9.5 Compression question

Lostfisher

Petty Officer 2nd Class
Joined
Nov 2, 2009
Messages
147
I have a 9.5 evinrude that I had just purchased. It only had 50lb of compression on both the top and bottom cylinder. I put some oil in the plug holes and the compression went to 60 psi. I than took the cylinder head off and saw that the powerhead had been honed out at one point in time. the cylinder walls look great no scratches etc. Now my question is since I had 60lbs on both cylinders what are the chances of both cylinders going bad and having 50lbs dry and 60 lbs wet? Is this more on the order of a sign of a bad head gasket?
 

Rick.

Captain
Joined
Jul 30, 2006
Messages
3,740
Re: 9.5 Compression question

It's really hard to say what the problem is, or even if you have a problem. 9.5's seem to be a lower compression engine right off the top. I would flatten your head , put on a new gasket and try to get it running. I don't know the history on your motor but your rings might be a little stuck from inactivity so once you get it running do a seafoam treatment to it and that may loosen up the rings if they are stuck. Either way it might work very well with the compression numbers you found. A different gauge might well give you better numbers. Best of luck. Rick.
 

emoney

Commander
Joined
Jul 19, 2010
Messages
2,551
Re: 9.5 Compression question

Have you tried starting it? Like Rick said, you may not have a problem. Could even be a faulty test result.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: 9.5 Compression question

50-50 is marginal, but not unheard of, in a healthy rope start engine. Some chance that the head gasket is bad between the cylinders.

Give her a new head gasket and do a decarb. My guess is that you will be good to go.
 
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