I'm looking at used 500EFI, what should the compression be?It has 400 hours on it. Change valve springs? Anything else? I figure I would run it for a year or so then freshen it. Any idea what its worth? Thanks, Doug

compression should be ideally over 150 with all cylinders within 10% of each other cylinder will fire with approx 100 psi realistically comp with 400hrs will prob be closer to 125.

really you should do a leak down test it will more accurately give you a better idea of the cond of the motor

From the Merc 500EFI Service Manual

......still stand by what I said....how many 400 hr motors do you know with 175 psi fresh broken in mtr yes........

Hey GOODT ..... maybe we should get your old Buddy Mr Cozzi in on this thread ???

actually we spoke hes really a great guy........

Joe,
I too was surprised that they called for a minimum of 175PSI. Seems high. It's also strange that it differs so much from the 525EFI Service Manual (below).

Dave

and both have the same copression ratio.........

with compression test I still go by the gen rules that I was brought up with ie...over 100 cyl is firing but bearly...all cyl within 10 % but the best way to tell the cond of a mtr is to do a leak down test....

yea ... he seems ok .... alot of friends here ..... I feel his pain though ...(52) .... not easy when the years pile up and you realize there is a stronger smarter YOUNGER generation ...........

42 here not much younger and I can feel the years piling up also......