250E Drive Belt
49 1/2 X 1 3/8 is what my nos vintage belt measures (edited for content by moderator). As for removal and set-up, start by loosening the slide bolts in the tracks under motor mounts and slide the motor forward a little then rotate the inside sheave on your secondary(large sheaves) in a clockwise motion while pushing inward(standing to the left side of the sled) while simultaneously forcing the belt down into the groove, sounds hard but isnt. Then lift the sagging portion of the belt out and over the inside sheave and pop - its off. As for adjustment once the new belt is on start by measuring the closed distance between the outer edge of the secondary sheaves, then install new belt( reverse of removal) and slide the motor rearward a little until the belt has opened the distance of the secondary sheaves 1/8 of an inch, tighten bolts and Rotate to check. While your here you can check and adj. drive chain(light slack). A point to ponder, the tracks are reinforced with steel cable and can stiffen. Merc put a kickstand at the rear to lift sled and run motor to loosen up track then drop-er down and go. Have fun !