So what actually happened, what broke first?, looks like the rod just let go. Its always a bit of myth and in theory this stuff can happen but ive never actually seen it. Ive worked on/rebuilt probably over 100 of these motors so i know what to look out for regarding imperfections in the rods. Was the sludge trap cleaned? what was condition of the main bearings? its gone bang thats for sure.
One time when i had to just do a top end build on one of these, new pistons, valve grind etc, when i was getting ready to put the
cylinder back on i noticed the inlet cam was worn, pretty badly. Phoned the owner told him now the whole motor has to come out for a tear down to fit a new camshaft (and we would check over the big ends etc). After i split the cases I found as broken RH main bearing. The bearing fell apart when I removed it. The cage that holds the balls had broken and the balls were about at the point of rolling to one spot which would have locked up the motor and done some damage like above. When i removed the bearing it just fell apart and all the balls were loose. Pretty lucky really considering this bike had been ridden a few weeks before hand and was only in to stop the smoking and top end rattle and the owner was happy we found that before it was too late and got to it just in time! So yeah bearings can wear out and fail.
