Wednesday, November 22, 2006

AV - Flying On The Cheap - Fabric




In describing how it is possible to build a safe, reliable airplane for very little money I mentioned covering the wings with polyester fabric shrunk tight with a clothes iron and sealed with urethane varnish into which you've mixed some powdered aluminum. (The original message, posted a couple of years ago, was titled ‘Flying on the Cheap.' It has since been reposted widely and has generated a lot of email.)

Boy, did I catch hell :-)

Alas, the majority of the mail was negative, some politely so, the general tenor being that all good airplanes were always made entirely of materials certified for use in aviation. Then there were those a bit less polite, telling me I was stupid, foolish or running some kind of scam.

Well... okay, however worthless that opinion might be. And it is worthless, since it means the Wright brothers would never have flown, nor would the Pietenpol, Jeanie's Teenie, Sonerai and virtually everything designed by Burt Rutan except the Vari-Viggen. But thank you for taking the time to offer your opinion. You can be sure it will get all the attention it deserves :-)

For all you other yahoos with a yen to fly, the original message is valid. Indeed, in telling you how you can fly on the cheap I did little more than read a page from the history of American aviation, describing wooden wings and fuselages of welded steel tubing. But time marches on and some of the things I said, such as using fabric from your local fabric store and picking up a packet of powdered aluminum from your local paint store, are no longer correct, at least in detail.

The truth is, powdered aluminum is still available. But not from your local paint store, as it was here in Vista, California (and I assume everywhere else) at least until 1975 or thereabouts, when I last bought some. Nowadays powdered aluminum is considered a pyrotechnic, probably because it is one of the components in thermite. All that means is that you must register with a supplier of pyrotechnic chemicals and buy the stuff from him. The internet can provide you with the addresses of several who sell to the public... once you fill out their forms.

Or you can buy powdered aluminum paste from someone like Wag-Aero or Aircraft Spruce.

In a similar vein some of you have discovered that heat-shrinkable polyester fabric is no longer available from most local yardage stores. I didn't know that and apologize for sending you on a snipe hunt. Let's see what we can do about it.

Using the internet I tracked down four varieties of 100% Polyester fabric and bought sample quantities of each. Then I tested them.

But the first step was to establish a standard.

Out in the shop there's some boxes of scrap fabric, remnants of Covering Jobs Past. The certified stuff is in one box, generic stuff in another. Along with rat turds and lotsa other crud the box of uncertified, generic 100% Polyester fabric scraps yielded up a piece about two feet wide by 66" long. Filthy of course, but you can wash it, which is what I did. Cold water. Not a lot of soap. Two rinse cycles. Air dry.

After being washed the dacron fabric came out wrinkled like a piece of aluminum foil that had been wadded up then flattened out. Looks like hell but looks can be deceiving. I made up some test frames, gave them a seal coat of varnish and glued the Standard fabric to a frame.

As soon as that stuff even saw the iron, the wrinkles vanished. A little more heat and it shrunk up so tight it threatened to warp the frame. Given a coat of Home Depot dope, it got even tighter and when cured, sounded like an Inuit drum. Bottom line: This is good stuff for covering a simple airplane. (The fabric is probably from Aircraft Spruce, catalog number 09-00300. Three ounces per square yard [or thereabouts], 66" wide and probably about four bucks per linear yard at today's prices.)

So there was my Standard, against which I could compare my Internet Fabric Store Wing Covering Fabric.

The first test was to cut a 2x10 inch strip of fabric and iron it, first on the ‘low' setting, then on ‘high.' Only one of the samples shrunk and then only by 2% or so. The next step was to attach the samples to frames to see if I could produce a drum-taut surface. The results were... marginal. The fabric that did heat-shrink came out pretty good but the others took a couple of coats of nitrate dope to tighten up and didn't have that resonant drum-like BONK! when tapped. (If it don't BONK!, don't fly.)

One of the fabrics I tested was unbleached 100% cotton muslin. I included it in the tests because a couple of you don't live in Detroit. Or even in the USA.

