low compression issue
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Staging Lane
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Joined: Mar 2010
Posts: 82
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From: Fredericksburg, Virginia
low compression issue i have a 93 silverado w/ rebuilt 350 tbi, my friend did the rebuild for me and instead of putting the factory heads back on he put some sort of higher flowing marine heads on it, well he didnt check the heads or anything and it turns out that they were on a 350 boat engine and the guy had a supercharger on it, and melted a hole in one of the pistons. So, i have a low compression issue in one cylender, is there any way to check to see if its a bad valve, or valve seat without taking the heads back off? the block had 230,000 miles on it and he just rehoned the cylenders. So this was obviously not done perfectly. any suggestions?
first thing is pull the rocker cover and make sure the rockers aren't overly tightened causing the intake or exhaust valve to hang open. I would just loosen both rocker nuts, get the cam on base circle then tighten to near zero preload, but don't but any preload into the lifter. Then do a compression test on that cylinder and see what you get. If good then it was incorrect lifter preload. If it's low, then sqirt some 15w-40 or other high viscosity oil into the cylinder via spark plug oil and retest. if compression improves then that points to ring seal, if not then it could still be rings but also could be valve seats.
Unless you know the casting number of the new heads, and what work was done to them, I wouldn't assume they are "high flowing" heads just because they were off a marine engine with a supercharger. All the stuff prior to the one-piece rear main seal vortec 350's were crap.
Unless you know the casting number of the new heads, and what work was done to them, I wouldn't assume they are "high flowing" heads just because they were off a marine engine with a supercharger. All the stuff prior to the one-piece rear main seal vortec 350's were crap.
