1969 115hp ate the piston?

[MTUJeeper]

What would cause the piston to almost appear eaten away? I was going along and it fell on its face. I pulled to check for a fouled plug and saw aluminum shavings built up on one of the plugs. Put a new one in, that had shavings on it in the 5 minutes it took to make it to the dock. Pulled the head and the better part of the deflector on the piston is gone. Looks like I'm tearing it apart, but need to know what caused it.

 

[oldrudedude]

Re: 1969 115hp ate the piston?

Probably blew a piston ring. --> broken ring goes through the port into the combustion chamber --> Beats the crap out of the top of the piston and cylinder head. Same thing happened to mine.

Check out this thread. It has some pictures. http://forums.iboats.com/showthread.php?t=342774

 

[Bamaman1]

Re: 1969 115hp ate the piston?

I'm like you. Everything I own is getting old, and I cannot afford to replace my toys.

My pontoon with Yamaha 115 is 26 years old, and needs upholstery.
My 165K mile Lexus SUV needs tires, windshield and tires.
My ATV needs tires.
My daughter's motocross cycle engine needs attention.
My pristine 1999 Jaguar XK8 convertible needs a fuel pump before I can address a CAN/BUS code on the ABS system.
My 03 Superduty diesel had a wire short out--the first repair in 92k miles ($300 including wrecker bill.)

And, it's too hot to address any of these issues.

Sometimes, things just get past repairs--and, it's time for replacements.

 

[MTUJeeper]

Re: 1969 115hp ate the piston?

Thanks for the help, looks like I'm just gonna tear her apart, bore the cylinder out, and put in a new piston and rings. Probably replace the rings on the other pistons as well. I just graduated so I might as well sell it and get something a little newer with less headaches when I get a "real" engineering job. Thanks!

 

[MTUJeeper]

Re: 1969 115hp ate the piston?

I checked the bore tonight with a dial indicator, I got 3.432, so barring errors in measurement, its still at stock bore. The cylinder walls are still in good shape, a little scratching around the exhaust port where the ring must have broke. Pretty sure I can just hone it put in a new standard bore piston and rings rather than paying money at the machine shop to bore it over. Where is a good place online to order engine parts from on the cheap? Thanks! Christian