After being tacked to a frame (the other samples were attached with contact cement) the cotton tightened up beautifully with water and gave me a good drum sound after two coats of dope. But it wasn't as smooth as Grade A cotton, weighed about 6.5 ounces per square yard going in and one hell of a lot more after it soaked up two coats of dope. That wouldn't be so bad if we were talking Pietenpol's and Model A Fords swinging an eighty-inch prop. But we're talking single-place, VW-power and a twenty-four foot wing span. And cheap. The biggest part of the secret to flying on the cheap is to keep things light.

In some parts of the world unbleached cotton muslin may be your only option. It'll work but it's going to run about four times heavier than dacron, so plan accordingly.

The polyester fabric that did shrink and did play the drums was ‘Poly Suit Lining' material from fabric.com. Ninety-five cents a yard. Width is about 45" and the weight something under two ounces per square yard. No, you can't buy none because you apparently already have, you rascals! After the tests, which I've been sharing with the guys who are actually building the Practice Wing, I tried to order some more... and was told they were sold out.

So what's the bottom line? I think you should buy the good stuff; save yourself some headaches. (A suggestion I've voiced before.) But yeah, if you know what you're doing and if you want to invest some time in testing fabrics that are locally available, you can probably find something suitable for covering a light airplane. The Dream stays alive but the path is a bit steeper.

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After receiving the fabric via UPS, cutting the first test-strips and discovering they did not shrink, I devoted some time to trying to find out why, since I'd been able to buy heat-shrinkable polyester from local stores in the past. (I've already mentioned part of this in an earlier post; what you see here has to do with the fabric I got via the Internet.)

Now this was kinda funny so bear with me.

After a bit of effort (quite a bit, in one case) I managed to reach humans at the places from which I'd ordered fabric. But any mention of having the stuff shrink produced Instant Denials. Not our fabric! No way, Jose! All of our polyester fabrics are pre-shrunk!

It took a while to get across to them that I wasn't angry, didn't want my money back and wasn't accusing them of anything. At least, for two of them. One lady remained convinced I was trying to lodge a complaint and insisted I do so in writing. Ah well... But with the other two, the penny finally dropped and here's what I was told. Heat-shrinkable polyester fabric was fairly common at one time... but no one has made anything like that for at least ten years.

(Now here's the funny part :-)

...but if I did receive some non-preshrunk fabric, and if it was one of their Clearance Sale Items (which the Suit Lining Material happened to be) then I had no recourse because somewhere in the fine print on their web site was some legalese boilerplate bullshit stating that all such sales were final.

So, no, heat-shrinkable polyester fabric is not commonly available. And if it was, they'd never admit it :-)

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So... whatcha gonna do? One option is to do what I did: Buy samples and test them. And there's a bit of a tale here, too, because heat-shrinking isn't the only way to tighten fabric. As I mentioned above, the sample of unbleached (and I assume un-Mercerized) cotton that I tested shrinks like a cheap wool suit, very similar to the way Grade A Cotton aircraft fabric shrinks. Just sponge on warm water and let the stuff dry. My particular sample of unbleached muslin had quite a bit of sizing and would not accept a light sponging of water. But after adding one drop of liquid detergent to a gallon of warm water (i.e., as a wetting agent) and scrubbing it onto the framed fabric with a sponge, it soaked it right up. And as it dried, it shrank.

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If you are very careful to apply your fabric with no wrinkles at all, you can get a usable surface by shrinking it with dope or some form of sizing. The Colditz Glider was covered with cotton bed-ticking, carefully sewn and tacked to the airframe. It was then made taut by coating it with a starchy sizing the prisoners produced from some kind of cereal; oatmeal or millet or something like that. This is similar to what happens with common wall-paper paste (which is basically wheat flour). Boiled to release its gluten and applied wet, the stuff shrinks as it dries.

I don't expect anyone to paint their airplane with library paste. What I want to get across here is the process of applying some form of coating or sizing that shrinks as it dries. And the best example of that is aircraft dope.

But here again, the success of this procedure will depend largely on your experience. And if you haven't used dope you should do some experiments to teach yourself how. Which leads to the next part of this story :-)

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After sticking the fabric to the frames and seeing the stuff remain as limp as Odie's tongue I grabbed a can of dope and... I grabbed the next can of dope and...

