Stripped threads for sprocket bolts in cast rear wheel (XS650 Special)

[Buccaneer]

Hey all. I found something a bit worrying on my 79 XS650SF (special) last week. The heads of two of the bolts securing the rear sprocket to the cast rear wheel were no longer flush with the sprocket. One was so far out that if it went another couple of mm it could have fouled the chain tensioner or something and locked the rear wheel; not nice! The little bent metal tang that stops the bolts rotating was in place ... a bit manky, but still looked fully operational... I don't think the bolts could possibly have rotated. So of course I levered the safety tangs out of the way and tried to tighten up the bolts. They would not tighten down. On taking them out, the bolt threads look a little bit chewed over a few mm (which corresponds to a point after the bolt going through the sprocket and where it would mate with the top of the thread in the wheel) but anyway the bolt threads certainly not gone completely and futher down the bolt (further from the head) looked more or less perfect. Thus, I imagine the threads in the softer (alloy) wheel must be completely shot. Presumably a previous owner must have overtightened them. I've had the bike a couple of years, only do low mileage - maybe 2k a year, and have never touched those bolts before.

So my questions are: is this a known problem? Is it both possible and advisable to helicoil the threads in the rear wheel? If so, would it be necessary to increase the bolt size? Any special spec on those bolts? Would it be better to just buy a used rear wheel on eBay and swap the rest over? Any other advice?

 

[gggGary]

Threads are standard metric fine, the bolts are high spec and the full size bolt shank ensures the sprocket doesn't move. I think I would first get some longer bolts and see if there is still any good thread deeper in the wheel. If it's just one or two holes, and you can get a longer bolt to hold, I'd put longer bolts in the stripped holes and call it done, maybe some blue thread lok. The length of thread in the wheel, and corresponding bolt length did vary a bit through the years. IIRC many, most, some? rear wheels have threaded steel inserts cast into the aluminum. Keep an eye out for a used wheel? 16" disk mags can be had for about nothing this side of the pond, it may be different in the olde country.

 

[Buccaneer]

Threads are standard metric fine, the bolts are high spec and the full size bolt shank ensures the sprocket doesn't move. I think I would first get some longer bolts and see if there is still any good thread deeper in the wheel. If it's just one or two holes, and you can get a longer bolt to hold, I'd put longer bolts in the stripped holes and call it done, maybe some blue thread lok. The length of thread in the wheel, and corresponding bolt length did vary a bit through the years. IIRC many, most, some? rear wheels have threaded steel inserts cast into the aluminum. Keep an eye out for a used wheel? 16" disk mags can be had for about nothing this side of the pond, it may be different in the olde country.

Hey ggggGary thanks for the super fast reply. Yes it's a disc rear, I should have confirmed that. The stock bolts seem pretty long already and actually the bolt thread that would end up deeper in the wheel looks a bit dirty (as well as otherwise perfect), rather as if the threaded part in the wheel is not very deep and the bolt then goes into either thin air or possibly into an unthreaded hole in the alloy - or something! Spose since I am going to have to disassemble at some point whatever happens, the thing to do is disassemble now and see if I can find out a bit more. I doubt that longer bolts are going to help though, unfortunately. Importing a wheel from USA may well be the answer if none show up locally on eBay, and I can't find a way of reusing the current wheel....

 

[gggGary]

Yes the hub is hollow. Give a helicoil a go (there's a different brand also) seems like a good plan. Check that the other bolts will all hold spec'd torque too.

 

[Ratranger]

Helicoil would be an easy fix, just buy the right kit and it will have the drill bit needed, the right tap, and the install tool.

 

[xjwmx]

My rear sprocket has two helicoils (done by machine shop). No problems. Tried everything else. If you use locking tabs, be sure to not hammer them thin and weak, just up and against the bolt head.

 

[DogBunny]

For what it's worth, Helicoil is a brand name that you probably won't find in the UK. The generic name is "threaded insert" or more specifically "helical insert," or even more specifically "stainless steel helical insert." There are plenty of brands, and they are all pretty much the same. If you're not in a hurry, you can get kits that will work just fine from China on eBay very cheaply.

 

[XSLeo]

I know on the front wheel the cast use a shorter bolt than the spoke. The cast are a blind hole, spoke are open ended.
Is the rear the same way.
So far I've not had any trouble with sprocket or rotor bolts. I have always gotten them out and reused or replaced with te same size. I always chase the threads with a tap before I install the bolts. Proper torque and with the lock tabs or lock washers I have not had any come loose.
Leo

 

[Buccaneer]

Hey thanks all for the useful info. Just a belated completion report here. In the end, getting the other bolts out caused a fairly major prob - two of them seized in the wheel and snapped off. I didn't know I was that strong - it wasn't a very long arm on the socket! A used rear wheel came up on eBay so decided to go with that... cost a lot shipping the wheel from Canada, my fingers were so crossed! ... but all its threads seemed to be perfect so with new bolts (again, luckily, found a set of NOS Yamaha ones on eBay) it all went back together smoothly (for a price). If anyone wants the old wheel with nackered threads and two bolt ends sheared off in it, I still have it lying around and it can be collected FoC (UK, Sussex) or I could put it on eBay with some minimal start price for international, but postage will be a killer. I figure it won't be worth anyone's hassle ... but just in case I'm about to throw something useful on the tip, now it has come to a clear-out?.... Post here if you want it.