Saturday, September 15, 2007

Design by Concensus


Back when the world was young and I still had hair the Navy hired a gaggle of eggheads to contribute to the design of what eventually became the Spruance-class of destroyers (i.e., DD-963 class). At that time I was the Leading Chief of the computer shop for Pac Fleet's cruiser-destroyer force. I was told to give the eggheads access to anything they wanted in the way of maintenance and repair data, which I did with a cheery aye-aye, sir.

Marvelous stuff, watching those eggheads at work, doing their computerized statistical analysis of equipment failures, tracking everything back to the manufacturer on one hand and the Navy schools on the other.

The product of their work was a list of recommended equipment to go into the new ships; only the best stuff as determined by its failure rate, required maintenance man-hours, mean time to repair and so forth.

Which was all bullshit, unfortunately.

At that time (early 1970's) ComCruDesPac had about 137 ships. The analysis covered such things as electric motors, pumps, air compressors, ammo hoists and so forth, the ancillary systems that are the glue of a modern-day warship. (The hull design and the turbine powerplants were determined by other groups.) The objective of the study was to determine the best of that equipment and on the surface, their methods of analysis appeared valid. But in providing them with data I noticed that while all destroyers had high-pressure air compressors (for example) some of them had never failed. (Not many... four, I think.) Same thing for the other components. All of the ships used a certain type of gear-head motors but a few ships had never reported any problems with them. Which brings up a point worthy of mention.

Even though built to the same plan, vessels within a given class are not identical. The ships are built at different yards and while their specs were identical their equipment came from a variety of manufacturers. In the case of electric motors for example, while most of the ships used motors from General Electric or Westinghouse a few of them had motors from manufacturers I'd never heard of. The key point here is that some ships had never reported any form of failure for certain pieces of equipment.

The bottom line is that the study failed to consider the possibility that some equipment had never failed. Their final report identified only equipment that had failed, giving high marks for designs and manufacturers that failed the least often.

Which completely ignored the Really Good Stuff.

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

So what's all that got to do with airplanes? Quite a bit, when it comes to home-builts.

A fairly common thread on various aviation-related mailing lists and newsgroups is someone polling the subscribers in hopes of determining the ‘best' ...whatever. The best way to paint a spam can; the best brand of tire; the best vacuum pump and so on. Which gets down-right scary at times. (One such poll decided that the ‘best' aluminum was 6061 :-)

Polls and surveys, and the methods of statistical analysis that supports them, are valid tools. But only when your sample is an accurate reflection of the population being polled. Ask a room-full of pre-schoolers to define a balanced diet, don't be surprised if the answer is graham crackers and milk. In a similar vein, wood makes the best fuselage (according to builders of Pietenpol ‘Air Campers'), welding is easy (according to experienced weldors) and flying is inexpensive (according to people earning $100k p/a or more). In the case of the New Ship Design Study Group they failed to include the entire population of ancillary equipment, inadvertently limiting their investigation to equipment having a history of failure. (They were aware of the others but deemed them ‘statistically insignificant.’)

SO WHAT'S THE POINT?

The Internet offers unprecedented access to information but does not provide any means of determining if that information is valid. Indeed, within the field of home-built aviation only a small percentage - - probably less than five percent - - of the available information is valid and even then, only in a particular case. The remainder is either skewed by commercial interest or is a reflection of ‘conventional wisdom,' wherein the poster is simply parroting something they have heard.

Common sense has become remarkably uncommon stuff in modern-day America. Given the risk inherent in rising above the ground on wings I believe the wiser course is to treat all information on the internet as invalid until you can test it yourself. Fortunately, with a technical subject such as aviation the required tests are fundamental and well defined. For the homebuilder, especially those lacking an engineering background, the tricky bit is devising methods of applying such tests to their particular situation.

-R.S.Hoover

PS - - So what happened with regard to selecting failure-prone equipment? I've no idea. By the time the first of the new class slid down the ways I'd been retired for a number of years. But it's interesting to note that several of the Spruance-class have been scraped after barely twenty years service. (Navy ships are designed for a minimum service life of thirty years.)

I identified the Really Good Stuff aboard our own ships and submitted a report on the matter, producing a minor controversy with regard to maintenance. Sailors know what I'm talking about and it really doesn't apply to anyone else.

