CH - Chugger's Progress

Chugger is an exercise in low-cost construction, a sturdy little bird built mostly from Box Store lumber, powered by a converted Volkswagen engine spinning a home-made propeller. The landing gear uses go-cart wheels with tires from a baggage cart.

Chugger would normally be called a fabric-covered wooden airplane but the truth is, wooden airplanes use steel fittings at every stress concentration point, such as where the landing gear attaches to the fuselage or the wings to the pylon over the pilot's head. A major cost-savings was to be the use of inexpensive mild steel rather than chrome-moly for fittings, as Erik Clutton has done with his F.R.E.D. This was the standard method in the early days of aviation, prior to the advent of malleable high-strength steels. The only down-side is that when you make a fitting from mild steel it needs to be as much as three times thicker than when made of alloy steel. And that means three times heavier as well, since all steel weighs about the same.

Still, it was obviously do-able and I forged ahead, working out the weight of every single piece of wood and every fitting too, for airplanes are the ultimate Balancing Act. Spread-sheets were a big help here because like most balancing acts you must concern yourself not only with the mass but how far it's located from the point of balance. Mass times distance becomes moment and a relatively small change can have a significant impact when the part is located far from the center of balance.

The hand-maiden of low-cost was ease of fabrication; a flying machine literally anyone could duplicate. But Chugger is also meant to be realistic and today most American's are fat so it had to be big enough to carry a fat person, which caused the wings to grow a bit. Still, it had to be small enough to build in the typical garage. I wanted the landing gear to also serve as a durable trailer, allowing the airplane to be towed on its own wheels. Accordingly, the wings had to fold. Unfortunately, I've since learned that most airport managers will not allow a towable aircraft to be erected and flown from their field unless it first undergoes an inspection by a 'certified' mechanic.

Drag increases exponentially with velocity but I've flown some real tumbleweeds that were not only safe but whose controls had a delightfully positive feel. Since tumbleweeds are never very fast I was more than happy with an expectation of 75 to 80mph for cruise. Accordingly, I paid scant attention to streamlining. But here in the western United States, for an airplane to be useful it must have a range of at least 300 miles, and more would be better. I included tankage for twenty gallons of fuel -- about one hundred and twenty pounds of the stuff. Add that to a 250 pound pilot and I found the wings were acting like Pinochio's nose, which forced me to redesign the fittings.

A ten gallon tank fit nicely in each wing but made it impossible to fold the wings without first draining the fuel. Defueling an aircraft is another thing airport managers get a bit huffy about.

Somewhere along in there it became pretty obvious that in order to fly really well my heavy, draggy, inexpensive, road-towable flying machine was going to need more power than I could get out of an inexpensive engine.

One reason I'd avoided aerodynamic drag was because I'm not very well educated and some of the equations cause my eyes to bleed. Fortunately I found some design texts from the 1930's that addressed low-speed drag in terms I could understand. With the help of a spread sheet I quickly learned that my light-weight, easily built -- but slab-sided -- empennage was generating about six times as much drag as a thicker but more streamlined design. The streamlined design was more difficult to build but the reduction in drag combined with a strict diet put the Chugger back into the realm of Volkswagen-powered aviation.

Like all diets, this one proved expensive, for it meant re-designing all of those lovely, low-cost mild steel fittings for SAE 4130 chrome-moly steel. While this appears to violate a basic tenet of the design, the cost of the 4130 is several thousand dollars less than the cost of replacing the converted Volkswagen with a small Continental. In keeping with the goal of easy fabrication I'm redesigning the fittings to allow them to be made from 4130 steel strips of standard dimensions. Which I should finish any year now :-)

In the meantime the engine is coming along, as is the 68x38 propeller. More detailed drawings and the occasional photo will be posted to the Chuggers Group on Yahoo.

-R.S.Hoover

Valve Spring Tester

Do-It-Yourself Valve Spring Tester

By

Robert S. Hoover © 2003




A Volkswagen cylinder head contains seventy-seven individual components, the majority of which are capable of rendering the engine inoperable should it fail. Some of the components, such as the studs and the head casting itself are static and not subject to friction but due to the large number of dynamic components and generally poor valve train lubrication, they make up a significant portion of the engine's pumping losses. Since the pumping losses represent the engine's 'overhead,' any reduction in the pumping losses appears as an increase in the engine's output, usually for no increase in fuel consumption. By focusing on the details of those pumping losses, experience has shown that it is possible to achieve a significant increase the output of the engine.

