Tuesday, November 28, 2006

AV -- The Valve Cover IQ Test

Back in the Good Ol' Days, whenever that wuz, one of the most common of the lo-buck tricks me and the other fools applied to Volkswagens was to install a set of rocker arms that had a ratio higher than the stock one-to-one. That should give you the clue that I'm talking the 1950's here. (The rockers on later engines were one-point-one to one and the VW industrial engine that ran on alcohol was one and a quarter to one... but I'll get around to that in another message).

There were lots of tricks in making up a set of 'ratio'd' rockers. You'd usually have to bush the bore, since the VW uses a rocker shaft having a rather small diameter. Once you'd bushed your donor rockers you'd hone them to match the VW shaft. Or not bush them and make a new shaft and modify the heads to accept it. Lotsa ways to skin that particular cat.

American custom is to put the adjusting screw on the push-rod side of the rocker-arm. (Stock VW rockers have the adjuster on valve-side.) Unfortunately, the adjuster would often hit the valve cover, which could be kinda interesting if you hadn't figured that out ahead of time. If you had, you'd heat up the valve cover in the area where the rocker was making contact and forge a little blister to make room for the adjusting screw. Which worked fine, so long as you stuck with the stock cam, which like most chuggers doesn't have a lot of lift.

In the early 1960's following the introduction of the 1300cc engine things got a lot more interesting, with folks offering high lift cams and higher ratio'd rockers specifically for the VW. Now the rockers weren't just hitting the valve cover, they were knocking the thing clean off the engine.

What was needed was a deeper valve cover. And as you've probably guessed, they soon appeared on the scene. Cast aluminum. Leaked like a bitch.

Turns out, those pretty cast aluminum valve covers not only leaked, they ran hotter than the steel covers. That's because folks liked to polish them up, get them shiny as a silver tea pot. And that shiny surface did exactly what all shiny surfaces do and reflected the heat of the oil back into the valve gallery. And of course, they leaked like a bitch.

The leaking is an artifact of the casting, which is just a thin shell. A thin cast shell. Not real strong. Clamp or bolt the thing to the head of a Volkswagen engine, as soon as it heated up it would distort and as soon as it distorted, it would leak.

The solution to the leaking problem was two-fold. First, you had to cast some ribs inside the valve cover; you had to make it stronger. The ribs stiffened it up so that it didn't distort so badly once it heated up. You also had to make the casting thicker. It weighed more of course but nobody cared about that. Second, you had to abandon the stock valve cover gasket and go to a specially molded O-ring type jobbie that socketed to the sealing surface of the cast cover. Expensive as hell but if you wanted to run ratio rockers and wanted to keep enough oil in the engine to finish the course, you didn't have much choice.

They still ran hotter than the steel covers but the cure for that was pretty simple. You blasted those mothers to within an inch of their lives then had them anodized black. The blasting gave them an `infinite' surface and the black dye improved the thermal transfer properties of the anodized layer.

Of course, they ended up costing one hell of a lot more than the stock valve covers and weighed nearly twice as much but that's what was on the engines crossing the finish line first so naturally all the kiddies had to have them. Until they saw what they cost. So the after-market retailers whipped up these cheapie cast covers and sold millions of the things to naive youngsters.

And naive airplane builders, too :-)

Seeing cast aluminum valve covers on a flying Volkswagen is one of those reverse IQ tests that tells you quite a bit about the fellow who built the engine.

Don't take my word for any of this. Go weigh the things. You are the Mechanic-in-Charge of your flying Volkswagen, even if someone else did the work.

Be sure to include the bails with the steel covers. And the studs, barrels, O-rings and what-not with the aluminum covers. Their thermal emissivity is equally easy to check, especially if you have one of those IR thermometers. Most impressive of all is an IR photo. Just put an aluminum cover on one head and a steel cover on the other. Saves you a thousand words.

No one believes it of course. Conventional Wisdom sez cast aluminum covers are a necessity for any flying Volkswagen. Indeed, almost everybody uses them, especially those folks trying to sell you dune buggy engines with a fan on the nose :-)

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So what about the real engine builders running high-ratio rockers with blueprinted valve train geometry that requires a deeper valve cover? You section the original steel covers and make up new bails. Not nearly as pretty but if you're more interested in the steak than the sizzle, sectioned valve covers were the way to go.

Herez how:

Have you got a stock valve cover handy? Weigh it. 345 grams, right? About three-quarters of a pound. That's a VW valve cover. [Look for the VW logo just to the right of the center rib.] There are some after-market covers made from thinner gauge metal that weigh as little as 250 grams [just over half a pound]. Okay, now look at the area of the valve cover just above the flange for the sealing gasket. Notice that the side wall of the valve cover has only a slight amount of draft; it's almost perpendicular to the flange of the sealing rail. (You know it can't be perfectly perpendicular because it's a one-shot stamping; all such stampings require some amount of draft.)

You can section a VW valve cover by nearly an inch, although that would be unusual. The typical high-lift rocker needs less than half an inch of additional clearance. Most guys section the cover at about three-quarter inch above the gasket rail then allow the donor valve cover to overlap. Do a few tack welds to keep things lined up then dress the edge for a gap-free fit. TIG is best here; the valve cover holds the gas and you can really roar along. But gas or even MIG works too. I've heard of them being brazed but I've never seen one done that way.

After it's welded you can clean things up with the grinder. Some guys leave the donor gasket rail hanging right there. They say it stiffens the thing up. When using a stock valve cover for the base I've never found any need for additional stiffness and usually cut away the donor's gasket flange before doing any welding. If you use a stock valve cover as the base and a lighter, after-market cover as the top, it should end up weighing about the same as a stock cover yet it will be about five-eighths deeper.

