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Crankset / Bottom Bracket / DerailleurCage compatibility

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Crankset / Bottom Bracket / DerailleurCage compatibility

Old 09-26-13, 12:38 PM
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DaveP
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Crankset / Bottom Bracket / DerailleurCage compatibility

Hi,

Fairly new to bike maintenance - decided to have a go as my front chainrings were slightly bent causing a rotational rub. So bought a new crankset (https://www.chainreactioncycles.com/s...t/rp-prod46021) thinking it would be fairly straightforward to fit (borrowed some tools from a mate). However once fitted the derailleur cage wouldn't extend out far enough. I played with the high limit screw but it just won't go our far enough (even when moved by hand). The arrangement on the new crankset does make it look like the rings sit further out.

So then looked at bottom brackets and discovered you can get ones with shorter spindles. Old one was > 120mm. Bought a new one () that was 113mm wide. However the problem whilst a bit better is still there - the cage won't extend far enough to move the chain onto the outer ring.

So do I need to get an even narrower spindle - there was one at 110mm but presumably that would only move the rings in 1.5mm? Or am I missing something fundamental? Is it possible the crankset just isn't compatible with my bike / derailleur?

Any guidance appreciated.

Dave
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Old 09-26-13, 01:05 PM
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skoda2
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What type frame do you have? 110 sounds about right for an MTB with a 68mm bottom bracket width, if you BB is 73mm it should still give you good chain line. We need to see a photo of the bike!!! I suspect the old crankset had less arm offset, needing a 122.5mm spindle. What front derailleur are you using, and was your old crank set a double?. Hope we can help you.
Cheers

Last edited by skoda2; 09-26-13 at 01:08 PM.
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Old 09-26-13, 01:20 PM
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A Shimano UN54/55 or Tange LN-3922 in a 110 or 107(yes, they are the same DS distance) will be 2.5mm shorter on the driveside than a 113. The Shimano is 20mm , the Tange 20.5mm on the driveside, so the Shimano will likely work best here. The only difference between the 107 and the 110 then, is the non DS. You likely have more than enough clearance for the 107 with this crankset, but either is fine.

If this is still too long, something isn't good with your front dearailleur !

When you say your current FD won't go out far enough, how much are you short, in mm's ?
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Old 09-27-13, 01:20 AM
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Thanks for the replies guys.

I'll try and get some pictures tonight. With regards the original crankset having less arm offset - that looks about right. I'll check derailleur model - bike is about 12 year old Specialized.

It looks to be short by a few mm's - with the high limiter full unscrewed, so the 110 width may do it - I may give that a go as it's not too expensive.

Just noticed the link for the BB isn't showing above. It's this one here: https://www.chainreactioncycles.com/s...t/rp-prod34652

Cheers

Dave
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Old 09-28-13, 06:53 AM
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Here's a link to a couple of pictures: https://plus.google.com/111285482109...ts/AVTo3Sr8Ni5

The one with bike upside down isn't great but shows there is probably room for a narrower BB spindle. What do you reckon to try first - narrower BB, or new front derailleur?
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Old 09-28-13, 07:34 AM
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It is a bit difficult to decipher but I believe Shimano is recommending a 110mm BB for a 47.5mm chainline.

https://techdocs.shimano.com/media/te...9830657937.pdf
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Old 10-05-13, 08:58 AM
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Hi Guys,

Just wanted to say thanks for the help again. In the end I bought the 110mm BB and also a new front derailleur (as listed in the Shimano tech doc). Once both were fitted it all works great.

My first bit of proper bike maintenance - certainly learn a lot on the way, including how to and how not to take off a chain!

Dave
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Old 10-05-13, 09:04 AM
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Originally Posted by DaveP View Post
Hi Guys,

Just wanted to say thanks for the help again. In the end I bought the 110mm BB and also a new front derailleur (as listed in the Shimano tech doc). Once both were fitted it all works great.
Everything on a bicycle works together. If you assume that you can never update just one component, you'll be right way more often than you'll be wrong. Some other change is almost always necessary to make it work.
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