Loose Crank

Downtime

Hi. I was wondering if anyone had any ideas on this. My left side crank keep coming loose. I brought it to the shop (Joe Daly's) and the guy replaced the crank and bolt which didn't work. I then got a new bottom bracket and crank and this worked for about a week and it is loose again.

I don't know what is causing it but am beginning to think that it may have something to do with my foot position in the pedal (Shimano SPD-SL). Is this possible? I do a good bit of cycling at weekends and for my commute so having the bike constantly in the shop without much progress is annoying. Should I replace the chainset? Any ideas appreciated. The bike is a Giant SCR with TruVativ Toura Chainset.

biker_joe

Use Thread lock on the bolt or bolts that keep coming loose .......you get it in most hardware stores ....

ednwireland

is the bottom bracket like this ?



or one of the other new fangled types

square taper shouldnt come loose once its on clean and tight.
i've fitted loads once they go loose and you pedal any distance on them the crank is ready to throw away tightening wont make any difference.

the crank arm is soft alloy and the axle steel so it deforms

Downtime

Thanks - I think it is a Shimano 105 type.



I presume it should last more than a week though.

seamus

My guess is that he didn't replace the crank arm as that wouldn't be very cheap and you seem pretty relaxed for a guy who's had it happen twice

While your foot position may push unduly on the crank arm, the bolt should be sufficiently tight to prevent this making any significant difference.

Either way, my suspicion is that he never replaced the crank arm. If the bolt is coming loose despite being tightened properly, then it means the crank arm is loose on the taper.
If the bolt is staying on, but the crank arm wobbles, then it's loose on the taper.

A cheap investigation method would be using threadlock on the crank bolt. Lock it, try it out for a while and if the crank arm becomes loose despite the bolt staying in place, then the crank arm is screwed.

At the point, replace your crankset with a set of Hollowtech cranks and you'll never have this problem again.

Downtime

Cheers - thanks for the advice - will try threadlock and see what happens

tomasrojo

I had a problem with the right crank falling off (square tapers). It was because the crank had received a blow and the socket to receive the taper had become very slightly deformed.

Maybe the same can go for your type of taper?