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Discussion Starter · #21 ·
I found what seemed like pretty heavy carbon buildup on the piston heads (esp. 2 & 3), and the baked-on carbon on the intake valves had to be sanded off (not on the sealing surface!). I cleaned all the gasket surfaces off, put a new head gasket on, and have the head installed and torqued to spec. I visually checked the pistons against the TDC marks before installing the cylinder head, and everything appears correct there. So before I struggle with getting the camshafts back on, I'm going to try a leak down test, and see if lapping the valves improved or eliminated the cylinder leakage. My leak down tester directions say that the engine should be at normal operating temp, but that's not possible. Still, if I get a leak percentage of less than 20% on every cylinder when it's at ambient air temp (about 40F today), then I should be able to get it started when it's reassembled correctly. Without the camshafts on, there shouldn't be any issues with valve clearance, as there's nothing there to be pushing them open.

Also, valve spring retainers are very, very small, and entirely too easy to drop and lose when you're trying to put them back in.
 

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Discussion Starter · #22 ·
Well, this is clearly part of the problem. With a leak down test, cylinder 1 is holding at 95%, cylinder 3 is 99%,cylinder 4 is barely marginal at 80%, and cylinder 2 is a whopping 40%. All of the air leakage right now is from the exhaust valves. So I'll need to pull the head off again, clean up and lap the exhaust valves--more chances to lose valve spring retainers!--and then check again.

My working hypothesis right now is that the compression failed due to carbon buildup that got into the valve mating surfaces. I had a period of time with a bad thermostat (and I was too dumb to realize it was a problem, because I'm dumb) where my engine was only getting up to 140F, and I'll bet that caused the excessive carbon buildup.

I think I'm solidly on the right track.

(BTW, if anyone wonders why I keep updating this - maybe this will help someone else in the future.)
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