what is the lowest compression test reading measured that just new rings and cyclinder honing revived?

Question

basically for those that have experiance working on motorbikes what was the lowest compression reading you ever saw that a simple rings and cylinder honing job was able to bring the compression back to specs? can new rings and honing boost a low 70ish psi back to 150 or higher ? Or is there a point where low compression indicates more then rings ?

Answer 1

As was previously mentioned, have a fully charged battery and the throttle wide open. Take and record the compression readings, then pour a teaspoon of motor oil into the spark plug hole. Crank the engine over a couple of turns and then take readings again. The oil will momentarily seal the area around the rings. If you started out at say 70 psi and the pressure with oil added only goes up 10 or 20 psi, then you probably have a leaking valve or a very low cranking speed. If the reading goes up to say 100-120 psi, it means the rings are likely leaking badly and need to be replaced.

If it's a multi cylinder engine and all cylinders are reading fairly evenly but low, then it's probably slow cranking speed causing it or a high mileage engine with evenly worn rings (barring it was ran without an air filter for a very long time). However, I've seldom seen a tired engine with evenly low readings, invariably one or two will be considerabaly lower than the average. Readings that vary widely or say one is very much lower than the others is usually a broken ring or burned valve.

Answer 2

Hi, If you got 70psi dry, try doing a wet test w/a fully charged bat, and wide open throttle. if it goes up considerably, then rings are suspect. But even if it does'nt you could still have a cracked ring. A low comp. pressure really just means that a tear-down is required and then you'll know exactly what is wrong.