Ring Damage

[Archnawan]

Motor is 78 Evinrude 115. Took both heads off to find both starboard pistons and the head have evidence of damage from sheared/broken rings. The lower piston is completely trashed (0 psi), while the upper although damaged was still holding 110psi. The port pistons/head are both in good shape. No evidence of damage and holding 120psi.<br /><br />My question, Is there anything that would cause one side to fail that I should be replacing or is it just chance due to age and wear?

 

[Indymike]

Re: Ring Damage

Hey Cap,<br />Follow the links around this thread. It will answer some of your questions.

 

[Dhadley]

Re: Ring Damage

The starboard side runs slightly hotter on that engine. That promotes coking a bit faster. Nothing unusual. especially if the motor is not set up at 5800 rpm. The lower the top rpm, the faster coking builds up. Eventually the ring will stick in on the back side, the piston loses support and the gap end shears off.<br /><br />The good news is that a repeat is preventable. Look at the set up and decarb more often. Again, the further below 5800 it is, the more often you'll want to decarb.

 

[Archnawan]

Re: Ring Damage

That would seem to describe my engine perfectly. I thought I had it propped about right but didn't realize it was that sensitive. <br /><br />This motor does have alot of hours though, I'm guessing over 1000. Is there anything that I must/should also replace when doing the rings and pistons?<br /><br />Thanks for help, I will certainly start decarbing now!

 

[Dhadley]

Re: Ring Damage

Once it comes apart the machinist will measure it to see what needs to be done as far as boring etc. With that much heat I'd guess we're looking at boring 4. <br /><br />1000 hours isnt much for a 2 stroke outboard. What's the set up now?

 

[marinemech1]

Re: Ring Damage

when you remove piston examine where little pins that locate the piston ring are. i think you will find at least 2 little pins missing. when they fell out piston ring turned until it got caught in a port.<br />ring jumped into port and was broken off on next stroke of piston.<br />if this is the case? it happened due to old age.<br />or you are using rubbish oil or both