[Walt Fricke]

I had the same reaction as others when I read what you were thinking - that you could compensate for the fact that the tops of the spigots were not level, so to speak, but for either side some were higher, some lower. Middle ones were the most off? And you planned to compensate by thinking the copper gaskets would crush differently, so you'd end up within the 0.025 tolerance Magnus points to. But they really don't crush any appreciable amount.

If the spigot tops on each of the sides are "level" with respect to the crank centerline, but are at slightly different heights, I don't think that is apt to present a significant problem. Probably not enough to impair cylinder head or valve clearances, or to change the compression ratio enough to worry about.

The goal is to have the tops of the cylinders all in a line. If they are not, then when you bolt the cam carrier on and torque the heads, you are apt to find that the cam is binding. Many of us have felt a little bind when assembling a motor, and have counted ourselves lucky that loosening the fasteners and retightening them solved the problem. But with things dimensionally wrong you can't solve that problem.

I'm now supposing the tops of the cylinders are where you measured (maybe you said that), as it is much easier to do with the cylinders slipped in place. If the copper gaskets could be had in 0.025mm increments, maybe one could fiddle with them to get the cylinder tops right.

Alternatively, one could hunt around for different height cylinders, and see if mixing things up might bring things into tolerance.

Or one could have a machine shop remove just the right amount from the lower mounting surfaces of cylinders, sinking the tall ones a bit. I don't think you can take much off the tops of the cylinders, lest the CE ring groove gets too shallow.

And, of course, for a cylinder a bit too tall you could have its mating surface turned down a little. I suspect a good machinist could come up with a scheme using these alternatives to get the tops of the cylinder heads, on which the cam carrier rests, to be parallel with the crank centerline.

But none of these things really makes any long term sense - you end up with a bastard motor. And I suspect a good machinist would try to dissuade you from trying something like this. I think it would take less machinist time to set up the case and machine the spigot tops true.

The benefit of using a shop which has experience with this kind of thing is that such a shop knows from experience how these mag cases do or do not squirm around, or change shape when all torqued together, and so on. Not something us home brew motor assemblers really know about. You knew enough to put the straight edge on, notice the problem, and ask about it.

There are an awful lot of good Porsche race shops in the NE. I bet most of them would take a call and tell you what machine shop they use to true case spigots, if they don't do that kind of work themselves.