Piston to Cyl clearance

[Bushwacker1]

I have an air cooled single cyl 250 cc indy lite that needs a piston. I was able to find a .010 over kit that is marketed for the 250 cc 4 wheeler that shares the same part # on the cyl. The new aftermarket kit calls for .0025 - .003" skirt to cyl clearance, and the polaris manual calls for .004 - .0065". The old polaris piston has much thicker skirts and is heavier than the after market piston. I am thinking that the difference in the enviroment ( cold ambient air keeping the cyl cooler and not allowing it to grow at the same rate that the piston will grow / and the fact that the sled engine is enclosed ) is why more clearance is required on a sled. I am leaning toward using the polaris specs to avoid a stuck piston. I am only speculating on this and any input on what you guys think is welcome.
Thanks

 

[Kraven]

I have an air cooled single cyl 250 cc indy lite that needs a piston. I was able to find a .010 over kit that is marketed for the 250 cc 4 wheeler that shares the same part # on the cyl. The new aftermarket kit calls for .0025 - .003" skirt to cyl clearance, and the polaris manual calls for .004 - .0065". The old polaris piston has much thicker skirts and is heavier than the after market piston. I am thinking that the difference in the enviroment ( cold ambient air keeping the cyl cooler and not allowing it to grow at the same rate that the piston will grow / and the fact that the sled engine is enclosed ) is why more clearance is required on a sled. I am leaning toward using the polaris specs to avoid a stuck piston. I am only speculating on this and any input on what you guys think is welcome.
Thanks

I would NOT use an aftermarket piston in a trail sled, IMO

Stick with the POLARIS OEM, or you'll be replacing the aftermarket piston down the trail somewhere

Been there, done that, far too many times, kinda sux the fun out of ridin'

 

[Bushwacker1]

When looking for a piston I found that the OEM was no longer available. So I was forced to buy from the aftermarket. That is when I found that the four wheelers shared the same cyl. There must be a bigger market to keep the 4 wheelers going. The positive on the aftermarket (if there is one) is that they offer it in .010" increments up to .040 There are not a lot of options out there for this old sled.

 

[Kraven]

When looking for a piston I found that the OEM was no longer available. So I was forced to buy from the aftermarket. That is when I found that the four wheelers shared the same cyl. There must be a bigger market to keep the 4 wheelers going. The positive on the aftermarket (if there is one) is that they offer it in .010" increments up to .040 There are not a lot of options out there for this old sled.

I would suggest trying dealers like:

1) HELENA'S CYCLE in Helena, Montana

2) KEN'S SPORT in Wisconsin

They stock a lot of "old stock" discontinued OEM stuff

Helena cycle had a bogey wheel mounting bracket for my daughter's 2000 POLARIS when it was discontinued for a while

Same story for a POLARIS 120 wheel kit

 

[Bushwacker1]

Kraven
Thanks for your input and sugestions on where to find NOS parts. I agree that in most cases you cant beat the OEM for durability, and i am sure someone somewhere has a NOS piston kit, but I already have this kit and am willing to take my chances on it. I am still interested in any input as to why the fit clearance for the two applications are different. I already have the cyl sized to the tighter spec and am having second thoughts about leaving it that tight. If it will not seize with the tighter clearance I would rather leave the cyl sized to that spec. When searching for the OEM piston I did find a stock bore OEM piston for a four wheeler and it was simmilar to the aftermarket piston I bought in weight and thickness, the ones for the snow are just more robust. Another difference in the pistons from snow to dirt aplication is the placement of the ring gaps. The one application has them on the exhaust port side and the other application has them on the intake side. Also this cyl is common to both applications so it would seem that this substitution is not that much of a stretch just to get an old piece of iron back on the snow.