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(The above was originally posted to RAH in 2004. Recent posts to this blog [Chugger's Rib, 4 July 2007 and Chuggers Progress - III on 3 Sept 2007] have generated quite a bit of mail from folks who are upset by my failure to use Sitka Spruce, aviation-grade plywood and T-88 glue. The whole purpose of the Chugger files is to explore the use of less expensive materials that are commonly available. This isn't really a new idea. During World War II aviation was forced to use other woods, different glues and so on. History shows the planes (and gliders) flew just as well. Unfortunately, there isn't a lot of quantified data for those alternative materials. )

Monday, September 3, 2007

AV - Chugger's Rib

Labor Day, 2007.

Weather has been hot. A few miles north of us a mountain lion was seen drinking from a swimming pool and the coyotes are staying close to the few creeks that still have water. To hot to work in the shop, even with both fans going. Even the breezeway is pretty warm.

Too hot for welding and too sweaty for working on the fittings, I turned my attention to Chugger's wing. I have tentatively settled on the 4415 airfoil and needed some ribs for testing. I converted the 4415 coordinates into a rib drawing of the required chord, laid a few lines across it for alignment and printed it out. You'll find it in the Wing folder in the Chuggers Group, along with a pattern for the nose rib.

I didn't have a suitable piece of 3/4" plywood for the rib jig but did have some particle board that was wide enough. I don't like to use particle board for jigs because it's nothing more than thick paper and warps like a bitch but I glued a couple of stringers across the bottom and after the glue had cured, soaked it good with dilute varnish. That was a couple of days ago.

The several sheets that made up the pattern were trimmed along one edge using a straight-edge and razor. The jig board was given a coat of un-thinned varnish and each page of the pattern was painted with varnish on its back-side. The pages were then stuck to the varnished jig-board and aligned. Bubbles were chased to the edge of the sheet with my thumb and the whole thing was left to dry. But if you've never used this method, don't. It happens to be a quick & dirty method but varnish isn't a very good adhesive when applied to typing paper. It will hold the paper in position long enough to install the bits & pieces that will hold the rib's sticks in place. In doing so it will also fasten the pattern to the jig board. The whole thing will then get a coat of Deft Satin Finish Wax, which I understand is no longer available in the USA due to the tree-huggers. (The advantage of a wax finish is that nothing sticks to it.)

At this stage the thing looks like hell but it should work okay and only took a few minutes, if you don't count the clean-up :-)

I'm going to try using an Ison-type wing with wooden drag/anti-drag struts instead of wires or rods. The red hatch-mark is where the diagonal struts will pass through the rib. I'm also going to try building the ailerons in situ following the lead of Leonard Mulholland. I've not yet decided how to do the leading edge. I'd like to use 1/16" (1.5mm) birch ply but it is fairly expensive. Unfortunately the less expensive foam & fiberglas alternative, of which I've already built several samples, is about 3X heavier than the plywood.

I'm still tinkering with the leading edge but it looks as if I'm going to have to bite the bullet and run up to Corona (ie, Aircraft Spruce) for a couple of sheets of 1/16" ply.

After posting an article about building stick ribs in which I used 1/8" doorskin gussets attached with 1/4" aircraft nails and Weldwood 'Plastic Resin' glue I got several messages from people who found it impossible to use such small nails, having found they couldn't hold them with their fingers. The secret is to not hold them at all but to use the magnetic end of your tack hammer to pick them up and drive them into place. Unfortunately, that takes a bit of practice and since most of you are first-time builders I'll try using staples and/or pneumatically-driven 23 ga. wire brads.

The wing span will be a tad more than 28 feet, dictated by the available work-space (ie, about 15'). Chord is 56" so the wing's area will be approximately 125 square feet for a gross weight of 850 lbs, giving a 1-g loading of about 7 lbs per square foot. At 3.3-g that's about 22 lbs. With a rib spacing of 12" that's about 100 lbs per rib. Given the lift distribution of the NACA 4415 at its maximum angle of attack that means the portion of the rib between the spars will see about 80 lbs, the trailing edge will see almost no load at all and the remainder will be concentrated near the leading edge. One reason for cobbling-up a rib jig at this stage is that I want make and then break a few ribs to ensure they'll be strong enough.

