XX1 crank mount interface
I am looking at acquiring a XX1 crankset, but am a bit confused about its mounting interface.
Shimanos has a detachable non-driveside arm that has a pair of pinchbolts that squeeze it onto the axle/spindle. FSA is similar.
Raceface has their press fit system, and play is taken up by adding/removing spacers onto the axle/spindle.
Looking at the Sram/XX1 service manual, it looks like it is also a press fit (similar to raceface?) but there is no mention at all of spacers to add/remove play/tension in the bearings.
Then I read this in the manual:
"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"
And now I am super confused, - if there is play, just keep adding grease until it is gone? WTF?
So if anyone can confirm the type of interface that is used on the XX1 cranks (and if grease really helps take up the play - does too much grease cause it to bind up?)
The instructions you give are for a GXP crankset. The play is taken care of by sandwiching the NDS bb bearing between the crankarm and the spindle (there is a step on the spindle). If there is not enough grease on the spindle splines, then the crankarm will not slide on far enough to bottom out on the bearing, hence the instruction for adding more grease. Adding grease lets it slide further with the same torque on the bolt.
Press fit GXP systems work the same way, but they add spacers and a wavy washer to keep the bb adapter cups from walking out of the frame.
BB30/PF30 cranks use an adjuster on the NDS to take up play in the system.
Pretty sure I would be using the GXP bottom bracket (threaded 73mm?)
Originally Posted by Roger that
So the cranks just press up against the bearings of the BB to the tune of 45-54N.m ? Does that not cause premature bearing wear?
I have re-read the SRAM instructions for the GXP / XX1 installation, and there is no mention of preload the way there is for the pressfit / bb30 systems.
I am assuming then that they are expecting the BB that these are installed on to be EXACTLY 68mm (or 73mm) so the placement of their bearings/cups are at a precise point - then when the cranks are torqued properly there is the correct amount of preload on the bearings?
Yes, a threaded 73mm shell would need a GXP crankset. There is no "preload" with a GXP bottom bracket - the spindle and NDS crankarm sandwich the NDS BB bearing inner race. It doesn't put any preload on the bearing, it simply clamps the NDS bearing. This is NOT the same as putting 45 Nm of preload on the bearing. This is what keeps the crankset from moving side to side. The DS bearing is larger and floats on the spindle, which makes up for differences in frame bb width and BB variation.
Hope this helps.
I think I am getting what you are putting down. Sounds like an interesting setup - one I am very interested in trying.
Originally Posted by Roger that
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