To section the bails, cut them on the side. Don't cut them to length, allow them to overlap at least 1". Set up a head and a sectioned valve cover as a welding jig but do not install a gasket. Position the parts of the bail so that they overlap uniformly on both sides (I put one wire down below the other, relative to the engine running position). You want the bail tight to the valve cover, and you want a heat-sink on the little end, where it hooks into the head. Do a couple of tack-welds with MIG or TIG then do the finish weld on the bench. I generally use MIG because it's faster; way back when, I used gas. Be sure to keep the heat away from the little end; the bail is music wire - - high carbon steel - - you don't want it to lose its temper. Clean and paint the bail. Use an enamel if you got it and give it a good heat cure. Add the weld to your pre-flight inspection (just look for any cracks in the paint).

Keep in mind, the only reason to section a valve cover is when you need additional clearance. Most engines do perfectly well with stock covers and bails.

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"Ha!" the prize-winning VW-flying fat man barked. "Shows how much you know. You gotta use bolt-on aluminum valve covers because that bail thing will break on you. An' besides, there's no way to safety that bail."

In more than fifty years of almost-daily hands-on VW experience I have never seen a broken valve cover bail that wasn't due to a collision. Nor have I ever even heard of one breaking, except from the fat man in the funny jump suit at the Ramona fly-in twenty years ago.

As for securing the bail, you safety-wire it. Just like we've always done. Go dig up a picture of those little Jodel's from the 1950's, lookit the way the safety wire runs down from the top of the head, around the bail, and is secured to the bottom of the head.

Cast aluminum valve covers are standard equipment for the Dune Buggy set although they are rarely seen at the finish line of off-road events. That's because the stock valve covers cost less, cool better, weigh less and seal better than the typical after-market cast aluminum valve covers. Plus, they tell you a lot about the guy who built the engine :-)


AV - Honest Engines

2180cc equals the total swept volume, or about 133 cubic inches. (Conversion factor: .06102 x cc = cu. inches)

133cid represents all four cylinders. Since this is an Otto Cycle engine and there are only four cylinders, there are only two intake cycles per revolution so we're really only interested in half the swept volume or 66.5 cu. inches.

Airflow is normally measured in cubic feet. There are 1728 cubic inches in a cubic foot and since one revolution pumps 66.5 cubic inches of air that's equal to .03849 cu. feet.

Optimum prop speed is across an rpm range from about 2250 to 2850.

2250 x .03849 = 86.5 cu. feet 2850 x .03849 = 109.7

That's for 100% volumetric efficiency, of course. And that can't happen unless the engine is supercharged. But at those speeds, with the valve train properly set up, a VE of 80% is possible if we can keep the temperatures down. That would give us a flow-rate of about 87 cubic feet per minute.

Air weighs approximately 0.08071 pounds per cubic foot so every minute we are pumping 7.081 pounds of air. (Keep in mind, this is for AIR, not OXYGEN)

The stoichiometric ratio for gasoline and air is 14.7:1 so every minute I'm burning about .481 pounds of gasoline, which means I will burn about 28.9 pounds of gasoline per hour at a throttle setting that produces 2850 rpm at a manifold pressure of about 3" of mercury. Since gasoline weighs about 6 pounds per gallon I will be burning about 4.8 gallons per hour. (Hint: Stoke is based on the mass of the fuel & oxidizer rather than its volume.)

Based on accepted standards for Specific Fuel Consumption (i.e., .5 lbs per horsepower-hour for a well designed air cooled engine) my 2180cc engine should be producing about 57.8 hp. And it probably will. But only during take off. That's because VW has not increased the size of the fins on its cylinder heads since it introduced the heads we all now use. Originally, the heads were designed for the 40 horsepower 1300cc engine. VW eventually bored the engine out to `1600' (actual swept volume 1584cc) but kept the same heads. The fin-area of the heads puts a thermal limitation on the output of any VW engine NO MATTER THE SIZE. The thermal limit is determined by the cylinder head temperatures, which should be kept at or below 325F. if you want the valves to last.

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There are lots of variables in any on-paper exercise of this sort but even when everything is selected for the optimum output the difference is barely 10%. In reality, the nominal output of an on- paper engine is usually quite a bit better than anything you'll get from the real thing. Paper engines are goals to shoot for. So you do the best you can, isolating one factor at a time, making modifications to improve that single factor and running another series of tests. It teaches you a lot about engines. And about yourself.

On a broader scale, one of the most interesting aspects of the figures above is that they are in general agreement with figures produced by actual torque measurements on the Whatley test stand recently (Fall, 2003) discussed on various flying Volkswagen groups.

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The numbers are interesting but the engines themselves are more so. And more fun. I've spelled out the figures I used so you plug in your own numbers for displacement and rpm, which I think you'll find to be the most significant factors. But there's a good chance you'll be mislead and the reason deserves mention.

As you increase the rpm the on-paper horsepower will rise dramatically. All else being equal (it's not, but bear with me here), you'll tend to fix your prop-speed at something more than 2850 rpm. But actual tests with real engines and real propellers shows that the efficiency of your prop falls at a faster rate than can be offset by any increase in horsepower. This is definitely one of the tricky bits because you end up with a `strong 70hp' engine that is producing barely 35hp-worth of thrust. I believe you will find that you can fly farther, faster, by using the longest prop your engine can swing.

Rather than give you a Break Mean Effective Pressure I used a nominal manifold pressure that is conservative compared to real aircraft engines. I used a conservative figure because I'd like to save you the trouble of blowing up an engine :-) Manifold pressure is also easy to measure whereas BMEP is not.

