Oh bugger. I broke two conrods in mine back in "74 in the days of no conrod kits & had to buy a complete crank. luckily for me Honda paid each time--or supplied all the parts. I'd had the cylinder off regularly after the first disaster but still got me. Big end revolved smooth & felt like new but don't think each time it was a bigend issue--it just broke the rod[Got sick of being revved to the limit]. first one happened when they started 100 bikes in probably 3 rows at the winter series down Otaihanga Road Paraparaumu [yes a real place name for you aussies]. Lap scorers though their pencils & paper away after a lap so stopped it & divided it into ods & evens & a final. Lead the pack at the end of the start straight & BANG [fk it], stepped out sideways locked up & took the weight on my right leg. Not broken but black & blue lying on the couch thinking--send me another motor [& leg]. Honda said go around the corner & get a new one from the opposition [CZ & Honda--we were Yamaha & Honda at Tim Gibbes]. New bike felt so damn good in every way as old one was getting baggy although probably less than a season old. Anyway--Eventualy the same thing happened after quite a lot of meetings. Pretty certain i whizzed the splines off the output shaft where the sprocket runs too. Still liked it--i think!!. Anyway--forgotten the subject--oh yeah & i feel ya pain. ps, they had bobweight flywheels like an old villiers eh?, why i don't know but would've been better with full flywheels in my opinion. just too snappy light flywheely. Wonder if the MT250 has full wheels & are interchangeable. Umm, if your case damage wasn't from a rod--then i've worn out my computer ink typing lol.
Edit, just re-reading it sounds like tis a rod or same end result.
