Yamaha 2400 compression

[joshuajim]

My 10 year old Yamaha 2400 is still running fine, but I like to make sure that it continues to do so. I ran a compression test and it is reading 75# to 80# which seems to be adequate at starting RPM. Anybody know what it should be?

[Chum_lee]

The Yamaha site doesn't list the static compression ratio for your application. For common OHV utility engines a reasonable compression ratio (guess) would be about 7.5 : 1.

Testing the compression ratio should be done with the choke off, throttle wide open, and, the engine at operating temperature.

That said, a reasonable pressure would be 14.7 x 7.5 = +-109 lbs. So you could be a little low. But, if it runs fine, doesn't smoke or use oil, and makes rated power, why worry? Just keep using it until it starts having symptoms of failure. You don't list the running hours, but at 10 years of age, you are ahead of the game.

The static compression ratio for my Onan 4000 gas genny is 8.5 : 1

Chum lee

[romore]

That is excellent cranking compression. It is equipped with an automatic compression release, without that the kickback would make your fingers hurt.