward, covered with fabric aft. The typical structural member is 3/4" square hemlock or fir. To ensure adequate strength I made samples of the various joints used in the fuselage and tested them to destruction. Experiments included plain joints, joints having filler blocks, joints having gussets on one or both sides, and joints having both filler blocks and gussets. The latter type of joint lead to some interesting problems in that I could not get it to fail with the test equipment I had at that time. When I was finally able to load them to the point of failure, the nature of the failure was unlike anything I'd seen before. A number of iterations proved the unusual mode of failure was not related to the test sample, which lead me to digging through books on structural engineering, where I eventually found that mode of failure described. Over all, it has been an interesting is rather slow education.

A basic tenet of flight is the ratio of strength to weight but materials having the optimum ratio, such as Sitka Spruce and aviation-grade plywood, are expensive. When building on the Cheap, using commonly available materials to achieve the required strength causes the resulting structure to comes out heavier than one built of aviation-grade materials. Experiments tell us how far we can go with our weight reduction efforts before the structure becomes unsafe. Experiments also show how the use of non-traditional tools can result in a significant savings of time when assembling a complex structure.

The Chugger will be inexpensive compared to virtually all other designs. And it can be assembled rather quickly. The result may not be very elegant but it will not be unsafe.

-R.S.Hoover

Monday, July 2, 2007

AV -- Fitting the Dynamo's Upper Bracket


A couple of weeks ago I posted an article...

http://www.itwtr.com/2007/06/av-reliable-ignition.html

...showing how to install a Permanent Magnet dynamo on the pulley-end of a VW engine. In the article I mentioned that VW crankcases are not identical. That came as quite a surprise for a number of folks who had somehow gotten the notion Volkswagen engines were pretty much the same. In the non-technical sense I suppose you could say they were a close match but in the same vein you could say a .30-‘06 cartridge was a pretty close match to an 8mm x 57 cartridge, which is to say they are visually similar. Functionally, the two cartridges are not interchangeable, which is also true for VW crankcases when you’re installing the coaxial dynamo.

Race-winning reliability comes from keeping things simple; eliminating anything not absolutely required, a philosophy that also applies to Flying Volkswagens. Once you have reduced a part to its bare essentials all that is left is to make the parts accurately, install them securely and ensure the fasteners can not come loose in normal use. Fortunately, doing all that isn’t as difficult as it may appear and the dynamo bracket serves as a nice example.

Creating a part with CAD allows you to make the usual prototyping mistakes on paper. So long as your printer is accurate enough you should be able to eliminate the task of laying out a part by simply printing an accurate pattern like the one shown in Figure 1. Also shown is the piece of scrap I’ll use to make the bracket.

The pattern is cut out (Fig. 2), the metal is given a spritz of spray-glue and the pattern is affixed to the metal (Fig. 3). The chore of fabricating the part is now reduced to simply cutting, drilling and filing. This also applies to the other parts that make up the dynamo’s mount, which I’ll eventually post in DeltaCAD format in the archives of the Chuggers Group.




After the part has been roughed out I center-punched the intersections (Fig. 4) and opened them up to about 11/32", since the fasteners are going to be M8-1.5 cap screws.

Figure 5 shows how the part does not fit on an aluminum crankcase from Brazil, one of two in the shop at the moment.

Nor will the bracket fit the machined curve on a German crankcase with its characteristic asymmetric curve as shown in Figure 6.

But the bracket is a nice fit on a recent Mexican crankcase shown in Figures 7 & 8, since I made the original bracket pattern to match this particular case. (Actually, it needs a tad more filing; note that the poor centering of the bolt hole.)



When satisfied with the fit of the part the central hole is opened up with a step-drill (Fig. 9) to accept a common pipe plug as shown in Figure 10, allowing the opening to be used as the oil filler port.


In a future post I’ll show how the bracket is aligned to the dynamo mount and the two are riveted together, although you probably won’t see this bracket again. Upon removing the pattern (dampen it with a wipe of lacquer thinner, peel it off then remove the spray-glue) I saw that I’d included a series of extra holes along one edge, making the part look a bit too tatty.

