What happened to my piston?

sleddheadd

sleddheadd

New member
Joined
Sep 11, 2003
Messages
660
Age
56
Location
Manhattan, Illinois
I have rebuilt these 600 twins in the past and gotten thousands of miles on the rebuild. Last winter we rebuilt another one, put 50 miles on it before seasons end and added another 80 miles last weekend before she broke loose on us again. can anyone tell what happened by looking at the damage? We are guessing water in the fuel. Did we rebuild it wrong? Any thoughts?

Vmaxpiston2.jpg


VMaxpiston-1.jpg
 
i would say it caught a ring on a transfer port, breaking the piston above the rings and then the ring piece beat between the head and the piston a few 1000 times and caused the rest of the mess you see... any marks on the cylinder?
 
I let a buddy borrow it for his girlfriend and it was returned with a blown motor. 7000 miles on the original so I couldn't bitch to much about it. We took this one apart and bought a new jug and head along with 2 new pistons and rings but never measured anything on this one. If we put something together wrong, I would have thought it would have blown up sooner than 130 miles....
 
from what i see it doesnt look like a fuel problem or oil problem, the skirt looks pretty good, how are the crank bearings,rod lower bearing? there sould be no up and down movement. so this is the pto piston exhaust side ? do you have clearer pics of all sides? i cant really see that well, but damage to head doesnt look all that bad, seen way worse head damage with less piston damage.
 
That is similar to the way mine looked when I toasted the mag side rod bearing this past Saturday. Mine didn't break any pieces off the piston.
 
sleddheadd said:
I let a buddy borrow it for his girlfriend and it was returned with a blown motor. 7000 miles on the original so I couldn't bitch to much about it. We took this one apart and bought a new jug and head along with 2 new pistons and rings but never measured anything on this one. If we put something together wrong, I would have thought it would have blown up sooner than 130 miles....
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Was this the "new" jug? Was this truely a "NEW" jug or was this a new to you, used jug?

I'm with mbarryracing, one of those is likely where you messed up.
 
parepadarappa said:
Was this the "new" jug? Was this truely a "NEW" jug or was this a new to you, used jug?

I'm with mbarryracing, one of those is likely where you messed up.
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It was a used jug that had been honed, now I am thinking that it was honed a little too much, which caused the ring to spin, catch a port, break and the rest is history.
what kind of clearance should I have between cylinder and piston, just so i know what exactly to measure for the next time.
 
sleddheadd said:
It was a used jug that had been honed, now I am thinking that it was honed a little too much, which caused the ring to spin, catch a port, break and the rest is history.
what kind of clearance should I have between cylinder and piston, just so i know what exactly to measure for the next time.
Click to expand...

Honing a cylinder doesn't cause a ring to spin. What causes a ring to spin is when the anti-rotation pin backs out. I would tear it down to the crankcase, and inspect/clean all main bearings and rod bearings. Then put together w/new seals/gaskets/piston. What brand of piston and rings did you use for the rebuild?
 
mopar1rules said:
Honing a cylinder doesn't cause a ring to spin. What causes a ring to spin is when the anti-rotation pin backs out. I would tear it down to the crankcase, and inspect/clean all main bearings and rod bearings. Then put together w/new seals/gaskets/piston. What brand of piston and rings did you use for the rebuild?
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To be honest, i do not remember, I did replace both pistons and rings to keep them the same and they were not oem. I was trying to get a spare sled going with as little money as possible. I am thinking it is time to get rid of a spare sled for friends and let them worry about themselves.
 
sleddheadd said:
To be honest, i do not remember, I did replace both pistons and rings to keep them the same and they were not oem. I was trying to get a spare sled going with as little money as possible. I am thinking it is time to get rid of a spare sled for friends and let them worry about themselves.
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"I was trying to get a spare sled going with as little money as possible."......this usually leads to something negative happening in the end. Is by chance the anti-rotation pin in both ring grooves on the piston?
 
mopar1rules said:
"I was trying to get a spare sled going with as little money as possible."......this usually leads to something negative happening in the end. Is by chance the anti-rotation pin in both ring grooves on the piston?
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X2
What brand pistons did you use?
Are they cast or forged?
I ran across a similar issue with "less expensive" replacement watercraft pistons a few years back.
 
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