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Old 09-01-2020, 06:05 PM
bob w bob w is offline
Still crazy after all these years!
Join Date: Jan 2008
Location: Stillwater, MN
Posts: 12,313

Finally got back to the Jeep engine. Went to drop the crank in and found out I had the wrong main bearings. They were the right size but the tangs were in the wrong place. They were for a 258. Ordered mains for a 242 (4.0 L) and all is okay. I put the crank in and one piston/rod assembly in the #1 cylinder. Measured deck height, the amount the piston is below the deck at Top Dead Center. It is .044". Put the same piston/rod assembly in the #6 cylinder and measured .047". Ideal quench clearance is around .040". I ordered a couple different head gaskets to measure their thickness. Ideal quench is .040". So if the head gasket is .040", the pistons will have to be flush with the top of the block. That means milling .044" to .047" off the block. Unless my engine guy can angle mill the block front to back.

Compression ratio should be 10 to 1. I'd like more so I'll see if milling the head is an option.
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