[krazymad]

I tore up the threads in my crank when I hastily installed temporary platform pedals and now need to replace my crankset. I have an XTR (M952) crank set laying around and have found the matching BB (M952) for $20. However, I'm concerned about spindle length as my current setup is 121mm spindle and the new BB is 116mm. Will dropping down from 121mm to 116 mm on spindle length be an issue?

The bike is a 2004 Stumpy.

Current setup:
BB = Shimano ES-30 Octalink spline, 68mm shell, 121mm spindle. 50mm chainline.
Crank = M540

New setup:
BB = M952 BB 68mm shell, 116 spindle
Crank = M952

 

[custom_fab]

2 things will be affected. The cranks will be closer to the frame. One chainring may be touching the chainstay - a recipe for disaster. The crank arm spindle could also bump into the frame. This isn't really a factor with MTB, but road bikes experience this alot. Finally, the front derailleur will be effectively moved outward and it may do a poor job shifting into the small chainring in front. A frustrating experience especially if you're climbing hills. So check into the front deraileur / BB compadibility. There's a chart somewhere on SHimano's website. You could also adjust the FD to the inside as much as possible. Then look how 'far in' it is beyond the chainring. If it is 5mm you're fine. If there's no adjustment left to go in then I would say you'll run into a problem there and a new 121 will have to do.

hope that helps

 

[hannibal smith]

Typo? Should be either 112.5 or 116 on the M952 BB.

Unless I am on crack, just run the driveside without any spacer and you should be A-ok- Your legs/body won't be able to tell that you are catty-wompus by 2mm. But there are thicker spacers too with 116 BB- Your chainline will be 50mm??

Somebody with some brains double check my math so that I am not spewing bogus crap! Now I am confused.

 

[Bikinfoolferlife]

The spindle length of the old crank has nothing to do with the new one, they're different matchups. It's in the design of the crank. Since I had pulled out the setup instructions for another thread, here's a cut and paste from that thread:

I happen to still have the instructions for the M952 bb, so here's the scoop. They came in two spindle lengths and you could adjust them with spacers for adjusting chainline for 68 and 73 mm bb shells.

112.5 mm spindle use 2 x 2.5 mm spacers, one each side, for a 47.5 mm chainline on a 68mm shell; for the 73mm shell use no spacers for the 47.5 mm chainline.

116 mm spindle uses 2 x 3.5 mm spacers, one each side, for a 50 mm chainline on a 68 mm shell; use 2 x 1 mm spacers, one on each side, for 50 mm chainline on a 73 mm shell.

If using an E type derailleur bracket, for a 47.5 mm chainline you use the 112.5 mm spindle with a 2.5 mm spacer on the driveside on a 68 mm shell, for a 50 mm chainline use the 116 mm spindle with no spacers on the 73 mm shell.

 

[hannibal smith]

The spindle length of the old crank has nothing to do with the new one, they're different matchups. It's in the design of the crank. Since I had pulled out the setup instructions for another thread, here's a cut and paste from that thread:

I happen to still have the instructions for the M952 bb, so here's the scoop. They came in two spindle lengths and you could adjust them with spacers for adjusting chainline for 68 and 73 mm bb shells.

112.5 mm spindle use 2 x 2.5 mm spacers, one each side, for a 47.5 mm chainline on a 68mm shell; for the 73mm shell use no spacers for the 47.5 mm chainline.

116 mm spindle uses 2 x 3.5 mm spacers, one each side, for a 50 mm chainline on a 68 mm shell; use 2 x 1 mm spacers, one on each side, for 50 mm chainline on a 73 mm shell.

If using an E type derailleur bracket, for a 47.5 mm chainline you use the 112.5 mm spindle with a 2.5 mm spacer on the driveside on a 68 mm shell, for a 50 mm chainline use the 116 mm spindle with no spacers on the 73 mm shell.

Thanks! There it is- I won't admit that I am still confused though.

 

[Bikinfoolferlife]

Thanks! There it is- I won't admit that I am still confused though.

About seeing Mr T?

You could also get creative with spacers and do your own thing, like you said in the other thread...this is just Shimano's recommended setup. It's not like you're setting preload on the bearings (which negates as much flexibility in setup on say an external bb Shimano crank).

 

[krazymad]

Thanks Bikinfoolferlife, perfect information! I'll be going with the 116mm spindle and 2 3.5mm spacers on a 68mm shell. Derailleur is standard so no e-type stuff to mess with.

The spindle length of the old crank has nothing to do with the new one, they're different matchups. It's in the design of the crank. Since I had pulled out the setup instructions for another thread, here's a cut and paste from that thread:

I happen to still have the instructions for the M952 bb, so here's the scoop. They came in two spindle lengths and you could adjust them with spacers for adjusting chainline for 68 and 73 mm bb shells.

112.5 mm spindle use 2 x 2.5 mm spacers, one each side, for a 47.5 mm chainline on a 68mm shell; for the 73mm shell use no spacers for the 47.5 mm chainline.

116 mm spindle uses 2 x 3.5 mm spacers, one each side, for a 50 mm chainline on a 68 mm shell; use 2 x 1 mm spacers, one on each side, for 50 mm chainline on a 73 mm shell.

If using an E type derailleur bracket, for a 47.5 mm chainline you use the 112.5 mm spindle with a 2.5 mm spacer on the driveside on a 68 mm shell, for a 50 mm chainline use the 116 mm spindle with no spacers on the 73 mm shell.