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Broken Piston ` any ideas?

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Broken Piston ` any ideas?

Postby ZRT800 » December 18th, 2001, 3:25 pm

Went for a ride last Friday. My brother was riding our old '80 Eltigre 5000 complained about it bogging so I hopped on it & blew it up with in 2 minutes!! I just tore it apart & the right piston has the back side broken off. I have to crack the cases to clean out all the shrapnel & will probably replace all the bearings & seals while I'm in there ( I think the cracnk bearing r.s. has some play). It also went through 1/2 tank of gas in 13 miles!! Just for curiosity, any ideas on why the piston would break? Just Fatigue, or worn bearings, or something else? Surprisingly the cylinder is still mint!! Thanks in advance!
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Broken Piston ` any ideas?

Postby ZR500PA » December 18th, 2001, 9:49 pm


broken diaphram in fuel pump may of flooded the block.
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Broken Piston ` any ideas?

Postby Xtreme XC » December 19th, 2001, 2:02 am

A heated up piston will break... ZR5 is probably right. Not enough oil mixed with gas, heated up and cracked.
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Broken Piston ` any ideas?

Postby KneeDeepInSnow » December 19th, 2001, 6:47 am

how often do you clean your carbs?
maybe you got some of that green algae s**t sucked through...
the oil may have settled in the tank or somthing
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Broken Piston ` any ideas?

Postby ZR500PA » December 19th, 2001, 8:24 am

All fuel pumps work off of the pressures in the crank case, this being an old cat you need too mix fuel. When an diaphragm breaks in the pump, this will fill the bottom of your block with fuel,They will run doggy unless they are wide open, and then they go like hell. you could of hydrolock the case, causing the skirt to break. It could also be from being use and very worn, with loose fits. I have and old pantera 5000 that never been rebuilt, Just been waiting for this too happen to me. Had the sled since new in 1978. Im going too run it to it blows apart.
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Broken Piston ` any ideas?

Postby ZRT800 » December 19th, 2001, 3:07 pm

Yeah we also have a "80 Pantera 5000, I'm guessing it may fly apart next! Both bought new one year apart, so the Pantera may blow up next year! I took the piston to the local Cat dealer, they said it was just fatigue. I showed it to my truck mechanic who also snowmobiles, he said over heating. Running it too hot (along with being 20 years old) makes the most sense. It was only 0 degrees celcius when we were out. Normally I only ran this sled when it was cold (because it's free air). But I was riding the ZRT & didn't even think about the old Cat running hot! It was the 1st thought in my mind once it blew though!! Too late! Thanks for the replies! I split the cases tomorrow, start cleaning, then rebuilding. The fuel pump idea is a good thing to check. I don't think that's the cause, but if I'm making a new engine it would be good to check out & maybe rebuild that just for peace of mind. Don't want to sink alot of $$ into a 20 year old sled, but it's an awesome spare sled!!! Plus, after more than 20 years, it's part of the familly!!!
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Broken Piston ` any ideas?

Postby Snotcicles » December 20th, 2001, 2:39 am

If it's a skirt, it's probably due to being just worn, if it's a crown, that could be hydrolock like ZR5 said. Even if your cylinders look good, have them mic-ed, they may be past their service limit. I know you would'nt want your new pistons to break from slapping on a worn out cylinder wall. Good Luck! Cat Pride!
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