Just a little experiance I would like to share about compression test and why I take them with a grain of salt. When I repaired lawn mowers we used to check the compression of evry engine we repaired. Typically you wanted to see 60 PSI for your typical 3.5 HP Briggs and Stratton engine. 50 PSI or less or 70 PSI or more would typically result in noticable problems with the way the engine ran. I found high compression to be just as bad as low compression in fact it was worse because this was always cased by rings. The high compression would result from the rings leaking allowing the oil to saturate the cylinder and essentially case a wet compression test to occure. So therefore leaking rings caused high compression. You should be scratching your head now.

The Briggs and Stratton recomended method for checking compression was to remove the cover and spin the engine by hand backwards. The technichian was to observe the bounce back of the engine. It should bounce back at least 1/2 turn (180°). Engines that had 80 PSI compression would not bounce back more than 10°. Some times you would have an engine with 60 PSI that would have a lazy bounce of only 1/4 turn (90°). Any engine that bounced back less than 1/2 turn ran poorly despite its compression. This bounce back method never failed but it did required some disassembly of the engine to get at the fly wheel and therfore was not used as much as the compression check.

It's too bad this method cannot be used on autos. The problem with leakdown is it only checks the rings at TDC and its a real pian in the but to do.

John Roncallo