Thursday, April 26, 2007
Stoning Your Rods
Last Sunday after church I was chatting with an Eager Young Airman building a Volksplane. Started around Christmas, he’s just finished covering the wings and was about to start on his engine.
“The parts are due to arrive tomorrow,” the Eager Young Airman said. “I’ll put the engine together after I get home from work.”
I must of done something because he squints at me and sez: “What?”
How do you explain chartreuse to a blind man? In the end I merely shrugged, “I generally take a bit more time.”
“Yeah,” he smiles. “I’ve read some of your stuff.” He doesn’t laugh aloud but you could hear it. “I’ve put together a lot of engines,” he brags. “I won’t have any trouble.”
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(And with that kind of a lead-in you can guess what comes next :-)
Around noon-time Thursday he called me from work, a bit less perky than before. Was there a chance I could come by his house that evening? He’s having a bit of trouble with his engine.
No. In fact, hell no! He lives some distance away and the local freeways slow to about 15mph between five and seven. “What’s the problem?” I ast him.
Pregnant pause then: “Nothing seems to fit!” His voice is filled with frustration, exasperation and - - to his credit - - a hint of embarrassment.
“Well... the rods lock-up.”
“You got the right bearings?”
“STD’s,” he sez. (In Engine-Tok that means ‘Standard,’ rather than a dose of clap.)
“On the carton or on the bearing shell?” He doesn’t answer, which means the carton was marked STD. He’s got no idea in the blue-eyed world what was inside of the box. “Didja mike the crank? ID the rods?”
His answer is: “It’s all brand new stuff!” (Which means 'no.')
I can’t help but laugh at that. “Yeah, but from where?”
Turns out, he doesn’t own a 3" mike; doesn’t even know the spec for the crank’s journals. I tell him to bring it by the following day, let me take a look at it.
Friday evening he shows up with an engine’s worth of parts rattling around in his back seat. I’ve cleared some bench space and as we’re hauling the parts into the shop he mentions that it’s twenty-seven miles from his house to mine, which is about five dollars-worth of fuel each way. He sounds sort of surprised.
“No kidding?” (Okay, mebbe with just a hint of irony :-)
His crankshaft is one of those Chinese jobbies, an 82mm stroker for which he’d paid less than $200. Why so cheap? Partly because it's not very good. The #2 rod journal miked more than a thou over spec and the #1 Main was 2.1638" - - four tenth under the lo-spec of 2.1642". Run-out is seven-tenths, right on the outer limit. He starts yelling about returning the parts, suing the retailer for his lost time and other Yuppie bullshit.
“Don’t bother,” I tell him. “Shop by price and this is what you’re going to get. This is the norm nowadays." Trying to sue the people who sell this junk is throwing good money after bad.
“But it doesn’t fit,” he wails.
“Of course not,” I said. He makes a WTF gesture. “Making things fit is your job,” I tell him.
“I’ve never had any trouble before,” he says. Which means he’s probably only worked on stock engines.
I’m checking his rods. They aren’t new, they are stock rebuilt units that happen to be too short for use with an 82mm crankshaft. Enormously popular, of course. But as rods go these happen to be a pretty good set, with a weight span of only 4 grams. He follows me back & forth as I lighten the two fat rods to match the two skinny ones, each of which weighs within a tenth of a gram of the other. Of the two heavy rods, one is a tad less than two grams out, the other just over four. Four grams is a lot of grinding, followed by smoothing things up with the belt polisher.
He has never seen the jig for doing big-end/little-end balancing, asks: “What’s that for?” Which tells me I’m wasting my time.
I split the rods, pull them apart. None have been stoned; all show the usual burr created by honing. (Note: Stoning away the sharp feather-edge left by the hone produces a distinctive line of light. Steel-backed bearing shells usually require the same treatment, at least on the back-side of the shell.)
I show him the burr, let him feel it. On one rod the burr has a wrinkled appearance, apparently folded under when he installed the shells. It's more than enough to cause the rod to lock-up. He can’t believe it. “Where’d that come from?” I toss his new bearing shells into some lacquer thinner while I stone his rods, wiping away the burr. Then I clean his bearing shells and do the same with them.
“I never had any trouble before,” he says again in a voice small enough to ignore, which I do.
Chucked into the vise and torqued to spec, the mikes show the usual spread across the rod’s big-end ID’s and I paint a big ‘2' on the fattest of them. Over on the clean side of the shop is two shelves of bearings, odds and ends acquired over forty years of building VW engines. Which happens to include a set of ‘Silverline’ conjinetes para motor that I know to be a few tenths under spec. I clean the rod and install the shells, put the assembly in a plastic bag. “Take your crank to HDS in Escondido and have them polish a couple of tenths off the #2 rod journal.” Since shit happens, I use fingernail polish to mark the correct journal. “When you get it back, after you pull those damn plugs and clean the thing, install this particular rod on #2.”
Some of the oil passages on his Chinese stroker are drillings sealed with 4mm socket-head set-screws. They need to be pulled and the oil passages cleaned then re-installed with Loc-tite and straked. Which he hadn't done. But even as I explained the what & why I had a hunch he wouldn’t bother. After all, he’s built a lot of engines. And never had any trouble.
He’s been here nearly two hours. His particular collection of parts will probably need another twenty hours of work before they’re ready for assembly but I've a hunch it's never going to happen. It’s late, I’m tired and he still thinks its all bullshit. So I wish him good luck and wave him on his way. Maybe he'll read this and get the hint. But after spending two hours with him, I doubt it. Really good engines are more than an assemblage of parts.
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Is this sort of thing common? Nowadays the answer is a loud ‘Yes!’ The surface-finish of the guy’s crankshaft was pretty bad (it should look like a mirror), a fact he’ll learn for himself when he sees the difference between the journal polished by HDS (an automotive machine shop) and the other journals. Other than being the wrong rods for the engine, they were okay but the cam was a joke, intended to move the power-band well above the point of optimum efficiency for a propeller. But trying to explain such things is usually futile. This particular builder has some prior experience but it’s of the ‘Compleate Idiot’ variety, where you’re told it’s okay to scrape machined surfaces with a pocket-knife and pound on bearings with a sledge hammer. (I’m serious here, folks.) He's convinced that my attention to detail is unnecessary. After all, he's assembled a few engines and they ran just fine... in a car.
I wouldn’t want to fly behind the guy’s engine but that applies to most of the converted VW’s I’ve seen. So long as the ‘experts’ are telling people it’s okay to paint their engine with barbecue paint and that it will rust out before it wears out, we’ll continue to see newbies risking their lives behind improperly assembled engines.