I am new around here so I will just say what happened to me.
I was up in the north woods of Wisconsin ( 10ish miles from the northern border ) riding with friends and family from December 27 until January 1st. We were taking our sleds out for our first ride of the year and 5 to 10 miles down the trail, my sled started to have acceleration issues, (engine ran normally but seemed down on power) the brakes were getting hard to squeeze, and I was smelling what seemed like a belt burning up. (I have burned a belt before and it smelled the exact same) I figured if the belt went then the belt went so I kept riding. After about a mile of this, I went to slow for a corner and the track locked up. Looking back I suspect that the brakes and fluid were heating up and locking the track up, but the engine still ran, even though it only went up to 6k rpm. When I slid to a stop the sled died and my friend practically pulled me off the sled yelling that there was fire underneath on the right side just beneath the brakes and chaincase. A few seconds later it was gone, but I am thankful that it didn't explode and that no one was hurt. It got hot enough to melt the chain case and left side of the tunnel.
I would like to know what you think caused this. A few things to note: we were going about 35-45 on twisty trails, temp was 15F, chain case oil was black and had metal stuck to the magnet on the dipstick, sled had new motor mounts (broke old ones), full oil tank, 1/4 full fuel tank, grease all the way around, and 3400ish miles.
Ideas on the cause?