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Old 02-04-2012, 09:11 PM   #1
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Default no compression in cylinder 7

Hey guys i have a 98 chev 4x4 w/305 vortec. installed intake gasket at 165000 and its been trouble free. it now has 195000 its been running great no oil consumption between oil changes. driving the other day out of nowhere it started missing bad. compression check has 150 on all except seven. tore down thinking bad valve but #7 valves dont look bad. no antifreeze in oil and head gasket doesnt show any clear signs of blow out. i would really appreciate some input i love this truck and want to fix it. thanks Tim
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Old 02-05-2012, 12:29 AM   #2
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How did the valve spring on that cylinder look?.
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Old 02-05-2012, 09:27 AM   #3
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By no compression are you saying zero? Or just a lot lower? Zero would be a stuck valve. I did see one time here, billboost have zero compression. Took the head off and he didn't have a piston. It was in the oil pan. Put your compression tester on and hook up a air hose. Then try to track down where the air is leaking. Take out the plugs. A blown head gasket you will feel air coming out the other cylinder. Check the intake, and exhaust. As well as the oil fill port.
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Old 02-05-2012, 10:06 AM   #4
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Zero compression would almost certainly be a valve hanging open or burnt out. A holed piston would be another but you have plenty of other symptoms if that was the case.
A lifter pumping up, bent pushrod, broken valve spring, sticking valve, all these faults would give no compression. Broken rings or piston would give low compression but still give you some.
What state were the plugs in?, reading a plug can tell you a lot about how the the engine is running.

Roger.

Give us more information and we can hopefully help narrow it down. Bear in mind 195000 miles means your engine will be worn anyway, I know a well looked after engine will often run for much longer than that, but it may be a rebuild might be the best long term solution.
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