I didn't have any dope. I had several cans that used to contain dope. Now they contained a cellulose potato chip.

Dope is cellulose nitrate lacquer. It isn't very expensive and it's fairly common although if you want it to say ‘Aircraft Dope!' on the can you'll probably have to order it from an aircraft supplier and pay a premium to boot. I used to buy it at the same paint store where I used to buy powdered aluminum :-) The paint store is no longer in business, thanks to Home Depot so that's where I went. Sure enough, tucked away on a shelf in the paint department were several gallon cans labeled ‘CLEAR CELLULOSE NITRATE LACQUER.' I bought a can. (So who uses dope besides airplane builders? Luthiers, for one. Sandy Eggo county, especially up here in the northern part, is over-run with luthiers. You rarely see them but on nights when the moon is full you can hear them, playing out there in the hills.)

The stuff from Home Depot looks and smells like real dope but doesn't tighten up as much, although more so than ‘non-tautening' aircraft dope. It worked well enough for the tests. If I couldn't get anything better I'd be willing to fly with it. But I don't think you should; not unless you've got a lot of experience with fabric & dope (in which case you probably wouldn't be reading this :-) The experience-factor is fairly critical here because the first coat of dope is the one that does most of the tautening and you need to apply it properly, which means encapsulating the fibers when you're working with polyester and that calls a fairly thick viscosity. But with cotton (or other absorbent fiber) you want to saturating fabric, which calls for a fairly thin viscosity. The tricky bit here is the ‘fairly thick' vs ‘fairly thin' because there really isn't that much difference between them. To adjust the viscosity you pour some dope into a can and leave it set to thicken (i.e., increase the viscosity) or add thinner to reduce the viscosity. Temperature is also a factor as is the orientation of the work. Some experiments will show you which direction you need to go... but only for that particular set of prevailing conditions. Fortunately, when covering just one airplane, the tail feathers usually provide enough experience to let you do a good job on the wings.

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I've mentioned test frames a couple of times and can see the question marks slowly rising over several heads, so...

Home Depot sells what they call "1x2 Whitewood." That's Yuppie-speak for Western Hemlock furring strips, 3/4" thick, inch and a half wide by eight feet long. Price varies according season, store and availability. I've bought them for as little as thirty-nine cents and as much as $1.49. I tend to keep eight or ten lengths on-hand. Like most of Home Depot's wood it's mostly crap but now that they driven all the real lumber yards out of business, for lots of folks they're the only source of lumber.

So go buy yourself some of that 1x2 whitewood crap. We're going to make some fabric frames.

A fabric frame is just an open box over which we stretch a piece of aircraft fabric in order to teach the newbies how to tack, glue, stitch and dope. Back in the Good Ol' Days, whenever that was, we'd use an old drawer or a lug-box. The size isn't especially important but for polyester the frame should large enough to accept a standard clothes iron, which is what we use to shrink polyester fabric.

Never built a fabric frame? See the drawings - FABRIC01 thru FABRIC03 (These are in the ‘Files' section of the Chugger Group, under WINGS.)

Keep in mind that our goal here is to work with fabric rather than the frame. Don't go overboard on the thing. Chop the furring strip into lengths, start a 4d nail on each end, smear on a dob of Gorilla Glue and nail that puppy together. Then hang it up and do another. Make three or four of them.

Then leave them alone for at least 24 hours.

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Looks like hell, don't they? :-)

Don't worry about it. In fact, there is an extremely valuable lesson in those awful looking fabric frames. Follow me through here and see if you can pick it up.

Got your angle-head grinder? Install a flat flapper-type sanding disk. Coarse is good. Fire it up and get rid of all the glue squeeze-out. Keep the sander flat; don't gouge the wood.

See how those corners are mis-aligned? Make them line up. Go on; use the flapper wheel to even out the high side, taper it back a couple of inches. Yeah, it's a mess. Don't worry about it. (You gotta trust me here.) Chamfer all the edges. Just knock them down, mebbe a sixteenth of an inch. Use nice, even motions with the angle-head grinder, almost no pressure at all; let the flapper wheel do the work. If you spend more than a minute per frame, you're missing the point.

