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#895738 11/18/22 3:59 pm
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jfligg Offline OP
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Hello I was wondering if anyone has repaired triumph unit cases that are broken above the primary chain. Thanks Jeff

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Broken due a final drive chain failure? - yes

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It needs a very good welder to avoid distorting the primary

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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.

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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

Last edited by NickL; 11/19/22 6:51 am.
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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.

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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

Last edited by dave j; 11/22/22 5:39 pm.
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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!


1958 5TA / T100
1967 T120R
1969 TR6C
1970 TR6C

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