Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Broken unit crankcases

Hello I was wondering if anyone has repaired triumph unit cases that are broken above the primary chain. Thanks Jeff

Broken due a final drive chain failure? - yes

Photos?

It needs a very good welder to avoid distorting the primary

Depending on the 'hole/crack size' you may need a steel plate bolted to the primary side, plus bolt both crank case halves together to avoid distortion as the cases cool. A very slow cool is better than a fast one, some use slake lime, others use fine sand. But done right the cases will be good as new.

This one was welded up and is good but the cover was scrap.
https://imgur.com/a/tPGamTl


Once welded
https://imgur.com/a/BfK76ud

Not a primary chain failure, but mine had broken just above the final drive sprocket ie in the crankcase behind the primary drive.

Not as a good as an 'invisible' weld, but a PO cleaned up the carnage in the case and made a neat little aluminium plate that fills the gap. This is glued to the crankcase. You can see it if you're looking ie anybody who has had this experience with a unit twin (!), but a reasonable compromise, and presumably didn't involve having to strip everything to pieces.

I had mine welded and the result was excellent . However, after the work the circular cover behind the clutch didn't quite fit! I had to file it very slightly but all seems well. It was done a long time ago.

Rod on this site made up a new piece that fitted the hole after cleaning it up and used a strong glue to fix it . The result was hardly noticeable. There is a thread he started with pictures somewhere.

Dave

I have successfully shaped and fitted in a piece of alloy by filing slots in the case and a point on the new piece ends. Then JB weld into place. Good alloy welders are hard to find now!