1977 evinrude 85hp time bomb

I was speaking to a mechanic today. He informed me that 77, 78, 79, came stock with "High Ring Pistons" From the look of my motor the case has never been split, thus never rebuilt. Compression is 115 on all 4. Are these pistons truly a liability. Am I correct with the years. I am planning to remove the port cover to see if I can see if they are these pistons. Any information appreciated.

Re: 1977 evinrude 85hp time bomb

Confucius says, "If it aint broke, don't fix it."

Re: 1977 evinrude 85hp time bomb

Just wondering what the deal is with these pistons. He told me it was evinrudes stab at getting more compression.

Re: 1977 evinrude 85hp time bomb

The motor has been fine since 1977?? And you're going to listen to a "mechanic"???

Re: 1977 evinrude 85hp time bomb

Originally posted by Mark A64:<br /> He told me it was evinrudes stab at getting more compression.

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Evidently it worked. I got a new compression guage a couple days ago. Checked my '77 35hp - 145 lb. both cyls. But it's been working a long time and I'm not touching it.

Re: 1977 evinrude 85hp time bomb

a lot of crapola was generated about the high ring pistons, same as VRO. the high ring piston really needs correct fuel and cooling system maint. keep the carbs clean and the fuel fresh and the cooling system maintained and it will go and go. most problems I ever saw with the high ring pistons were failures caused by something other than the piston. most times failed pistons are a symptom not a problem. just the high ring piston did not tolerate any subsystem degradation, much like the merc 1500 inle six. worked great until a system was allowed to degrade. then it would detonate a psiton at or near WOT cause it would heat up or lean out.

Re: 1977 evinrude 85hp time bomb

What is a high ring piston? Does my '76 135 Johnson have them?

Re: 1977 evinrude 85hp time bomb

Let's think about this..... that motor is a '77, that's 28+ years and the case aparently hasn;t been apart. Sounds like a solid motor to me. I wouldn't touch it unless its broke.

Re: 1977 evinrude 85hp time bomb

Cricket,<br /><br />Apparently these were only used in 77, 78, 79. Then apparently they went away from this design because of the high failure rate. This mechanic, who has been working on OMC's for 30+ told me that OMC was even fixin this problem, beyond the warrantee period, if you barked loud enough, cause they knew it was a bad design. True, my motor has been a champ. I have to check to see if the entire power headhas ever been replaced. The only place where this motor was ever split is the port cover on the #1 cylinder. that is what got our attention.<br /><br />Boatbouy...This was on V4's, not 2cyl's. Sorry I should have been clearer.<br /><br />Yater, Some of the guys considered Guru's on this site have been mechanics with OMC for a long time. Guys like me, are just trying to learn a little about our motors.

Re: 1977 evinrude 85hp time bomb

Has anyone heard of this before.^

Re: 1977 evinrude 85hp time bomb

Lets see here....wasnt that about the time the fuel changed dramatically??? Well, yes, I believe it was!!<br /><br />Heres the deal -- think about this and then re-read Rodbolts answer-- when the fuel had lead as a "cushion" the pistons were fine even if the motor was being lugged. When we lost the "cushion" we started to really learn about combustion temps and its relation to rpm. <br /><br />Motors set up in the low 5000 range then started to break rings. Now these pistons had been fine for years so how can it be a bad design all of a sudden? You have to realize what changed. The fuel, not the piston.<br /><br />If you think folks are reluctant to set up at higher rpms now, imagine what it was like in the mid 70's. OMC had to make a choice. Try to re-educuate everyone, including themselves or re-design a piston that would survive in the worst of scenarios.<br /><br />Which do you think would be faster? And easier?<br /><br />OK, now here we are 30 years later and those pistons still exist. Bad design? Hardly. <br /><br />Yes, there was some truth to the rumor about the compression but not like you think. The engineers and racers were panicked that the low ring design would cause a loss of power. For a while the racers would fight over a set of high ring pistons. But guess what? It didn't matter!<br /><br />A time bomb? Must be one heck of a long fuse......

Re: 1977 evinrude 85hp time bomb

Thanks Dhadley,<br /><br />Is there anything I should do special with this motor,Run seafoam evey couple of tanks to keep rings clean. Just looking to keeps the old girl going.