brittle broken rings in 1977 Evinrude

[ghelman]

I have a 1977 Evinrude 115 hp outboard motor. It came with an older boat I just purchased. I had the boat out on the lake and it seemed to run fine with a few what I thought were fuel supply issues. In taking the boat and motor in for a ?summer? tune up and to have a new water pump put it, I was told I had damage to one of the cylinder?s rings. The ring apparently got brittle and cracked and then damaged the spark plug. I was told models of this motor during this period had ?high? placed rings for better performance. The caveat was they had to run on gas with a 96 or thereabouts octane rating. Apparently the US government outlawed 96 octane gas in the 80?s and this results in increased heating to the cylinders/pistons/rings with lower octane gas causing heat related damage to the rings and my problem. Is this a correct understanding? If so, can new pistons/rings still be purchased to repair this problem.

 

[R.Johnson]

Re: brittle broken rings in 1977 Evinrude

Somebody has got to stay up night' coming up with some of these stories. I once went to purchace spark plugs' for my son. The dealer told me Q plugs were ment only for use in Canada.

 

[Dhadley]

Re: brittle broken rings in 1977 Evinrude

OK, your info source is a bit off. The high ring pistons made by OMC had virtually no issues until the lead was taken out of the fuel. It had nothing to do with octane but simply the lead coolant.

Even with no lead in the fuel the rings were OK as long as the motor wasn't being lugged, had the right Champion plugs and has fresh 87 octane. The rings don't become brittle, they get stuck from coking (very sticky carbon). They first stick on the side opposite the end gap. The more the backside sticks the more the piston loses support and eventually will shear off one end by the gap. Usually the ring to the right of the gap (don't know why). It usually shows up on the startboard side first because the starboard side runs a tad hotter.