Its a 36mm nut and the std chain is 122 links for the XC and 120 links for the roadie.
There is a lockwasher crimped on to it.
I just changed the front sprocket -1T to a 15 tooth.
What I did..
remove 8mm bolt holding gear shifter.
remove 2 x 8mm bolts holding sprocket cover on.
Un-crimp the lockwasher carefully.
slide on the shift linkage temporarily*
put in neutral and get someone to operate the rear brake
I used a rattlegun to remove the sprocket nut - its on tight with threadlocker.
take off shifter linkage again
slipped the chain and sprocket off the spline without adjusting the chain tensioners - there is about 35mm of slack and you can rotate the sprocket as you remove to gain some slack - sounds odd but when your in there you will see what needs to happen.
put on new sprocket - tip fit chain to sprocket to chain THEN slip both on spline again get some clearance by rotating the sprocket same as when removing.
put on lock washer BUT don't crimp it there yet.
threadlock sprocket nut, install to 85Nm (93ft/lb) torque and crimp lock washer again.
adjusted chain tension to 35mm slack.
replaced sprocket cover used threadlocker on bolts.
replaced gear linkage bolt - use threadlocker here too.
Took for blat and enjoyed the extra pickup and low speed rideability.
Riot screwed with this post 11-05-2012 at 04:39 AM