Got them all cleaned up? Then take your powered sanding block, clip on a sheet of #80 grit and get rid of the sanding marks from the flapper wheel. Smooth things up.

Get a rag, dip it in some mineral spirits and wipe down the frames. This will pick up most of the sanding dust.

Open up a can of VARNISH. Spar varnish is good but so is urethane. If you're an aircraft type you know that nitrate dope will also serve to seal the wood, which is what we're doing. But I'd rather you use varnish.

Lay on a full, wet coat of varnish then hang the frames up and use the brush to smooth out any drips. If you don't have someplace to hang them, figure that out before you make them.

Now go do something else. Allow the varnished frames to cure for at least 24 hours.

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The varnished frames will come out rough as a cob. If we wanted a dense, shiny finish we'd go after that rough surface with some #120 grit, knock it down and lay on a second coat.

But in this particular case the one thing we don't want is a dense, shiny finish. We want that rough-but-sealed finish because we're going to lay down a layer of contact cement. And contact cement works best when the surface has some tooth. Which is also true in the case of real airplanes and real fabric cement. That was #1 in the Valuable Lesson Dept. Lesson #2 is the fact that you can do the same thing with an airplane.

We always try to do the best we can but being human and building just one airplane, sometimes things don't come out perfect.

Valuable Lesson #2 is the fact that most of the time, things don't have to be perfect to work perfectly well and this is especially true when doing fabric work.

Does the fabric lay smooth? Try it out and see. Just stretch a piece of fabric over the frame and look for irregularities. Sharp corners that have escaped your notice for months are suddenly evident. So smooth them off. Ditto for unexpected low spots, except you fill them; just glue on a filler and sand it flush. Awkward angles that threaten to leave a puckered corner? Glue in a block of balsa and convert the empty corner to a smoothly faired surface.

So long as such irregularities are neither frequent, abrupt nor large, they will have no effect on how well your airplane performs. Resolving minor problems of this sort is one of the realities of fabric work

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I used contact cement to attach the fabric to the frames. Regular fabric cement (FabTac, et al) will work at least as well and costs about the same. I used two coats of cement on the wood, allowing the first to dry before applying the second. The fabric was applied while the second coat was still wet. A third coat was applied over the fabric and squeegee'd through the weave with my thumb. The goal is to encapsulate the fibers of the fabric with the cement. Nothing bonds very well to polyester so we force the cement through the fabric and allow it to bond to itself. There are a host of variations on this theme; for a wing I would use a different method. Experiment; find a method that best suits your situation.

Shrinking was done with a clothes iron reserved for that purpose and already described in earlier posts. I did all the shrinking on the ‘high' setting... then realized you wouldn't have any idea whathell I was talking about. Dug out a thermometer that read to 400 degrees and measured the iron. The second mark on my masking-tape dial produced a consistent 350 degrees Fahrenheit.

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In closing, allow me to offer a word of explanation about ‘Flying on the Cheap' and other messages some folks have found so disturbing.

My dad was an aircraft mechanic. I used to help him. The first time I can recall helping him, I was about seven years old. I stood on a lug crate to push needles back at him through the wing of an airplane. Such chores were kinda interesting for the first five minutes after which I'd hear the Call of the Wild and he'd usually let me go. But most times it was kind of neat to just hang out with my dad, and between the two of us, me poking and him pulling-through and tying-off, we'd do a whole wing.

Other times it was driving rivets. Or helping him sand. Or helping him paint; masking off the NC numbers on the left while he did the right. Pulling wire. Making up fittings. Polishing plexiglas... scrubbing the grime off the belly of the Cub... It never seemed like work.

My dad never ‘taught' me to work on airplanes, as in Major Instruction, with quotation marks and so on. He'd ask me to ‘give him a hand.' Nothing complex; nothing I couldn't understand. Always demonstrated rather than being told or ‘taught.' Always one small step at a time; ‘Do it Right, we won't have to do it Over,' a shared joke always spoken with a smile because that was one of my grandfather's favorite expressions. Waxing the thread, spinning two thin threads across my thigh to make a thick thread, cleaning the oil off the needles before and replacing it after, laying on dope or glue or cleaning brushes or... No ‘teaching' at all. About twenty years of it off and on, from the time I was a child until his death when I was in my mid-thirties.