Complex by modern-day standards, where an increasing number of engines are OHC, despite its high parts-count the VW valve train is reasonably robust thanks to seventy years of use during which the most failure-prone components have been identified and re-designed to improve their durability. That is, durability in vehicular terms. When compared to features found in aircraft engines, Volkswagen heads are something of a joke. When the displacement of the '1600' (actual displacement is 1584cc) is increased, as is commonly done when converting the engine for use in aircraft, durability takes a further hit. Fortunately, it takes only a modest amount of effort to improve its durability by an order of magnitude.

Most of the valve-train durability enhancements are covered in the so-called HVX modifications, previously posted and discussed. Although rarely seen on engines built for the Kiddie Trade and not found on any of the commercially available VW's converted for flight, the HVX mods have proven their worth through forty years of use in professionally built, high-output engines. Most recently, the use of thick-film lubricants have enhanced durability even further. (Specific How-To information for applying thick-film lubricants to valve train components will be found in the chapter on Coatings.)



Valve Train (Springs)

Poppet valves are a one-way sort of creature The cam pushes them open but they are closed by the action of the valve spring. The spring needs to be strong enough to close the valve tightly enough to make a leak-free seal but the valve spring merely initiates the sealing process. The real sealing is accomplished by the tapered sealing surface of the valve being wedged into the cone of the valve seat by the enormous pressure of combustion.

Modern-day valve springs are coiled compression springs installed around the stem of the valve and connected to it by a retainer that is free to rotate. The retainer is secured to the stem of the valve by a pair of keepers in the form of a cylindrical wedge which mates with grooves machined into the stem of the valve.


The strength of the stock VW valve spring is determined by measuring the amount of force needed to compress the spring to a height of 31.0mm (~1.220"). A number of factors can effect the strength of a coil spring and like all other VW specs, the tolerance is quite large, ranging from 117 to 135 pounds.

The valve's spring must be compressed when the valve is opened. The energy needed to compress the spring is part of the Otto Cycle's 'pumping losses' and anything that helps reduce those losses will improve the engine's efficiency. For a low rpm engine the lower valve spring value is more than enough to ensure proper operation and since the lower value reduces the pumping losses, it also serves to improve performance. Further enhancement occurs when the strength of all eight springs is equal or as nearly so as possible. For those reasons, a standard practice in any properly built engine is to use a set of springs that have been closely matched.



Matching a set of valve springs to within a pound or so can be quite difficult if you're drawing upon used parts. Not only are there different varieties of VW valve spring, each time a VW engine is stopped at least two valve springs will be compressed. In a vehicle that is driven daily this is seldom a problem but in an airplane engine that may sit for weeks between flights, the compressed spring is liable to weaken. When doing a valve job on a VW engine modified for flight, it's a good idea to re-test the valve springs.

Ideally, a new engine or a rebuilt head should include a set of new valve springs but with the number of registered air cooled Volkswagens in steady decline, it has become increasingly difficult to locate quality parts. It isn't uncommon to find after-market VW valve springs which are not square, in that the ends of the spring are not perpendicular to their axis. Such springs do not provide a symmetrical force when compressed and should not be used, an item mentioned in the factory service manual. You will also find new springs wound of lighter gauge wire than stock springs and which fail to provide the required strength when compressed. Springs longer than stock are also fairly common, often needing excessive pressure to be compressed to the specified height. Such junk is often advertised as 'racing' equipment, clearly meant for mechanically naive youngsters.

Volkswagen valve springs are progressively-wound, with the coils being closer together at the bottom than the top. Some after-market springs are not progressively-wound. (It pays to inspect all after-market VW parts before you buy.)

Twenty years ago I would never put used valve springs in an engine. Nowadays, used stock springs are often better than new, after-market stuff. If a used spring isn't rusty and shows no signs of fretting or jamming, I'll go ahead and test them.

New or used, it is extremely risky to use any valve spring without testing..

Valve spring testers are commonly available but even the least expensive model is several hundred dollars if purchased new. Fortunately, a common bathroom scale may be used to make your own spring tester. Unfortunately, inexpensive bathroom scales are not very accurate. Accuracy - - at least enough for the task at hand -- is assured by calibrating the scale with a mass of known weight, such as your own body, immediately prior to use. That of course assumes you know your own weight to within a pound. Balance beam type scales tend to be more accurate than low-cost spring-type scales. To calibrate the valve-spring's scale simply weigh yourself on a balance-beam scale then adjust the bathroom scale to read the same amount.

If you do not have access to a balance-beam type scale you'll have to create a test-mass of known weight. Having a specific gravity of 1.00, water is the handiest mass but you'd need at least fifteen gallons to verify the accuracy of your scale and the container would introduce some amount of error.

