rousseau

How did this happen?

I've got a ten-year-old carbon Centaur Ultra-Torque crankset. The last few days there has been a disturbingly loud creaking noise when climbing steep hills. One per crank revolution, and louder as the effort was harder. It would go away as the terrain levelled off. Having searched BF for suggestions (what a terrific resource this is) I decided to go out and lube my new-ish chain, having not done anything to it since I got it. In the process of going over the drivetrain I discovered that my big ring was wobbling side to side as I turned the crank.

Whoa! Crazy. I could manually move it back and forth a good several mm, it was that loose. The four chainring bolts away from the crank arm were practically on the verge of falling off.

So, two weeks ago I replaced the original big ring with a 51-tooth TA ring, but I know for absolutely certain that I greased the threads and tightened those bolts up properly. There is simply no way that I would have put it on and neglected to tighten four of those bolts while tightening only the crank arm bolt. I'm not that scatter-brained (yet).

What gives?

MoAlpha

I don’t know what bike folks have against threadlockers, e.g., Loctite or Permatex. They’re just as good as grease for preventing seized fasteners and keep them from vibrating/working loose.

Wouldn’t think of NOT using it for any critical automotive or marine application.

rousseau

Maybe I'll have to give that stuff a go. But this was just a totally bizarre thing that I didn't see coming. Since when do four chainring bolts come loose like that? In all my years of riding I've literally never encountered such a thing before.

MoAlpha

Dunno, but I’ve certainly had a couple get rattling-loose simultaneously and once there’s play, they all go.

TimothyH

+1 on threadlocker for chainring bolts.

I don't use grease on chainring bolts.


-Tim-

Kimmo 

Shimano use to be pretty keen on it... They used this green stuff that set so hard, it'd threaten to strip the threads in the crank on triples.

I'd probably steer clear of thread locker on Campy cranks that use those silly undersized bolts, in fact on any ally crank bolts. The Campy ones are particularly vulnerable to shearing, though.

MoAlpha

I don’t recall ever having difficulty undoing something I screwed in with the blue stuff. Loctite makes a purple product especially for delicate stuff, but I’ve never tried it.

Kimmo 

Yeah, I guess when it comes to ally chainring bolts, the window between too tight and too loose can be pretty small. A gentle thread locker would help with that.

But concerning the OP's hassle, I can't help but think there might have been something else going on - perhaps a ring got snagged on the shoulders of the lands slightly, and those four bolts were only tight until the ring moved? Seems slightly less weird than the situation described.

Trsnrtr

I had a similar thing this spring with a Red 22 crank. I was JRA and a shift put the chain between the chainrings. I stopped and saw that I had lost two bolts and two more were loose. What!? In 38 seasons of riding, I've never had this happen. I've found maybe 2 loose chain ring bolts in my life but never something like this.

Kimmo 

If one is loose, that makes it easier for others to work loose...?

rousseau

I guess that's possible, but surely that would have made the ring totally wonky? Like intermittently scraping against the derailleur? I pretty sure I would have noticed that.

This is the best hypothesis, I'm guessing. I always tighten the chainring bolts two-handed when I take the rings off to clean them (flat-head screwdriver in one hand, hex wrench in the other), but somehow I must have neglected to tighten the one all the way, and it worked itself, and subsequently the others, loose.

I'm going to be keeping a close watch on the chainring bolts from now on!

rousseau

Fug sakes, it happened again. Same creaking, though for some reason known only to the nether regions of my weak brain, I didn't recognize what was happening. Although this time I actually lost a nut-bolt combo out there on the road somewhere.

I went to lube my chain, thinking it was the culprit, when I saw the empty slot on the crank arm. Fug me...will I ever learn?

I'm getting some Loctite post haste.

big john

Had them fall out of a Chorus crank. Blue Loctite fixed it. If you have trouble undoing a fastener with Loctite on it, just heat it up a little.

rousseau

Thanks for the advice, though I gotta ask: with what? A lighter? I don't have anything industrial in my toolbox.

Kimmo 

Hairdryer.

terrymorse 

If a bolt is long enough, it will have enough spring tension when torqued to keep it from unscrewing.

Chainring bolts are are too short to have much spring tension, so use a light thread locker to help keep them in place.

Kimmo 

Campy chainring bolts used to be the business; the old school ones had fine knurling under the heads on the nuts, IIRC. The modern undersize ally ones are a joke. They'll shear if you look at them funny.

big john

Like Kimmo said, a hairdryer might work but I've used a heat gun or a small butane torch, like the ones crackheads use to light their pipes.

Kimmo 

I'd keep a butane torch away from my bike... especially the carbon bits. Flame is like 1500C.

I don't think you want carbon getting as warm as 80C...

RGMN

Don't feel bad. I once lost a derailleur pulley on the road after fighting with a fussy derailleur for almost 20 miles. You would have thought at some point I would have noticed the pulley bolt sticking out of the cage.

If you have a Campag Ultra-Torque chainset you should already have Locktite 222 (purple) around for the chainset bolt. Just use that on the chainring bolts.

ThermionicScott 

I don't think I've ever had a chainring bolt come loose -- is this an aluminum bolt thing?