You'll probably find this funny but somewhere in the back of my adult mind was the notion that everyone who flew planes or worked on them or wanted to actually build one, knew all that stuff that I'd learned without ever being taught. Like the fact it's a Seine Knot (except we called it a Net Knot), tied flat instead of with your toes holding the mesh, your netting bobbin flashing in and out, fast as you could, as automatic as a woman knitting while rocking the baby and carrying on a conversation at the same time. When (and where) I grew up, every boy knew how to make nets. Not just for catching minnows but for basketball hoops and summer-time hammocks and string-bags for your mom and all sorts of other things. Common Knowledge; the stuff that never needs to be mentioned because it's something everyone knows. Like dope and fabric and welding and woodwork and engines and...

Turns out, everyone don't. Which is probably why I see a simple, reliable airplane as something everyone can build, and inexpensively, too... where others see it as a Type Certificated, Approved Aviation-Quality Bureaucratic Impossibility. And they're right. Absolutely. Because if they're positive they can't build an airplane, they won't even try.

-R.S.Hoover

VW - Pre-Luber

According to studies by Ford (in the 1960's) and Mercedes-Benz (in the 1990's) the most significant factor in determining the service life of a properly maintained engine has more to do with how often it is started than with how many hours it has accumulated.

Here's why: Go out and jump in your ride. Turn on the key. See those light? One of them is telling you there is no oil pressure. Now start the engine and notice how long it takes for the oil pressure light to go OUT.

You've just started your engine `dry.' How dry depends on a number of factors such as how long the engine has been standing, the type of oil you are using and the ambient air temp. But the basic fact is the engine starts and runs for a period of time without adequate lubrication. No mystery at all as to why this produces so much wear.

Wanna see your VW or Toyota engine last virtually forever? Add a pre-luber. Go on. No big deal. See that screw-top aerosol canister from Harbor Freight? Buy one. Make a mount for it. (Upside down, please). Now pull the Schrader valve and replace it with a 12vdc continuous-duty solenoid valve. You may use a fuel tank purge valve from the junk yard, if you wish. But the real thing -- about $40 -- will work better. Now wire the solenoid valve into the ignition circuit. (Circuit ON, valve OPEN) Then plumb the thing to your main oil gallery.

Now, when you turn on the key about a pint of pressurized oil will be delivered to the engine before anything starts rotating. After the engine begins to run it will pump that amount of oil back into the pre-luber... and will trap it there, under pressure, when the key is turned off. (You may elaborate upon this scheme if you wish but the Plain Vanilla version will work just fine for an engine as small as a Volkswagen.)

www.autoenginelube.com

If you do a bit of reading on the factors governing engine wear you'll find a lot of data regarding the size of contaminants, filter effectiveness and so forth. It is pretty obvious that full-flow oil filtration is good but all filtration systems contain a potentially harmful loop-hole in that the contaminants must pass through the oil pump before they can be trapped by the filter. (And no, you can't put the filter on the inlet. See the literature. The output of your oil pump is very sensitive to any restriction on the inlet. Low-restriction filters are huge things, unsuitable for use in a car or light plane.)

Since the most destructive contaminants are metal particles wiped from the cam and lifters, and since these particles are magnetic, I added three high-Gauss NIB rare-earth magnets to the outside of the sump plate, converting the entire plate into an extremely powerful magnet. The magnets cost about $10 each and were purchased as new/surplus from American Science & Surplus. That particular magnet is no longer available but they carry others.

Since I fit all of my engines with full-flow oil filters I've no need to remove the sump plate. But after a year of use I was curious as to how well the magnets were working. When I removed the sump plate it held a dense sludge of magnetic particles. To determine the fineness of the residue trapped by the magnets I washed the residue with MEK to break down the oil and passed it through a coffee filter and then a piece of filtering media removed from a new Purolator oil filter. In each case a significant quantity of particulate contaminant made it through the filter... and would have gone into my oil pump and then to the bearings... were it not for the powerful pull of the neodymium-iron-boron magnets.