Lead is a very handy mass, having a specific gravity 11.34 times that of water and if you have a graduated beaker (which is easy enough to make) it's fairly simple to determine the volume of a given lump of lead. Unfortunately, pure lead is rather rare stuff and since other metals often make up as much as half the mass of wheel weights and other common lead alloys, it is impossible to calculate the weight of such alloys based volume alone.

If you have an accurate scale, such a laboratory type, you can of course weigh a sample of melted wheel weights, plumber's solder or other lead alloy, determine it's specific gravity and apply that to the mass as a whole.

When you are forced to create your own calibration mass without access to a precision scale you'll probably find plain old fashioned mild steel to be the best choice. This is because the amount of carbon and trace elements is typically less than 1%, allowing you to use a specific gravity of 7.93 or about 495 pounds per cubic foot ( about 4.4833 ounces per cubic inch ).

Since mild steel comes in standard sizes, even when purchased as scrap you can determine it's weight with good accuracy by simply measuring the piece, calculating its volume and applying the figures above. Then too, many scrap yards now use electronic scales accurate to a fraction of a pound, allowing you to simply buy a test-mass of the appropriate weight. Of course, being able to calculate the weight is a handy means of keeping them honest. (Hint: Weigh yourself on the junkyard's scales. Everyone does :-)

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NOTE At one time it was common for EAA chapters to maintain a tool crib and test-mass for use by its members. The test-mass was usually pigs of lead- alloy cast in convenient sizes from five to twenty-five pounds, clearly stamped with their weight after being accurately weighed. The fact EAA headquarters no longer puts any emphasis on such basic needs is good evidence of their growing disinterest in supporting grass-roots aviation.
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(I use a mill-end of 6" steel bar as my test mass. It is about 16" long and weighs 128 lb, 4-3/4 oz).

Volkswagen's valve-spring specification calls for a compression of 117 to 135 pounds at a height of 31mm. I made a gauge of this dimension that allows me to set the height of a bolt screwed into a pallet which sits atop a bathroom scale. The scale sits on a wooden base to which a fulcrum has been attached. The spring being tested is sipped over the bolt and a lever is used to compress it. When the lever touches the bolt I know the spring has been compressed to a height of 1.220" (ie, 31mm). And I know precisely when that happens because I've rigged the lever to turn on an LED when it touches the bolt. The LED is taped to the dial of the bathroom scale; all I have to do is keep my eye on the dial. When the light comes on I read the dial and jot down the weight on a stick-up. To eliminate human error each spring is tested at least three times. Any obvious flyers are thrown out and the testing is repeated until I have a cluster of similar values.

I try to do forty or fifty valve springs at a time. The first step is to clean them and inspect each spring visually for scratches or pitting anything that might serve as a stress-riser. They are then gauged for total length, then for squareness, both tests done on a surface plate allowing me to do a handful of springs at a time. Alas, when dealing with new, after-market springs those two tests may reduce the batch by half.

Any springs that pass the initial tests are then tested for compression height. They are then sorted according to their stick-ums and made up into matching sets, coated with preservative and put aside until needed. It isn't the Bureau of Standards but it's better than guess-work, which is what you have if you don't test your springs.

In making up a set of springs for a low rpm engine I want the lowest strength and the narrowest range. Of the two, I think matching the range is the most important factor. If I can't make up a set within a pound or two of a given strength, I'll generally keep looking.

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NOTE: Many fail to appreciate the importance of 'balance' in an engine. The reason professionals put so much emphasis on balancing is because the engine must use power to overcome any imbalance before any usable power can appear at the crankshaft. That means any imbalance is effectively multiplied by two. Using springs of equal strength is part of the balancing process.
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If you are building just one engine you should try to find someone who has a valve-spring tester. Baring that, you should cobble up your own using a bathroom scale.

So what happens if you simply buy a new set of springs and throw them in? Hopefully, not a lot. There is a chance the set may contain a spring having a radically different value but with a tolerance of 18 pounds, the odds are the engine is going to run. Sorta :-)

I should also mention that I don't know of a single non-professional engine- builder who tests their valve springs. This is another of those details they deem 'unimportant.' And when addressed in isolation, perhaps it is. But a professional engine builder addresses all of those 'unimportant' details, picking up a little torque here, better fuel consumption there, optimizing each unimportant detail for better efficiency, more power, cooler running and slower wear. No single one of those unimportant details results in a dramatic change. But add them all together and it isn't uncommon for a professionally built engine to produce up to 25% more power than a poorly built engine of exactly the same displacement. And to last twice as long as well.

