Z1R Mk2 D3 Crankcase damage

That's why I asked for pics of the other side. Looks like there's enough material for the ring to do it's job. I'd clean it well then use JB Weld Liquid steel or the like to fill where the damaged areas are. I'd seat the ring in the epoxy and let it set using the bearing to be sure it's level. A light coat of oil on it should keep it from sticking. What does the bearing look like?
Steve

I have attached photos of both top and bottom. The original bearing is destroyed (I have a genuine Kawasaki replacement) - I think it cracked along the ring groove and fell apart but there was minimal damage to anything else in the transmission apart from the parts of the crankcase that hold the bearing. So what you are suggesting is to permanently fix the ring in place and fill any gaps in the crankcase surfaces with JB Weld using the bearing to level things out - is that correct? I'm fairly new to this sort of thing and want to make sure my understanding is correct.   
 

I recently watched a guy fix that exact problem on a Honda 750 case, he used a brass bar machined so the  end was  the same size and diameter as the circlip, the end was then placed into the circlip slot, he used a cut out section from a damaged engine case he had lying around to clamp the brass bar in place,  he then  tig welded the damage up. He then unbolted the case section he used to keep the brass bar seated in the  bearing circlip and  cleaned up any excess welding that was in the way and it was fixed, this was on a race bike engine with more than double stock HP.... Did I explain that well enough ?    Its a pity you are stuck in lockdown as the guy is just north of the Gold Coast, not too far from you...

wrote:

I have attached photos of both top and bottom. The original bearing is destroyed (I have a genuine Kawasaki replacement) - I think it cracked along the ring groove and fell apart but there was minimal damage to anything else in the transmission apart from the parts of the crankcase that hold the bearing. So what you are suggesting is to permanently fix the ring in place and fill any gaps in the crankcase surfaces with JB Weld using the bearing to level things out - is that correct? I'm fairly new to this sort of thing and want to make sure my understanding is correct.   
 

Yes. Looks like there's enough of that ring land to hold it in place. Don't forget the punch marks like I showed in the clips. Embedding the ring would help to secure it. I've run bad chains and sprockets before but it never went this far. In the 80's I switched out the tranny and looked at the bearing. It was noisy but no where near as bad as the one you have. Got a pic of it? BTW click insert all  in the attachment section. I fixed yours this time. 
Keep us up to date. 

Steve
 

This is what's left of the bearing. Thanks for your help. It might be a while before I get around to doing anything more as I would prefer to do this with someone with a bit more knowhow than me and we are in a COVID lockdown at the moment which means no visitors. Thankfully I can still ride. 

A little duct tape and hot glue should fix that in no time 

wrote:

This is what's left of the bearing. Thanks for your help. It might be a while before I get around to doing anything more as I would prefer to do this with someone with a bit more knowhow than me and we are in a COVID lockdown at the moment which means no visitors. Thankfully I can still ride. 

Was this a drag bike or turbo?  If you're going to wait  I'd take the  suggestion of cutting a new groove  and turning the bearing around. My suggestion was to just get the bike back on the road as a normal street bike. if no shop is available  Keep in mind the the gear clusters can't walk around or tranny damage will be the result. Take a look at the shift forks and shifting dogs as well. You may have more than one problem. 
Steve
 

That ring groove would be ok IF it wasn't /isn't worn wider than the location ring.
You need to avoid any chance of bearing float.
Once that is addressed ( ideally by having another groove cut and flipping the bearing round ) you should just center pop the surface of both halves of the cases equally where the bearing sits and assemble with a light wipe of bearing fit.
Once bolted up it isn't moving.