Help with Yanmar 3GM30 compression

[garrocha]

Dear all, I would really appreciate if somebody could tell me the normal and minimum values of the piston compression for a 2001 Yanmar 3GM30-YEU engine. It should be easy to know, but I have two technical opinions, one with 470PSI=33 kg/cm2 (28 minimum) and the other 340PSI=23,9kg/cm2 with a tolerance of 20%-30%.

By the way, the official dealer got 20-15-16 kg/cm2 (284-227-213PSI). Could anybody with a similar experience tell me what should I expect about that?

Thank you very much.

[djmarchand]

A diesel engine's compression is a highly subjective test and doesn't tell you much. It is subjective because it is highly dependent on the starter speed. It doesn't tell you much because diesels can run well right up to the point significant compression failure.

If you are concerned about the health of your engine, does it start easily cold. That is an acid test. Also disconnect the blowby hose from the aft top of the rocker cover to the air intake and in gear feel for blowby pulses. If they are minor or non existant, you don't have a compression problem.

David