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My (78) Darmah keeps breaking the sprocket to carrier bolts. Its not that they break weekly but I certainly have to replace 1 or 2 a year. The bolt that just broke is a Grade 5. I also have them safety wired as the stock sprocket lock tab brackets got wiped out by previous broken bolts and I figured it would be a little safer than the bend over tabs.
There is no indication that there is a mechanical issue with the carrier and certainly no visible damage at all. I have been fortunate to catch when these bolts have broken and not had them cause any damage on the way out. I am going to use Grade 8 bolts to replace all the existing Grade 5 bolts. I'm not sure what came with the bike as I started having the problem with them breaking in 81-82 and soon all the made in Italy bolts were long gone.
I ask you guys about my problem and if you think I have another issue thats causing the problem. I would of thought Grade 5 hardware would of been more than sufficient.

Ghostdog wrote:My (78) Darmah keeps breaking the sprocket to carrier bolts. Its not that they break weekly but I certainly have to replace 1 or 2 a year. The bolt that just broke is a Grade 5. I also have them safety wired as the stock sprocket lock tab brackets got wiped out by previous broken bolts and I figured it would be a little safer than the bend over tabs.
There is no indication that there is a mechanical issue with the carrier and certainly no visible damage at all. I have been fortunate to catch when these bolts have broken and not had them cause any damage on the way out. I am going to use Grade 8 bolts to replace all the existing Grade 5 bolts. I'm not sure what came with the bike as I started having the problem with them breaking in 81-82 and soon all the made in Italy bolts were long gone.
I ask you guys about my problem and if you think I have another issue thats causing the problem. I would of thought Grade 5 hardware would of been more than sufficient.

Hey Ghostdog,
Just a thought. (Dangerous for me sometimes. ) Are you sure that all of the distance spacers are in correctly? If they are not you could be stressing the carrier and causing the bolts weaken over time.
Dean

Are the rubber sushes in good shape..ne exeseive play? Is the wheel tracking completely straight ?

All the spacers and bushings appear to be correct and match the manuals I have. The cush looks OK but maybe I should give it a more critical look. While the bike is a daily/weekly driver it doesn't have a lot of miles on it, still under 20K.

Got a picture of the broken bolt .. might show up whats going on .... just a thought.

Ghostdog,

I strongly suspect that unfortunately the problem isn't with the bolts, it's with the aluminium carrier holes. Further without the correct 'fix' the problem will just get worse.

The holes have become elongated (oval shaped) allowing the bolts to move backwards and forwards as you accelerate and downshift. This movement weakens bolts till they break. Elongation may not be visible to the naked eye but it only needs to be a few thou to allow movement.

Solution is to have the holes milled out so that they are truly round again and then press fit steel sleeves. Inside diameter of sleeves obviously needs to match bolt diameter. This isn't a job for the home drill. Best done by an engineering shop to ensure accuracy.

Mick

Thanks Mick! I'll measure the holes (in the morning) and post what I find.