Thursday, August 9, 2007

Tappets As Field Mice


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

-R.S.Hoover

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

2 comments:

Steve Ballantyne said...

Interesting method there Bob. I split my case last spring, and had no business doing so as I was not "experienced". But I learned a hell of a lot. I tried to keep mine in place with the "four finger technique". But I have big hands and long fingers. Also, I must have mated and separated the case a million times trying to get the case to tighten down and not bind up. I needed an align bore! At any rate, I made a similar tool to hold mine in out of old coat hangers. Stiff copper "bailing wire". Worked good. I thought myself some sort of genius, but your "loop" design looks much more practical. You shoulda' patented that little item. ;-)

-Steve Ballantyne

Hal said...

"dropping your tappets on the floor -- or forgetting to install the damn things -- was almost a National Sport, at least among VW mechanics."

Not only are your articles informative, but it's parts like this that make them an absolute joy to read.

Keep up the great work, Bob. ;-)