According to the classic design formulas as published by Raoul J. Hoffmann (and others) in the 1930's, the aileron should be about 40% of the semi-span in length and 20% of the chord in width. As with the leading edge structure, this is another area I'm still tinkering with. If everything works out I'll post the required patterns in the Chuggers file archive.

-R.S.Hoover

PS -- Be sure to read Chugger's Progress - III posted on 4 July 2007. This post (ie, Chugger's Rib) produced a couple of comments that made it pretty clear their authors were not aware of what has gone before.

Thursday, August 23, 2007

AV - Crankcase Basics - II


Before wasting any time here, go read:
http://www.itwtr.com/2007/05/av-crankcase-basics.html

...especially the part where I say:
you will need nuts and washers and bolts to fasten the case studs and parting-line. Here again, there are kits available but most are the shoddiest stuff imaginable and price is no guarantee of quality. The nuts and washers may have a wash of zinc plating, good for at least a week’s exposure to the weather. Or they may not. And you can toss the ‘exhaust nuts.’ They are copper plated steel. (The good stuff is bronze.) Before you can use any of this crap on an engine you must provide it with some form of corrosion protection. If you don’t, not only with the nuts rust to the studs, you’ll see galvanic corrosion between the washers and the crankcase that will eventually cause the fastener to loosen.

Although any after-market VW retailer will be delighted to sell you that shoddiest stuff imaginable, the hands-down winner is J.C.Whitney because they usually charge more than most.

Back when I had hair I wrote an article ('Cows') explaining why it was a good idea to not buy VW parts from J.C.Whitney. Fig 1 offers a nice example of why this is still true. In the picture you can see the supposed 140-piece contents of JCW's catalog #xxx380749. (The 'xxx' is the catalog prefix which changes from minute to minute but the basic number stays the same.) A fellow chugger paid $15.99 plus shipping for what you see in the photo only to discover that most of the fasteners were unusable or not needed. (As of 8/23/07 the price is $17.99 making it even worse.)

Here's why: See those sixteen M10 nuts? (Lookit Fig 1A) Didja notice the M8 head stays illustrated in the 'Crankcase Basics' article? The M10 nuts & washers are for a pre-1971 crankcase, which you are not using if you're building your engine an a Universal Replacement Crankcase. And if you are starting out with a used crankcase then the odds are you already have a perfectly suitable collection of M10 nuts & washers.

Indeed, other than the six M12 nuts shown in Fig 1B everything else shown in Fig 1 is available from the local Borg for significantly less than JCW prices. But even then, the JCW parts are not the sort of stuff you want to use when assembling a good engine.

A point often overlooked by the shade-tree types is that several VW fasteners are also oil seals. The washer and in some cases, the nut, must be prepared and installed in such a manner as to prevent oil from leaking out around the fastener. The best example of this is the four lower head stays on each side of the engine that are terminated inside the valve galleries but this rule also applies to the six M12 nuts, the pair of M8 studs adjacent to the #1 cam bearing and the two M8's that support the #4 Main Bearing.

Fig 3 shows the type of M12 nut used on later-model Volkswagen engines. The red ring is an elastomeric seal that bears against the heavy washer which itself is bedded in Permatex or other non-hardening sealant, another of those 'unimportant' details casually disregarded by non-professional engine builders, most of whom insist that it's normal for the VW engine to leak like a bitch. Being a stock VW part, the nuts are commonly available but their price varies wildly from an honest thirty-five cents or so to more than a dollar from the typical Screw-the-Newbie suppliers (who always seem to run the biggest ads :-)

I'll cover the proper application of fastener sealants at the appropriate time. Or you can dig it out of the VW factory service manuals.

But the most regrettable failing of such hardware kits is their failure to provide real exhaust nuts. What you get is a regular steel nut with a wash of copper plating, guaranteed to last for at least thirty minutes before welding itself to the exhaust stud. What you want is a bronze or brass nut, installed upon a bronze, brass or copper washer with a lavish application of anti-seize compound. If you have a small lathe these are easy to make from bar stock but they are also available from the Usual Suspects.

Fig 4 shows a baggie of brass exhaust nuts sized to accept a 12mm wrench, allowing them to be used on the lower exhaust studs without interference when using a custom-built exhaust manifold as is common with aircraft engines.

