Johnson 4hp No Compression

[gssd]

My 1977 Johnson 4 hp overheated several years ago. It continued to run (not well) until last year. I was using it one day and it just quit. I have marginal compression in the top cylinder and no compression in the bottom cylinder. The head gasket, pistons, and cylinder walls look good. There is some piston slop.

Does anyone have an idea why there is no compression on the lower cylinder?

 

[JB]

Re: Johnson 4hp No Compression

Stuck or broken rings.

 

[1946Zephyr]

Re: Johnson 4hp No Compression

Yep, sounds like a rebuilder. It's likely you'll need new rings and possibly new pistons. When they over heat, often times they score so bad that the rings stick and your compression goes way down. If this is a motor that you plan on keeping and one that you really like, it'll be worth the investment to fix 'er up.

 

[bktheking]

Re: Johnson 4hp No Compression

Cylinder worn, bad rings, bad head gasket. I'd put a head gasket on and try it. If you don't get anything on the bottom, pour some oil in the cylinder in question and point the plug holes upwards. Then try it, if compression goes up the rings are worn or stuck.

 

[kenmyfam]

Re: Johnson 4hp No Compression

Did you ever decarb the motor ??

 

[kyron4]

Re: Johnson 4hp No Compression

Did you ever decarb the motor ??

Just curious , I see this term alot here .What does "decarb" mean ? -Thanks

 

[bktheking]

Re: Johnson 4hp No Compression

Just curious , I see this term alot here .What does "decarb" mean ? -Thanks

To remove the bi product of burnt mixed fuel that is accumulated in 2 strokes in this case from normal use, using a product like seafoam to liquify carbon so it is removed from the internals. Kinda like using oven cleaner in an oven.

 

[kenmyfam]

Re: Johnson 4hp No Compression

Just curious , I see this term alot here .What does "decarb" mean ? -Thanks

Here's a link for you.

http://forums.iboats.com/showthread.php?t=302825