crankshaft replacement

hello fellow kzriders.
well i was looking for some insight on replacing a kz750 b3 (78)crankshaft. not sure how much pain this is going to be the threads for the left handed threading on the crankshaft for the flywheel are pretty much done. i bought a new crankshaft and found a brand new bolt (that bolt new was hard to track down). I was hoping to be able to replace it without affecting my upper half of the engine. the motor is solid and ran solid. is it possible to break the lower half of the engine starting first with the oil pan than the lower half and replace any bearings and seals with the engine being upside down mounted to a jig. or is it going to have to be a complete rebuild sitting upright? i own a service manual. i just never tore into one of these verticle twins to this extent..
thank you for any direction you might be able to send my way.

I did it to my Ford truck but I never tried it on a bike.
Steve

well at least i can spread some sort of knowledge to the forum once i start this project i know i can do an overhaul. i'm just not doing well on the financial aspect. if it comes down to it if i have to tear it down to get to the crank shaft i might as well totally rebuild the engine. that i guess is the question.

You need a factory manual. To change the crank is a complete teardown including a chain driven balancing mechanism the engine has in it.

Is it feasible to rethread the hole to th next larger size?

What you really are trying to do is split the cases without taking the top end apart. I don't know if that is even possible.
Just thinking out loud for a minute...

You would need to pull the engine from the frame, pull the valve cover, remove the cam chain tensioner, then pull the cams - to get enough slack to get the chain around the crank, The flip it over and split the cases. Then remove the counter balancer chain, then pull the primary shaft and primary chain. Finally remove the rod caps and push the poisons down a bit. Then you could swap the crank

Maybe in theory it could be done, but you may just be the first person in history to try it on a 750 twin. Kawasaki would have you completely disassemble the entire engine to get to the crank. So trying to shortcut the whole thing and swap a crank may not be possible.

Some times the easy way is the hardest.
Steve

no i wish, its on the crankshaft. i won't fill and re-tap it either only cause the shaft is is holding the flywheel and i don't want that to be untrue and short out my charge system or damage it while I am riding it but thanks for the suggestion texaskz.

so it might actually be a good point on ordering a complete engine gasket set or make my own. and order any new parts as needed after i see what is worn or out of tolerance. i have the service manual already. now would be a good time to up the engine to a bigger piston set and hone it. There is a motorcycle shop near by that said they could handle any machining that i may like to have done to it. any suggestions it's currently stock.
if you can point me to any references I would greatly appreciate it.

A new set of high performance pistons, $500 and go from there.
Steve

Theres no reason why you or a good machine shop could not put a Helicoil in the stripped hole.
As for the rotor it locate's off the taper not the bolt so thats a none issue.

I'd Heli coil it like Zuk says the 500 dollar pistons are just the start......