Increasing your compression ratio will improve your BMEP and thus the output of the engine but on the VW, as the output increases the heating effects become critical and announce themselves by a catastrophic drop in your volumetric efficiency... just before you eat it. That's because the incoming fuel-air charge absorbs a lot of that heat, which gives you a very lean burn. At high compression ratios a lean mix leads to detonation, quick like a bunny, and there you are surrounded by white smoke with a blown engine hanging off the test stand.

Which is better than having it happen when you're half way to Catalina. So be cool.


AV - Dynamo, Again

Electricity is produced when you pass a coil of wire through a magnetic field... or pass the magnetic field through the coil of wire.

If you wish to convert mechanical energy into electrical energy, if the input is rotary motion the output will be a sine wave -- alternating current.

The generic term for such devices is 'dynamo.'

The terms 'alternator' and 'generator' are used as a handy means of defining which type of dynamo is being used. In the generator the magnetic field is fixed and the coil(s) rotates through it. The output is an alternating current that is converted to pulsating direct current through the use of a mechanical switching system mounted on the shaft supporting the coil (ie, carbon brushes and a segmented commutator). In an alternator the magnetic field rotates while the coil(s) remains fixed. The alternating current that appears in the coil(s) is converted to direct current by a rectifier.

The output of any dynamo is a function of its rpm, the number of pick- up coils and the intensity of the magnetic field.

The most common means of controlling the output of your dynamo is to control the intensity of the magnetic field by regulating the amount of current that flows through the magnetic field winding.

If a variable output is not required you may replace the magnetic field winding with permanent magnets.


The key points here are that 'alternators' and 'generators' are both dynamos. Each uses brushes. Each has a magnetic field and regulates its output by controlling that field. Since the advent of solid- state rectifiers, alternators have come into general use because they are less expensive to manufacture but they aren't really new. The Leese-Nevil alternator using copper oxide rectifiers has been available since 1921. Nor are permanent magnet dynamos 'new' in that they've been around in the form of magnetos since the 1890's. The reason we're seeing more of them nowadays is a reflection of economies of scale in the production of rare-earth magnets.


VW - Stainless Steel Craftsman

Today I witnessed one of the most astounding feats of craftsmanship I've every seen. Roland Wilhelmy, owner of a '56 VW Sedan that is undergoing a hands-on body-off restoration, replaced the bug's original steel fuel pipe with one of stainless steel. The astounding part is that he didn't take the easy way out and run the new pipe along-side the tunnel, Roland installed the new pipe in the tunnel, and in the original brackets, to boot! And all without cutting or welding on the tunnel.

The early Volkswagen shop manual describes how to do this (Step 1. Remove the body...) but I have never heard of it being done. The labor and shop-space requirements are so high that everyone I know used the Alternative Procedure, running the new fuel pipe through the passenger compartment.

"I didn't like that idea," Roland said quietly.

So how did he do it? I'm not too sure; the shop manual sez you need a helper to guide the thing; Roland did it all by himself. (But I did notice a Pentacle on the floor of his shop :-)

My contribution to the job was to provide him with a piece of solid steel guy-wire exactly .156" in diameter. Working alone, he had already installed the new tubing almost the entire length of the tunnel, managing to thread it through the four intervening support brackets. He slid the heavy wire into the tranny horn where the original fuel pipe exited and somehow managed to insert it into the stainless steel tubing, out of sight inside the tunnel. Returning to the front of the vehicle, he commenced tapping on the end of the new tubing, projecting about four feet beyond the front axel. The stainless steel tubing inched its way around the bend where the tranny horns mate with the tunnel, following the line of the heavy wire, which now acted as a guide. In a few minutes the tip of the new tubing emerged from the tranny horn neat as can be.

Making the terminal bends in the new tubing and coaxing them into their respective positions took a bit more slight-of-hand but the job was finished in less than an hour.

I thought it was about the neatest thing since electric lights but Roland shrugged it off as no big deal. Perhaps not, considering what has gone before. He's already replaced all of the brake lines, done an IRS conversion to the rear suspension and there is a pair of disk brakes lurking up front, along with a steering damper, an important handling improvement lacking in early bugs. And the four-joint TransForm transmission has their special tag showing non-stock gear ratios. Roland is building a Porsche-eater, disguised as a Volkswagen. Yet the original 36hp engine and stock 1965 running gear was neatly stored on welded racks, preserving the option of returning the vehicle to all- original condition. Roland also drives a suspiciously quiet bus that has a few more carbs than most other '65 models.

As I was leaving, I noticed the body of the bug lurking back in a corner of shop, remarkably smooth under about a zillion coats of hand-sanded primer. Strictly stock. Perfectly straight. He's replaced a couple of body panels, including the forward engine compartment curtain, fitting one from a late model chassis, allowing him to use the larger engine's tin without modification. This is the kind of subtle attention to detail that you only see on race-winning road cars. The work was so neatly done I wanted to rub it against my belly. Asked how it was going, he gave another shrug. "Coming along." And grinned. That grin is going to make a lot of Porsche owners trade up to a Yugo.

-Bob Hoover
-Aug 1995

VW - Getting It Home


There are a couple of tricks that can get you home, or at least off the freeway should your cable break.

If you advance the idle adjustment screw to about 1,500 rpm you can make about 30 mph. You gotta eat a little clutch to do it, but it will get you off the freeway.

Bailing wire or stainless steel safety wire can be used as a wildly dangerous substitute for an accelerator cable (BT,DT). The problem is, you can't get the stuff straight enough; all those lazy bends bind in the tube going through the tunnel. Push your foot down, engine roars. Lift your foot (as when bearing down on three Mexican women who decided to cross the highway at that particular instant) AND NOTHING HAPPENS! The throttle stays open, you keep doing 90mph, and the women keep sauntering along. (Hello sagebrush, goodbye road.)

