Possessed crank arm

garrbo

Hi folks,some help and advice badly needed here before i go off my rocker. My never ending problem is a left side crank arm and bolt that continuously loosens and comes off after ten minutes cycling. I've changed bottom brackets twice now to brand new ones incase i'd over tightened the bolt and damaged the threads,new bolt,new cranks too but to no avail. Of course i can locktite the bolt in place but i'm looking for a more permanent solution. I wonder at this stage could the frame(aluminium) be damaged somehow and causing it to loosen but can't see any obvious cracks/ faults.Any advice or possible solutions would be hugely appreciated.

nicklouse

so what cranks?

But it is most likly that the cranks need replacing if you have done the bb change. As the crank/bb interface on the crank is the one that tends to get damaged NOT the one on the bb.

garrbo

Changed the cranks too,new set of deore square tapered,new bolts,new bottom bracket,same problem.

chilledsandwich

Any change of returning them as a Deore Hollowtech II crankset and BB is cheaper than the square taper. Also much stronger, less problems.

If not an option, you can't over-tighten the bolts on the cranksets, they are the only ones you want done as tight as possible (standard arm power of course) Take the crank that you are having problems with off and look at the square part that goes onto the axle. If that is slightly out of shape you are going to have issues for the life of the crankset. Even the slightest misshapen-ness, because of all of the force you are putting on it, ie body weight + powerful legs, it will always work its way loose and amazingly quickly.

nicklouse

garrbo wrote:

Changed the cranks too,new set of deore square tapered,new bolts,new bottom bracket,same problem.

well then you can not be fitting them correctly. I sugest returning the bike to the place that fitted it and get them to sort it. If self fitted take it to a bike shop and get them to sort it.