Ls1 reads 0psi on All 8 cylinders
12-27-2012, 11:49 AM
#23
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no i dont remember the head gasket part number they are the copper head gaskets not composite ones i removed from origional heads. head work was done by west coast corvette. they were bought brand new from a guy who purchased them from wcc.
12-27-2012, 12:30 PM
#25
The only way you would not have compression is:
False gauge reading (or bad gauge)- But you have checked this gauge on another engine so that rules this out.
Hole in piston or broken rings- But hard pressed to think that would be that away on all 8 cylinders, plus you know it ran correctly before the head swap and I take it there was no blow by coming out of the oil fill cap when removed to indicate a bad ring set or multiple pistons with hole in them.
Wrong head gasket- not sure if this is even possible on the LS engine series. I think they all use the same head gasket- something to check.
Leaking valves- either the valves are open due to pushrod length, cam tming, or they are a bad set of heads (it would not supprise me seeing as how they are in fact second hand heads)
Bad cam lobe not opening the intake valve- still hard to believe all 8 cylinders have bad intake lobes.
If the intake system is completly blocked off where no air what so ever can get into the cylinder then it can show low compression due to the lack of air to compress, but that is unlikely as well.
It sounds like to me you have a valve sealing issue. Now if it is due to a pushrod/valve timing issue or someone selling you a bad set of heads you will have to determine.
back the rocker arms off just a little where you know for a fact both valves a cylinder are closed but not enough for the rocker arm to move over. Check compression again on that cylinder. If the pressure does not come up remove the head and put water into each intake port and look for water leaking past the intake valve, do the same for the exhaust valve.
False gauge reading (or bad gauge)- But you have checked this gauge on another engine so that rules this out.
Hole in piston or broken rings- But hard pressed to think that would be that away on all 8 cylinders, plus you know it ran correctly before the head swap and I take it there was no blow by coming out of the oil fill cap when removed to indicate a bad ring set or multiple pistons with hole in them.
Wrong head gasket- not sure if this is even possible on the LS engine series. I think they all use the same head gasket- something to check.
Leaking valves- either the valves are open due to pushrod length, cam tming, or they are a bad set of heads (it would not supprise me seeing as how they are in fact second hand heads)
Bad cam lobe not opening the intake valve- still hard to believe all 8 cylinders have bad intake lobes.
If the intake system is completly blocked off where no air what so ever can get into the cylinder then it can show low compression due to the lack of air to compress, but that is unlikely as well.
It sounds like to me you have a valve sealing issue. Now if it is due to a pushrod/valve timing issue or someone selling you a bad set of heads you will have to determine.
back the rocker arms off just a little where you know for a fact both valves a cylinder are closed but not enough for the rocker arm to move over. Check compression again on that cylinder. If the pressure does not come up remove the head and put water into each intake port and look for water leaking past the intake valve, do the same for the exhaust valve.
12-27-2012, 01:21 PM
#26
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It all boils down to popping off the valve covers and taking a look. It only takes a few minutes to get the covers off. Just start by backing off the rocker arm bolts to see if the valve are hanging open.
12-27-2012, 07:13 PM
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I've had stock engines show no compression after a head gasket/ mill/ crack repair job and fluctuating compression ,,,,,,,,almost good 1 test and the next test really low or none ,,,,,,,,,,I did'nt soak lifters or pour oil on them but I did lightly sand the head deck surface and after maybe 150 or 200 revolutions the compression in all the cylinders finally came back to where it was supposed to be . I noticed with that much pre-load in the newer vortecs and similar engines that if You're turning motor around by hand after a valve closes it is'nt always closed for a few maybe 15 or 20 seconds . So for whatever reason something in the valve train can be sticky but usually will free up normally at some point