To me, an engine is a forever kinda thing. There is no Magic Bullet. The reliability of any machine is nothing more than a reflection of paying the keenest possible attention to the smallest details of its assembly. Using the correct fasteners is a big part of that.

-R.S.Hoover

Sunday, August 19, 2007

AV - Chugger's Progress - IV

A recent thread ('REAMING') on the Usenet Newsgroup devoted to homebuilt airplanes brought to light the fact that a basic tenet of building with wood was so misunderstood as to make the job of attaching fittings far more difficult and time consuming than it needs to be. The basic tenet is this: When a fastener penetrates a wooden member for the purpose of transferring the primary load, the hole for the fastener ALWAYS begins as a loose, over-size fit.

There's two reasons for this rule, the first being the fact wood isn't very strong, the second that 12% to 15% of any piece of wood consists of water.

For example, in the first case let's suppose you're attaching a wing-lift fitting to a spruce spar. Sitka Spruce is only good for a few hundred pounds in tension. If we were using quarter-inch bolts to secure the fitting we might very well drill a 3/4" hole instead of the expected 1/4". Why? Because that would allow us to install an aluminum or hardwood bushing into the spar, increasing the tensile load-limit per fastener by approximately 8x for hardwood and more than 20x if we use aluminum. The fit of the bushing in the spar doesn't have to be especially precise since it will be installed using a gap-filling epoxy such as JB Weld for the lo-buck homebuilder or 3M's 'Scotch Weld' structural adhesive for the Rich Folk. (The aluminum bushing would of course be reamed to matched the fastener.)

In the second case, since the rule is to never allow a fastener to come into direct contact with wood, we would start with a hole at least 1/64th over-size and butter a suitable sealant into the hole. Additional sealant is applied to the fastener which is then installed. If the fitting requires periodic dismantling (and all primary load carriers do, to facilitate inspection) then the bolt would be treated with wax or other release agent before being coated with sealant.

The sealant would typically be an epoxy or resorcinol glue -- something 100% waterproof (*). The engineering behind this procedure is based on the fact that all modern-day adhesives are stronger than wood.

Back in the Good Ol' Days, whenever that was, the typical sealant was varnish and frankly, it didn't do a very good job. A hole is mostly end-grain and to ensure it was adequately sealed you'd often have to flood the hole with varnish for an hour or more, allow it to cure then re-drill the hole. Not many bothered to do so. Instead, they'd hook a patch on a piece of safety wire, saturate the patch with varnish and pump it back and forth through the hole a few times. This was a virtual guarantee that the fastener would corrode down inside the hole and become almost impossible to remove.

Often times a cursory examination of an airframe or set of plans reveals fittings and fasteners that appear to violate sound engineering practice. In such cases it's always wise to take a closer look. A massive landing gear fitting that appears to use nothing more than a couple of AN3's in tension usually proves to bear the landing loads in compression, the AN3's serving only to hold the fitting in position and not subjected to any portion of the landing load. I mention this because these are areas where home-builders tend to improve on the design by replacing the perfectly adequate #10 fasteners with quarter-inch or even 5/16".

Finally, I've included a couple of url's that will be of benefit to anyone thinking of duplicating the 'Chugger.'

http://www.bowersflybaby.com/tech/testing_wood.pdf

http://www.bowersflybaby.com/tech/latex.html
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* - 'Waterproof' as defined by Forest Products Laboratory testing procedures.



Sunday, August 12, 2007

Adjustable Push-rod



One of the trickier bits in building a high performance engine based on after-market VW components is your valve-train geometry. Here's the situation: The lobes of the cam impart about three-tenths of an inch of linear motion to the cam-follower; what most American's refer to as 'tappets.' A rigid push-rod conveys that motion out to the heads where a lever called a rocker arm is used to reverse the direction of the motion, converting the upward push of the cam into the downward shove of the rocker arm. The rocker arm bears against the head of the valve's stem and the downward shove causes the valve to open by some amount, once it has overcome the pressure of the valve spring.