The trick? A bungee cord. And grease. Two wraps around the fuel pump then wire the bungee cord to the throttle arm. Grease the dickens outa that sucker before you push it into the tunnel.

The problem? Your foot's going to get awfully tired fighting that bungee cord. And it ain't doing the carb much good, either.

Here's the drill: Fan belt, clutch cable, throttle wire, six feet of rubber fuel line, all in one package. Inside the package is an adjustable wrench big enough to handle the generator nut, a pair of vise grips, two screwdrivers (big & little). The 'package' is a piece of sailcloth about one yard wide by two yards long. Tie it up with about ten feet of light line. Tie it up tight; makes a bundle about as large as a big thermos. Lash it to the roll cage with bungee cords.

I've seen some rigs, the guys don't even carry a regular tool kit. They've got their tools distributed all over the rig, tools and spare parts taped, lashed or wired right beside where they'll be needed. Doesn't make much sense in a daily driver but comes in at the genius level when seconds count. (I remember one guy who appeared to be wearing his tool kit. DNF'd)

-Bob Hoover
-Aug 1995

VW - Keeping Clean

Keeping Clean

>-Bob, >I love the idea of taking charge of my life and not being cheated >by dishonest mechanics, but my first (and last!) attempt to do my >own tune-up left my hands in such a state I'm terrified of >trying it again. I know you'll think it silly, but the appearance >of my hands is very important in my work. >-AnyMouse


Dear AnyMouse,

I don't think it's silly at all; the appearance of my hands is very important in my work as well. For example, if they are dripping blood and missing a finger or two, I tend to get real upset :-)

But in all seriousness you have a valid point. Cars are dirty and that dirt gets onto your hands. And when a good, black greasy goo gets ground into the dead skin around your fingernails and on your knuckles, about the only thing that gets it off is pumice -- you got to grind of the skin to get out the dirt. But when you do that, the result is sore, red hands that aren't much good for a couple of days, even to a hairy-chested mechanical type.

The trick to keeping your hands clean is to not let them get too dirty in the first place; you have to seal up your hands before you get them dirty using stuff like hair gel as a sealant. One brand is called 'Invisible Gloves' and forms a barrier strong enough to protect you from mild chemical burns; people allergic to epoxy resin and the like use it to keep from getting a rash. Just rub the stuff in like hand cream and let it dry. Soap and hot water takes it off.

My grandfather was a Mason, very involved with their affairs. He did all sorts of blacksmithing and machinist work yet had 'gentleman's hands' (my grandmother's choice of words). He used the hair-gel trick. He also scratched a little Ivory soap under his fingernails when he had an especially messy job.

There's a stuff called 'Machinist's Soap' that contains a chemical that will keep your hands from sweating. Politicians probably use more of it than machinists but you get the idea. If you can keep your hands from sweating you can wear surgeon's rubber gloves, or even those cheap throw-away plastic gloves, and still do some useful work.

You can buy both Invisible Gloves and machinist's soap from machinist supply houses (check your Yellow Pages) or outfits like Aircraft Spruce & Specialty Co., of Fullerton, California. They sell a lot of epoxy and the like. They're kind of expensive but you get what you pay for. Call them at (714) 870-7551. But if you check around, chances are you can get hand-stuff locally. (Everyone's got hands.) And after you're all cleaned up, go in and do the dishes! Washing dishes (or just soaking your hands in hot, soapy water) is one trick every mechanic uses to keep his hands presentable. (But most don't have the courage to admit it :-)

The down-side of scrubbing your hands with pumice and the like is that you'll literally wear out your skin. So you use an emollient. Since the days of the Romans common aloe has been used by mechanics, armorers and the like. Just break off a spear of the stuff, crush it in your hands, smear the green goo all over your hands and let it dry. It not only forms a protective barrier, the goo contains an anti-bacterial agent that will keep your hands from getting sore.

The other side of the Getting Dirty coin is keeping your engine clean. It's no different than anything else; if it's dirty, wash it. Auto-parts places carry special stuff for scrubbing engines but your veedub engine is mostly painted metal; treat it like you would your refrigerator or stove. So long as you don't go at it with a fire hose, a little water won't hurt nothing. You don't want to get water in the alternator, or down the carb, and covering the distributor with a plastic bag makes good sense, but aside from that, just jump in there and give that puppy a bath.

If your engine is dirty you're bound to get dirty working on it. So clean it up. No oven cleaner or scouring powder, soap & water will do just fine. I use dishwashing soap, the cheap green stuff, and a stiff paint brush (cutting the bristles shorter makes them stiffer). A toothbrush is just about the handiest thing ever invented when it comes to keeping your engine clean; worry about the nooks & crannies and the open areas will sort of take care of themselves. Once you've gotten the engine clean, spend a little time keeping it that way. It will do both you and the car a lot of good; it's one of the ways you take charge of your life.

Another factor in keeping clean is Dressing For the Occasion. That means long-sleeved shirts buttoned at cuff and collar, long trousers, and shoes that cover your ankle. Working on a car is a job, not an adventure; dress like you're going to do some work. Then let the clothes get dirty instead of you. As to style, I can't say I ever thought about it. Good mechanics tend to be neat by nature; they'd starve to death otherwise. I wear levis or khaki trousers, khaki or denium shirts, good serviceable American-made stuff. You can wash them every day and they'll still last for years. Avoid synthetics and blends; plain cotton is the stuff you want.

There's no mystery to getting grease out of cotton fabric. Use something like trisodiumphospate (try dishwasher soap) or Washing Soda and let the things soak. You're playing chemist here. You've got to give the chemicals a chance to work.

