Okay. Let's see. Intakes are fine, exhaust is causing interference. Maybe Bill got aggressive on the exhaust cam lobes when he had it made. Minimum clearance, intake, at any position on the crank, was .060. With the exhaust rocker at .110 lash, I end up with zero clearance on the exhaust valve. My head gasket is approximately .060. Exhaust valve is 1.75" diameter. I didn't measure, but eyeballing in the intake port, there is roughly 1/8' between intake valve and cylinder. I'm assuming the exhaust would be similar. I stuck a feeler gauge between the piston and wall, and best I can tell, I have just over a 1/4" until I hit the compression ring from the top of the piston. Since this isn't a high revving engine, I'm thinking I can get away with another .080, AFTER I cut the piston .110 just to get zero lash, fudge in my hot lash of .020 (or less because of aluminum head on steel block?) So that means a total crescent shaped cut of .190 deep, leaving plenty of piston underneath. I don't think groove depth will be an issue, either.
Worst case, I kill the piston and have to replace the six. Or tag a valve and have to replace valves. But, ain't that what makes these one off special builds fun? I wonder if Bill had all this planned out already when he was building the thing. I gotta think he did, but no one will ever know! Everyone associated with building this thing have passed in the last few years.
2 new head gaskets are on order. The fly cutter also on order. Plan is to cut the .110, set zero lash and check exhaust clearance again before deciding final depth. I should be right where I started with zero clearance exhaust.
How does .080 piston to exhaust valve clearance sound for a late 50's GMC 302? More? Less?
