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Ambisinister
10-15-2017, 07:54 AM
Hi all,

I own a Big Boy TSR 250, a South African re-brand of a Hi-Bird. About a month ago third gear disappeared and was replaced by the sounds of grinding gears. I set off stripping the motor to try find the source of the noise and the cause of the issue.

After making good progress over the past few weeks, I made a rather large mistake, in attempting to remove the nut on the balance shaft to split the crank (which didn't really need to come off). I managed to strip the nut and quite badly damage the threads on the balance shaft.

https://photos.app.goo.gl/9dBTI0GTQ3Qsj4cG3

https://photos.app.goo.gl/WUF7zZ5McnPmQ8R02

Is there a good place to get a replacement shaft and nut, i'm struggling to find one online that looks like mine?

Is there something else I can do to fix this, my thoughts have been to get a machinist to machine some new threads on the shaft and make a matching nut. I've also thought of using a die to true up the shaft, but as it is a fine pitch left hand thread it would probably easier to get a new shaft.

Thanks.

PS:
I found third gear in pieces in the bottom of the crank case. Ill have to replace the main and counter shaft gears, but I can get those parts locally, so no issue there.

Mudflap
10-15-2017, 08:51 AM
The balance shaft nut on my Lifan has a left hand thread. Wonder if you could just remove the balance shaft completely.