If you own a washing machine, figure out how to make the thing run two or more cycles. On ours, I just leave up the lid. It won't spin with the lid open. Next time I happen by, I reset it to start sloshing again. Do that a couple of time and even the greasiest levis come clean. Sorta faded, but clean. Same thing applies to getting the soap out of your clothes. After you get them clean, run them through another wash cycle with no soap; really rinse them puppies.

If you don't own a washing machine, get a 5-gallon plastic pail and start your own Grungy Laundry. Use a toilet plunger to slosh the clothes; you don't want to get that TSP on your hands.

The other thing you mentioned, the strength factor, is related to your remark about cutting your hand when the wrench slipped, but let me give you a little background on the problem. If you look at a new spark plug you'll see it comes with a washer, that circular metal thing just above the threads. Your spark plug is properly installed when it's tightened enough to compress that washer. There's a torque spec for spark plugs, and as you become more adept as a mechanic you should always torque your plugs to spec, but for now just get them tight enough to compress the washer and they'll work fine.

The compressed washer is why they were so hard to loosen. As you mentioned, once you got the wrench to turn, the plugs unscrewed easily so lets focus on loosening them. The secret here is to use a bit more leverage; a longer wrench. No, you don't have to go out and buy a special wrench, what you want to find is a piece of pipe or tubing that will fit over the wrench you already have. And yes, Craftsman tools are good ones. But Sears probably can't sell you a 'cheater,' which is what you call a piece of pipe when you use it to gain leverage.

What you want is a piece of electrical conduit about a foot long. Or even a piece of plastic water pipe. The diameter is determined by your tool.

When you've got the socket on the spark plug, position the wrench so you can slide the cheater over it and still have room for a short pull. Support the wrench -- you never want to get too rough with spark plugs or you'll break the ceramic insulator -- and take a strain on the cheater. Never jerk on the thing; you've got more than enough strength to loosen the plug if the lever is long enough. The plug will come loose with surprising ease, so don't pull too hard or your hand will come flying off and you'll bark another knuckle.

It didn't come loose? Lengthen the cheater a little and try again. And make sure you're turning the plug in the right direction. On your Ghia the plugs on the passenger side will unscrew when you PULL on the cheater, assuming it is pointing UP. On the driver's side you'll have to PUSH on the cheater. (The manuals will say "Loosen in an anti-clockwise direction," or something equally unclear.)

And of course, you do the same thing when you put in the new plugs. Use your cheater to tighten them. Just be careful not to overdo it; with the right lever you'll have more working muscle than Hulk Hogan.

The principle of lengthening the lever-arm of a tool may also be applied to the generator pulley nut and those 'impossible' lug bolts you mentioned. Fact is, the lug bolts on your wheels should never be run up tight with an air-wrench or you won't be able to change the tire without help. Use a nice l-o-n-g cheater to loosen them, then re-tighten them, snug as you can. You don't have to take them out, just loosen then re-tighten them to your specification. The stock Volkswagen lug wrench was designed to be used with a cheater. Get one made out of pipe, not plastic, and carry it in the boot. That way you'll know you can always change your own tire.

Along with the cheater you may want to carry some of those disposable plastic gloves; tires are dirty too. I've never used the 'paper' coveralls you mentioned but if the 'paper' is Tyvex, I know what you mean and I think it's a wizard idea; there's no reason to get filthy just from changing a tire.

I'm sincerely sorry you hurt yourself working on your car. It wasn't the cars fault, nor yours. The blame has to fall on a society that simply doesn't care all that much for the details of life. I hope this note will provide the encouragement you need to give the mechanical arts another try.

-Bob Hoover

VW - Custom Hat

He kept looking at my head. Every time I reached for a tool, the guy was alooking at me. I finally eased the creeper all the way under his bus and out the other side, got up and took a peek in the passenger-side mirror to see what was hanging out of my nose. Nothing. And no funny smears of grease. Beard wasn't on fire. Teeth hadn't fallen out. But he kept looking at my head!

Finished up, told him he could rebuild the starter if he wanted to but I didn't know any source of new solenoids and that was the real problem. He didn't care; as a mechanic he probably made a fine programmer. Paid me; told me I could keep the old starter if I wanted it. I didn't, which kinda surprised him (I got enough junk to worry about). Then he sez: "I don't suppose you'd consider selling your hat?" My hat?

Took it off to see the gold coins I'd missed. Nada. Old, faded olive-drab looking thingee, kinda greasy around the bill. Got a little VW bus embroidered on one side; you gotta look for it. Over on the other side it sez 'VANS'.

"Where'dya get it?" He's all puppy-eager. Clean hands. '73 Westy, all polished up and neat.

I couldn't recall. "Some race... " SNORE? Some guy was handing them out to the pit crews.

"Would you take ten dollars for it?"

That caught me. It was a second before I started to laugh.


Hell, the damn fool was serious! I handed him the hat; he handed me a twenty. He put on the hat, one size fits all. Drove off happy as a clam.

Couple days later I was over by the airport, stopped in at the VANS sneaker factory, picked me up a new hat. $4.95.

"You wouldn't believe what happened to my old hat," I told the kid. But he didn't want to hear unless it involved ten foot waves. Took my money, gave me the hat.

Veedubers is some strange folk.

-Bob Hoover
-July 1995

VW - Camping, Tents, Baja and Buses

I don't use a tent when I knock around down in Baja, not that it doesn't get cold and sometimes, rarely, there are reports of rain. (I've seen rain in Baja, but only from a distance.)

Standard Baja camping equipment is two tarps and four metal poles; metal, because if you use wooden ones some damn fool will put them in the fire. Lotsa rope; rope is very handy stuff in Baja.