-R.S.Hoover

AV - N666RH

Guy comes by the shop hoping to bum me outta some ammo for his machine gun and finds me stitching a spar together with a gnu-matic brad-driver & foamy glue. He's okay watching me smear on the glue. And he's still happy when I put the plywood into place, aligned by a couple of 3/4" #20 nails previously driven, now with their heads snipped off. He even helps me clamp it to the bench. But when I pick up the pneumatic brad-driver and start to stitch he begins to frown, as if he's never it done before.

"I've never seen it done like that," he sez.

"Saves a buncha time," I say as I shoot 5/8" #18 brads about every inch and a half. It's the spar for a horizontal stabilizer, sorta-copied from Pete Bower's 'Fly Baby.' It's about six feet long and
three inches deep in the middle, tapering to an inch and a half at each end. The spar caps are 3/8" square Western Hemlock, ripped out of a 2x4. The plywood shear-web is a piece of doorskin; 1/8" Luan. It's the third one I've built, the first two having been destroyed in
various tests. Not counting the glue and brads, each cost about a dollar. Plus a few hundred hours of design time.

"Is that an Approved Method?" he asks.

The brads are tacking the assemblage to the work bench, which is protected by a layer of waxed paper. (Live & lurn :-) I'll leave it to cure for a couple of days then pry it off, at which time it will
look like hell warmed over. But it cleans up nice with a disk sander. Then comes some filler blocks to be fitted and interior varnish before I can apply the closing face, which is left a bit over-size and malleted down onto the exposed tips of the brads.

"Beats the hell outta me," I tell him. "But it seems to work pretty good."

"Jesus!" he shouts, jumping back and making the sign of the cross. "You... you're EXPERIMENTING!"

That's when I turned slowly toward him and smiled, showing him my pointy teeth and red LED's for eyes. He gave a tiny shriek and ran off, shouting: "Pope Paul! Pope Paul!"

-R.S.Hoover

Cam Hard = Chunkie Attacks

Failure to properly prep the cam is one of the most common methods of trashing an engine. (Originally posted in 2003 after being rejected by the usual magazines :-)

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Stock VW engine, you’re looking at more than fifty years of continuous development and production.

Not a lot of secrets in a stocker. Which wasn’t always the case.

When it was introduced the Volkswagen engine violated many Conventional Wisdoms associated with automobile engine design. For example, each lobe of the cam actuates two cam followers. Conventional Wisdom insisted the four lobes on a VW wiggle stick would wear twice as fast as the eight lobes on all other four-banger cams... unless you came up with some way to precisely control the hardness of your cams and lifters, which no one had back then. Oh, there was that new gaseous nitriding process but that only worked with steel. VW cams and lifters were cast iron and no one had come up with an accurate hardening process that was economical enough to be used for mass produced cast iron parts. Except an outfit called Krupp.

Ditto for that magnesium alloy crankcase. Never work, not for mass production. Way too expensive. Unless you can come up with a better method of extracting magnesium from sea water. Like that Dowmettal company. Same story for those crazy molded rubber parts in the torsion-bar suspension system. Just won’t work, unless you can come up with a synthetic rubber that’s actually better than the real thing. Maybe some of that Buna stuff would work... (nowadays we call it Neoprene).

Professor Porsche and his gang of engineers didn’t see such things as limitations, they saw them as challenges and came up with an engine that remains in production today. (You can get new replacement engines from the VW plant in Puebla, Mexico. Pretty good little engines.) And if you liked the torsion bar suspension system on the original People’s Car you’ll find it still going strong under our main battle tank.

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One of the tricky bits on a VW cam is getting the hardness just right. Not a big problem nowadays, thanks to Krupp and Adolph Fry. Today you simply look it up on a chart and set the dials to produce whatever hardness and depth is required, duplicating a process that has been in common use now for more than sixty years. It’s no more difficult than, say, programming your VCR. (Yeah, I know... But there it is :-)

For those of you not familiar with surface hardening, take a look at CAMHARD01. Nowadays there are lots of ways to harden the surface of iron, steel or cast iron but one of the handiest heats the metal in an atmosphere of nitrogen gas. The depth of the hardened surface can be controlled by the temperature to which the metal is raised, how long it stays in the oven, the concentration of nitrogen inside the oven, how the part is cooled and so forth.

Hardening a cam is a bit tricker than most other hardening chores because cams have lots of corners. When hardening a part the corners are exposed to the heat & gas on two sides and tend to become harder than other areas of the part. To give you some idea what I’m talking about go see CAMHARD02.

