Compression readings

There are several factors that can effect the results of a compression test on any engine including the tester you use, the engine temp and even the weather. The most important thing to look for is that all the cylinders test about the same. The engine should be warmed up to operating temp and the throttle held wide open durring the test. Crank the engine over and watch the testers gauge. The gauge should reach its highest reading in 3 or 4 compresion strokes. If it takes more than that it indicates a problem. If the engine won't start and you can't warm it up you can still do the test but it may take a couple more cranks to reach max reading. Any engine in decent shape should reach at least 100 PSI compression. But once again the important thing is that all the cylinders are close to the same reading. So say if you get a reading of 50 PSI on one cylinder and the rest are 125 PSI that would indicate that the low cylinder has a problem ( stuck or broken or worn rings or blow head gasket). The next step is to squirt a tablespoon or so of oil in the cylinder and retest it. If the compression rises then you probably have bad rings in that cylinder. If it doesn't rise you have a blown head gasket or hole in the piston.