keraba2

I have a GRX FC-RX600 going through a First Components P237SA eccentric bottom bracket. After maybe a year of use, the crank axel is a little loose. I noticed when I was pedaling that, at a certain spot, it would "tick". I can feel the far arm move when I move the near arm, so I know it's the axel that is loose, not the crank arm that is loose from the axel.


The strange thing is that it is only loose when the arms are straight up and down. When the arms are level to the ground, it's as solid as I would expect.


Have I simply worn away the bearing race in that spot while cranking away up hills? I would take it apart but I'm not sure that my eyes would even see the difference, and wanted to check with the group first.


I've heard of Walmart bike bottom brackets dieing after a year (maybe due to lack of bearings?) but never "real" components.


thanks for any insight

oldbobcat

Your first job is to figure out where the looseness is. Is it the crank interface to the spindle or is it the spindle interface to the frame? You should be able to figure this out without taking anything apart. Like, for instance, when you wiggle one crank, does the other one wiggle in response?

keraba2

Hi oldbobcat,

Thanks for the reply. Once again, yes, "the other one wiggles." The bottom bracket does Not wiggle. The cranks wiggle only when vertical.

Is it toast?

zandoval 

Sorry... Little confused... Is the crank armature doing the wiggle or the crank arms?

sweeks

Sounds like the cranks and spindle are moving as a unit.

FBinNY 

While bearing wear in one axis only is possible, (typical wear pattern for heavy duty lathes) I've never heard of it on a bike. In any case, it would take a ton of miles and/or a seriously crappy BB.

Keep in mind the possibility of the entire unit moving with respect to the frame. This is actually more common.

Given that you've already done the diagnostic, you might as well open it up to confirm, and repair or replace as needed.

Kontact 

What's a crank armature?

keraba2

FBin NY,


Indeed, to do this at one spot in the rotation would require wearing in the _race_, not the balls. I can't even imagine. But neither side of the BB moved when I jiggled the cranks.


I have now done a little research and replaced the BB with a Dura-Ace + chain tensioner (which is noisy and stiff so the bike is essentially useless.) Someone on another site ran into an issue with this BB and blamed the tiny bearings that they claimed it has. (Note that I can't confirm. I have not torn apart either end.)


When I rotate them, they behave... strange. The inner sleeves - sorry, not sure what else to call it, but the thing that the spindle rests within - want to _stop_ about half-way around each revolution. The sleeves on both sides do this. So _something_ happened to the races. They also seem a little loose in the axial direction, but this may be ball wear or just manufacturing tolerance.


Unfortunately, I can't tell you how they behaved when I installed them, but this current behavior doesn't seem right at all (compared to other BBs that I've installed.)

sweeks

He means "crank axle" or "spindle". Sounds more like an electric motor, though.

zandoval 

You are right, sorry... For lack of a better term. I was confused as to weather it was the Crank with Spindle or Crank arms. So I just called the whole Kit and Caboodle an armature. I guess I could have called it an Axial Alignment Adjusting Coupling with Drive.

Of course I have never really gotten close to an Eccentric Bottom Bracket that I know of. Still I find the problem interesting. If I was having the same problem I would certainly be upset. I might even ask the geezers on the bikeforum for advice. Just ta see If they were interested...

Kontact 

It strikes me that the problem with this BB design is that getting the right and left eccentric aligned with each other comes down to feel, rather than the two being mechanically linked or having guide markings:


I would suspect that the problem is that they aren't even and the spindle is not parallel to the bore of the BB shell.

Iride01 

I can't fathom the purpose of that BB. But are you certain you put it, the BB, together properly. Or might that play be necessary for it to work and do whatever it is that BB is supposed to do for you?

https://www.firstcomponents.com/wp-c...2-assembly.pdf

Kontact 

Eccentric BBs allow you to change the chain tension on a fixed drive system - like a single speed. Or they allow you to adjust BB height.

This unit allows you to do so on bikes not designed with an eccentric in mind.

Iride01 

Yes, but didn't imagine this was a fixed singe speed bike. With a GRX crank it seems like the chain line would be way off. Or is this an IGH on the rear with no adjustment?

Kontact 

Not if you are adapting a geared bike to single speed. The eccentric does the job of the missing horizontal dropouts.


Other possible problems with this system: You could have one eccentric loose, and it is what is moving vertically.

keraba2

Kontact,

You certainly don't want the two halves being completely (180 degrees) different. You couldn't slide the spindle through in this state. But if the two halves are a couple degrees different, I doubt you or the BB would even notice.

Iride01,

The point of an eccentric BB is to be able to adapt to the quantized length of a chain by being able to adjust the distance, at least within a single chain link. They're used for bicycles without track drop-outs *or* a derailleur:
- trying out fixed gear or single speed on a non-track bike
- putting an internal hub gear on a non-track bike
- tandem bicycles which have to have a chain between the riders' cranks

In my case, I have an IGH because the derailleur hanger broke.

Kontact 

A couple degrees different would be a very big deal, and would lead to the bearings being damaged in use from the side load of being twisted to try to align with the spindle.

So if you didn't think it mattered when you assembled it, that is likely why it is now not functioning correctly.

Kontact 

Another effect of having the spindle not aligned is that the bearings could wallow out their hole in the eccentric, ovalizing it. So bearing damage you could fix with new bearings, but damage to how the bearings are seated in the eccentric might require replacing the entire unit, or at least using Loctite 609 or some other gap filling agent to keep the bearings centered.

keraba2

Kontact,

Please don't assume that I "didn't think it mattered". I aligned them when I installed it, and they were still aligned when the issue manifested. I'm simply pointing out that, while there is a lot of movement of the spindle when you rotate one shell when they are out of alignment, there is NO movement when you rotate one shell when they are nearly aligned, and that I don't think this is what caused the issue.

Kontact 

I don't see how this pertains. If there is no movement of the spindle, that could be because the spindle is wedged between two non-aligned bearings.

One way to align the spindle on initial installation would be lock down the drive side, set your bearing preload, and then rotate the non-drive side back and forth to find whatever rotational range it has, then set the NDS in the center of that range and lock it. Then recheck pre-load and tighten crank pinch bolts. That might not work now if something is damaged, though.

keraba2

Oh yay. Let's play, "Let's speculate about a BB we've never seen and ignore the written instructions." hmm...

I'm quite certain that I've gotten everything I'm going to from this thread. I'm out.

choddo

A question born of absolute ignorance - what purpose does a bottom bracket like this serve?

FBinNY 

Eccentric BBs are the smart way to work a single speed or fixed gear hub on a bike with vertical dropouts. They allow a simple and reliable to adjust chain slack, not relying on moving the wheel.

The concept is neither new nor unique, having been SOP for tandems for half a century. What is different is that with fixed and SS now trendy, we have a greater need as folks convert vertical dropout derailleur bikes to SS.

FBinNY 

Not quite.

Given that you've gone to a conventional BB and chain tensioner and not pleased, you might reconsider the Eccentric BB, though perhaps another brand.

One reminder ---- just in case ---- Proper SS chain tension is ZERO tension, requiring some slack to work right. Running with tension in the return (lower) causes greatly increased noise and chain, sprocket and bearing wear.

choddo

Thanks. I did wonder if it might be related to fixies. And apologies, Kontact and Keraba2 had already answered this, I somehow completely skipped that part of the thread.