Hi all, did a compression check yesterday, two at 150, two at 130 one at 140 one at 135 one at 145 and one at 80. the low one must be where it was siezed? what are your thoughts on this? will the rings seat at some point in the low one or is the engine toast? sure runs nice!
Ive seen engines with a weak cylinder or two after initial start up (after sitting for years), clean up after a couple heat cycles. The rings can get gummed up from sitting and dont provide a seal. A couple heat cycles can loosen up and blow out the gunk that is preventing the seal rings from expanding. But its a bit of a long shot, and it is a bit risky. The low compression could be due to a broken ring (just how much force did you have to use the break it free?) Or it could be due to a sticky valve. You might be able to hear those with a stethoscope. If a push rod or valve were bent, Id expect the a ticking noise, but not if it just isnt sealing properly, It might be mostly silent.
A broken ring might stay put for years, or it might decide to gouge into the cylinder wall on the next power stroke. Or, if its a non-seating exhaust valve, you could burn a seat out by running it. If it was a numbers matching LS6, Id be tearing it down now. If its a junkyard 350 that was thrown in 10 years ago, Id probably chance the few heat cycles.
Its a crap shoot really. The engine could have had low compression on one cylinder when it was parked. If its a common engine and youre not concerned about numbers matching I would run it for a bit. If its not doing anything odd, low oil pressure, overheating on knocking I would run it. It will probably have a miss at idle due to the 80 lbs compression on one cylinder and I would change the oil again after warming it up. It may come back. I have seen a couple revived after years of sitting and many that didnt survive.
If it doesn't clear up, do a "wet" test. squirt a few shots of oil in Cyl [just enough to coat top of piston] and do comp. test again. If low cyls. come up you've got a ring problem, stays the same? valve issue!!! Did you do your test with all plugs out & throttle "WIDE OPEN?
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Some times I wake up GRUMPY, but today I let her sleep in !!!!!!!!BLACKSTOCK Ont.
ok, took all plugs out and held throttle wide open, its no 7 cylinder , back drivers side. engine sounds great, it's a 283 so im not too concerned if its hooped, ill put a 350 in with an upgraded trans. ill turn it some more and test it again, maybe squirt some more ATF in the cylinder? Deep Creep?
