compression problems
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compression problems
1969 351 4v
new rebuild, balanced, rv cam, mostly stock, bored .030 over and new kit.
Did proper breaking after 1500 miles #3 is still at 100 psi while all others are 210 psi plus or minus 5psi. Put 2cc oil in and bumped up to 215psi.
The rebulider said that it still needs more break in time so what is actually wrong??
Rod :--(
new rebuild, balanced, rv cam, mostly stock, bored .030 over and new kit.
Did proper breaking after 1500 miles #3 is still at 100 psi while all others are 210 psi plus or minus 5psi. Put 2cc oil in and bumped up to 215psi.
The rebulider said that it still needs more break in time so what is actually wrong??
Rod :--(
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From: Lakewood, Ca.
Hi Rod, and welcome to FTE. I moved your post here to the engine specific forum 
Just to be clear, are you saying that the compression in #3 came up from 100psi to 215psi after you put oil in that cylinder?
Just to be clear, are you saying that the compression in #3 came up from 100psi to 215psi after you put oil in that cylinder?
Last edited by SteveBricks; Sep 27, 2012 at 02:24 AM.
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From: Lakewood, Ca.
With such a drastic increase after you added the oil, I'd have to say there's some kind of a problem with the rings in that cylinder. I'm not buying the "needs more break in time" theory that the rebuilder gave you.
Last edited by SteveBricks; Sep 27, 2012 at 03:13 AM.
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neither am I but I don't have a good baseline to draw from in this kind of knowledge.
some one told me that the rings weren't offset 180 degrees and I am thinking bigger problems like broken rings or incorrect rings in the kit. the builder said that one cylinder may have bean washed out with rich fuel but that would apply to other cylinders due to the intake configuration. Still baffled and bummed. Its a good 15 hrs to r&r.
thanks
Rod
some one told me that the rings weren't offset 180 degrees and I am thinking bigger problems like broken rings or incorrect rings in the kit. the builder said that one cylinder may have bean washed out with rich fuel but that would apply to other cylinders due to the intake configuration. Still baffled and bummed. Its a good 15 hrs to r&r.
thanks
Rod
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From: British Columbia
You probably don't need to remove the engine to check the cylinder. You should be able to take the oil pan and cylinder head off with engine in chassis. Then remove piston and rod and see what's up.
I would guess broken ring(s) as well.
I would guess broken ring(s) as well.
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compression problems
Thanks
what else could it be that drops the psi down to 100 but a broken ring?
when I debate this with the builder he says just needs to settle in but I would have thought to achieve higher than 50% with good rings even if they weren't broken in.
Rod
what else could it be that drops the psi down to 100 but a broken ring?
when I debate this with the builder he says just needs to settle in but I would have thought to achieve higher than 50% with good rings even if they weren't broken in.
Rod
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From: Lakewood, Ca.
Like you mentioned before, the ring gaps might not be offset properly. Maybe for some reason the piston isn't the right size for the bore. Though unlikely, it's possible one of the 8 pistons was .010 smaller than the others, maybe #3 cylinder was bore too large, maybe it got honed way too much...the only way to find out for sure is to pull it and take a look.
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