My Brother has a 98 Frmula III 700 and the sled constantly whines (like a supercharger) at high RPM's. Any ideas? Could it be the crank?

I could be mistaken but it sounds like a bearing failing. *I hope I am wrong. *$$ *http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/nervous.gif *http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/confused.gif

With that sled I wouldn't doubt it!
I guess mine kind of sounded like that just before.... http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/biggrin.gif

My 98 FIII 600 used to do something like you describe, mine would "squeal" under acceleration, and at sustained high trail speeds. After some investigation I found a few things, but what fixed the problem was clutches out of alignment. I was trying to set it with a straightedge and a ruler.....big mistake, I bought one of those aluminim ones made specifically for my sled for $20 from SLP and voila noise gone. I will never go without the proper clutch alignment too again.

ZMachMan gave me a good piece of advice on bearing failure.
Start your sled, then shut it off and listen carefully for a spinning noise, if you hear it, it is your PTO bearing spinning in the case http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/wow.gif