Z1R Mk2 D3 Crankcase damage

Hi,

I'm attempting to restore a 1980 Z1R D3. I have now separated the cases but have found that the crankcase is damaged where the output shaft bearing sits. I knew that the bearing had failed at some stage but underestimated the amount of damage that had been caused. See photo.
My local engineering shop says that the only way he can fix it is to rebore the the opening for the output shaft a couple of millimeters larger and fit a larger bearing. He would then have to cut the groove for the bearing setting ring. I can source the larger bearing but it wouldn't have the groove for the setting ring which would then have to be machined into it. I'm not sure if he would be willing to undertake this. This bearing would also not be rated as highly as the one that has failed, which could be a concern.
Another option would be to source another set of crankcases, not an easy task given the rarity of the D3 model bikes.
So I have two questions:
1. Has anyone undertaken a crankcase repair of this nature and, if so, how was it done?
2. If I can't locate a set of D3 crankcases, what other ones would be suitable? I know that the later model J series are not compatible but what about late 1970s KZ models? There are a few on Ebay with engine numbers starting with KZT00AEnnnnnn. Would the D3 barrels, gearbox and crank slot straight in?

 

This may be a dumb question, but would it be possible to add metal to the damaged area by welding and then machining the surface to the original size? Ed

As ED says building up then machining back to original spec would be better, or another set of cases.

It's not as bad as it seems .
If the case grips the bearing then it's just the location groove that needs addressing.
Simply get the machinist to cut a new groove in the correct location towards the out side of the case and flip the bearing round.
Much better than risking case distortion with welding or miss alignment with re-machining for a bigger bearing.
Here's a pic of one of mine that's been done .

The new groove seems like a good suggestion. Assemble with loctite bearing retaining compound on the bearing seat. If that won't work the case could be bored for a thin brass shim that wraps around the bearing.

zed1015 wrote: It's not as bad as it seems .
If the case grips the bearing then it's just the location groove that needs addressing.
Simply get the machinist to cut a new groove in the correct location towards the out side of the case and flip the bearing round.
Much better than risking case distortion with welding or miss alignment with re-machining for a bigger bearing.
Here's a pic of one of mine that's been done .

zed's advice is spot on. This is a common mod done when building high-output dragbike KZ's. The stress of launching with a sticky rear slick & wheelie bars would cause engine case failure at the input shaft bearing on the clutch basket side. Moving the groove inboard solves the problem. If you live in the U.S., Mark Doucette at R&D Motorsports is the man to talk to: www.rd-motorsports.com . Although, in your case, it's the output shaft, maybe Mark can provide a solution.

Good luck with your project.

Mike

I think you have a MK2 engine, which was in use for 1979 and 1980. Any cases from those years would be a direct replacement. However any cases back to 1973 would also work.

Paul Gast would fix that right up for you.

Thanks for the replies. I'll see my machinist again and see what he thinks of some of the suggestions.
I live in Port Macquarie, Australia and the engineering options are limited.

Hi again,
This project has been has been on hold for a long time but now I'm ready to get back into it. As I said in my original post, there is damage to the crankcase where the output shaft bearing sits. Although I have managed to source an oversized bearing I'm trying to avoid having to machine the cases as it could possibly cause more issues than it would solve. But now I find that when the original bearing is fitted without the snap ring and the case bolts torqued to the correct spec, the bearing is not tight in the cases. It is not actually loose but I can move it by hand. I'm unsure of just how tight it should be. Would the application of Loctite Bearing Retainer be enough to hold it in place?           

That's a high stress area. If you're not going to have it machined I'd use the ring, fill the voids and use a punch to tighten up the land surfaces. That bearing retainer stuff might be a good idea as well. Before I installed the 903 crank there was a chattering noise at idle. I knew the bearings were loose in the cases. It was caused by one of the crank pin journals being broken in the wreck so the crank was walking side to side. Had it welded and fitted a bearing race to the case then punched the lands to tighten up the bearings. Now there's no noise at all. Not as good as suggested but it might be worth a try.
BTW I rode the bike that way for years before I changed the crank. 
Steve


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Thanks for the info. One more question - what does fill the voids mean and how do you do it?