'79 Johnson 6hp with low compression..is it worth rebuilding?

[Navigator]

Greetings,<br />I have a 1979 6hp Johnson that I just recently rebuilt the lower unit. (Its more of a project engine to tinker with). The engine fires up on the second pull and idles down real low. Its not an extremely smooth idle so I went and checked the compression. 80lbs in top cylinder, 63lbs in lower cylinder. Technically, I'd think this thing shouldn't be running at all, but it is! I've tried fogging the engine and rechecked the compression several times. Its 80 and 63. <br /><br />My question...Is it worth rebuilding and if so, do I need to have the blocked bored out or can I simply hone the cylinders and get larger rings? <br /><br />Any suggestions?<br />Thanks,<br />Nav

 

[JB]

Re: '79 Johnson 6hp with low compression..is it worth rebuilding?

Ahoy, Nav.<br /><br />You need to inspect the cylinder walls and pistons to answer that question. If the walls aren't scored and the loss of compression is merely aged rings you might get by with honing and new rings.<br /><br />On the other hand, if your cylinder walls are torn up you might do better to find another engine and use the one you have for parts.<br /><br />Good luck.

 

[Navigator]

Re: '79 Johnson 6hp with low compression..is it worth rebuilding?

Thanks JB,<br />I'll try to pull the head off sometime in the next few days and check the internals. hopefully the cylinder walls are nice and smooth.<br /><br />Nav

 

[Chinewalker]

Re: '79 Johnson 6hp with low compression..is it worth rebuilding?

Hi Nav,<br /> I agree with JB. More often than not on those small motors, a simple honing of the bores, cleaning of the piston ring grooves of carbon, and replacement of the rings will bring your compression back up. You don't even need to go to oversize rings. There's a good chance your rings are gooped up with carbon and they're not springing anymore. If you get a manual (which I am assuming you did since you rebuilt the LU) and do the work yourself, it is most certainly worth doing - try finding a new 6hp for less!<br />- Scott