I had previously attempted to do this but gave up when I remembered that I already owned a sled and would rather be out snowmobiling. This winter though, Woo and I found the motorized couch (snowmobile), to be boring. Having two donor bikes and piles of old sled parts we attacked the snowcycle project with new energy.
The first five pictures are of my 1974 Yamaha DT360 Enduro. This is a 360 cc 2-stroke bike. It was my intent to leave this bike as stock as possible so I could ride it again in the summer. This decision almost killed this project for me. So many fabricated brackets, a live axle with bearings, new chain tensioners and the list goes on. I made a lot of my bikes parts using my mill and lathe. This added countless hours compared to Woo's weld-it-in-place-by-the-seat-of-your-pants method. In the end, they both worked.
The last two pictures are of Woo's 1970's vintage Ossa 360. Woo was not too interested in saving this bike for summer use so he removed the spokes from the rear wheel hub and created a drive sprocket cut out of 0.1875 in. steel plate that mounted directly to the wheel hub. However, the hub has been heavily modified and can never be re-spoked again. This was definitely the easiest way to go about this as it allowed the use of the stock drive chain, brakes, axle and chain tensioner.
The only tools used on the Ossa kit were a welder, something to cut 0.1875 mild steel plate (a jig saw, reciprocating saw, or a metal cutting band saw), a drill, a hand-held grinder and a basic set of wrenches and sockets. We got the drive tracks from a single 15 in. x 121 in. snowmobile track. A horizontal metal cutting bandsaw was used to cut the track down to size. The tracks we cut into were constructed of rubber, fiberglass bars and nylon / aramid / kevlar type cord. Other people have used table saws and circular saws for this.
All in all, these things are pretty fun. They are useless in much more than 10 in. of powder but a blast on firm snow and groomed trails. They are tricky to ride and we definitely wiped out while learning to ride. If we try another build it will be on 450 cc. or larger four stroke bikes and it will look more like the Timbersled Mountain Horse kit (http://www.timbersled.com/snowbikekits.htm ). $5,000....OUCH! Time to fire up the welder.......