If this engine was to be fitted with a fuel pump the bracket would be made of mild steel .050" to .063" in thickness. The stock phenolic thermal insulator would then have that amount removed from its upper surface or the fuel pump’s push-rod would be extended by that amount (a common repair procedure for a worn push-rod).

At the moment there are eight engines in the shop, most using new Mexican crankcases but that number includes two aluminum crankcases and a few post-‘71 German cases, all of which have slight differences in the area where the dynamo’s mount is to be installed. Accommodating those differences is not difficult but if you’re not aware of the wide variation in VW crankcases it can come as a nasty surprise.

Although the part shown above is about as simple as it gets, novice builders have told me the most daunting aspect of building from scratch is the amount of time and degree of precision needed when laying-out the parts. Those road-blocks are removed when the builder has access to drawings they may print-out and use as patterns. This same method will be applied to all of the other metal fittings needed to for the Chugger's airframe and engine installation.

-R.S.Hoover
-2 July 2007

Sunday, July 1, 2007

VW - Techy Operations

(Ed.Note: The following exchange took place a few years ago on RAMVA, the Usenet Newsgroup devoted to air cooled Volkswagens.)


>All I meant was that it
>isn't alway necessary for a person to CC the heads or some of the other
>techy operations that you tell/show us all

---------------------------------------------------------

Hahahahahahahah...wheez..

That's so dumb it's funny. In fact, it's so dumb my normal reaction would be be to hit the big red button and add your name to the world's largest kill fill. But you made it a public post and that presents something of a problem because you just said black is white and it ain't.

Your message touches on two areas, one purely mechanical the other having to do with personal opinions and their interpretation. Let me hit the mechanical stuff first. Then I'll beat you over the head with the other :-)

Where do you think I get all this Hot Poop I post?

I didn't invent the Volkswagen. By my standards I'm not even that good of a mechanic. My dad was a pretty good wrench and there's several fellows on RAMVA who are better than me in the Fixin' Dept. (What I am is a pretty fair teacher... who happens to be something of a Jack-of-all-trades.)

So what's the source of those 'lofty standards' you feel compelled to ignore?

Would you believe they came from Volkswagen? Yep! Right out of the Factory Workshop Manual.

It ain't me saying you gotta cc your heads, it's Ferdinand Porsche... and every other competent mechanic in the world. And the workshop manual shows you how, right down to making the sealing plate and telling you how big the chamber otta be (and usually isn't).

The factory tells you to cc your heads because the volume of your combustion chambers is a critical factor in determining your compression ratio. And if you don't understand why that's important you shouldn't even think about building an engine.

In writing about stuff in the factory manual, what I've done is explain not only how to do it but how you can improve on the rather sloppy standards that were required for the serial production of an engine in the 1930's... and which VW unfortunately continued to follow long after better methods became available.

Volkswagen was willing to compromise quality to keep the cost of production low. The cost of production was probably around 60% of the sticker price meaning everyone's profits -- the factory, the distributor and the dealer -- had to come out of that 40% slice of the pie. By comparison, cost of manufacturing a mega-buck SUV is probably around 40% of the sticker price, providing a much larger margin of profit clear down the line... which is why no one wants to make a cheap car if they can possibly sell an expensive one.

But the point here is that the VW was conceived in the 1930's as a cheap ride. It's fabled quality was largely the result of a superb propaganda campaign by Doyle, Dane & Bernbach, the ad agency who lucked into the VOA contract largely because none of the more prestigious agencies would talk to a bunch of used car dealers trying to sell a funny looking little car from Germany, which is what VOA was before it became the tail wagging Volkswagen's dog.

