Cheap and easy jackshaft/reverse unit
 

[B[/B] This is what I did to get reverse with a 400cc two stroke enduro motor. First I chopped the final drive section with the reverse box off of the blown up gy6 motor that was in the buggy when I got it. Then I gutted it and cut the gear that goes on the output shaft down to the center hub and welded a 16t sprocket to it. Then I notched the case to allow room for the chain and sprocket. Next I fabbed some brackets for mounting the unit to a 3/8" steel plate across the swingarm above and forward of the axle and made to pivot to allow for chain adjustment. The sprockets and chains I used are a 14t 520 on the motor to a 16t 520 on the jackshaft. Then a 16t 530 from the jackshaft to a 35t 530 on the axle. The gearing on the enduro motor is a bit high and 5th gear is a major overdrive but the 400cc two stroke has enough power to make the first four gears alot of fun. 5th keeps the motor from winding up on long runs on pavement or dirt saving gas. The reverse box is a planetary setup and geared pretty low so backing up is easy and slow. Haven't found out what the top speed is but I've had it up to 66mph in 4th so far. So far this setup has handled everything the motor can put out with no issues. Chains don't get hot or snap.