Adventures in broken rear sprocket bolts

[TedBell]

On my new-to-me XS650, when I took the rear wheel off to replace the tire I noticed one of the sprocket bolts was broken. I removed the other bolts and sprocket, and then with a fair bit of work was able to drill and extract the broken bolt. I figured since I had everything removed I would replace everything with new, so I ordered new bolts and a new sprocket. Got some time last night to work on it. When I went to install the new bolts I ran into some difficulty when one of the bolts would only go in about halfway before being obstructed by something. In the same hole as the broken bolt I had extracted. I removed the new bolt and shined a light in the hole to see what I could figure out. Imagine my surpirse when I discovered there is a second broken bolt that was below the broken bolt I extracted! Aargh! I'm guessing whoever installed the second broken bolt probably broke it forcing it down on the original broken bolt. Fun times.

Thanks,
Ted

 

[Jim]

The joys of working on bikes almost half a century old....
Good luck to ya!

 

[gggGary]

Think of that as a warning of fun yet to come.



You will quickly learn to trust nothing anyone else has done on that bike.
If you didn't know LH drill bit sets are the mechanics friend.

 

[Jim]

Throw some bike pics up here. In case you weren't informed... we like pics here.

 

[5twins]

Those sprocket bolts can be a bitch, lol. They're an M10 fine thread. On the drum wheels, their holes are open on the back, into the brake drum area, and that allows all kinds of crud to get in there. Once you get the old ones out, be sure to use some anti-seize on the new ones so they'll come out easily the next time.

 

[jetmechmarty]

Those sprocket bolts can be a bitch, lol. They're an M10 fine thread. On the drum wheels, their holes are open on the back, into the brake drum area, and that allows all kinds of crud to get in there. Once you get the old ones out, be sure to use some anti-seize on the new ones so they'll come out easily the next time.

I had one back out, even with the lock plate on it. That bolt hitting the swing arm will get your attention!

 

[Jan_P]

M10 is a fairly large bolt .. Normal strength class 8 .8 has a tightening torque of about 47 Nm
typical
say the wrench is 1/3 meter you need to pull 15 kg.
there is marginal to breakage say 20 - 30 %
So the mechanic has maybe pulled at " King Kong " force and done it twice breaking 2 bolts
If i get this right
Dont remember how it looks but if it is aluminum threads less force than 47 Nm is used


About that

If not used an air driven tool for auto wheel bolts ..
Maybe not an experienced MC mechanic Inspection of the threads is something to do after drilled
everything out . I suspect the thread is gone ...in that hole

 

[TedBell]

Inspection of the threads is something to do after drilled
everything out . I suspect the thread is gone ...in that hole

I agree on the inspection. I hope the threads are still decent. We will see.

Thanks,
Ted

 

[gggGary]

Those threads tend to be really deep (long) IIRC some years have steel sprocket thread insert collars cast into the aluminum hubs.