-Bob Hoover

AV - More VW Oil Temps

> My oil temp sender is in the case at the back on the left hand side. I've insulated it and installed a blast shield, as the temp's never seemed to come up. >

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You're probably reading the temperature of the crankcase rather than of the oil it contains. (Easy to check. Use an IR-type thermometer.)

Volkswagen installed full instrumentation on some of their industrial engines. The oil temperature sensor was installed in the opening immediately adjacent to the right-hand side of the oil pump (when facing the pulley). The tip of the sensor was in the flow of oil entering the pump.

Oil temperature within a Volkswagen engine may vary by up to 200 degrees, depending on where the temperature is taken. The hottest oil is in the vicinity of the exhaust valves. Oil adjacent to the walls of the sump tends to be the coolest due to the partitions cast into the case under the cam-follower bores, breaking the sump into a series of stall-like compartments in which the oil does not circulate. In placing the temp sensor at the inlet to the pump, Volkswagen was trying to measure what they called the 'core' temperature of the oil.

Another temp-sensing location to avoid is the sump plate. The popular VDO sensor that replaces the drain plug typically reads about 100 degrees Fahrenheit less than the oil measured at the inlet to the pump.

-R.S.Hoover

AV - VW Cam Details

>When it comes to cams all I've ever seen listed is lift and duration<

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That's because all the after-market cams advertised in VW-specific magazines are based on the assumption you're only interested in Peak Horsepower.

Torque is largely a function of displacement whereas 'horsepower' is a city slicker method of computing a certain amount of work done over a certain period of time. To produce a hundred horsepower from a VW engine all you have to do is spin it faster during that interval of time. Of course, the thing won't last very long but when you're selling junk to the Kiddie Trade you don't bother to mention such things :-)

What most people tend to overlook is the efficiency factor of their prop. In simplistic terms, your prop is a wing and as such responds to the same rules of lift, drag and aspect ratio, meaning a longer prop tends to be more efficient than a shorter prop. If you start with one of those gee-whiz 80hp VW's turning 4000 rpm the odds are your prop is going to be painfully inefficient, converting as little as half your torque into thrust. That means your expensive '80hp' engine with its dune buggy cam is burning 80hp-worth of fuel and wearing out at a 4000rpm rate yet delivering only 40 horsepower's-worth of thrust.

But that also sez the airplane is able to fly with 40hp. So why not simply turn the equation around? Start with the longest prop you can swing without mowing the lawn then use a high-torque cam to build an engine that will swing your longer prop at its point of maximum efficiency. Odds are, you'll end up with a slow-turning, long-wearing engine. Of course, it will only be producing fifty or sixty horsepower... obviously not as 'good' as 80hp, right? Yet in the air each engine produces the same 40hp-worth of thrust. Vast mystery, eh?

The advantage here is that a high-torque cam results in a slower-turning engine that will last longer and produces less 'waste' horsepower to satisfy the prop -- meaning you'll fly farther on the same fuel and enjoy a longer TBO than when you use a hot-rod cam. All of which is common sense when the task is to produce thrust with a directly-driven propeller, a fact easily verified by by simply examining the spec of cams used in small aircraft engines.

-R.S.Hoover

AV - Selling Junk to the Kiddies

> I came across a really nice rebuild kit for the Volkswagen that includes Big Bore cylinders that don't require any machining. Have any of you heard of this? <

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It's junk; a package assembled for the 'Kiddie Trade' -- technologically naive youngsters who don't know anything about VW engines.

