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Crossfire 700/f7 Piston melt

2K views 1 reply 2 participants last post by  ronnyhugo 
#1 ·
I bought my sled used about 2 years ago(2006 crossfire 700), I have had to replace and dump abunch of money in it so far. I really do like the sled. I had done a compression test and it tested 125psi each side. I know this was abit low but I was trying to go one more season with it because of all the recent costs with it.
Sure enough I melted a piston this week. I have ordered a new top end kit and I will be checking the boots and gaskets leading to the reeds. Is there anything else I should be doing to find the cause of blow up or is it possible that it was just an old piston that needed to be replaced. The sled has 7300 miles and the piston is a cat piston that came out so im not sure if it was original or not.
Any help would be great guys,
 
#2 ·
Check that the cooling system is A OK because its easy to drop low on coolant if you roll it just once, or if you side-turn enough to wash out some coolant from the stock pressure-release hose.
You could also install ice scratchers (the good ones not the steel cable ones), especially if you have tall lugs and run trails.
Also, the sled is running right on the edge of what the stock hood can get rid of in terms of heat, so drill holes on the top of the hood and install some fine mesh, so you get rid of that engine compartment temperature. The 800 crossfires in the years after 2006 suffered fire-spitting from the exhaust that melted the plastic, and complete cylinder melt-downs and sleds went up in flames due to this lack of vents. So AC made the ECU run pig rich which resulted in a lot of backfires and terrible fuel economy and terrible power. All because of lack of vents which wasn't a problem in the other models (xfire 700 and M8 and F8 etc) because they either made slightly less power or had a different hood design.
Also, install a temperature gauge if there isn't one. The water temp is crucial information. A wideband sensor to see fuel mix is also nice to have but that costs quite a bit much more than just a temperature sensor system. Though, if you buy a good aftermarket system for water-temp and fuel mixture sensing, you can move that between snowmobiles for years to come.

PS: My own crossfire 7 2006 had the exhaust put back by the previous owner slightly wrong, which is easy to do. So it probably spat a tiny amount of exhaust out between the Y pipe and expansion chamber, that could easily make the under-hood temperatures slightly raised, heating up the huge air-intake system in the hood and front, making the intake air significantly warmer. So make an extra pass on that, and keep an eye on underhood temperatures as you do passes. If the plastic on the inside of the hood is too hot to touch, you can probably have a drink and a snack while the sled can cool down a bit.
 
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