What surprised me about the pistons in my sled is they were galled on the intake side as if the engine had partially seized previously. When I measured them they were actually smaller in the piston skirt area, not larger as they are supposed to be.
I do have a foam filter on the top of the airbox that filters snow (and plugs up, required banging out when running in very deep snow). For some reason though, Polaris decided to install a simple unfiltered tube on the right hand side of the air box that leads up to near the handle bars. This side sucks snow directly into the air box.
One day about 4 years ago I got caught in an insane blizzard with around 5' drifts and cold temperatures (-25°ish not counting the 60 mph winds). The drifts were so tall that I basically was driving through them. I eventually ended up getting lost in the white out and the sled started really acting up (stalling constantly - very difficult to start). At first, simply banging out the filter would get me going again, but after a while the carbs started to individually seize wide open with ice buildup. Another problem as night settled in was each time I plowed through a drift my headlight got packed with snow. At one point I couldn't get the engine going again, so I pulled the top off the airbox and found it was practially full of snow - with the snow entering throught the right hand tube. I cut the tie wrap that holds the tube to the handlebar area and left it hanging under the hood (hoping less snow would get in). I eventually got the thing running again and it did work better. Eventually I made it home. With the engine acting up so badly I also got stuck about 20 times and was totally exhausted (actually the experience was quite scary - at one point the sled was stuck and wouldn't run and I was so tired I lay back on the seat against the handlebars for about 1/2 an hour to recover and the machine and I completely disappeared in the snow. I was probably 20 miles from any house in a complete white out with a stuck sled that wouldn't run and the snow was almost up to my waiste not counting the drifts).
The next day the sled ran fine (and the conditions were awesome - best powder conditions I can remember in 23 years of sledding; actually that might not be true - I can remember times over the years when there was too much snow to get my 1966 Olympic, 1972 Olympic or 1978 340 RV through). I think it was shortly after that that a mild bog started to appear (it always bogged off the line a little though).
Anyway, I was trying to figure out what caused the galling on the intake side and thought ice crystals might be hard enough to initiate galling of the pistons (keeping in mind how quickly the pistons are moving and it takes some time for snow/ice crystals to melt). The piston bores, rings, and upper piston regions are in great condition, just the intake pistons skirts damaged.
I was expecting to see perfect looking pistons with cracked skirts due to fatigue; not galled skirts. I'd estimate 0.015" of material is missing off the center piston skirt (I can fit a 0.020" pin gauge between the piston and cylinder in some areas of the piston, no matter where in the bore I measure it). The mag side was missing the skirt entirely, and the clutch side had only minor damage (comparatively). On the dreaded blizard day, when I had looked inside the airbox, the mag side had by far the most snow in it.
If it wasn't the snow, what else could cause that sort of damage?