Bottom Bracket Spacer

itboffin

I know each manufacturer has different requirements and arrangements of bottom bracket spacers but i'm curious to know if missing out .5 or 1 mm of spacing has a significant effect of longevity and or performance?

Having fitted lots of types of BB i've only had to use spacers on MTB fittings so i fitted a Token TK877TBT a few years ago without the .5 mm each side the manufacturer specifies, in part because it came without install instructions and i ASSumed it would be the same as a Shimano BSA 68mm.



I removed this to replace it with a SRAM GXP BB and crankset, which has now died leaving me with the Token + R23 adapter, the Tiramic bearings feel rough i'm wondering have i killed this BB as well?

Always RFTM

nicklouse

Ok let us look at the shimano set up. On these the bearing need to have a minimum distance between their outer faces. This is so that the bearings can be correctly preloaded before the crank arm bottoms out on the axle shoulder of splines.

Now let us look at the SRAM set up. This does not use preloaded bearings so there is a maximum distance between the bearing faces so as not to preload the bearings and kill them. The SRAM drive side bearing is just free to rotate while the ND side does the locating as well.

So now you want to use a different bearing set up. Here is the fun bit. Have you damaged the bearings by over tightening them or by not tightening them enough.

Fun ain't it.

itboffin

well i have the adapter fitted but no spacers and there is a little play, its also a tad rough therefore tomorrow morning i'm going to try it again with the 2 x .5 mm spacers

then there's the small matter of torque settings, i have a large torque socket which i suspect is useless

nicklouse

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19627163#p19627163]itboffin[/url] wrote:

well i have the adapter fitted but no spacers and there is a little play, its also a tad rough therefore tomorrow morning i'm going to try it again with the 2 x .5 mm spacers

then there's the small matter of torque settings, i have a large torque socket which i suspect is useless

SRAM cranks? Then spacers are not part of the set up. As the cranks are clamped on a single bearing race.

If you have play then that is the bearing that has it. Adding spacers will not allow you to correctly tighten the Nd arm onto the axel without possibly crushing the DS bearing.

Rightarmbad

Straight out of the SRAM manual for GXP installation:

Install the non-drive side crank arm onto the crank spindle and use
a torque wrench with an 8 mm hex bit socket to tighten to
48-54 N.
m (425-478 in-lb).
Check the assembly for play by rocking the crank arms back
and forth away from the frame. If the crank moves, tighten the
crank arm bolt until no play is detected. If maximum torque of
54 N.
m (478 in-lb) has been achieved, remove the non-drive side
crank arm from the spindle, apply additional grease and repeat
installation procedures until play is eliminated.

itboffin

Yep its not a SRAM BB its a Token see the diagram above where it states 2 x 0.5 mm spacers for BSA Road 68 mm

itboffin

Ha I got a reply from token which started with thanks for the very technical question then said after checking their docs it does need spacers which is in fact the opposite of their documented recommendations

Happy days