You use one tarp as a shade. The only tree in Baja is in front of the mission at San Ignacio and they don't like you to camp there. So you tie one side of the tarp to the roof rack and prop up the other side with your metal poles, lash everything down with rope. Use bridge spikes as stakes to secure the rope. Bridge spikes are those humongous nails you've seen at Home Depot (and wondered what they were for). Now you know. Bridge spikes are Baja tent pegs. (Because you can't drive a wooden tent peg into the ground anywhere south of Maneadero. And some damn fool will put them in the fire.)

You use the other tarp as a ground cloth. That's where you sleep, on the ground cloth. Under the shade. (Down in Baja it's even sunny at night.) You set-up your table on the ground cloth, and your cot, and your Coleman stove. Leave the porta-potti in the bus, along with the icebox. And the magazines. Put the shotgun near the Coleman stove, down by the propane bottle.

In Baja you fish; that's why it's there. You don't shoot; guns are illegal everywhere in Baja except in Tijuana and then only at night in the downtown section. Everywhere else you gotta use a machete. But a machete or even a pistol is no good against flies, least ways not against Baja flies. Oh, I used to use a pistol on them; most guys start out with a pistol. But if you don't hit them suckers square you won't kill them. And a wounded fly will get madder than hell. So use a shotgun. I know; it's not a sure-thing either, but it will knock them down, give you a chance to go after it with your machete. Once you got the wings off them suckers you can get in close, finish them off with your pistol.

It takes about thirty minutes to set up camp in Baja, unless you've got women along. It takes longer with women along; give yourself lots of time. Set up camp, take a stand, knock down the Boss Fly to let the others know you mean business, then go fishing.

Women always want you to bring a tent along. And extra clothes; stuff like that. Truth is, you don't need that much in Baja; the fish don't give a damn what you got on. But woman are handy things to have around, especially in Baja, what with all that gutting and cooking to do. So mebbe you'd better plan on a tent. And wearing clothes.

If you've got a VW bus you can get one of those nifty little tents that hooks on to the spray rails, sets up quick as bunny, lets you get the boat in the water that much sooner. But they're hard to find; you might have to make one.

Here in southern California they've got these fabric supermarkets, big as a football field; sells nothing but fabric. Sailcloth. Upholstery stuff. Foam. Dacron for airplane wings; every sort of fabric you can think of and all the gee-gaws to go with it. Go down there and get you a buncha' tent-fabric, take it to an upholstery shop. Or a sail loft. Hell, mebbe they even got tent shops; check the yellow pages. The fabric will cost more than the sewing and he'll need a pattern. I'll leave the pattern up to you; mebbe you could ask a woman, they mess with patterns. If your wife is handy that way, mebbe you could just take the tent fabric along the next time you go to Baja; give her something to do while you're out fishing; let her run up her own tent.


AV - The Wandering Prick Mark

The typical aviation apprentice, military or civilian, is a teenager fresh from high school. Homebuilders are rarely that young but unless their background has been in aviation, they too are an apprentice of sorts, at least with having to undergo the same Rites of Passage of an apprentice aviation machinist or metal smith. One of those Rites is layout work, long the bane of every aviation apprentice. Mature in years, albeit not in aviation, this particular Rite can prove especially trying for the homebuilder because any emphasis put upon layout work often appears to be a waste of time. Every adult is familiar with rulers and pencils; with the measuring and marking of things. Why should doing so for airplanes be any different?

In a purely engineering sense, airplanes are not different from other automotive machines whose design is optimized to yield the highest strength for the least weight, even though that achievement has spawned a body of procedures, techniques and specifications unique to aviation. I’ll address a couple of those aviation-unique things in a moment but in a philosophical sense airplanes will always be different because man can not fly. If a boat or car should fail us, we can swim or walk. But airplanes embody a form of implied trust not found in any other auto motive device, in that the mere use of the thing, properly and correctly, will not kill us.

Each new physician is required to swear that at the very least, he will do no greater harm. There is no Hippocratic Oath for aviation but if there were it would probably be: Let’s try not to kill anybody today. And that’s why airplanes are different.

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Note: Automotive means a machine capable of moving under its own power. The Society of Automotive Engineers encompasses everything from paddle-wheel steamers to the Lunar Lander.

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I hope this doesn’t come as a surprise but when using a machinist’s combination square, steel ruler, tape measure and so forth, your best efforts at laying-out will always be off, plus or minus, by some amount. This is normal. The error reflects the precision of your tools and your experience using them. For example, the width of the markings on your tools introduces some degree of imprecision, as does the way you look at the markings, as well as the manner in which you make marks upon the workpiece. So long as work must be laid out by hand there will always be some degree of error. For the sake of safety, that error is always taken into account in the design of airplanes and the layout of their parts.

(Personal Note: Always buy the best tools you can afford. A quality tool will last your lifetime. Or more. I’m in my sixties. Some of my tools belonged to my grandfather, others to my dad. A quality tool is a practical legacy and daily memorial.)

One of the realities of aviation is that airplanes are still built by people rather than robots and human abilities as tool users varies from one individual to the next. Much of the basic training for aviation sheet metal workers and machinists is devoted to teaching standardized methods that reduce human error to an acceptable norm. Scribing a line or pricking an intersection offers a good example of the subtle differences in our ability to use common tools. In a class of about twenty-five, when using a combination square, pre-set to a given dimension by the instructor (but each student using their own scriber), it is rare for any two lines scribed by the students to fall upon the same point.

A similar variation is seen in the student’s efforts to place a prick mark at the intersection of two lines. Magnified and displayed on a video screen, the crater of the prick mark will be canted to the left or right, depending on the handedness of the student, and however canted, seldom falls exactly upon the intersection. This is not a graded exercise but a demonstration, without which the tasks to follow might seem a waste of time. Everyone knows how to scribe a line and use a prick punch. Or think they do. The demonstration makes it painfully clear that all lines are not created equal :-)

As with any of the manual arts, practice makes master of the man. An experienced machinist, working with his own tools, will usually have a scribing error between one and three thou. For a student, the error is typically between eight and fifteen thou. Learning how to hold and use the tools will reduce the error. A useful exercise is to lay out a grid upon a coupon of aluminum or steel and to prick punch the intersections, an obvious waste of their time... without the prior demonstration.