Such kits typically come with standard-size bearings. The odds of finding standard-size bearings on any air-cooled VW in need of an overhaul is about the same as for finding lips on a chicken. In fact, most of the schlock shops that offer such kits don't even carry the full range of bearings. That's because the of the remarkably wide range of possible bearing combinations available for the VW engine. Since the crankcase usually needs to be align-bored to return the saddles of the main-bearings to true circles, the mains may be as much as +1.5mm larger in OD, graduated in 0.25mm steps. That's seven sizes assuming you start with STD. (The factory only allowed two over-sizes but at the insistance of after-market rebuilders, famous for their $300 'overhauls', have provided the additional over-sizes. In the same vein, the crankshaft probably needs to be turned & polished -- and probably already has, since the youngest Type I air-cooled VW engine sold in the States has to be at least 25 years old. Here again, while the factory -- which used to overhaul its own engines (and offered the same warranty as for a new engine) allowed only one under-size, after-market bearing manufacturers offer under-size mains all the way down to -1.0mm. That's five ID's. Then you've got the thrust face on the #1, which you can get in up to three different combinations, plus STD. Seven OD's plus five ID's plus four Thrust Flanges gives you one hundred and forty possible main-bearing combinations for a used VW engine and we haven't even gotten to the rods. And the dingalings at Jaysie Whipme sell the kiddies a set of STD/STD bearings with their famous 'rebuild kits.'

The 87mm barrels are called 'slip-in' Big Bores because they fit the same spigot bores as the stock jugs. Trouble is, the over-boring results in a sealing surface that is so narrow it's impossible to maintain a reliable seal between the barrel and the cylinder.

Then they offer the kiddies a set of valve guides.

Have you any idea in the blue-eyed world how many mechanics are even qualified to replace VW guides? They are a shrink fit in the aluminum heads and the spec calls for a 500 degree differential.

To remove the old guides you core-drill them then heat the heads to 350 degrees and drive them out. If the bores will accept a new guide it is put to soak in a slurry of dry ice and 100% alcohol, which lowers the temp of the guides to about -120 F. then heat the heads to about 350 F and -- assuming you have the right tools & jigs -- drive the chilled new guides into the hot aluminum heads. But the schlock shops don't do that. They simply hit them with a chatter gun. That galls the bores as the guides come out and splits the guide-boss when the new guides go in; no big deal since their typical customer wouldn't recognize a good head if it walked up and pee'd on his leg.

But the best part of the joke is that the typical 'overhaul kit' costs more than buying the parts individually!

Such kits are enormously popular, of course. Which helps explain why a sturdy,well designed little engine acquired such a terrible reputation for reliability.

-R.S.Hoover

VW - St. Muir Revisited

>One thing I have never understood is why this book has so much controversy surrounding it.

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Dear Peter (and the Group),

It's largely a matter of competence. Or perspective. To an experienced mechanic the Idiot Book is an hilarious collection of good information and bad, like that bit on pg 85 of the 19th edition (Step 3. Check Sensor) where John tells his Disciples, "be sure to get a six volt [oil pressure] sensor if your car is 6 volt and a 12 volt sensor for a 12 volt system" And if that sensor fails to work, you should take it back and get a replacement... because "You have checked everything else." (emphasis added)

First off, like 99.99% of all low-voltage switches, the VW's oil pressure sensor switch is not voltage-specific. Volkswagen used one sensor from 1949 thru 1981 (go find the microfiche; look for yourself).

Secondly, the switch is the Normally Closed (NC) type. When it's just laying there on the bench smiling up at you, to find out of its good, bad or indifferent, all you gotta do is stick it with your VOM. Or your trouble light (and a source of power). Or a continuity checker. No need to screw it in, screw it out and screw it up running back & forth between your car and the dealer, praying to find that one magical six volt sensor that works... when the problem is somewhere else in the system. (Even though you've checked everything else.)*

To an experienced mechanic, this sort of foolishness is funny as hell, an enjoyable break in a life devoted to detail. And a point completely beyond the ken of people who's lives are not.

Logically, the two branches of this decision tree, as indicated by the state of the lamp [ie, on or off] should be addressed systemically. But they are not. Over on page 87 John finally addresses the second branch of the diagnostic tree -- the lamp staying on for no readily apparent reason (such as overheating) and assumes the fault is in the sensor... which is the same error he makes when the lamp fails to light. Taken as a whole, John's diagnostic procedure is more akin to slap-stick comedy than auto repair.

