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Am I screwed ..? (valve to piston clearance) (archive)
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Posted by Steve Walsh on November 25, 2000 at 16:28:04:

I have a '71 '02 racecar. After snapping off 2 rockers in August I just got the head back togther after about $3K in work (I got a bit case of while-im-at-its). New 304 Schrick cam, new Korman-prepped intake and exhaust valves, new valve seats, new seals, new Korman lightened/polished/stress-releived rockers, Kormans rocker retainers,ported intake and exhaust passages.
It was an E12 head, and was milled to minimum thickness before all this work. It sits on a 71 block with 'Grand Piano' style pistons.,

Here's the problem. It looks like the machine shop milled the head some more, and with the larger cam, the new valve seats and new valves there is now insufficient clearanve between the valves and the pistons (actually none). With the head gasket in place I have about 4 thou clearance. Without the gasket the engine can't be turned (by hand) without the valves hitting the pistons. This was a method I learnt for checking clearance with the 304. If you can turn the engine without the head gasket, you'll have enough clearance with the gasket in place
I tried the adjustable cam sprocket in all the available range to see if I could retard the cam enough, but I don't have enough range.

Is my only recourse to fly-cut the pistons (in which case I might as well get J ane E 10.5 for 11:1's), or start with a new head (would hate to throw away all that head porting).
On one side I could always sue the machine shop for milling the head without my permission, but I'm sure they will say the needed to do it, yadda yadda. And new pistons would be nice :) But if I start on the bottom end, it'll be another $3k before I'm done....

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