I take it that the part number to the one you had on there is 138-4316U3. The new one is 144-4353U3. The 138 is a 1-3/8" X 43-1/4" belt and is correct for your machine. The 144 is a 1-7/16" X 43-53/64" belt and is for '97 & '98 MZ 670. A good reference for this is a Dennis Kirk snowmobile catalog.
the part number on the old belt is 138-4332. its hard finding info about my sled. its a 1996 and in general people don't list 1996 mxz 670's, only 97 and newer but the tunnel says 12/1995 or 1996 is what it translates to. my question is will it hurt my machine to run the bigger belt?
The 138 and 144 makes a world of difference when it comes to engagement. On mine a guy had a 138-4353 when the 144-4353 is used. It engaged at a higher rpm and bogged cause it sat lower in the secondary. When i ran the proper belt it flew. The 138 blew out in less than 100 miles and i got almost 400 out the 144 and its still on there, gunna replace of course. If you run a shorter or longer belt or narrower or wider than the oem belt required it can have adverse affects and could lead to being stranded. Try this,http://126.96.36.199/Skidoo_OEM/Skidoo.asp select the year and make and it will give you every part number for the entire sled. on the belt in the drive pully section type in "1" and hit enter and it will give you the proper belt number.
so the suggestion would be to run the oem belt? I know oem is always better be it car parts or sled parts. so running a longer or shorter or narrower or wider only effects take off? does it have some adverse effects to the clutch or the secondary?
OEM is the best, next to ultimax but id rather have the oem. Longer belts wont grab right and wearout fast. Short belt ride the clutch center and burn up, unless you have a roller, but either way it will rip out under constent pull from being short or the adjuster for the clutch alignment will stripout and blow belts that way. Worse case scenario is when the belts ripout over time the engine can lock up from overrevving too much.