Cranks?

[Colinmclelland]

Misaligned would create a circular mark, because it would be misaligned for the circumference of the rotation. Loose seems more likely, because it would rub unevenly based on contact created by uneven pressure. If the bare patch faces up when the drive side crank arm is pointed at the ground, then I'd say that something loose on the drive side is allowing the spindle to act like a lever against the NDS bearing.

If anything was loose it must have been the wave washer not being wavy enough! When taking it apart the fastener was still correctly torqued to tight as buggery

But no - the bare patch is in the same direction as the crank arm...

[Sascha Roszak]

Misaligned would create a circular mark, because it would be misaligned for the circumference of the rotation. Loose seems more likely, because it would rub unevenly based on contact created by uneven pressure. If the bare patch faces up when the drive side crank arm is pointed at the ground, then I'd say that something loose on the drive side is allowing the spindle to act like a lever against the NDS bearing.

Trying to think this out in my head too but this sounds the most plausible to me.

[RichTheRoadie]

Haven't seen mention of Rotor Aldhu/Vegast here, both available in 24 and 30mm spindles. What do people think of them for this situation -- or overall?

I'm a past Rotor fan. The 3D+ was a lovely crank. I have no reason to doubt the Aldhu and/or Vegast, but the 4-arm design doesn't appeal to me as much. The modularity is good if you need it, though - the 24mm axle option means it makes for a nice alternative for Giant or older Trek BBs that could otherwise only take 24mm chainsets.

Sorry if I missed this, but are the bottom bracket bearings pressed in or threaded in? If they're pressed in I suspect a poorly aligned bearing is the culprit here.

I believe it's the threaded T47 Praxis BB - the Praxis 'M30' BB format has the same step-down approach as SRAM GXP, except it's a 30>28mm step-down on the NDS.

But no - the bare patch is in the same direction as the crank arm...

Same direction as which crank arm? Can you share a more descriptive pic?

[Mark Kelly]

We can derive that info from Colin's pic in post #22 since Praxis cranks have the label on the spindle aligned with the drive side crank arm.

With the drive side arm at 12 o'clock the damage appears to be from 1 to 3 o'clock so it's about 60 degrees out of phase with the crank axis.

[Colinmclelland]

Same direction as which crank arm? Can you share a more descriptive pic?

Yeah sorry, I just noticed I read Jorn’s highly ambiguous drive side reference as NDS. You get what you pay for!

[j44ke]

We can derive that info from Colin's pic in post #22 since Praxis cranks have the label on the spindle aligned with the drive side crank arm.

With the drive side arm at 12 o'clock the damage appears to be from 1 to 3 o'clock so it's about 60 degrees out of phase with the crank axis.

Ah well, that makes more sense actually for something loose. Pushing forward and then down on the right crank arm.

But still could be caused by other parameters not just adjustment.

[El Chaba]

It amazes me how problematic cranksets and bottom brackets have become since they were improved with oversized axles and bearings, etc....

[sk_tle]

It amazes me how problematic cranksets and bottom brackets have become since they were improved with oversized axles and bearings, etc....

I think everybody has had a few ticking square taper bottom brackets as well.

[thollandpe]

If anything was loose it must have been the wave washer not being wavy enough! When taking it apart the fastener was still correctly torqued to tight as buggery

Is the wave washer supposed to go on the right or the left side?

[j44ke]

Is the wave washer supposed to go on the right or the left side?

I think on those cranks it goes on the right/drive/chainring side. Should be switched out whenever bearings are done. They are not immortal.

[thollandpe]

I think on those cranks it goes on the right/drive/chainring side. Should be switched out whenever bearings are done. They are not immortal.

Which side did @Colinmclelland have it on? Is is possible that the left crankarm was bottoming against the outer shoulder or spindle end instead of properly clamping the inner race of the bearing?

[RichTheRoadie]

If 180s will work for you, @Colinmclelland, you might want to have a word with @Clean39T about his ad across the hall...

[Colinmclelland]

Which side did @Colinmclelland have it on? Is is possible that the left crankarm was bottoming against the outer shoulder or spindle end instead of properly clamping the inner race of the bearing?

Chainring side...

[Mark Kelly]

Ah well, that makes more sense actually for something loose. Pushing forward and then down on the right crank arm.

Not sure about that. The way I see it, since the damaged area leads the DS crankarm by 60 degrees, when the DS crankarm is forward and down the damage would be at the bottom of the BB while the reaction force on the NDS bearing is at the top.

[RichTheRoadie]

Based on that ^^ I’d say out of spec crank arm - then it’s back to a warranty claim, IMO.

[Gattonero]

We can derive that info from Colin's pic in post #22 since Praxis cranks have the label on the spindle aligned with the drive side crank arm.

With the drive side arm at 12 o'clock the damage appears to be from 1 to 3 o'clock so it's about 60 degrees out of phase with the crank axis.

Good point, but it's only part of the whole picture. Ought to be a combination of the whole: manufacturing of the cranks, BB shell, BB cups and last the bearings which are most likely to be be made with the strictest tolerance of the whole ensemble.
And here is the rub. Industrial cartridge bearings of this type do not like side loads, hence the installation could be problematic unless you leave enough tolerance for a "slip-fit", which is bound to give you any sort of trouble. An interference-fit would be much better, and especially where the inner race of the bearing stays with the crank axle. But then you'll have to redesign the whole thing, in a two-piece fashion like the Campag Ultra-Torque and use dedicated tools for bearing replacement (when it needs to).

This sort of marks on external-bearing cranksets are more common than what people can imagine, in fact most of the cranks that I will remove during a service (and I remove/reinstall over two thousand cranksets per year) will show light discrepancy in the form of rubbing where the bearings land.
In most cases this is not a problem, as long the the marks are as even as possible. But the material of the crank axle plays a big role, with aluminium being the most problematic, for obvious reasons. And the quality of the BB threads is just as important as the facing of the shell is.

Like said, it all goes down to the ease and speed of installation, we live in a time where everything has to be churned out as quick as possible, and likely be done by the final user.

[Daschund]

It amazes me how problematic cranksets and bottom brackets have become since they were improved with oversized axles and bearings, etc....

Somehow Shimano managed to make a simple system that works 99,9% of the time. I'm amazed why anyone would choose something else excluding heavy aesthetic preferences.