47t sprocket & chain replacement; sprocket bolt hole stripped
 

I'd been meaning to fit my 47t rear sprocket for a while, finally my new Unibear chain arrived and I decided to fit it today.

I remembered how much I hate dealing with wheels...but everything was fine, however the four sprocket flange bolts were very tight; I couldn't budge them using my short 12" breaker bar. I use power tools as a last resort, and for the first time since removing my Kawi sprocket nut last summer, I got my trusty harbor freight impact wrench out of its box. The impact wrench struggled a bit but got the bolts out. They looked in pretty good condition, but I was a little concerned about the holes.

When I put the new sprocket on, I actually under-torqued the bolts. Not being able to find specific values, I played it safe and looked up M8 general specs and chose 12-13 ft-lbs. This felt loose to me, so I looked further and foundCSC's updated tutorial and saw they call for a whopping 35 ft.lbs - the same as the axle nut.

I backed them out slightly and re-torqued, and the second one I got to immediately span round with no resistance - the threads in the hole were gone; this was barely re-tightening (maybe one full turn) it after backing it out a little.

I'm a little bit annoyed as I was looking to test the bike today, and of course i have to have the damn wheel off again...

I might let CSC know, but I think all they could do is offer a new wheel. I might go for a helicoil kit as I suspect the other holes are in similarly poor shape and I'm not confident they'll take 35 ft.lbs from what appear to be very hard bolts.

I'm guessing they were way tighter than 35ft.lbs from the factory; they did not appear to have any threadlock on. I was honestly expecting to shear the heads straight off.

You could try a timesert repair. They are way better than a helicoil.

https://www.amazon.com/s/ref=as_li_s...6ee773b37700bf

I think that is probably preferable for this application, but the cost of a kit is getting near a replacement wheel. As this wheel has been through a winter and is pretty weathered anyway, I need to decide what to do.

I've mailed CSC for advice, if I need to spend some money so be it, but I think they were way over-torqued from the factory and this is likely a factor.

CSC said a helicoil would work, and indeed it did. I was surprised how easily the various tools ate into the hub. It's pretty soft.

Only one thread needed fixing, the rest were okay. Pretty happy with the 47; it's had virtually no effect on the bike's pull but the rpms are a lot more civilised at 60mph.

I actually called CSC and talked to Gerry when I swapped to my 45 tooth rear to ask about the torque spec and he said that they should be torqued to 15 ft-lbs. So that's what I torqued them to with a little blue Locktite just to be sure.

Yes, I thought it seemed high but I've looked at torque specs for various m10x1.25 bolts (I thought they were m8) and they'll take 35.

Interesting thread.... This same thing happened to me on Monday. I stripped out 2 of the four threads in the hub. I re tapped deeper and got longer bolts from my hardware store. I wish I had know only to torque to 15 Ft Pounds and would not have stripped out hub threads. A note for those changing out sprocket get longer fine thread bolts as you loose about 1/4 thread engagement because of spacer washers to maintain the sprocket offset. I used loctite red 680 to hold them in.

The hub is very soft. I was surprised how easily I could drill out the hole, It was like wood. and the tap cut the metal very easily too. I spent a lot of time cleaning the bolts and chasing out the holes as I think a lot of swarf was in them.

I didn't loctite the old ones, just the helicoil.I did tighten to 35ft.lb very, very carefully and they've been fine.

These things happen on bikes but it's always a pain when you don't have the bits you need available.