Help! Shimano 105 chainset keeps coming loose

[postedoverseas]

Hi all,

This is my first post on here, I am just getting back into road cycling.

My wife purchased a shimano 105 bike for me recently and it was bought "as seen".

The same day I started riding it the left peddal shaft was loose and kept slipping forward when the shaft reached the 12 o clock position.

After taking it to my local store the tech there said that the coggs inside the chainset had been work down and he would have to order a new one. 2 or 3 days ago I picked it up and today I have noticed that the problem is back. I have been taking it very easy since the problem arose

Does anyone know of an under-lying problem that could be causing this? I am not keen on throwing money away on a 250 euro chainset if the problem is just going to keep re-appearing or if the problem is permanent.

I have tightened both sides of the chainset several times but the problem keeps coming back.

Help please

Thanks
John

 

[gclark8]

If he fitted a new cassette (cogs) then a new chain should have ben fitted at the same time. A 105 chain is about $25 US.

I don't know what you are tightening, get some locat mechanical advice.

 

[John M]

Hard to say exactly but sounds like a worn chain to me. The chainrings may be worn but have to be really really worn for the chain to actually slip.

Maybe try a different shop and have a different mechanic take a look.

 

[postedoverseas]

Sorry, my mistake, let me try and explain further.

It is not the chain and therefore I suppose it is not the chainset but the crank (I think that's what they call it) where the pedals are connected.

Every time my left leg pushes forward on the pedal the pedal/stem/shaft moves forward approx. 5 mm.

The pedals are secure on both sides. Most of the time when I try and tighten the "crank" the left hand bolt (the lone pedal stem) is not as loose as the righht hand side (the side with the chain). I hope all this makes sense, when I rode racers last BMXs were in and mountain bikes weren't around.

 

[John M]

Sorry, my mistake, let me try and explain further.

It is not the chain and therefore I suppose it is not the chainset but the crank (I think that's what they call it) where the pedals are connected.

Every time my left leg pushes forward on the pedal the pedal/stem/shaft moves forward approx. 5 mm.

The pedals are secure on both sides. Most of the time when I try and tighten the "crank" the left hand bolt (the lone pedal stem) is not as loose as the righht hand side (the side with the chain). I hope all this makes sense, when I rode racers last BMXs were in and mountain bikes weren't around.

OK, now I suspect that the splines on the bottom bracket (the proper name for the axle of the crankset--BB for short) are damaged or the interface on the crank arm is damaged. Either way the damaged part will need to be replaced. Have a qualified mechanic take a look and help determine. I suspect that the original assessment is correct in that the notched interface that receives the splined BB axle is damaged and that you need a new crank arm.

 

[postedoverseas]

Is the bottom bracket different from the crankset as I had it replaced last week and it has started to do it again.

I don't mean to ask too many questions but if the bottom bracket is different from the crankset, does this now mean that the new crakset is unserviceable and I have to pay out for another new one?

Thanks again

 

[artemidorus]

Is the bottom bracket different from the crankset as I had it replaced last week and it has started to do it again.

I don't mean to ask too many questions but if the bottom bracket is different from the crankset, does this now mean that the new crakset is unserviceable and I have to pay out for another new one?

Thanks again

If the BB splines were damaged and the new crankarm slipped, then, yes the new crankarm may well be ruined. If so, then the crankset should be replaced free of charge by the IDIOT bicycle shop. It would be fair, however, for them to charge you for the new BB.

 

[John M]

Is the bottom bracket different from the crankset as I had it replaced last week and it has started to do it again.

I don't mean to ask too many questions but if the bottom bracket is different from the crankset, does this now mean that the new crakset is unserviceable and I have to pay out for another new one?

Thanks again

I agree that a damaged BB can ruin a perfectly good crank arm as the aluminum crank arm is much softer than the hardened chromoly steel BB axle. If they missed the problem and put a good crank on a bad BB, then you should not have to pay again for the crank, but just the BB. And yes, only a few miles with a bad BB on a good crank arm could ruin the crank arm.

 

[CJ Smith]

Hi John M... I think this person (and many others perhaps) should add

http://www.sheldonbrown.com/glossary.html

to his favorites. It is a great glossary of bicycling terms that has helped many people I know get better acquainted with our sport. I keep it kicking around on my notebook & PC because it is an above par site.

B.T.W. - I have read several of your (John M) posts... You're on time with the advice. Nice job!

 

[benkoostra]

Maybe they didn't grease the threads on the crank bolts when they had it apart. It wouldn't be the first time. That can cause a little slipping, but 5mm seems like a lot.