1986 150 hp Evinrude minimal compression. need assistance.

[randyray41]

I have a Evinrude 1986 150 hp motor. It ran hot the other day on water. I guess overheat alarm wasn't functioning. But only on the starboard cylinder bank. Compression on port side is 90 all three cylinders. Starboard side has 20, all three cylinders. What confuses me is the loss of compression on all 3 cylinders. Could this be a head gasket? Any thoughts would be great. Thanks

 

[flyingscott]

90 is fine try a different gauge if the results are the same pull the head.

 

[racerone]

Remove cylinder head.-----And I think check the cylinder bank and your bank account.

 

[randyray41]

I pulled head. Only problem, I'm no engine expert. The cylinder walls and pistons look good to me. The pistons do move slightly. no scarring or heat gaulding (sp).

I also confirmed my compression test with another tester.

Boat was running fine, never heard of losing all three cylinders on one side at one moment in time.

 

[emdsapmgr]

Once an engine overheats on one side, it is very possible that the actual head has warped. Once the head gets out of flat, it will affect compression. So, lay the head on a flat pc of glass and see if it's warped. If so, you may be able to plane it back to flat and install a new head gasket. This is pretty much all minimal expense. If that does not help, then you are probably looking at a rebuild. It's normal for the crossflow pistons to have some slop in them. The aluminum pistons have to have clearance so that when they heat up, they will expand against the cyl walls and maintain good/proper compression.

 

[flyingscott]

Take a pic of the head gasket, head and block surface