Can this do-it-yourself mechanic get away with using wedge shaped head?

Dear Car Talk

Dear Car Talk | Nov 01, 1995

Dear Tom and Ray:

I specialize in old Hondas and have had remarkably good fortune with a '76 Civic hatchback (the Yellow Peril) and an '83 Civic station wagon. Both are on their second engines; I put an Accord engine in the '83 Civic, which has run like a scalded dog now for three or four years. Both cars have over 200,000 miles. Recently, I found an '81 Accord hatchback that had been abandoned on the side of the road near here. To make a long story short, I got in contact with the owner, bought the car for $200, and towed it home. The car had had an engine fire after the former owner allowed it to overheat. I pulled the head and took it to a machine shop. The machinist said it was not cracked, but was warped, so he milled it. When I got the head back, I measured its thickness and found it was thinner on one end by about 0.020 inches and therefore is a bit wedge-shaped (he milled it on one end, but not the other). When I diplomatically questioned the machinist about this, he said "Aahh, it doesn't matter!" Aside from the engine, the car appears to be in good condition, and I intend to use it as a replacement for the Yellow Peril, which I will give to my son. My question is: Is the 0.020" head thickness difference significant, or should I follow a mechanic friend's advice, put it back together and turn up the volume on the radio? Right now, I'm inclined to take it to another shop, have them shave off the excess, and install a spacer that I understand Felpro offers. As you may gather, I'm very frugal regarding automotive expenses. I collect parts cars, and when I need a "new" vehicle, I simply assemble it from stuff I have on hand. The same holds for other appliances, all of which I maintain could be virtually free to innovative people in America these days. We can rid our roadsides of junk cars and washing machines simply by recycling them. I can't understand why most people throw this stuff away!

TOM: My, oh my, William. I can only imagine what your front yard looks like. If the Vatican calls looking for nominations for saints, I think we're going to have to suggest your wife!

RAY: But I don't like this wedge shaped head. The reason I don't like it is because you'll have different compression ratios in your cylinders. When you machine a head to make it smooth, you, in effect, make the cylinders smaller and increase their compression. But when you machine only part of the head, you increase the compression in only some of the cylinders. And my guess is that an engine with such a head will always run somewhat unbalanced.

TOM: My brother's head is also out of whack, and look how unbalanced he is!

RAY: William, since you're the kind of guy who keeps things a long time, I'd be inclined to get this head done right before you drop it into this new limo of yours.

TOM: So I'd do one of three things. I'd either take this head to another machinist and see if he can "repair" the work done by the first guy. If that's not possible, you can go to a junkyard (or your backyard) and pick up another old head.

RAY: Or, just hide in the bushes by the side of the road, and when the next Accord overheats and catches fire, jump out with your checkbook and make a deal!

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