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Author Topic:   compression checks
Dirt Forum Champ
Total posts: 1565
posted June 04, 2002 02:17 AM UIN: 54865418
got my engine hot a couple weeks ago and ran a compression test tonite my question is how much of a difference is a sign of a blown head gasket? i have one cylender on each bank that is a little lower 5# on one and 10# on the other

Dirt Forum Racer

Total posts: 87
posted June 04, 2002 02:58 AM
That doesn't sound like alot of compression loss at all. Most of my experiences with a blown head gasket have been more noticable, such as water in the oil, water on a cylinder, adjacent cylinders sharing compression, or getting a CO2 reading from the radiator. You can look at the spark plugs on those 2 cylinders that are down on compression a little and see if you see any traces of water or possibly rust deposits if the problem is just starting. The last time we blew gaskets the engine ran fine and we never had a heating problem for the heat races, but would always heat up for the feature race. Once I pulled the heads off I could tell that the gasket had been partially blown for some time (there were rust pits on the combustion chamber area of the head on the cylinder in question). That was the only thing I could determine that could have been happening to cause that. Maybe someone else might know if anything else causes that sort of thing. Perhaps doing a leakdown check on those cylinders might be more helpful in determining if there is a problem. Hope this helps you and good luck!

Dirt Full Roller

Total posts: 69
posted June 04, 2002 06:34 AM
A leakdown is the way to go. my cylinders all checked within 5 lb. compression. but 6 cylinders had 5 percent leakdown, and 1 had 12 percent, and the one next to it had 16 percent leakdown. Head gasket?

Dirt Forum Racer

Total posts: 90
posted June 04, 2002 07:48 AM
Hey Glide. Did you put some oil in the cylinders before you tested? With leak down you at that the mercy of your ring gaps, piston clearance, etc. If you didn't make provisions to "clog" that area, then you can't tell if the loss in pressure is isolated to the head gasket. Yes/no, anyone? I agree with Gent, 5-10#'s of pressure between opposite cylinders is not a lot to worry about. You should have a more pronounced loss between adjacent cylinders. 17J, your poundage difference could be associated to rings and valve train geometry. Just my couple pennies.....

Dirt Full Roller

Total posts: 69
posted June 05, 2002 05:50 AM
Yeah I know about the oil trick. I was in a hurry (go figure a racer in a hurry)it sounded like it was leaking onto the crankcase. I am going to try the oil thing this week. Thanks.

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