Horrible compression

[bskye85]

I have a 1985 evinrude 70. The OB came with my new project boat, but has now become more of a project than the boat itself I had the compression checked today at my local marina, and its not good news at all!!!
This OB is a 3 cylinder and they read like this..

Top: 95
Mid:80
Lower:20

YIKES!! these readings are horrible. This leads me to think someone overheated this and blew the head/gaskett??? is this a correct assumption?

I have no idea where to even start Looks like more grinding on the boat and less time on this @%$& motor...

 

[kencat]

Re: Horrible compression

88 60hp here. Top cyl was 45 psi, others 105 and 110. I did not overheat the motor, it was actually cool after it went. Took of head and found piston ring fragments embedded in the head and piston. Have some nice pictures in another thread here if you want to take a look.

I think what happened in my case is related to the rings getting gunked up with carbon and sticking then one broke. The damage is surprisingly minimal. The other pistons feel loose as well, so when I get them apart I'l be able to see if they are carboned up.

I now understand the recommendations to decarburize your engine periodically.

Anyway, the short of it is there could be many other causes of the low compression. You'll have to tear into the motor to find out and assess the damage.

I'm wondering if these 3 cyl OMCs have a tendency to wear out rings or carbon up ?

 

[ezeke]

Re: Horrible compression

Motors often tend to throw rings from being lugged; usually due to being over-propped. The excess carbon is often a by-product of lugging or running without proper thermostats among other things.

 

[tashasdaddy]

Re: Horrible compression

well, it is time to pull the head, and see what is going on. i ended up donating mine to the school for a project motor.

 

[kencat]

Re: Horrible compression

Motors often tend to throw rings from being lugged; usually due to being over-propped. The excess carbon is often a by-product of lugging or running without proper thermostats among other things.

Good to know ezeke. When I get it all back together I'll be looking for a tach and temp gauge so I can make sure everything is working as it should.

 

[jonesg]

Re: Horrible compression

Good to know ezeke. When I get it all back together I'll be looking for a tach and temp gauge so I can make sure everything is working as it should.

Smart move.