The tricky bits involve the fact that the motion of the rocker-arm is not linear but is an arc, whereas the rocker-arm itself is not symmetrical, with the out-put side being slightly longer than the input. To add to the complexity of the problem the push-rod on the input-side of the rocker-arm is at an angle of about minus three degrees, whereas the valve stem on the output side of the rocker-arm is at an angle of plus 9.5 degrees, both relative to the traverse centerline of the rocker-arm's fulcrum (ie, the rocker shaft).

Which means less than nothing if you are dealing with a bone stock VW engine. So long as you do not alter any of its dimensions the losses in the valve train are but a trifle.

(The above offers some idea as to why most designers of high-output engines use the cam to actuate the valves directly (as in old flat-head Ford V8).)

Shade-tree types prefer to ignore valve train geometry -- another of those 'unimportant' details. But the sad truth of the matter is that it isn't unusual for a big-bore stroker with a hot-rod cam to perform worse than the stock engine.

Fortunately, for a particular engine configuration, full understanding of the topic is not required. For the two engines, the assembly of which I am describing in this blog, I will provide a 'cook-book' approach that should allow the reader to come within a few percentage points of the ideal geometry. But you will need a couple of special tools. One is an adjustable push-rod, which I'll describe below. The other is modified stock adjusting screw, which I'll describe (and illustrate) in a future post.

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To make an adjustable push-rod you start with a stock push-rod. I prefer the older style because of the smaller head diameter but the later model will also work. (Fig 2 will give you some idea of the difference in head diameter. Some steel push-rod kits use the smaller diameter heads, leading to an error if you check push-rod length with the larger heads.)

Using a hacksaw, cut the push-rod in two. Make the cut approximately in the middle of the rod. Then cut 5/8" to 3/4" from one of the pieces.

Dress the cut ends square with a file. If using the old style, ream the ID with a drill bit suitable for threading to 1/4-20. That would be a #7 but if you don't have a set of number-sized drill bits, you may use 13/64". The later model push-rod has a slightly larger ID and I believe it will accept a 1/4-20 tap without reaming (but check).

Tap each half of the push-rod tube to a depth of at least one inch.

Prepare a section of 1/4-20 threaded rod about 2-1/2" long being sure to chamfer the ends. Run a pair of 1/4-20 nuts onto the rod. Give the threads a drop of oil and screw the rod into the ends of the modified push-rod. The nuts will be used to lock-in the length once it has been determined.

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Fig 3 shows a handful of parts heading for a fellow engine-builder trapped in the Nevada desert. Since I didn't know what type rockers or push-rods he'd be using, I sent one of the old-style adjustables.

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Adjustable push-rods are available from after-market retailers but they usually put the thread at the very end of the rod, making them horribly inconvenient to use.

-R.S.Hoover

Thursday, August 9, 2007

Tappets As Field Mice


Back when I built engines for sale (*) I usta haul all that crap around, putting on a Dog & Pony show at fly-in's, swap-meets and chapter meetings, showing folks how easy it was to convert a VW engine for flight and why my engines were a bit different from all those Other Guys.

Waste of time, pretty much. Oh, I sold a few engines, along with lots of Azusa wheels and the little axle I'd made up for them. But most folks wanted an engine '...just like Ken Rand's' or whatever. All tolled, I only sold three with the fan on the clutch-end of the crank. But I think the main reason for my lack of success was telling the truth when someone would ask about horsepower. (Like all air-cooled engines the Volkswagen has specific thermal limitations. Exceed them and your TBO takes a heavy hit.)

Drive all night to get someplace, unload a ton of tools, jigs, fixtures, parts and brochures, then spend the day showing folks how to put Tab A into Slot B, it sorta takes the thrill out of it, especially when you do something dumb such as dumping your tappets on the ground.

Unlike a Lycoming or Continental which is usually assembled around the crankshaft whilst standing on its nose, the VW crankcase has a number of studs anchored in the left-hand case half and you usually assemble the engine with the left-hand case-half open-side facing up on the work-bench or in the fixture. To mate the two halves you pick up the right-hand case-half, align it with the studs and slide it down onto the left-hand case half. The crankshaft and camshaft is supported in the bearing saddles in the left-hand half of the case while the right-hand half has nothing in it except four tappets.

