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Old 08-03-2012, 08:54 AM
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loss of compression

ok was getting this blowby in my new engine sbc everything is new but the heads so here goes,,,,,getting this blowby all of a sudden and so did a compression check # 1,3,5 cylinders are all low like in the 50's to 60's range it's got to be my heads theres no smoke at all if was rings theres going to be smoke so going home this weekend and pulling that head off. wanting to know what I'm looking for i have no idea what I'm looking at and what to look for someone told me to blow air in the cylinder and listen for leaks is this right I have no idea thanks guys for all your help.....

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Old 08-03-2012, 09:00 AM
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Quote:
Originally Posted by gaurdian101 View Post
ok was getting this blowby in my new engine sbc everything is new but the heads so here goes,,,,,getting this blowby all of a sudden and so did a compression check # 1,3,5 cylinders are all low like in the 50's to 60's range it's got to be my heads theres no smoke at all if was rings theres going to be smoke so going home this weekend and pulling that head off. wanting to know what I'm looking for i have no idea what I'm looking at and what to look for someone told me to blow air in the cylinder and listen for leaks is this right I have no idea thanks guys for all your help.....
What that person is telling you is to loosen the rockers so the valves are both shut then take that piston to TDC. You then use an air chuck that is designed to thread into the spark plug whole and you put air pressure into. The listen through the carb, exhaust pipes, and air breathers. You can use a small strip of paper over all of these orifices if your hearing isn't the best to see the air flow. This will give you a better idea if its rings or valve seals.

If you decide to pull the head I would be looking at the head gasket sealing surfaces and also when the head is off pour some gas, parts washer fluid, or paint thinner down the runners and look for fluid to start seeping around the valve seat seals. Obviously dry it off the best you can before so you can see better.

Also depending on cam lift and valve to piston clearance I would be looking for little scuffs on the tops of the pistons and the edges of the valves.
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Old 08-05-2012, 05:40 PM
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ok just got home tried the compression check again but this time it's about 70 pounds in #3 and 75 in # 2 did the air thing couldn't hear anything coming out of the heads or carb put an old head on and compression gone done to about 50 or so in both heads but still can't believe that the rings would be gone alright there new only about 7000 miles on them I've been running it pretty hard but still thought the rings would last longer now to see if i can replace rings without pull the engine hope that pan come out easy
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Old 08-05-2012, 06:08 PM
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Put a couple squirts of oil in the spark plug hole and make sure you get it around the wall of the cylinder and not on top of the piston so it can help seal the rings. Do the compression test again and if the numbers go up then you know the rings are leaking because the oil helped seal the leaking rings, thus the higher compression numbers. If the numbers don't change then there is something else going on. I would do this first before you decide to tear everything apart. Good luck!
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Old 08-05-2012, 07:41 PM
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did the oil and they both came up to about 90 pounds so it's take the piston out and see got the head gasket off don't seem that you cylinder bore used at all still nice and smoth like brand new so that's a good thing I'm hoping the ring gap is the problem not something diff i just cant believe these new rings have already wore out it's only 7000 miles on the engine granted my foot don't leave the floor it's pretty much all gas and hard
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Old 08-05-2012, 07:46 PM
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Quote:
Originally Posted by gaurdian101 View Post
got the head gasket off don't seem that you cylinder bore used at all still nice and smoth like brand new so that's a good thing I'm hoping the ring gap is the problem not something diff i just cant believe these new rings have already wore out it's only 7000 miles on the engine granted my foot don't leave the floor it's pretty much all gas and hard
The cylinder bore should not necessarily be "smooth"... it should still have the honing cross-hatch showing. If it doesn't have the cross-hatch there is nothing to hold the oil coating on the cylinder walls. That sounds like why your rings wore out prematurely. They need to be honed and have about a 30 cross-hatch pattern.
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Old 08-05-2012, 09:03 PM
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If you wore out a set of rings that quick you have alot more problems, like dirt. You do have a good air cleaner I hope
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