A brittle corner on a cam can be fatal to an engine. The corners approach the hardness of a diamond (seriously! Nitriding can produce a Mohs hardness of better than 9. [Diamond is a 10]).

Talk about the perfect abrasive! Microscopic fragments of diamond-hard material being chipped off and distributed around the inside of an engine... You can bet your bean-bag it caused the VW engineers more than few headaches before they figured it out.

Corners on a cam? (Someone said.) Where the hell are there corners on a cam!


See Figure 3. That’s a picture of a typical after-market cam, fresh back from nitriding. See all those nice sharp edges? That is where the metal turns a corner. Those edges are so brittle that casual handling can cause them to chip like glass. (Look closely. See that tiny notch near the nose?) Even, worse, see the mold-lines on the cam? (Remember, cams are just high-density cast iron.) The blank comes out of the mold with a chilled hardness that is nearly as good as nitriding (although not nearly so deep). Nitride a chilled-cast surface, you end up with hardness well past 9 on the Mohs Scale and a virtual 100% guarantee of chipping those edges unless you do something about it.

Figure 4 shows the pointy end of the lobe on an after-market cam. It also shows all those un-dressed edges. This is normal for after-market parts. It is up to the person assembling the engine to determine which edges need to be chamfered, by how much and the method most suitable for doing so. For comparison, Figure 5 is a stock VW cam. (Notice that the end of the stock cam is not as sharp.) Note that all of the edges on the stock cam are nicely chamfered.

Take another look at CAMHARD02, the drawing showing how the hardness penetrates the metal. The tip of the lobs concentrates the heat during the hardening process in much the same fashion as does a corner. In fact, the tip of the cam’s lobe has to be harder than its slopes or heel if you want the thing to wear at a slow rate. And if the tip is harder than the heel, you can bet your bippie that the edges of the lobe’s nose are even harder still.

You simply can’t allow fragments from those edges to get inside your engine. Even with a full-flow oil filter such debris still gets one shot at your oil pump. And with stuff approaching the hardness of a diamond, one shot is all is takes.

So we don’t let that happen. And neither did Volkswagen. But I don’t have to tell you that because you can see it for yourself. See those nicely chamfered edges in Figure 5? That’s a stock Volkswagen cam. Look at Figure 6; there it is again. That’s a used VW cam, something I pulled out from under the bench. But you can clearly see the chamfering and, if you look real close, the VW logo cast into the metal.

See the lower lobe in Figure 6? You can see that the chamfer is a bit smaller than on the heel of the upper lobe. The chamfer doesn’t have to be very big if all you want to do is get rid of the chunkies. In fact, a chamfer of only thirty-thou or so is enough to make the edges of an after-market cam safe for society. Sure enough, there’s a picture of a lightly chamfered after-market cam lurking in Figure 7. (Wider would be better. I just whizzed this one up for the photo-op :-) If you’ve never clearanced a cam nor chamfered one, one slip of the grinder can screw the pooch in a major way, as in trashing the cam. I suggest you cover the lobes and journals with masking tape before doing any grinding.

Normally, you chamfer an after-market cam when you grind the notches that allow it to work with a stroker crank. That is, you do all your grinding - and clean-up - at one time, usually in a ‘dirty’ area of your shop. (Engines are always assembled in a clean area. It’s not an operating theater but the assembly area should be cleaner than the average kitchen.) No stroker? Then you can chamfer it any time you wish. (It’s called dressing the edges and is a standard pre-assembly procedure with any after-market part.) Just be sure to clean that sucker to within an inch of its life after doing any grinding on the thing. The idea here is to keep abrasive debris out of your engine. Grind on the cam (or anything else) then use the part without a perfect clean-up simply doesn’t make sense.

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Cams are made from cast iron because it is easy to grind to the required curves. After the lobes are ground, the surface of a Volkswagen cam is hardened to a precise degree. The result is a cam with lobes just hard enough so that the rate of wear for one cam-lobe is compatible with that of the distributed wear across the face of two cam-followers (i.e., the lifters rotate to distribute the wear). This results in uniform rate of wear allowing reliable long-term performance.

The process of surface hardening concentrates the harness along edges and thinner sections. By the time you have achieved the desired hardness in the middle of the piece any sharp edges will have been hardened to the point of brittleness.

Cast iron has a granular structure; harden it to the point of brittleness, it will chip like a piece of glass. But only if you let it. Standard automotive engineering practice is to ensure such debris is never allowed inside an engine.

