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I've traced a poorly running engine problem to one cylinder. Only 80 lbs on one compared to 160 on all the others. Where do I go now? Pull the head and inspect the valves? How do you know if its the piston rings?
 
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Rick, look at my post below from earlier today. A leakdown test is a great way to isolate where you're losing compression. I had the same problem - although you probably have a hydaulic valvetrain, you never know. A simple valve adjustment brought my compression on one low cylinder way up. Good luck.
 

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Could be a bad valve. Test: With engine running hold a piece of paper to the exhaust pipe. If the paper sucks in to the pipe then you've got a bad valve.
Ring test: Shoot a bit of oil into the clyinder & replace plug. Fire engine & see if it smooths out, then gets rough. If so, then it's a ring. Or check pressure & wait to see if the pressure drops. These are "shadetree" stuff, but pretty good. Sounds like maybe a blown head gasket. Either way looks like you're gonna be pulling at least one head! /forums/images/icons/frown.gif.
 

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Rick..I would pull the head if you can't get the compression up with a shot of oil..I had the same problem and traced it to a slightly bent valve stem..was an easy fix
 
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