1990 Mariner 3cylinder 90HP compression numbers?

jmmm · #1 September 2nd, 2003, 03:30 PM

Does anyone know what the compression number should be for a 1990 Mariner 3cylinder 90HP? I just bought a boat that came with a MARINER 90HP and a compression test reads Cylinder#1=90 #2=120 #3=120.

Should I try it with fresh gas?

Thanks.

Wellcraft 89 · #2 September 2nd, 2003, 05:35 PM

Well don't know correct #'s but they should all be within 5 to 10 psi of one another.

so it looks like you have a problem in cylinder #1!

Rich

The Marine Doctor · #3 September 2nd, 2003, 05:53 PM

Your numbers are reason enough for a rebuild.

TMD

andrewkafp · #4 September 2nd, 2003, 06:01 PM

Run the test a few times to confirm the no's. Confirm that they are as you have posted. I have service records from the previous owner of my motor that have the following no's

125,125,125,125 and 12 mths later 110,110,110,110. (Different technician) You would think that ALL 4 wouldn't wear out that much with about 3 trips... So just check'em first.

jmmm · #5 September 2nd, 2003, 06:13 PM

How high should the numbers be, and what can I expect as a fair price for a rebuild of that engine?

Thanks to everyone for the help.

andrewkafp · #6 September 2nd, 2003, 09:36 PM

High no's are not that important, although under 100 may be a bit low. Consistancy is what to look for and what TMD is pointing out may be that the number 1 cylinder is less than the others. This could mean it may have been receiving more heat or leaner mix. So it has deteriorated quicker and will most likely continue to do so.

ref here

http://www.iboats.com/cgi-bin/ubb/ul...;f=29;t=000212

bryanredfish · #7 September 3rd, 2003, 01:09 PM

I'd try a decarb with Mercury Power Tune or Seafoam and see if the low cylinder comes up. An extra rich carb on that motor (I have the same one) could cause some build-up. Also, be sure that the motor is warm, and the throttle is wide open. Good luck.