The sticky bit is when the kiddie, who may be fifty years old, insists you sell him a six volt 'sensor' and starts waving his copy of St. Muir in your face as proof of his certainty and your incompetence.

What to do? When it comes to theology there's no easy answers. Automotive engineering, yes. Retailing, for sure. But not religion and that's really what's involved here -- someone who has taken John's word entirely on faith.

A lot of parts-guys 'discover' a six volt switch lurking in the bin... little '6V' written right there on the corner of the box with ball-point pen... and sell it to the idiot for about five times the price of a "12V" switch. But most will simply head them down the road... Have you tried at...? No? Wellll... have a nice day. And go on to the next customer, because for them it's a business, not a religion.

So John made some errors. Let he who hasn't take the mound. And initially at least, it may not have been an error but merely a misconception. There is a later-model pressure switch for another VW vehicle that is identical in appearance... except for having an M10 thread instead of 1/8NPT. (and a completely different part number)

I've had parts-guys try to sell me this other sensor, saying it was 'Just as good' as that other part number... the one they don't carry any more because no one in town drives an air-cooled VW. When that happens just smile and take your business elsewhere. Because, while M10 will fit the START of an eighth-inch pipe thread, it jams after a few turns and will strip out the case. (Don't ask... but you run into the same thing with brake light switches. Pipe thread early, Metric thread late.) So mebbe that happened to John. VW shifted to 12v in 1967. Perhaps John thought the new part number (indicating the difference in thread) signified a difference in the car's voltage. Just a guess. But if you hold both types in your hand you gotta know your onions to be able to spot the NPT from the Metric thread.

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Now, were there a lot of errors? Again, we run into the Point of View. To the novice the errors are invisible and the book is therefore perfect. To someone with a little experience, the errors can be an embarrassment and cost them some time but they can usually work around them. But to the experienced mechanic... if he needs a doorstop he knows where to look.

So where do we draw the line? Again, it depends on who does the drawing. For me, I don't like to see folks using 'repair' procedures that end up doing more harm than good so I've pointed out alternatives for some of John's methods, such as not setting fire to your brake shoes... unless we're talking Model T's. Nor hammering on your axle nuts, trying to balance wheels mounted on the front spindles and a few others. Over the years I've also addressed a couple of safety issues that I felt should be mentioned in certain repair procedures.

But a lot of the 'errors' simply reflect the differences between a professional mechanic and an amateur. The fact Volkswagen taught its mechanics to do a valve adjustment in a way that takes only ten minutes or so (and is the same method advocated by every other car maker) does not mean the method John advocates is wrong. The valves still get adjusted. Eventually. In fact, I've actually had people tell me they enjoy spending an hour adjusting their valves, and make it clear they feel I'm denying myself one of the joys in life by spending so little time on that task.

Personally, I continue to recommend John's book to the newbies as the best way to demystify the mechanical arts. The work is technically flawed but philosophically sound. Were it not for John's untimely death I'm sure the hilarious gaffes, backward images, typos and missing parts would have vanished from the book.

But until then, Proceed With Caution, for no matter your level of technical expertise, you are the Mechanic-in-Charge. Not only of your vehicle, but your life.

-Bob Hoover

* - When you've checked all components in a system and found them functional, yet the system does not work, then the fault is in the system itself and not the components. So stop worrying about the lamp and the sensor and get busy checking the connectors, wiring and the socket. There's a lot of wire between the indicator lamp and the temperature sensor. If the lamp works and the sensor is good then bite the bullet -- you've got a bad wire or -- most probably -- a bad connector. Indeed, given that the indicator lamp only draws about 250mA, and is grounded at the engine, ten feet or more of wire away, you could have a wire that tests good conductivity yet has enough internal corrosion to not allow the lamp to glow brightly enough for you to see it. But that isn't the sort of thing that would happen from one day to the next; over a period of storage, yes.

So what's the answer to 'No Green Light!'? Usually, the connector at the sensor or the wire immediately adjacent to it. Next best bet is that funny little connector on the other end of the green wire, the one on the back of the speedo... that got mashed flat by a six pack of beer about five minutes ago when you whipped it up to beat the train across the tracks.

Life's funny that way :-)
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