Kick starter idler gear? Broken tooth, probably lunched some other gears or jammed between the ring gear and idler and spread the pinion and out put shaft enough to crack the case between the 2 right side bearings? I have seen this problem on 3 out of 5 RM100/125T Engines. If this sounds familiar, let me know. I think I have the fix for it.
There are 2 types of Kick starter idler gear, one (earlier) has holes in the gear web, the later model is solid. I believe the problem here lies with the kicker cam hanging up on the retract pawl, keeping the idler and kicker primary gear in mesh after the engine fires - something has to give and hey presto. Spend some time polishing the burrs off the cam and the pawl plate, grind a small chamfer to the cam lug leading edge, polish like chrome. Check the operation several times to make sure the primary cams out each time.
I believe a PE175 Gear will fit the RM125T if that helps.
