Compression questions for Y block
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From: Longmont Colorado
Compression questions for Y block
Ok, so right now we're just trying to keep the 292 running, we know its going to need a rebuild soon but it does run sort of. After 2 different trys with different carbs (holley 2300 and now a motorcraft 2100), we are thinking its not getting enough vacuum.
So we decided to do a compression check on the cylinders. out of the 5 we tried, 4 we're 110 but one was getting 40 (not sure of the oficial number, its the one closest to the radiator drivers side). we also noticed a not of oil blowby.
So does anyone have any rough guesses at to what might be causing just one to be 40? we're thinking a lifter but wanted to get some ideas before we start digging in. we have been hearing some noise from this area, like a clanking, but its not consistent.
thanks
So we decided to do a compression check on the cylinders. out of the 5 we tried, 4 we're 110 but one was getting 40 (not sure of the oficial number, its the one closest to the radiator drivers side). we also noticed a not of oil blowby.
So does anyone have any rough guesses at to what might be causing just one to be 40? we're thinking a lifter but wanted to get some ideas before we start digging in. we have been hearing some noise from this area, like a clanking, but its not consistent.
thanks
Fleet Owner
Joined: Jul 2004
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From: NM
The truck looks like it's been used regularly, i.e., not sitting in a field for a long time. Is that right? So I'd assume some kind of valve problem -- could be a lifter, or a bent pushrod, or a burned or stuck valve. (If you find a bent pushrod, it is likely because of a stuck valve) It's hard for rings to leak that much, that you'd be down to 40 psi. That is #1 cylinder, pull the valve cover for a look-see at the pushrods and valves.
My Motor Manual says a '58 292 should have 160 psi compression, but that's at sea level. There are two ways to correct for altitude;
1. Take 12.2 times the compression ratio to get some idea of where it should be. For 9.1:1, that would be 112 psi. (12.2 is approx. atmospheric pressure at 5000' altitude).
2. It is probably more accurate to do it as 12.2/14.7 x 160 = 132 psi
It's undoubtedly a worn engine, but would probably run OK if that valve were fixed.
My Motor Manual says a '58 292 should have 160 psi compression, but that's at sea level. There are two ways to correct for altitude;
1. Take 12.2 times the compression ratio to get some idea of where it should be. For 9.1:1, that would be 112 psi. (12.2 is approx. atmospheric pressure at 5000' altitude).
2. It is probably more accurate to do it as 12.2/14.7 x 160 = 132 psi
It's undoubtedly a worn engine, but would probably run OK if that valve were fixed.
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