Keeping a blade or straight-edge flat to the work while holding the scriber at the proper angle does not come naturally to all. Yet these seemingly insignificant details have a profound effect on the magnitude of your scribing error, as does the sharpness of the scriber’s tip and its shape. All scribers have a slightly different shape to their tip. Viewed with 3x glass, most define a ogee curve (ie, ogive, etc., similar to the nose of a Spitzer type bullet). That means the tip of the scriber will always fall some distance away from the blade against which it is pressed. That distance will vary according to the thickness of the blade the angle at which the scriber is held. Learning to polish a symmetrical needle point onto their scriber results in an immediate narrowing of their scribing error. (Some machinists stone a small flat on the side of the scriber’s tip, allowing the tip to fall closer to the blade.)

The fact scribing errors exist isn’t the object of the exercise - the errors are painfully evident when the workpiece is projected on the screen (or when viewed using a low power binocular microscope). The object of the lesson is for each person to understanding the factors that cause such errors. Once the problem is understood, we can move on to weightier subjects, leaving the student to reduce their particular error to an acceptable level through practice and self discipline.

Some error will always remain and while a small error is generally considered better than a large one, the real goal is consistency. Once their error becomes consistent we simply calibrate the student :-)

This calibration is nothing more than teaching the student to recognize their normal working tolerance - how large their particular scribing error happens to be. Once the error factor is known it can be dealt with by adding or subtracting that amount to your tool's settings when laying out a line. One way of doing this is through the use of shims, selected to match your rate of error. I'll have more to say about this in a minute. Right now, I want to address the Wandering Prick Mark.

Visual acuity in humans varies over a wide range and declines with age. Some can see divisions as fine as one hundred twenty eight to the inch at arms length with perfect clarity while others have trouble with sixty-fourths held close up. Even when a fine line is visible, variations in hand-eye coordination result in errors when transferring that line to the workpiece, pricking an intersection or setting a tool. When asked to set the blade of their combination square for a projection of one inch, it's rare for even one of the class to hit it dead on. (And if she does, you simply reset her square and ask her to do it again.) An experienced machinist can usually come within plus or minus 0.003" of a mark with a reasonable rate of repeatability but it's a more difficult thing to do than most realize.

So don't do it. Not with your naked eye. Unless you're an experienced machinist.

At the very least, a magnifying glass should be used when picking up your points. There are inexpensive optical devices that allow you to prick the intersection of two lines with repeatable accuracy of about +/- 0.003", which is very good for even an experienced machinist. (Look under Optical Center Punch in the catalog of your favorite supplier [ie, Travers, MSC, Enco, etc.] You'll also find plans for do-it-yourself versions on machining-related newsgroups.)

In a similar vein, you would not use the naked eye to set the extension of the blade of a combination square unless the allowed tolerance was on the order +/- 0.015" (ie, about a sixty-fourth). Instead, you would use a known standard, such as a stack of Jo blocks on a surface plate and set the blade according to that. The resulting setting will usually be within a couple of thou (usually + zero, minus something). Which should be more than enough. If greater precision is required, you wouldn’t be using a combination square. (What would you use? A template or drill jig, created using something other than hand tools.)

But the odds are you won't have a surface plate or set of Jo blocks in your kit. If you're the typical homebuilder, what you'll have is a collection of tool bits of various sizes, measured and marked so their dimensions are known. And your scribing shim is liable to be a piece of cigaret paper (!).

A cigaret paper is about one thousandth of an inch in thickness - thinner than a human hair. The thickness varies from batch to batch and brand to brand. (Buy yourself a packet of Zig-Zag or Bugler and measure them. You'll see a similar packet in the tool box of most machinists.) Dry paper doesn’t make a very good shim. (Paper tends to compress.) But when paper is treated or filled it serves quite well, as shown by its use for gaskets. On the job, the handiest filler is to simply soak the stuff with kerosene or light machine oil. The dimension of oiled paper is more than stable enough to be used as a shim for casual layout work, setting the height of a sharpened tool bit and so forth. (Indeed, paper shims were the standard method of adjusting cutter depth in rifling machines for more than a hundred years.)

To subtract your scribing error to the setting of the blade, put the shim under the blade of the square where it contacts whatever you’re using for a surface plate. To add your scribing error to the measurement, as when scribing off the frame of the square, simply add the shim to the stack.

In addition to tool bits, which usually range between plus zero and minus two or three and vary for each face (ie, they aren't especially precise), another handy source of inexpensive gauge blocks is precision ground tool steel or tooling plate, which is often within .0005" across one dimension (ie, either thickness or width - more precise than you’ll need to build an airplane).

Unless you’re using real Jo blocks on a certified surface plate, the accuracy of your stack-up gauge will wander around a bit. Its saving grace is that it?s quick to set up, inexpensive, highly portable and more accurate than your eye. If greater accuracy is needed you may set the blade using a beam-type caliper or depth mike but for this type of layout, that degree of precision is rarely needed.

Which begs the question: How good is good enough?

All dimensions have a tolerance related to them. This is an inescapable reality of machine work. (Or life itself, when you think about it. Nothing is perfect.) A dimension and its tolerance is inherently linked; you can’t have one without the other; they are a paired set. And since the two can not exist apart, when tolerance is not stated, it is implied.

