I know that alot of gearheads perform compression test to get a profile of the cylinder leakage and condition. I had asked about doing a leakdown test like they perform on small aircraft engines. This is supposedly the most accurate because it is not subjective to starter speed and oil splash in the lower cylinder bore. I had mentioned this in a later post.
Leathermang cautioned about having it at Bottom dead center, because it could turn over, but to perform a leakdown test, both valves have to be closed, and the piston at dead top dead center. This way the engine can't roll over. You can also check for exhaust and intake valve leakage by listening,by the exhaust or intake and you can check excessive ring blowby by checking the oil filler cap. With leakdown test it is not subjective as in a compression test, because of how fast the engine is turning over with the starter as you perform each cylinder test. Leakdown is a method of putting a fixed amount of air to the cylinder at T.D.C. and recording the difference of leakage from cylinder to cylinder. You can also look for the above. For instance, you set a regulator to regulate at 100 PSI with the end blocked off. You hook it up to the cylinder and you record how much the gauge is when hooked up to the cylinder. It should not drop more than 20% for gas engines and should not have a large deviation from Cyl to Cyl.
I am just asking. Maybe some experienced M.B mechanics know a better method and that may be a compression test, and know why.


PeterG



79 300 SD