After pointing out a few of the 'unimportant' details found in the workshop manual I went on to explain not only how to do the task but how to improve upon it. In doing so I wasn't whipping this stuff out of my ass, I merely described how I -- and everyone else -- was doing it. Because when you get right down to it the VW engine is an hilarious collection of compromises, bored & stroked until it leaked like a seive, it's power output jacked-up and lied about until it lost all credibility not only with mechanics but with the market-place, which saw its sales in steady decline long before the rise of CARB, cleaner air and the Revenge of the Tree Huggers.

Doesn't have to be like that. Building just one engine, there's no reason not to make it the best possible engine you can build. The funny part here is that it takes only slightly more effort on your part to produce an engine that is more reliable, economical and far more durable than anything to every roll out of the factory.

That's the Message I've been preaching since the 1970's. It isn't an especially popular message and as your post shows, most folks still don't Get It.

But not because I've stopped saying it. Nor because it isn't true. But you obviously don't believe me. Which gets us into the opinion part of my response.

Yeah, you're getting my opinion. And yeah, the fact I've been doing something a certain way for forty years is no guarantee I've been doing it right. But the point most seem to have missed is that my opinion is based not only on the manuals -- we all start with the Word... or should. My opinion is based on direct, personal experience, greasy fingernails and all. I've built several hundred engines and maybe fifty trannies over the last forty years. I've rebuilt the front-ends on buses and bugs and ghias and Things and about the only thing I can't say I've ever done is grind my own cranks, although I've worked in shops where we did, and cams too, including hardening and polishing.

Now, the thing I want to hit you over the head with is that 'lofty standards' business. Because they ain't. Lofty. Indeed, they aren't even as good as what you'll find in any modern-day Toyota, Ford or Chevy. But they come close and in doing so they give you lots of free horsepower. Same amount of gas going in but more power coming out, simply because an engine must first overcome any internal imbalances before it can deliver any power to the wheels. Eliminate those imbalances, the engine stops working against itself and you get to enjoy the power and durability you've been paying for but didn't get.

So go ahead and build yourself a piece of shit. Most folks do. Because when push comes to shove most people aren't bright enough to know a good thing when they see it. Or hear it.

In closing you said "...we both enjoy ACVW's". I don't, especially. They're what I know and they take me where I want to go. Which reminded me of TV because I heard a fellow talking about 'reality programming.' When I stopped laughing he asked what was so funny and I explained the 'reality' of making any kind of a TV show or movie, meaning the camera man and the grips and the caterers and the dozens of vehicles and platoons of people behind the 'reality' that appears on the screen.

I'll bet you watch TV. I don't. I'm too busy living my own life to waste time watching someone else's version of reality.

Maintaining your own Volkswagen is reality. Deciding not to cc your heads is fantasy.

Ever worked cattle? You gotta use horses, generally two a day. Terrible work; nothing at all like Hollywood's version of being a 'cowboy.' All of the horses were smarter than me as were most of the cattle but I was new to the game and figgered I'd wise up if I lived through it. Fortunately, I didn't have to; I spent most of my cowboying days servicing wind-mills and mending fence. Less than six months, thank God. (That's my Cowboy Story, by the way.)

I mention this because I once said I'd worked as a cowboy and someone immediately said they too enjoyed riding.

I've never 'enjoyed' riding in the sense they meant. Packing-in, having a horse means you don't have to walk but working cattle, most of our horses were old logger-heads with teeth like a crocodile and a disposition to match. If they couldn't buck you off they'd try to smear you into the fence. Survive that and they'd work for you. Until you missed one too many throws, then they were liable to lay down and roll on you.

My Volkswagens aren't pets. I respect them for what they represent but I don't 'enjoy' them in the sense you mean. But neither do I mistreat them as you are planning to do by not cc'ing the heads nor any of those other 'techy operations' you're planning to ignore.

-Bob Hoover

Friday, June 29, 2007

AV - Midnight Turning



It’s twenty-three minutes past midnight, Thursday the 28th of June, 2007. (Better make that Friday the 29th.) I’m just out of the shower, got my pipe going, scotch & water in hand. My wife has already gone to bed, probably mad at me for losing track of time out in the shop. Long list of mail awaiting answers, mostly from kids who’ve just bumped heads with Reality. (‘My bus is on fire!!!! Should I put it out or what?’) But I’m too tired tonight.

