1985 3.0 mercruiser compression #'s (181 CID )

[1987sylvanoffshore]

What should they be?

 

[CobiaXL]

Re: 1985 3.0 mercruiser compression #'s (181 CID )

145 -150 psi.

 

[Don S]

Re: 1985 3.0 mercruiser compression #'s (181 CID )

According to this service bulletin from Mercruiser (Service Bulletin 97-25) you need a minimum of 100 psi. Give it a read, and make sure you do the test properly.

 

[1987sylvanoffshore]

Re: 1985 3.0 mercruiser compression #'s (181 CID )

Thanks guys, I read the service bulletin and will do the "Using Air to Test Engine?s Combustion Chamber" tomorrow. I just don't get it, this is a fresh rebuild and the compression is 120 across the board. The machine shop pressure tested the head (it was fine), milled the head, honed the block, new dished pistons, ect, ect,. I did not cut any corners. Hopefully it is my valves that are open just a tiny bit, I will find out tomorrow. Can you trust a harbor freight compression tester?

 

[matthew colgate]

Re: 1985 3.0 mercruiser compression #'s (181 CID )

I have used a harbor freight compression tester with autos with no problems ever ....... it reads the exact same as my snap-on compression tester does

 

[1987sylvanoffshore]

Re: 1985 3.0 mercruiser compression #'s (181 CID )

I wanted to say thanks to the people who posted and give an update on the compression test. I was not doing the test correct, after reading the service bulletin Don posted I tried again and got 140 psi on all 4 cylinders. Will I reach the 145-150 psi mark after a few hours of break in? Thanks again guys!