When hardened debris passes through the oil pump, it will create a scratch or score. Once the metal has been scored, it will not heal. The more times such debris is allowed to pass through the pump, the more wear that will accumulate.

When building an engine, any edge capable of spawning debris is chamfered, rounded, stoned or even polished, as the case may be. ANY EDGE. Throughout the engine. The need for such attention to detail is understood by every competent mechanic. The proof of that need and the practices required is clearly evident by simply examining a professionally built engine.

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There are no secrets in a VW engine. Or so I thought :-)

Are you using an after-market cam? Did you clean it up and chamfer the edges? Gap your rings? Stone the edges? Balance everything? That’s your job, you know; attending to all those ‘unimportant’ details the phony experts brush aside. Because when you build an engine, you’re the Mechanic in Charge.

-R.S.Hoover

Drilling for Eight

Almost as soon as I posted '4-into-8' (which should immediately precede this article) I began receiving messages saying the drill-jig I've been using since the early 1970's didn't work. (!!) I even got a couple saying it didn't exist... and if it did exist, it wouldn't work. :-)

(That's it over there on the left. And just for insurance there is an uglier-but-identical home-made copy of it in my toolbox.)





What works (and exists) according to the instant experts, is a different type of drill-jig having six holes instead of eight. According to the folks who wrote, 'everyone' uses the six-hole type, pictured on the right.

I don't.

As I said, I've used the 8-hole type -- successfully -- for more than 30 years and think this whole discussion is a bit lame, partly because of the assumption on which it is based but more so on the fact that, having used both types, I've found the 8-hole version to be not only more accurate, since it is indexed using four dowels, but far easier to set-up and use.





Over on the right you can see the drill-jig installed in the spigot of a cut-down flywheel.













The four new holes are drilled using a 5/16" bit, a spindle speed of about 900 rpm and a liberal dose of cutting oil. (I use SulTex.)













After drilling, the holes are sized depending on their use. If they are in the crankshaft they are reamed to 8mm; if in the flywheel they are opened up to Letter Size 'O'. The edges are carefully chamfered, the part is cleaned and you're all done.





So what's all this nonsense about the thing not working? (Or not existing :-)

As a matter of fact, it is possible to screw things up. If you put the drill-jig on the clutch-side of the flywheel, for example, the off-set hole will now be off-set in the OPPOSITE direction. Hammer as long & hard as you like, a flywheel drilled in that fashion simply won't fit.

I think that's what's behind the messages. Somebody did it wrong, blamed it on the drill-jig, and told all his buds that the thing didn't work. And if you've been on the internet for more than five minutes you're probably aware that 99% of the 'information' you'll find there is hearsay; people parroting something they've read or heard, as opposed to direct, personal experience.

When the 8-hole drill-jig is used correctly, you'll end up with a tight, precise fit. And I've got pretty good evidence it will last a long time if given a bit of care.

-R.S.Hoover

Stoning Your Rods

Last Sunday after church I was chatting with an Eager Young Airman building a Volksplane. Started around Christmas, he’s just finished covering the wings and was about to start on his engine.

“The parts are due to arrive tomorrow,” the Eager Young Airman said. “I’ll put the engine together after I get home from work.”

I must of done something because he squints at me and sez: “What?”

How do you explain chartreuse to a blind man? In the end I merely shrugged, “I generally take a bit more time.”

“Yeah,” he smiles. “I’ve read some of your stuff.” He doesn’t laugh aloud but you could hear it. “I’ve put together a lot of engines,” he brags. “I won’t have any trouble.”

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(And with that kind of a lead-in you can guess what comes next :-)

Around noon-time Thursday he called me from work, a bit less perky than before. Was there a chance I could come by his house that evening? He’s having a bit of trouble with his engine.

No. In fact, hell no! He lives some distance away and the local freeways slow to about 15mph between five and seven. “What’s the problem?” I ast him.

Pregnant pause then: “Nothing seems to fit!” His voice is filled with frustration, exasperation and - - to his credit - - a hint of embarrassment.

“Like what?”

“Well... the rods lock-up.”

“You got the right bearings?”

“STD’s,” he sez. (In Engine-Tok that means ‘Standard,’ rather than a dose of clap.)

“On the carton or on the bearing shell?” He doesn’t answer, which means the carton was marked STD. He’s got no idea in the blue-eyed world what was inside of the box. “Didja mike the crank? ID the rods?”

His answer is: “It’s all brand new stuff!” (Which means 'no.')

I can’t help but laugh at that. “Yeah, but from where?”

Turns out, he doesn’t own a 3" mike; doesn’t even know the spec for the crank’s journals. I tell him to bring it by the following day, let me take a look at it.