The best excuse in the world for dumping your tappets is that it couldn't happen with the the early VW engines, in which the tappet and push-rod were a single unit. Assembly habits acquired acquired prior to 1960 were liable to make you look like a klutz after that date. Indeed, for a time following the introduction of the forty-horse 1200 engine, dropping your tappets on the floor -- or forgetting to install the damn things -- was almost a National Sport, at least among VW mechanics.

Which is kinda silly because it's easy to not dump your tappets on the deck. All you gotta do is grab a can of wheel bearing grease and smear a light wipe of the stuff under the head of the tappet. When you pushed the tappet into its bore the grease would cause it to stick long enough for you to put the right-hand case-half into position. (But only under the head. Too much grease in a tappet-bore is a bad, bad thing, since oil to the end tappets can only get there by passing through the middle tappets. Lard them up with grease, it was liable to block the push-rod tubes and prevent oil from reaching the end tappets. But a light wipe under the head of the tappet is okay.)

If you were one of those effete-type VW Mechanics with clean fingernails and a ducks-ass hair-cut you'd scrounge an old throttle wire out of the scrap bin, cut it into pieces about a foot long and twist it around the handle of a breaker-bar. Bend the free ends at right angles, trim them to equal lengths and you had a kind of Super Hair Pin you could poke down into the tappet's bores, where the tension of the spring would hold them in place.

Quick like a bunny, hair-pin tappet retainers appeared in all the magazines as an Absolute Necessity at prices ranging from Simply Silly to Absolutely Ridiculous. And remain so today. If you need a pair, make them. Fig 2 shows a pair made from brass welding rod and another pair made from 1/16th inch music wire. The singleton is a retail item.

You can make the things out of any reasonably resilient wire. Music wire, such as used on the VW throttle cable, is probably best but I've made them out of springy bronze welding rod and electrical fish-tape. But Home Alone, 99 times out of a hundred, I reach for the wheel bearing grease, give them a wipe and put the thing together. Which isn't worth a bucket of warm spit if you're 800 miles from home giving a spiel to a buncha guys and the grease is back home on the shelf.

You can try the Stealth Approach, which is to raise the left-hand case-half as near to the vertical as it will go before the crankshaft flops out on the floor. Then you smear a gob of Lubri-Plate on the right-hand lifters, pop them in place and try to get the case-halves aligned before the lifters come oozing out of their bores, which is exactly what they'll do if you get hit with a couple of questions between Tab A and Slot B.

So there I am at some fly-in giving my spiel on Short Block Assembly and there's my right-hand tappets bouncing around on the hangar floor like cast iron mice. Not what you'd call a good impression. But I can honestly say it was the last time I allowed it to happen. I adopted the Hair Pin Procedure. Which worked fine, until...

Let me offer a whiff of reality about doing demos at fly-ins (and one of the reasons I regularly decline such invitations): People steal things. If you don't have a crew of at least three, you're going to lose stuff. Roping-off your work tables helps, assuming you've hauled along enough rope and stanchions. But there's plenty of times when you have to take a pee, someone starts asking questions of your crew and when you return the far end of the table is bare.

Cost of doing business, right? Pass it along to the customer. But sometimes something critical, such as a magneto or prop-hub would wander off and you're left trying to do a demo without all the parts. So one day I'm just getting into the spiel when I notice the tappet retainers have vanished, along with a stack of shims and the magneto puck.

Doing demos, it's best not to count on having compressed air. If you haul in your own compressor you'll also have to provide a suitable extension cord and hoses, all of which is liable to vanish unless you've got it chained to your table. So I got into the habit of using 'canned air.' Back then, it wasn't air of course; usually some fluorocarbon. Nowadays it's liable to be propane mixed with something to render it less flammable. The key point here is that 'canned air' is usually a liquid under pressure, having a very low boiling point, such as minus thirty degrees.

Want your tappets to stay in place? Don't have a pair of hair pins? Left the wheel bearing grease at home? Then turn your can of 'Dust Off' or whatever upside-down and give the push-rod end of each lifter a shot of liquid. It will chill the lifter enough to harden the lubricant, locking the lifters in their bores at least long enough for you to mate the two case halves.

-R.S.Hoover

(*) If you'll dig through your pile of old 'Sport Aviation' magazines ('old' = mid-1970's ) you'll find my ad tucked away there in the back. Same address. Same engines.

