Compression numbers for a 1981 35hp OMC

[Billyjackreally]

What should the compression be on an 81 35 hp Johnson or evinrude and how low can it be before it affects operability adversely? I know if its 120 per cyl that's good and that's about the extent of my knowledge on it. I also understand it should be even - just wondering how low or how much wear they can have and yet run well?

 

[boobie]

Re: Compression numbers for a 1981 35hp OMC

Have you checked the compression yet?? It should have no more than 10% variation between cyls. Get back to us with what you have.

 

[Billyjackreally]

Re: Compression numbers for a 1981 35hp OMC

Have you checked the compression yet?? It should have no more than 10% variation between cyls. Get back to us with what you have.

I have not did a test on it was just looking for some ballpark numbers for a running motor not a new one or worn out completely, I have one here that has 65 and will run but quits when it feels like it. I was looking at a parts motor and wondered what it should be before it was designated as a parts motor rather than worth fixing. I will do a test on the one on my boat and see what it is . thanks anyways

 

[bonzoscott]

Re: Compression numbers for a 1981 35hp OMC

It's more important that the numbers are close (10% as Boobie stated), however, 65 is probably too low. If all cylinders were 65, it may run - just not very fast. I would say at least 90-100 would be the lower limit.

 

[boobie]

Re: Compression numbers for a 1981 35hp OMC

You won't know what you have until you check it.

 

[Billyjackreally]

Re: Compression numbers for a 1981 35hp OMC

Thanks for the info - I have not got around to sticking it on the back of my boat yet but plan to this week. Semi retirement seems to have become the busiest time of life