Crank Bent?
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Discussion

944fan

Original Poster:

4,962 posts

215 months

Sunday 21st July 2013
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I was adjusting the gears on my Trek 1.1 because the chain was rubbing on the front derailleur. I noticed that this was happening because the front crank has lateral movement in it.

I tried attaching a dial gauge to the work stand but I couldn't stop the bike swaying to get a good reading.

I removed the outer ring and checked that for flat, which it is.

There is no play in the crank or BB.

The bike is only 3 months old, although I have put a lot of miles through it. The crank is a Vuelta Corsa, which is cheapy st.

Is it bent? Is it actually a problem or should I just ignore it?

944fan

Original Poster:

4,962 posts

215 months

Monday 29th July 2013
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Its certainly buggered. Went to accelerate away when on the outer ring and it threw the can off the crank completely. It isn't the derailleur that needs adjusting. I taped a ruler to the frame and the there is about 3mm of lateral movement on the crank.

Can anyone recommend a reasonable 8 speed crank? The all seem to be 10/11 speed now. I assume if I got one of those then I would need a new chain, cassette and probably rear derailleur. Want to avoid that if possible.

IroningMan

10,598 posts

276 months

Monday 29th July 2013
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From memory - Sheldon Brown will give you the definitive answer - 8spd chain is slightly wider than 9/10spd.

If the chainwheels are flat, then you should be able to use them on any chainset of the same PCD, so get a cheap-but-good 9/10spd Shimano Tiagra chainset, upgrade to HT2 bottom bracket as part of the process, and stick your current 8spd chainwheels on it.

You may find an alternative that would look better with the design of your current chainwheels.

944fan

Original Poster:

4,962 posts

215 months

Monday 29th July 2013
quotequote all
The BB is the tapered 4 sided jobby.

The crank is cheapo ste and whilst they maybe quite strong, I weight 17 stone, and weighed more than that when I bought the bike.

I'll take the crank of and inspect the BB. Do you think I would need to remove it to see if it was bent?

IroningMan - Good idea about keeping the rings. Hand't though about that.


AndyDRZ

1,202 posts

266 months

Monday 29th July 2013
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I tightened up my chainring bolts and it eliminated most of the movement from mine. Might be worth a double check

944fan

Original Poster:

4,962 posts

215 months

Monday 29th July 2013
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Cheers. I have a crank remover somewhere in the garage so will take a peak tonight.

944fan

Original Poster:

4,962 posts

215 months

Saturday 17th August 2013
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WeirdNeville said:
I'll bet a bacon buttie it's a bent bottom bracket axle.
I will give you half a buttie. The axle did appear to bent button not massively. As it was I stripped the bloody thread replacing the cranks so had to get a new one anyway. Put that on that movement was still there. Finally tracked it down to a bent outer ring.

WarrenG

345 posts

227 months

Saturday 17th August 2013
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IroningMan said:
From memory - Sheldon Brown will give you the definitive answer - 8spd chain is slightly wider than 9/10spd.

If the chainwheels are flat, then you should be able to use them on any chainset of the same PCD, so get a cheap-but-good 9/10spd Shimano Tiagra chainset, upgrade to HT2 bottom bracket as part of the process, and stick your current 8spd chainwheels on it.

You may find an alternative that would look better with the design of your current chainwheels.
Sheldon Brown won't give you an answer, may he rest in peace, but his legacy will - best bike and bike stuff/tech website ever.

944fan

Original Poster:

4,962 posts

215 months

Sunday 18th August 2013
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WeirdNeville said:
How odd? did you drop the ring onto anything while riding?

I have an email from Sheldon Brown when I emailed him a question about chain length years ago. Top bloke! Sadly missed. Not often someone becomes an internet personality from the pre-youtube era.
I can't work it out. Haven't knocked it on anything. Only thing I can think is someone has banged it when it has been locked up somewhere but even that sounds unlikely. Both the crank and then rings are un-branded cheapo ste so not exactly strong.

agentnomad

412 posts

301 months

Sunday 18th August 2013
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If you replace it with a 9/10/11 speed the new rings will only be a tiny bit thiner and will work fine just wear out a little sooner, you will struggle to go the other way ie run 8 speed rings etc on 11 chain.


Jimbo.

4,224 posts

219 months

Sunday 18th August 2013
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944fan said:
I can't work it out. Haven't knocked it on anything. Only thing I can think is someone has banged it when it has been locked up somewhere but even that sounds unlikely. Both the crank and then rings are un-branded cheapo ste so not exactly strong.
Chainring bolts not torqued up properly, pulling the ring out of shape bit-by-bit?