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Hey everyone, id like a bit of advice especially from shaft drive experienced people! I'll try and be brief! Basically I had to get the final drive box off and find out how the clutch arm mechanism broke, me and my dad wrestled the thing out and two bits immediately fell into the oil bowl underneath, one bit was the snapped end of the clutch pushrod, so mystery solved there but the other was a big NUT with part of a bolt in it, within a few seconds I realized it would have been on the end of the output shaft, here's the thing, ever since I bought the bike 5 years ago there's always been a strange hollow sounding rattle from that drive area and my dad is of the opinion that the bike has been running with it broken for years...anyway after pulling off the gear with the three bumps and inspecting my dad thinks that there should be no difference without the nut! As in everything spins freely, nothing can move in or out and finally when you fit the outer cover back on another gear with three bumps interlocks and we think the hollow splined shaft in the middle of it all SHOULD ...press on the washer that's left, so the only change is no nut inside the hollow splined part.....
How on earth that thing broke in the first place is a mystery to me though! Anyway everything is all back together now and it's riding great but what are your thoughts on leaving the nut broken. ....?? Many thanks

Firstly I should start with I know NOTHING about shaft drive however, if its showing on the parts diagram Im sure Kawasaki put it there for a reason or they wouldn't have gone to the added cost of designing it in and adding it to the bike.

That nut has probably been over tightened to cause it to shear.
It really isn't a good idea to continue running the bike like that as the drive dog is only on sliding fit splines and the once tightened the nut also controls float of the output shaft which in turn maintains the correct position of the gears to prevent misalignment and gear change issues.
You should really split the cases and fit a new output shaft.
If you do decide to take a chance and use as is you should at least run a ring of weld round the end of the shaft and drive dog to tie them together in an attempt to limit further damage.

Hey Sheath, you are headed for certain catastrophe with that bike. You need to take it off the road now.
Kawasaki didn't put that nut on the end of that output shaft because they had a few left over from previous builds.
Imagine yourself riding down the highway at 70 Mph and then a total lock up or a sudden no drive situation, you now find yourself possibly losing your own life and being responsible for any other road users who die trying to avoid hitting you.
Sorry to sound harsh here mate but what you are doing is not cool, Get it off the road and have it repaired correctly.

The Kawasaki engineers put that nut on there for a reason and it was not simply decoration. Ed

I hate to be piling on but....get it fixed correctly before you hurt yourself, or worse...hurt someone else.

Thanks everyone, yes the reason I put the post on here is because in the back of my mind I knew a nut torqued to 87 pound with a tang to stop it moving had to have a job to do, now I've got two problems, one is ,there are few bike mechanics anywhere near me with the experience to do this job plus they would charge a TON of money and secondly, it took me hours with dad's help to simply get that drive cover off then back on! So I think splitting cases might be beyond our ability. ..... also check out my broken clutch pushrod compared with a normal one, what the hell happened to that Rod too?!!

Just curious. what particular shaft drive motorcycle is it?

A 1980 z1000st

There's plenty of people converting ST's to chain drive so the parts should be fairly easy to source.
You don't have to completely strip the engine, just the lower case and leave the top end untouched.
The actual gears are the same so you only need the bare output shaft and nut and then swap all the gears over.
With the correct tools it's a days job.

No eBay APP ID and/or Cert ID defined in Kunena configurationWith the shaft sheared off the output shaft could walk causing damage to the shift forks and gears. I wouldn't ride it until it's fixed.
Steve

Thanks very much for all the info, especially the videos! it looks like there's work to be done! Poor old bike, I spend more time working on it than riding it!!