47t sprocket & chain replacement; sprocket bolt hole stripped

Sullybiker · 03-26-2017, 05:02 PM

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.

03-26-2017, 05:02 PM	#1
Sullybiker Join Date: Dec 2016 Location: Western PA Posts: 363	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.
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