Mecrusier Compression

[Recelect]

I did a compression Check on my 120 horse mercrusier engine that has been sitting for a few years and these are the numbers I got

cyl 1 - 120
cyl2 - 110
cyl 3 -120
cyl 4 - 75

after putting alittle oil in the #4 cylinder it jumped to 100. are these numbers good? bad? any thoughts? I am rebuilding the entire boat and my plan is to re-finish the boat this year, and re-build the motor next winter ( I know, doing it backwards). do you think the motor will be ok for one season?

Thanks

 

[Don S]

Re: Mecrusier Compression

100 is minimum compression, the oil in the cylinder just proves the rings are bad, not that the compression is actually ok.

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

do you think the motor will be ok for one season

 

[Robj]

Re: Mecrusier Compression

I did a compression Check on my 120 horse mercrusier engine that has been sitting for a few years

No 4 hole is low, and the others are on the low side also. What was the procedure you followed when you did the test? If it has been sitting for a few years, could be the rings need to loosen up. I have seen that on my engine, sat for quite a few years, #4 was at 90 psi, ran it for a while, went up to 155. Now all holes are at 155 to 160 psi. You can try running it for a while and then redo your test. If the numbers do not change, then you need to start thinking of a rebuild.

Have a great day,

Rob.