It's a...
536.886331 Craftsman 10 HP 29 in. Dual Stage Snow Thrower (http://www.hammerwall.com/Manuals/Craftsman/Description/536.886331/Craftsman%2010%20HP%2029%20in.%20Dual%20Stage%20Sn ow%20Thrower/L0402225/)

The chain came off the sprocket and I'm having a hard time getting it back on.

Cold in Cleveland... Marty

Here is a manual.
Download Sears 536.886331 User Manual (http://www.manualslib.com/download/150330/Sears-536-886331.html)