I like making things but the enjoyment comes mostly from figuring out how to make them. I made my first coaxially mounted dynamo back in the early ‘70's using parts out of a Honda motorcycle. I’ve since made quite a few of them using different rotors, home-made rectifiers and other variations, figuring out how to mount them on either end of the crankshaft. In fact, if you’ll compare the drawing above to the one I posted a couple of years ago you’ll see that the dimensions have changed slightly. And even the drawing above isn’t carved in stone. Tonight I saw a way to save some time that will appear in the next one I make.

Time doesn’t count when you’re figuring out how to do something. Hours vanish in the blink of an eye. But making a copy of something you’ve already figured out is pretty boring, which is why you start thinking about ways to do the job faster.

The dynamo hub starts out as a three pound billet of aluminum, that lump on the right in Figure 1. It goes into the chuck and the work-face is cleaned up so you can poke a one-inch hole in the middle using a drill. Then you start shaving down the outer diameter, creating what will become the shaft of the hub. What will become the flange is being gripped by the chuck. The 12-inch lathe has a three-horse motor and can take a fair-sized bite but it takes time and you have to keep your attention focused on the job.

Once you’ve got the OD down to where you want it you swap tools, shift gears and cut a the oil-slinger thread into the OD. Then you change to a boring bar and open up the ID to match the nose of a Volkswagen crankshaft, using a broken crank as a gauge. At that stage the thing looks a bit like an aluminum toad-stool.

Now it comes out of the chuck, gets flipped end-for-end. With the shaft now gripped by the chuck you gotta dial the thing in. Since Permanent Magnet dynamos don’t seem to be very sensitive to alignment I’m happy with .001 or less.

I pick-off the overall length using another gauge and face-off the flange, leaving a little lip to index with the rotor. Then it’s back to the boring bar, opening up the forward face to accept a socket for the pulley-hub bolt. Which pretty much finishes the job, except for a few details.

From the lathe, the dynamo hub goes to the arbor press where I use a 6mm broach to cut the keyway. (No broach? Then rig your boring bar as a scraper and rack the carriage back & forth, adjusting the cross-slide to get the required depth.) Then it goes over to the milling machine or drill press where I’ve set up a rotary table, already centered and fitted with a spud to match the ID of the hub. Cranking the knobs of the rotary table through seventy-two degrees at a time, I drill the pilot holes for the five bolts that will secure the dynamo’s rotor to the hub. (If you don’t have a rotary table use the rotor itself as a guide to spot the location of the holes.) After drilling, the holes are tapped 1/4-28.

In Figure 2 you can see how much metal is removed when opening up the ID. In fact, the three pound billet has been reduced to a scant five ounces (leaving you with two and a half pounds of swarf to deal with :-)

There’s a few million minor details I haven’t mentioned, and depending on your tools & experience there’s dozens of different ways to do the job. So long as it fits the crankshaft and the rotor, and spins true around the stator coils, it will work. But I’ll tell you pard, after you’ve made a few, shaving that thing down gets damned boring.

I’ve been trying to find someone to make the hubs and mebbe laser-cut the mounting plate, leaving you to simply rivet the thing together and bolt it to the engine. But today I heard from the last (of three) local CNC shops and the lowest price was nearly three hundred bucks just for the hub... and that was in lots of ten.

I think that’s too much.

The whole idea here was to come up with a method of generating electricity that was inherently more reliable than a belt-driven system. If you can do that, you toss the magneto and use a lighter, less expensive more reliable electronic ignition system. Millions of motorcycles have confirmed the validity of this approach. But the system was also supposed to be more cost-effective than anything presently available. Having to pay nearly $300 just for the hub blows the idea right out of the water... unless everyone makes their own hubs.

Somebody drank my drink. And my pipe’s gone out.

-R.S.Hoover
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