1999 50 h.p. Mercury Compression

FisherAl · #1 February 19th, 2009, 03:59 PM

I am looking at a motor with 90,95,90 compression. I believe it should be 120. Should I stay clear? Any idea of cost for new rings?

Thanks

Laddies · #2 February 19th, 2009, 04:49 PM

Your more in the ball park unless the engine has not been run for a while and the cyls are dry.

JB · #3 February 19th, 2009, 04:59 PM

That is a mechanically healthy engine.

Don't know where you got the 120psi number, but it wasn't from Mercury.

Differences in guages, engine temp, battery voltage, preparation and technique can make as much as 50psi difference in measurement.

That is why no maker sets specs on psi. They do set a comparison spec. Usually +/- 10% span among the cylinders.

Your span is well below 10%.

Laddies · #4 February 19th, 2009, 07:49 PM

JB, is right in pasted years Mercury Marine never listed compression figures as even the fuel-oil ratio effects the reading, my figure of about 120# came from years of experience and many hundreds of compression tests on the 3 cyl. 49.8 cu.in Mercury power head most have a reading from 110# to 130# some run 140+