Sunday, August 5, 2007

SURFACE PLATE


[AirVW] Re: Oil pump leak

Wed, 24 Nov 2004 05:48:06

--- In AirVW@yahoogroups.com, "Steve Chilcott" wrote:
> Bob was correct. When I checked the flatness of the full flow face
> plate I discovered there was a cupped sort of channel across the face

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

Well, good for me, then :-)

Of course, I was probably out back sawing up stove wood while the Mechanic-in-Charge of Steve's engine was doing all the work so let's give credit where due, which is to Steve.

But Steve's message offers a nice opportunity for me to preach about a couple of things, one being tools, the other being the need to check every part that goes into your engine.

There's lots of ways to check for flatness. One is to bridge the part with a known-true straight-edge such as the blade of your machinist's combination square then hold the part so you can see if there's any light between it and the straight-edge. For something like the cover-plate on the oil pump, that would serve as a quick & dirty check.

A better check would be to use a surface plate and some Prussian Blue. You smear the blueing onto the plate with your thumb, drop the cover-plate in the mess you just made and give it a light twist. If it's truly flat the blue will transfer to the entire plate.

The only problem here is that if you're only building one engine you probably don't have a surface plate. (Fig 2 shows a 12 x 18 surface plate, about the smallest size suitable for blueprinting a VW crankcase.)

Surface plate is a big piece of cast iron or a thick slab of granite. Cast iron surface plates are kinda rare nowadays bu
t 'way back when every apprentice machinist made their own. Not the casting and curing but the flatting. Learning how to flat a plate lead to teaching the apprentices how to scrape and flat the beds, rails and tables of machine tools, which was a necessary periodic chore back in the days before they used induction-hardened demi-steel for machine tools. (Fig 1 is an 8 x 10 high-precision surface plate used for setting-up cutting tools.)

While cast iron surface plates were inexpensive and not all that difficult to make, they did change their dimensions with the seasons due to the expansion & contraction of the metal.

Granite was more accurate over the long term but flatting a hunk of granite took the task out of the machine shop. Which isn't to say you can't flat granite, just that it isn't a commonly taught skill. Unless you're into optics.


Nowadays you can buy a small surface plate for a very reasonable price but if you're only building one engine there are a number of substitutes that will fill the bill. The one most commonly available is a twelve-inch square of polished granite tile, available from Home Depot. To make it useful, get a piece of well dried 3/4" plywood, seal it up good with thinned varnish and after that cures, bed the tile in a layer of urethane painter's caulk. To ensure the caulking will cure, give the back of the tile a spritz of water before smooshing it into the caulking. Once it cures, the caulk will act as an elastomere, isolating the granite from the wood. (Fig 3. is an inexpensive 9 x 12 surface plate used for flatting, checking valve springs and other low-precision chores.)


Prussian Blue is the other head-scratcher for non-machinists, in that most of you won't know where to get it and will find it rather pricey for just one engine. So use lip stick. Yeah, they always look at me when I say that. Forget it. Go down to the Dollar Store or whatever and look for inexpensive cosmetics. Color isn't important. I generally look for stuff on sale, buy a couple of tubes of whatever.

Prussian Blue (or lip stick) serves as your 'spotting compound' when checking the fit of your valves after being lapped, and of the cylinder barrels in their bores and if the top edge of the barrels is true and the mesh of your cam-gear and lots of other stuff. Lipstick also cleans up nice.

Steve's experience with his leaky pump is a nice example why you can't just bolt parts together and expect to end up with a good engine. The fact it runs is not the definitive test. Virtually any collection of VW parts will run.

(NOTE: Indeed, the most common problem is that novice engine builders are not even aware of them, assuming that if the thing runs at all, it's okay to fly.)

The tricky bit -- and the enormous mass of detail not contained in all those swell manuals telling you how to bolt things together -- is what to do to correct the numerous problems that crop up along the way, such as the drips or a tight bearing (or a loose one), valve gears that don't mesh proper or cock-eyed valve train geometry.

Experienced engine builders have found the best solution is to not let such errors occur. To prevent them, they blueprint all of the parts first as individual components then as sub-assemblies, mating them with their associated parts in as many pre-assembly steps as it takes, correcting errors as they are discovered.

This method is an absolute necessity when you have only one engines-worth of parts to work with.

-R.S.Hoover
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