"84 Yamaha 115" Overheating? maybe?

[72rude]

I have an 84 115hp. Everytime I ran the motor last season it seemed to overheat after a few minutes of 75% throttle. Power dogged out completely but would continue to run and have enough power to troll. I shut it down for about a half an hour, it started back up, ran for 20 seconds and now won't start. One cylinder wall is kinda white and the other is brownish. Starboard pics below ... head has no severe damage. That one piston does have some.Any advice for a first timer?

 

[Bamaman1]

Re: "84 Yamaha 115" Overheating? maybe?

Have you checked your thermostats? They're tiny little things on the top of the head.

A bad thermostat or thermostats possibly wouldn't be kind to your engine. They may be sticking closed.

 

[72rude]

Re: "84 Yamaha 115" Overheating? maybe?

Have you checked your thermostats? They're tiny little things on the top of the head.

A bad thermostat or thermostats possibly wouldn't be kind to your engine. They may be sticking closed.

Yes, thank you, they seem to bee operating fine ... a marine mechanic friend spent a little time with it before winter last year and mentioned (possibly) the motor was being shut down by a faulty sensor. But that wouldn't explain the different color cylinder walls, I think ... I'm very new with marine motors

 

[99yam40]

Re: "84 Yamaha 115" Overheating? maybe?

My guess is it was running lean and toasted the piston and cylinder wall

 

[yamatech43]

Re: "84 Yamaha 115" Overheating? maybe?

Center of piston looks like classic detonation/lean burn....not usually from lack of water on a two stroke....if it can run hot enough it can get this detonation, but most likely lean burn condition did this....I see lots of severe damage to piston and if you mic the cylinder think you'll find it ain't right anymore either. Wonder what the bearings look like....
P.S. Kids watching....if you see daddy keep running his motor when it's got a serious problem....make him stop right then and there. An engine is a terrible thing to waste.

 

[72rude]

Re: "84 Yamaha 115" Overheating? maybe?

Center of piston looks like classic detonation/lean burn....not usually from lack of water on a two stroke....if it can run hot enough it can get this detonation, but most likely lean burn condition did this....I see lots of severe damage to piston and if you mic the cylinder think you'll find it ain't right anymore either. Wonder what the bearings look like....
P.S. Kids watching....if you see daddy keep running his motor when it's got a serious problem....make him stop right then and there. An engine is a terrible thing to waste.

So it looks like I'll be splitting the head or parting out the motor?

 

[Part-time]

Re: "84 Yamaha 115" Overheating? maybe?

I didn't find it to bad of a job to split the block. You'll need metric tools and a 10mm 12 point socket to get the conecting rod caps off.
I priced mine out and it would be a little over a $1,000 to get 4 aftermarket pistons and rings and the 4 jugs borred... plus whatever for gaskets that I havent priced yet.

 

[multimech]

Re: "84 Yamaha 115" Overheating? maybe?

The piston is burned. This engine needs a complete rebuild. Have the holes checked for roundness and bored if needed. Use cast pistons or make sure they bore it right for forged. All new bearings, rings. Check the rods and check the crank. \

Ensure the cooling system is tits. Set TDC and ensure timing is spot on. Rebuild the carbs. Check the timing to make sure no double fire.

This is not place to cut corners or you will burn another powerhead down.

 

[72rude]

Re: "84 Yamaha 115" Overheating? maybe?

The piston is burned. This engine needs a complete rebuild. Have the holes checked for roundness and bored if needed. Use cast pistons or make sure they bore it right for forged. All new bearings, rings. Check the rods and check the crank. \

Ensure the cooling system is tits. Set TDC and ensure timing is spot on. Rebuild the carbs. Check the timing to make sure no double fire.

This is not place to cut corners or you will burn another powerhead down.

Excellent, I can afford a grand or a little more to do this ... plus I'm ready for the learning and the challenge. I can't thank you gents enough as it's a great motor. What would guess be to the original cause? Maybe a faulty sensor? I never heard an oil warning. Does running lean mean not enough oil being mixed in? Seemed like I had a decent amount of blue smoke. The water cooling system seemed very good. And I should re-do all four pistons right? again, MY thanks for everyones help

 

[99yam40]

Re: "84 Yamaha 115" Overheating? maybe?

lean fuel/air mix.

When was the last time you checked to see if alarm system worked properly?

 

[yamatech43]

Re: "84 Yamaha 115" Overheating? maybe?

Would you happen to have the plugs, as they came out of the engine? A pic of those would be great....pics of engine internals with good color....looking for bluing to certain points....it's easy to mistake lack of oil/lack of cooling if you don't know what to look for....each can be disguised pretty good as the other...you are right to want to fix the problem that caused it, otherwise no point....get her apart and send some pics...plugs would be good first...and by all means go through the alarm system as suggested above...good luck.

 

[72rude]

Re: "84 Yamaha 115" Overheating? maybe?

My mistake, never have, will learn how soon

 

[72rude]

Re: "84 Yamaha 115" Overheating? maybe?



The plugs are upper and lower as shown (as head bolts). Upper cylinder kinda white, lower cyl.brown. Your input is appreciated!