Until the creation of the International Organization for Standardization (ISO) in the late 1940's, the minimum accepted tolerances for working layouts for airplanes (as opposed to patterns, fixtures or jigs) were plus or minus 1/64th for fractional dimensions, +/- 0.015" for decimal dimensions and plus or minus one-half of one degree for angles. Manufacturers often had their own minimums but trade schools generally used the tolerances above, as you’ll see by examining any of the manuals from that era.

ISO changed all that. When the United States went metric in the mid-1970's we did away fractional dimensions, which today are rarer than fur on a turtle except in the homebuilt community, reflecting the tools and non-aviation background of the typical homebuilder. You run into fractional dimensions occasionally when doing repair work on pre-ISO airframes but most American aircraft manufacturers had already gone to decimal dimensions by the time ISO arrived.

Today’s homebuilders manage to escape most lay-out chores, thanks to simple CAD programs such as DeltaCAD, a simple 2D replacement for the traditional T-square, triangle and engineer’s scaled ruler. Now we need only print the lay-out full-scale, glue it to the part with a spritz of spray glue and use an optical center-punch to pick up our intersections with an accuracy equal to that of a skilled tool & die maker.


AV - Douglas Fir Isn't


A fir, that is.

Doesn't really matter of course. Unless you're into botany.

But it's not hemlock, either. Although that's what it most closely resembles. Which is why its Latin name means 'False Hemlock.' (Pseudotsugo... pseudo = false, tsugo = hemlock). The complete name is Pseudotsugo menzieii and gives you a hint there's more than one variety of 'Douglas Fir'. In fact, there's about half a dozen 'pseudotsugos' including coastal, mountain, Mexican, Manchurian and a couple others.

Don't worry about it. Go to a lumber yard, ask for Doug Fir, you'll probably get the pacific coastal variety. Other than being a bit brash, Douglas Fir, also known as 'Oregon Pine,' is fine for all aspects of airplane construction, assuming you can afford the weight.

But don't mention airplanes. Tell them you're looking for sucker rods or stair treads or ladder rails. (A sucker rod is that thing going up & down on a windmill. Up to 28 feet long, perfectly clear- grained Doug Fir, up to 4x4 in the middle, thinned down to 2x2 on the ends.) Stair tread stock tends to be heavy, with ring-counts of 16 and up. Ladder rails were long the standard for airplane spars, in both spruce & fir.

Lumber yards that cater to this particular trade usually buy clear-grained balks of Doug Fir in 4x6 or 4x10 rough cuts, up to 32' long. They'll slice off what you need and finish it, too... if they've got the tools. Real lumberyard can start with a tree, give you rungs for a chair.

Here in Sandy Eggo county I think we've got three real lumber yards left. One caters to boaters, one to farmers, the third to yuppies. It's a sixty mile drive to the farmer place but always worth the trip. Little place. Been there forever. They buy about two truck- loads of Select Grade-A DF a year from a little lumber mill in British Columbia, turn it into sucker rods, wagon tongues, ladder rails, pruning poles and the like.

Sitka Spruce is lovely stuff to work with but there are more than a dozen alternatives listed in AC43-13. Lotsa Piper Cubs flew on spars of 'Oregon Pine' and the first Pietenpol used edge-glued Hemlock for spars (according to Mr. Pietenpol).

PS - Some Douglas Firs are bigger than others :-)

AV - Welding and The Big Lie

> The PHD of Metalurgy hosting the welding Forum at SunFun said TIG is the > best by far for welding 4130 despite decades of published preference for > gas welding. >


This is the sort of disinformation that guarantees the demise of grass roots aviation.

There is no question as to the superiority of TIG. Same for Rolls-Royce automobiles. But those wunnerful friendly experts at all the airshows leave the impression that other forms of welding will produce an airplane that isn't quite as safe. And that's where the Big Lie comes in.

So you do a simple T-joint in tubing with TIG and an identical joint with gas. Then you test them. Let's say the TIG'ged joint fails at 6000 pounds and weighs an ounce less than the gas-welded joint that fails at 5000 pounds. Obviously, TIG is 'best.' But when the 6-g stress in that particular joint is only 1500 pounds who the hell cares? Other than the guy trying to sell over-priced TIG rigs to novice builders.

The Welding Wars are similar to the Glue Wars in that both are usually fought by people who are either trying to sell you something or who have never actually built anything. All of the glues we use are stronger than the softwoods commonly used in aircraft construction. And all methods of welding may be used to produce a strong, safe airframe.

So while the welding guru didn't voice a direct lie, neither did he tell the whole truth.

So what's the whole truth? That depends on you. But you can't answer the question until you've learned to weld... with gas, stick, TIG and MIG. Then you can say "This method of welding works best for my airframe and my shop and my financial situation and my access to resources..." and for all I know, for your sense of style as well :- )

Airplanes call for welding. It is a skill we all should have in our warbag. For certain tasks and components some types of welding are preferred over others but that is not readily apparent to the novice.

Learning to weld with gas involves only a modest investment, most of which may be recovered by selling the rig. But the odds are, once you've learned to weld you'll never get rid of your gas rig, even through you will transfer the skills you've acquired to MIG and TIG.

TIG is great. I prefer it for landing gears, engine mounts, anything made of aluminum and all sorts of 'sit down' jobs small enough to do at the bench, inside the shop. But I also use gas and MIG, often in places were it would be grossly impractical to use TIG.

In the same vein, Rolls-Royce is great. But I drive a 1965 Volkswagen bus and it has somehow managed to carry me from the shores of Arctic Ocean to below the Tropic of Cancer, even though any number of people will insist an old VW bus is not the best vehicle for that purpose.

Airplanes are kinda like that. If you build one and go fly, you'll see that the Glue Wars and the Welding Wars and all the other wars of personal preference are just another waste of time, something that detracts from building your airplane rather than contributing to its completion.