johnson 4r71d compression loss

[terrybridge]

Lost compression after running for first time in years. Before I got it running compression was at around 100. Ran it for a couple of minutes and it started to smoke from head. Retested compression and it was at 60. I have tried seafoam treatment, changed head gasket and replaced impeller. Before i ran rings were free in block. Could the rings need replacement? There was no visible damage to cylinder walls. I would also like to thank those on this website who have taken the time to help me out. Does this motor have a thermostat?

 

[ONERCBOATER]

Re: johnson 4r71d compression loss

i would warm engine up.... seafoam direct into carb throat until engine dies... yes large amount...
then let it sit for 30 min.... fire it up and see where you are.... if you already did that then not sure... might try seafoam or marvel mystery oil directly into cylinders to soak rings... if comp was good when you tried it.... it likely had/has old stick oil/crud sticking rings... just my thought... though at 60psi it should still run decent.

Sean

 

[F_R]

Re: johnson 4r71d compression loss

Reading between the lines, can we believe that it overheated, causing the smoke? And you replaced the head gasket after that happened and the compression is only 60?

Hate to say this, but it sounds to me like you burned it up. Yes, stuck rings and scored pistons. In reality, they actually started to melt.

 

[hidef]

Re: johnson 4r71d compression loss

You did use TC-W3 oil mixed 50:1 in the tank right. There is no thermostat in these little outboards.

 

[Rick.]

Re: johnson 4r71d compression loss

Did you re-surface the head before installing it? It could be warped from an overheat. Best of luck. Rick.