Tycho Brahe 

Yes, common problem. I actually might know the cause, but I am hoping it might not be the case. I posted before that my cranks were creaking after installing new chainrings and it was resolved by applying anti-seize to the bolts. Problem is back, so let's start from the top.

I replace my chainrings 3 months ago, replacing the original Rotor chainrings with Praxis chainrings after 9400 miles. I did the job myself, with no torque wrench. Minor creak started to appear, but stopped after applying some anti-seize. Eventually my mechanic torqued the bolts.

The problem eventually returned with a vengeance about a month ago. Really loud. The PF30 bottom bracket was installed in April and did not even have 2000 miles, but my mechanic thought it might need to be serviced. When he removed the cranks, he noticed it was dirty, so a simple cleaning should work. THEN he noticed that the lockring that connects the crank arms to the spider was loose. Problem solved. Issue was that it was not able to be fully tightened. Something was worn, but it is impossible to tell what. The lockring, the crank, who knows? The solution is new cranks, including a bottom bracket if I go to Shimano. After tightening as much as possible, the problem went away. It is now back, but only under duress while climbing. However, I climb all the time!

Hoping for a much cheaper solution. Here are some scenarios that I am hoping for.

• The lockring does not tighten, but it only clicks when applying force in either direction. Since cranks are always rotated in one direction, the "click" should be in one position. Of course, it could just be loose again.
• The bolts were cleaned, but no lube was applied the second time. Could that be the cause?
• The bolts are original and were not replaced with the new chainrings. Could different wear be the issue?

I only own this one bike which I abuse. I do nothing but climbs, averaging over 100ft per mile, so a lot of stress in the small chainring. Current stats: bottom bracket 2,154 miles, chainrings 1,774 miles, chain 3000 miles. I will be going to the mechanic tomorrow to replace a bent spoke. I tend to do most jobs myself, but nothing involving expensive tools. Truing wheels is one of those tasks I do not do.

cpach

What crank is it exactly? You don't state directly but I infer a Rotor. There's not enough information for me to make an informed guess about what's up with the spider lockring--obvious causes could be stripped threads on either the lockring of the crank, stripped tool interface, or some kind of mechanical interference keeping the lockring from advancing as far as it should. This should be diagnosable with the spider disassembled. It also may be worthwhile to reach out to Rotor (or for the mechanic to do so).

Tycho Brahe 

It is a Rotor crank. According to the mechanic, it is impossible to visually diagnose were the wear is. It could be in any of the pieces, but you would need to replace them one at a time to find the culprit.

cpach

Rotor makes multiple models. Given lockrings are not that expensive I'd give that a shot. If it's been less than two years and you are the original purchaser it should also be under warranty if the spider lockring interface is failing.

Tycho Brahe 

Thanks again for the quick response. And forgive me if then I never responded, but I know the truth at heart, and I cannot bear to accept it.

After a bit more explanation, the issue is not the lockring, but the interaction between the spider and the cranks. The cranks are not one piece, so there is now wear between the teeth of the crank and spider (where they attach). Tightening the lockring can help minimize the movement, but ultimately there is little to do. My mechanic has an amazing eye for problems, but I was hoping that with his speed, he perhaps did not lube something. I do not remember him applying anything to the bolts, he said he did.

Disappointed that this will be a costly fix. Apparently these are nice race cranks, and racing components are not meant to last as long as I have been using them. And of course, the issue starts not too soon after the two year period.

Andrew R Stewart 

Some race equipment makes for frustrating club/local riding (meaning pretty much all riding where a mechanic isn't dealing with the bike weekly) because the trade off for weight loss or starting line bling is poor long term function without that frequent attention. One of the challenges the average non racer has is finding the balance between the click and play with little later maintenance stuff and the stuff that sets off his ego. This tipping point is shifting as the big companies make their top shelf stuff more and more race focused and the smaller companies that are trying to keep up in an oversaturated marketing world. Andy

3alarmer 

...the only reason cranks are designed like this (with a separate spider and chain ring), is to allow for replacement or change in gearing of the chain rings.

If you are happy with the gearing selection on your crank as it now sits, it's not a big job to remove, clean the surfaces at the interface, and reattach the chain rings, using a bedding compound like the ones used in rebuilding IC engines and bedding the bearing journals. You'll probably never be able to separate the rings from the spider again, but you will be able to get a few more years use out of your crank.

Anyway, in your situation, I would try that. Google Loctite to get their website, then select for bedding compounds. they have considerable shear strength and compression resistance, and are designed to fill small spaces like this to minimize movement when clearance issues arise with wear.

Tycho Brahe 

The issue is not the interaction between the spider and the chainring, but between the spider and crank. They are two separate pieces that are the fixed together with the lockring, whereas other cranks are one piece.

Although the pieces in question are different, the principal is still the same. Such a simple solution! My mechanic said it would be difficult to tell which pieces has more wear, the spider or the crank, so it would be difficult to replace simply one of them. Why not fuse them together. Almost zero cost to try.

EDIT: trying to find pictures to illustrate the interaction.
In the product PDF, it shows the drive side assembly as one piece (labelled H), but it is in fact three pieces https://rotorbike.com/catalog/default...ser_manual.pdf

In another PDF, the drive side assembly has a warning of DO NOT DISSASEMBLE. That's where the problem lies. I doubt there are even separate pieces to purchases even if I knew which one has the most wear. https://www.rotorbikeusa.com/pdf/3d_manual_8-18-10.pdf