Sunday, November 19, 2006


Fella comes by the shop, got his heads in his hands. "Any good?" he asks.

I've known him twenty, thirty years. He's putting together a VW-powered trike with his grandson. Kid don't know squat about engines but his welding is to die for. Break a razor blade, he can weld it back up, good as new. Mebbe better. But as an engine builder he'd make a good... weldor, I guess.

So his grand-dad, the fella I know, has been bringing parts by. "Any good?" I take a look, tell him yes or no. When I say no, he scrounges up another part, brings it by. Process of elimination. He's rounded up just about all the parts he needs to build a good engine, picking up pieces here & there. So far, he's only out of pocket about fifty bucks for bearings and a gasket set.

I put the heads on the bench, turn on the big light, check them for cracks. Single-port heads, -373A's, prolly the most common - and the best - single-ports VW made. Takes bigger valves than the single-ports used on the 1300cc engine.

Studs are okay. One head has been out in the weather, steel parts are kinda rusty. Chase a couple of studs - the rust is just surface stuff, should clean up okay. Seats are okay. They need to be stoned but there's plenty of metal, no signs of loosening. Need to be heated up to check them right, though.

Dig around, find the bristle brush most folks think is for cleaning the pump in a percolator-type coffee pot. Nah! It's a Valve Guide Brush. Give the guides a shot of WD-40, scrub them good. Nylon brush doesn't hurt bronze. Put a piece of white paper on the bench, peer down each guide looking for scratches. Okay.

Dig around in the drawer, find a new valve, mike it just to be sure. New. Poke it down the valve guides, one by one. Wiggle-wiggle. Wiggle-wiggle some more.

One head, all four guides are shot. On the other, the exhausts are bad but the intakes are okay.

"How do you do that?" he asks.

I show him. Wiggle-wiggle.

"What'd you do?"

I show him again. Little wiggle on the good intakes, lotta wiggle on the bad exhausts. He kinda looks at me. "That's all it takes?" he asks.

"That and forty years," I grin, showing off.

I dig out a new valve guide, give it to him, hand him the new valve. "Poke it in there," I tell him. He pokes it.

"Now wiggle it." He wiggles it, shrugs, does it again.


"Now try that one," I point to one of the bad exhaust guides. He slides the valve in, wiggles it. His eyes open up a little, go kinda round.

"Big difference," he sez.

"Yeah, on that one. Try this one," pointing him toward the good intake guide.

"This one's... okay?"

"It's bit loose toward the chamber but you can use it."

He plays with the heads, going wiggle-wiggle.

"Not that way," I warn him when he tries wiggling the valve side-ways. "Rocker pushes the valve just one way. Use a bore-gauge, it'll say the guide is okay in the middle or side to side. But it's all ovaled out on the ends, doesn't hold the valve straight, can't soak up the heat the way it should. Shoulda been using swivel-feet."

"Why's that?"

"They spread the load on the end of the valve stem, reduce the side-loading. Guides don't wear out nearly so fast if you're running swivel feet." He asks how much they cost, where to get them. I've a hunch the boy's engine will have a set when it comes alive.

He wiggles some more. Up & down then side to side. Wiggle-wiggle. "I think... Yeah! I can feel the difference."

Anybody can if they wiggle enough. But it's new to him, potentially useful. I can see him storing it away in his mind like a newspaper headline 'Old Dog Learns New Trick!' "So... can I replace the guides?"

"If you got the tools." I show him a core drill and the drift and the driver and the wooden jigs for holding the heads and top it off by unlocking my machinist's tool box and showing him the reamer, all shiny and new-looking in its soft plastic tube. The reamer is more than twenty years old, still cuts true. He looks at all the stuff and his eyes go kinda flat. Too much information for him to handle all at once. So I do it a step at a time, remembering to include the weldor's gloves for handling the heads when they come out of the oven and the three different stones for dressing the seats and the tool that holds the stones and how long you gotta heat the heads and stuff like that.. He nods as I explain why it's bad to just blast the guides outta there cold and why the seats should have three angles and the importance of getting the stems the same length and about a thousand other things.

When I finish he heaves a big sigh, asks where he can get it done. I give him the name of a shop, "But you probably can't afford it." They do racing heads. The other automotive machine shops just do repair work, good enough for most folks but not the sort of thing a grandfather wants for his grandson's trike.

"I don't suppose you'd be interested... "

Thanksgiving is tomorrow. We got folks coming and I'm in pie-making mode. But he's probably got folks coming himself. And just as many chores as me. Friends are a lifetime sorta thing and VW heads aren't. But both need a bit of help now and then. So we settle on a price - he's got a chain-saw and I've got a wood-burning stove -- we shake on it and I see him off down the drive.

-R.S. Hoover
-25 November 1998

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The Wiggle Test applies to all engines with poppet-type valves. The factory service manual for your particular engine usually provides a detailed procedure that allows you to determine the radial clearance of your valve guides by measuring the ‘wiggle’ with a dial indicator.

The exhaust valves are the VW’s weak link. Most flying VW’s will fail the wiggle test somewhere around 200 hours (about the same as the Continental A40). But some drop out of spec in as little as ten hours (!) while others soldier on for 400 hours or more. Why? Mostly because of cooling, or rather the lack of it in the case of short-lived valves. Loading, rpm and mixture play a roll but the gross symptom is accelerated valve guide wear and the most apparent cause is inadequate cooling.

Fortunately, replacing the valve guides in a VW head is a simple procedure. The old guide is cored out, the head is heated and the cored guide is driven out. The head is then re-heated to about 350 degrees Fahrenheit, the new guides are chilled to about -100 degrees Fahrenheit and pressed into the head, resulting in a shrink-fit. Chilling the parts is easily done by soaking them in a slurry of dry ice and sulphur dioxide, or in liquid propane.

Most VW shops don’t bother with such niceties. Instead, they use a pneumatic hammer to drive in the new guides at room temperature, resulting in a lot of split heads and loose guides. Which isn’t much of a problem in a dune buggy but can be bothersome when you’re half way to Catalina :-)

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I’ve reposted this message to the RAH newsgroup because a lot of homebuilts use the VW engine - or at least, VW heads and crankcases - and some of those pilots have reported dangerously short-lived exhaust valves. This lead to the discovery that some engine builders are not providing ANY cooling for the exhaust port and the exhaust valve guide. This is the second hottest part of the VW engine (only the exhaust stacks are hotter) and Volkswagen devoted considerable attention to insure this area receives the lion’s share of cooling air delivered to the heads.

Flying behind (or in front of) a VW? Getting less than 100 hours from your exhaust valves? If so, perhaps it’s time you audited your engine’s cooling system.


18 November 2006

I've posted drawings & photos of a DIY wiggle-tester in the HVX files. See the archives of the AirVW Group on Yahoo for how to gain access to the information.


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