I have worked on a lot of KZ650/750 fours.
I have blown both head and base gaskets on those engines. I have also seen pistons and cylinders destroyed, but have never seen any crank or rod related issues.
I have seen a sized KZ650 engine, but the crank and rods were just fine. The bottom end on those engines is pretty robust. Crank bearings is the last thing in the world you would check on these engines.
How did your guy come to suspect crank bearing issues? Was there no oil pressure?
Hence why I asked the questions I did ! the OP is saying bottom end but hasn't answered my questions ref symptoms and why he thinks this ? I suspect there is likely to be a lot of wasted money here if he isn't careful !! if there is a noise at the bottom it could also be primary drive etc ????
The primary chain has to be really shagged for it to make any noise or slap, basically needs to be at end of life to do that. Should go +100K miles (+160K KM) before that happens unless its been drag raced every single day of its existence.
The only thing I have seen that would make lower end noise is worn out clutch hub rubbers, that will make noise when running. Will actually clunk like a Harley when dropping it into first gear.
Crank bearings can wear but it would not make any noise. They could make noise if oil pressure was low (worn oil pump) and a bearing was wiped out (scored) by excessive heat generated by low oil pressure at high speed.
