My crank arm was aligned in the middle of the P2M power meter. What happened here and is it something I need to be concerned about? I’m annoyed I’m going to need to take the crank off to align it again.
1 Like
You’ll need to take it off to figure it out, but something is very wrong.
4 Likes
I don’t even know when this happened. I don’t notice anything when I am out riding. Did the BB just slip or something?
How is the spider attached?
This is about the crank and the spider (power meter), not the BB. I’d guess that whatever is holding your PM onto the crank (usually a lockring of some kind, I forget what the actual Rotor arrangement is) has come loose and allowed the crank to move. Get it sorted ASAP as if there’s something allowing this to happen it’s likely to be causing damage.
I have the same pm and chainrings, as well as a Rotor crank (Aldhu 24). I have had nothing but problems with the Rotor crankset. I hope you’re able to figure this out.
aldhu cranks hold the spider by sandwhiching it against the axle.
the steps to remediate is completely undo the big bolt in the middle of your cranks. i find it easier to have the non-driveside crank removed as well (also a big bolt… but the one on the other side).
the spider should sit on a splined interface on the drive side crank arm. it’s not a very thick spline though. to me that would point to the main culprit (and definite reason to stop riding and fix) is the drive side big bolt got loose.
2 Likes
Thank you for this info, when I have a little bit of time, I’m going to dig deeper into it. Unfortunately this means I’ll have to get my backup bike up and running, haha.
i said steps then listed one step.
undo the crank side crank/big bolt
take the spider off the crank (no tools necessary, it will almost fall off)
(inspect for issues with the crak or spider spline)
realign spider on crank spline
redo the crank side crank/big bolt
1 Like
check the matching spline on the spider.
if they’re all lovely formed splines, pop it all back together and torque to the appropriate specs
I suspect the spider was misaligned since the last time it was serviced. There’s also the possibility that the right bolt was loose (was it?) and that allowed the spider to slip relative to the spindle.
It could not have been the arm moving relative to the spline. Besides the sheer size of the spline teeth, the left arm is inline with the right.
The splines that hold the spider look sharp so that hasn’t slipped, but I’d be a little concerned about the damage to the cup as it might indicate that there isn’t enough clearance between the crank parts and the cup?
With the spider aligned and the crank torqued correctly to hold the spider in place, does everything spin smoothly with no tight spots?
The damage to the BB cups looks like damage from a slipping (maybe due to ill fitting) BB tool.
First picture is missing the self extracting cover and a shim that goes under it, picture below. Doesn’t lead to crank-spindle interface slipping, but with seemingly undamaged spindle splines leads me to think maybe installation error?
I have a number of Aldhu and Zegast cranks in the stable and that is the only explanation that makes sense to me too. In order for the spider to come off its spline and rotate, the crank would need to be quite loose, which would damage its splines. I also can’t see the spider spontaneously hopping back onto its splines and, even if it did, there would still be the issue of the loose crank.
1 Like