1982 Evinrude 115 HP Compression

[Wide_N]

Compression on one cylinder is low at 70%. I pulled the heads and the cylinder wall and piston look good. Any ideas on what else I should be looking for? Thanks

 

[batman99]

70% ??? What was PSI numbers across all its cylinders?

 

[emdsapmgr]

You may have intended on saying it was 70#. Low compression is usually caused by bad rings. Esp the top ring. With the head off, you will want to shine a light between the piston and the cyl wall. If you try to move the piston around by hand, you may be able to have enough sight clearance to see if the top ring is still in one pc. Compare it to the other pistons. May be that the ring is damaged or missing. You can also get low compression from an extreme overheat. Rings don't respond well to excess heat, and they may have lost some of their normal dimensional attributes.

 

[Wide_N]

Yes 70# Thanks for the help. Others were around 120.

 

[Barnacle_Bill]

If the motor has been sitting for a long period of time the rings could be stuck on that cylinder.

 

[metriccrescentwrench]

It'd be worth removing the bypass covers so you could check the rings. You can push on them with a blunt object and feel them spring back.

 

[emdsapmgr]

Agree with Metric. Depending on what you find, you will find out more about the rings if you pull the bypass cover off the low cyl.