I recently acquired two free three wheelers, a Honda ATC250ES (Big Red) and a very rough ATC250SX. After getting them home and doing a more thorough inspection, I discovered Big Red had some serious damage to the right side case of the engine. So much so that the end of the crankshaft was broken off. The SX had no plastics other than the seat pan and someone had nearly destroyed the wiring harness for reasons unknown to me.
First order of business was getting the engine in the SX to run. I cleaned the carburetor and got enough of the wiring fixed to get it running, and it sounded pretty good. The charging system worked and it ran through all the gears while I had the machine up on jackstands. This bit of initial success started my plan of putting the SX powerplant in the ES chassis.
Having stumbled onto this site, I read enough to figure out that the engines were identical, so one afternoon the broken ES engine was removed and the running SX engine replaced it. After a few shakedown runs in the alley behind my house, I loaded it up and rode it for a couple hours. The longer it ran the better it ran. My only problem was 5th gear was broken, but all the rest of the gears were fine.
Big Red is really in pretty good shape. It is missing the two plastic side pieces and some of the front fender. The wiring harness looks to be untouched and all the lights work as they should. I have nearly completed a snow blade for Big Red so I can use it for something. I remember reading that the rear axle ratios were different between the ES and the SX, but I didn't realize until later that the transmissions were also geared differently as well.
While there is not a huge difference numerically between the two, I am still considering moving the gears from the broken ES case to the intact SX case. I would definitely tear down the ES transmission first to make sure all the gears are good in it before tearing into the SX case. Before I go to this trouble, I want to make sure the transmission part of the powertrain cases are the same. Can anyone enlighten me in this regard?