Loose Crank

[Ootini]

Hi,

The NDS crank arm on my Ridley XBow keeps coming loose. Not to the point that it's falling off, but it wiggles after about an hour or so riding and needs tightening up. The bike's only a month or so old with just over 100 miles on it. Any thoughts as to how to stop it, or what's causing it?

Thanks

 

[Ootini]

Anyone?

 

[Cubist]

What sort of crank is it?

 

[Ootini]

It's the non-drive side crank arm from a SRAM Powerglide 48-34t chainset. I don't really know what other information I could give you, it's a cyclocross specific double if that helps? Sorry

 

[AndyPeace]

Hi,

The NDS crank arm on my Ridley XBow keeps coming loose. Not to the point that it's falling off, but it wiggles after about an hour or so riding and needs tightening up. The bike's only a month or so old with just over 100 miles on it. Any thoughts as to how to stop it, or what's causing it?

Thanks

where did you get the bike from? eaisiest solution is to take it back to the shop, they should fix the problem under warranty.

 

[Ootini]

I thought that might be the case, it's a bit of a drive and I'd rather not be without the bike but it does make sense.

 

[Globalti]

Unfortunately on some designs of crankset, if the big bolt isn't re-tightened a couple of times as it "settles" it will work loose and the interface will get damaged, so that it will never tighten properly.

Phone the shop, explain the problem and tell them you expect to get a new crankset under warranty, properly torqued up and you will bring the bike in for it to be fitted, which is a five minute job.

Once they've fitted it, ride the bike around the block and up a couple of hills then ask them to re-check the torque. Then do it again yourself a week later - you'll be amazed how much it has loosened.

 

[Ootini]

Perfect, thanks very much. I assume I have to get myself a torque wrench now, and not just tighten it with a run of the mill socket?

 

[Ootini]

Do you know roughly what a crank arm should be tightened up to in Nm?

 

[4F]

I would say that if it keeps working loose then it has had it now and will need replacing under warranty

 

[Globalti]

You don't really need a torque wrench, these are the most robust parts of a bike and most normal people will not be able to cause any damage using a hex key a few inches long and their own muscles. As long as you don't extend the leverage with a scaffolding pole you won't break anything.

Mechanics have a sense for the elasticity of various materials and know how far they can go before they cause damage. Try to develop that sense yourself. In my book of bodging there's nipped up, finger tight and eff-off tight, which requires major effort and bracing of parts. "Nipped up" would be non-stress carriers like the stainless steel bolt that holds the cable guides to your BB or the tiny hex bolts that hold the brake blocks in the shoes; "finger tight" would stressed parts like your stem cap bolts or your seatpost bolt or pedals, while "eff-off tight" would be major force bearers like the crank bolts or the saddle bolt.

 

[Ootini]

Cheers for all the advice. I phoned the shop I got the bike from and they're going to give it a service FOC and take a look at the crank arm.

Thanks again.

 

[Ootini]

I dropped the bike off on Monday and got a phone call Tuesday evening, to tell me the crank arm had warped somehow, according to the guy on the phone "These power spline bottom brackets are a bit crap so we'll replace the bracket and chainset all free of charge. Not sure exactly what will be going on it but we'll make sure the ratios are the same."

To me that sounds like a result. I should point out that I don't actually know what a power spline bottom bracket really is or why it would be "a bit crap" or what it could be replaced with. But I'm getting something replaced on warranty and that makes me happy.

 

[Ootini]

Well I've got the bike back. They replaced the original SRAM chainset with an FSA Vero 50/34. Not had chance to try it out yet but I'm off for a ride tomorrow.
To be fair they re-indexed the gears, sorted the brakes out, trued up front and rear wheels, replaced bottom bracket, chainset and chain. All FOC.

 

[4F]

What SRAM chainset was it ? I would say that the FSA Vero was a lower priced item to what you had on their initially.....