I have a chance to get a clean 83 RM125 that is complete in every way except for the tiny little problem of it missing the engine. the carbs, airbox, pipe, cdi box etc are all there, however. I found a complete 82 motor that is in need of a rebuild but otherwise complete and am wondering if it bolt right in. As the 81-83 bikes appear to be similar, it looks like it should.
What do you think? Any help is greatly appreciated.
with a little measuring you should be able to tell if it will fit. The crucial part will be at the back of the engine/swingarm pivot. If that's good, you can weld new tabs on the frame for the other motor mounts (if they don't already match up)
of course, you may want to check with your vintage racing rules to see if you are able to race it.
I would be doing first and foremost for restoration/collection purposes. Any Ultima class stuff would be a secondary concern. If the 82 motor fits, I gotta get this bike, I'll post pics of it sans engine as soon as I get some.
I used to own an 82 RM125 with an 83 engine so I assume the opposite would work. No mods were needed to make the engine fit. The engines themselves were very different. The 82 had a piston port with a power reed valve to the crankcase, and the 83 used a conventional reed block similar to a modern engine. In 84 they went back to the 82 setup. I've heard that the 83 engine was kind of a dog.
The 82 and 83s are the same bike except it got some different forks I think. Its the 81 that had the crankcase reedvalve and the 84 got different motor mods.
They wil fit, had them both. The 83 engine has the reed cage in the cylinder, the 82 is a case in reed engine which means the cylinder and transmission cases are not inerchangable. However the engine will fit in the frame. If I remember correctly almost everything else is the same. Back in the day those bikes were really good, just make sure you grease all those rear suspension bushings well, and there are allot of them!
Anybody know what year motor will interchange with the '84? I've got one and am having no real luck finding a spare motor. I ran into a few nutso's at a couple of salvage places too, so that wasn't much help.