Friday evening he shows up with an engine’s worth of parts rattling around in his back seat. I’ve cleared some bench space and as we’re hauling the parts into the shop he mentions that it’s twenty-seven miles from his house to mine, which is about five dollars-worth of fuel each way. He sounds sort of surprised.

“No kidding?” (Okay, mebbe with just a hint of irony :-)

His crankshaft is one of those Chinese jobbies, an 82mm stroker for which he’d paid less than $200. Why so cheap? Partly because it's not very good. The #2 rod journal miked more than a thou over spec and the #1 Main was 2.1638" - - four tenth under the lo-spec of 2.1642". Run-out is seven-tenths, right on the outer limit. He starts yelling about returning the parts, suing the retailer for his lost time and other Yuppie bullshit.

“Don’t bother,” I tell him. “Shop by price and this is what you’re going to get. This is the norm nowadays." Trying to sue the people who sell this junk is throwing good money after bad.

“But it doesn’t fit,” he wails.

“Of course not,” I said. He makes a WTF gesture. “Making things fit is your job,” I tell him.

“I’ve never had any trouble before,” he says. Which means he’s probably only worked on stock engines.

I’m checking his rods. They aren’t new, they are stock rebuilt units that happen to be too short for use with an 82mm crankshaft. Enormously popular, of course. But as rods go these happen to be a pretty good set, with a weight span of only 4 grams. He follows me back & forth as I lighten the two fat rods to match the two skinny ones, each of which weighs within a tenth of a gram of the other. Of the two heavy rods, one is a tad less than two grams out, the other just over four. Four grams is a lot of grinding, followed by smoothing things up with the belt polisher.

He has never seen the jig for doing big-end/little-end balancing, asks: “What’s that for?” Which tells me I’m wasting my time.

I split the rods, pull them apart. None have been stoned; all show the usual burr created by honing. (Note: Stoning away the sharp feather-edge left by the hone produces a distinctive line of light. Steel-backed bearing shells usually require the same treatment, at least on the back-side of the shell.)

I show him the burr, let him feel it. On one rod the burr has a wrinkled appearance, apparently folded under when he installed the shells. It's more than enough to cause the rod to lock-up. He can’t believe it. “Where’d that come from?” I toss his new bearing shells into some lacquer thinner while I stone his rods, wiping away the burr. Then I clean his bearing shells and do the same with them.

“I never had any trouble before,” he says again in a voice small enough to ignore, which I do.

Chucked into the vise and torqued to spec, the mikes show the usual spread across the rod’s big-end ID’s and I paint a big ‘2' on the fattest of them. Over on the clean side of the shop is two shelves of bearings, odds and ends acquired over forty years of building VW engines. Which happens to include a set of ‘Silverline’ conjinetes para motor that I know to be a few tenths under spec. I clean the rod and install the shells, put the assembly in a plastic bag. “Take your crank to HDS in Escondido and have them polish a couple of tenths off the #2 rod journal.” Since shit happens, I use fingernail polish to mark the correct journal. “When you get it back, after you pull those damn plugs and clean the thing, install this particular rod on #2.”

Some of the oil passages on his Chinese stroker are drillings sealed with 4mm socket-head set-screws. They need to be pulled and the oil passages cleaned then re-installed with Loc-tite and straked. Which he hadn't done. But even as I explained the what & why I had a hunch he wouldn’t bother. After all, he’s built a lot of engines. And never had any trouble.

He’s been here nearly two hours. His particular collection of parts will probably need another twenty hours of work before they’re ready for assembly but I've a hunch it's never going to happen. It’s late, I’m tired and he still thinks its all bullshit. So I wish him good luck and wave him on his way. Maybe he'll read this and get the hint. But after spending two hours with him, I doubt it. Really good engines are more than an assemblage of parts.

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

Is this sort of thing common? Nowadays the answer is a loud ‘Yes!’ The surface-finish of the guy’s crankshaft was pretty bad (it should look like a mirror), a fact he’ll learn for himself when he sees the difference between the journal polished by HDS (an automotive machine shop) and the other journals. Other than being the wrong rods for the engine, they were okay but the cam was a joke, intended to move the power-band well above the point of optimum efficiency for a propeller. But trying to explain such things is usually futile. This particular builder has some prior experience but it’s of the ‘Compleate Idiot’ variety, where you’re told it’s okay to scrape machined surfaces with a pocket-knife and pound on bearings with a sledge hammer. (I’m serious here, folks.) He's convinced that my attention to detail is unnecessary. After all, he's assembled a few engines and they ran just fine... in a car.

