Uneven Compression

[UNjim]

I bought a '57 Johnson 35hp and the compression test showed 45 on bottom and 65 on the top. Just how bad is this? I'm really surprised because the motor looks very clean. Can I try something in the cylinders or am I kidding myself ? THANKS for ANY HELP!

 

[JB]

Re: Uneven Compression

Do a decarbonizing procedure, Jim. Get SeaFoam and follow the instructions on the can.

Then do a new compression test. Let us know what you get.

 

[SKEETR]

Re: Uneven Compression

Could also be a bad head gasket. Maybe after 52 yrs it might be due.

 

[UNjim]

Re: Uneven Compression

So these seem to be fairly easy fixes. At what point is the motor just a parts motor. Do motors turn over and have no compression. Is it possible to have zero compression? THANKS

 

[dwco5051]

Re: Uneven Compression

Yes, it is possible to have 0 psig compression. Several things could cause this and none of them would be a cheap fix.

 

[Willyclay]

Re: Uneven Compression

If you need a service manual, I scanned and saved a non-factory manual that covers all 30-40HP motors built by OMC from 1956-1964 and will send you a copy. Please send me a Private Message with your email address and I will reply with the copy attached. Good luck!