I wouldn’t want to fly behind the guy’s engine but that applies to most of the converted VW’s I’ve seen. So long as the ‘experts’ are telling people it’s okay to paint their engine with barbecue paint and that it will rust out before it wears out, we’ll continue to see newbies risking their lives behind improperly assembled engines.

-R.S.Hoover

4 -- into -- 8

As originally designed the Volkswagen’s flywheel was located using four 7mm dowel pins. The pins were quite short, extending barely a quarter of an inch into the crankshaft and even less into the flywheel. When the Porsche 356 was introduced in 1948 it used many Volkswagen components including the engine, although with numerous modifications. One of those mods was to replace the flywheels four 7mm dowel pins with eight pins. When American hot-rodders began massaging the VW engine one of the first things they did was to re-dowel the flywheel following the Porsche pattern but using 11/32" (8.73mm) dowels three-quarters of an inch in length, seating the dowels deeper into the crankshaft and full depth through the flywheel. Volkswagen eventually followed the American’s lead - - as they did with many other hot-rod innovations such as case-savers and the external oil cooler - - but using only four 8mm dowels.

Four 8mm dowels proved sturdy enough even for fully laden Transporters but eight dowels have become standard for all high-rpm engines. One reason for this is that in the Porsche pattern one of the extra dowel pins is offset by 1.25mm, allowing the flywheel to be indexed to the crankshaft in a specific orientation. Since the crankshaft and flywheel are balanced as a unit for high rpm engines, the Porsche pattern ensures the as-balanced orientation will not be disturbed.

Nowadays most VW engines converted for flight draw upon the VW racing community for parts and while 8 dowel pins are not needed in a flying Volkswagen, after-market crankshafts usually comes with the extra dowels already installed. This leaves the homebuilder with two options. They may remove the extra four dowel pins, being sure to pull the set that includes the off-set pin, or they may re-drill the component that must mate to the 8-doweled crank.








Here's a Great Planes flywheel-end flange about to be drilled to fit on an 8-dowel crankshaft. Steve will sell it to you already drilled for eight. Or sell you a drill-jig (but not like mine) so you can do the job yourself.




Pulling a flywheel dowel is a no-brainer if you’re tooled up for it, which most homebuilders aren’t. The basic tool is a slide-hammer with a set of metric collets - - probably $150 at todays prices (2007). The tricky bit here is that collet sets aren’t created equal. In some, the collar is too large to allow the 8mm collet to get a bite on a VW’s dowel pin. Then too, even with the proper collet some dowels refuse to budge, usually because a bit of swarf was trapped in the bore when the dowel was driven home. And finally, there are homebuilders who simply can’t afford an 8mm collet, let alone a whole set.

A reasonable substitute for an 8mm collet is a cheap pair of vise-grips. Not real American-made Vise-Grips with their hardened jaws but a pair of cheap Chinese copies with jaws that flatten out the first time you use them. Find yourself a set like that and you can make a dandy dowel puller by simply drilling the jaws with a letter-size ‘O’ drill (which is pretty close to 8mm). (Dressing the jaws flat with a file will increase their grip on the dowel.) Add a whiff of valve grinding compound to the jaws and they will grab ahold of the hardened steel dowel even more tightly than a collet.

Heating the crankshaft to about 200 F. is always a help in pulling dowel pins.

Finally, when you get one that is seriously stuck, install a round-nosed punch in a chatter gun or riveting hammer, press it firmly against the bottom of the threaded bore on the pulley-end of the crankshaft and give it a brappp whilst pulling gently on the collet. The dowel will ‘walk’ out of its bore like a magic trick.

The other option - - re-drilling a part to match the 8-dowel crank - - is equally easy. You simply buy a suitable drill-jig from an after-market VW retailer. I took a snap-shot of the one I use, along with an assortment of dowels. It’s more than thirty years old and still works okay. But shop around. In writing this article I checked with half a dozen sources and found the price of a drill jig varied from less than $20 to more than $70.

The hole is always drilled undersize, of course, using a 5/16" drill bit. For a press-fit, once drilled, you use an 8mm reamer to bring it to size. The reamer you use for your valve guides will work but you’ll get a better finish on your guides if you reserve a carefully honed reamer for that task alone. For dowels, a cheap foreign-made reamer will work just fine. But again, shop around. Lotsa guys will charge you fifty bucks for an eight-dollar reamer. If you want a free fit you’d drill it out with a letter-size ‘O’ drill bit and not bother with the reamer. In either case, always chamfer the edges of the finished hole.

-R.S.Hoover