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Outer Ring Grinds Against Frame
Hello all, I hope you can offer me some guidance.

I recently attempted to replace a Suntour Double ring crankset with a new Sora like this - http://cycle.shimano-eu.com/publish/content/global_cycle/en/nl/index/products/road/sora/product.-code-FC-3450.-type-.html

I also replaced the existing 68mm Bottom Bracket with a Shimano BB Cup - SM-FC4500 - as recommended on the Shimano page above.

My problem seems to be with spacing as the outer ring grinds against the horizontal part of the frame. If I push the right crank out a bit, the left crank clips against the frame on the left side.

Should I get a 70mm BB cup or would a 1mm spacer on each side be better?

Or something totally different?

Many thanks.
What bike are you fitting this to?
Ride hard or ride home alone!
(07-18-2010, 05:50 PM)cyclerUK Wrote:  What bike are you fitting this to?

It's a 2005 Carrera Subway I took with me when I relocated abroad.

I cannot find any specs on it and can only go on what I removed from the bike, although the Suntour crankset I removed doesn't give me any clues.

It looks exactly like this one:


but their site does not list a double ring version, which the old one has.

The cost of bike labour in Switzerland is highly prohibitive so I am trying to do as much as I can myself.

I should have clarified that the outer ring is rubbing against the chain stay.

A not uncommon problem when you don't replace like with like, because the chainset mounts on a very slow taper there only needs to be very slight difference between the 2 makes for there to be a big difference in the stand out of the arms. You can try spacers, it's the cheapest option if you have enough thread to accommodate them, but, have you replaced the bb with the right one, you said it was a 68, but you can also get different axle lengths, it should be marked on the bb shell.

113 is the commonest axle, but others are available.

I have recently had to try 3 different set ups on a bike to get a satisfactory chain line because the old chainset was no longer available.
Thanks Trev.

I cannot find anything that mentions an axle length on the outside of the BB cup or on the crankset (including the relative pages on the Shimano site)

My understanding is that the bottom bracket is built in to the Sora crankset.

I took out the old bottom bracket and installed this BB Cup:


I then threaded the Sora through as per the Shimano instructions.

When I took it out for a rideit was shifting OK then the crankset seemed to shift to the left, jamming the large chainring to jam against the chainstay. Gear change throughout the range was pretty good until the chainstay jam.

There is about 2 - 3 mm of play in the crankset, you can visibly see there is space between the inside edge of the crank and the BB cup.

I am wondering if I need to hammer it all a bit tighter?
Sorry, I hadn't seen it was a hollowtech, not worked on one of these yet, I assume you have looked at all the tech docs, including this one?
it does say you have to tap it on assembly to get proper seating.
Hopefully, some one who has worked on one will get back to you.
Thanks for the link. That's exactly how I went about installing it.

I do note that the width to which the chainstays come out on the bike in the diagram is much less than on my bike.

At the moment because there is some play / space between the edge of the crank and the BB Cup, if I tap în the right crank arm, it ends up wedged against the chainstay.

If I then correct this by tapping in the left crank, that crank clips the left chainstay at the top of the crank.

I am tempted to just hammer them together more fimrly and see where that gets me.
I am not sure but I think you should have chosen an MTB crankset.
The "Subway" bikes are Hybrids and tend to have wider chainstays than normal road bikes.
The Sora is designed for standard chainstays so will come very close to the chainstays as you have found out.
Unfortunately the new Sora cranks design does not allow the fitting of a wider bottom bracket as the old ones used to.

MTB cranks are angled (curved) wider to allow for wider chainstays.
With "square taper" cranks you could fit a wider BB to overcome the problem.

The bad news is, unless you can find a way of stopping the sideways movement, then I can only think you will have to get a different crankset???
Ride hard or ride home alone!
I think that even if I could get hold of some spacers, I would always have problems.

That, coupled with the look of my chainstays leads me to agree with cyclerUK.

I guess I will have to ebay the Sora I bought.

Many thanks for the quick advice on here. Hopefully I can get this running again.
Hopefully I will get better luck with this:

MMMM,, so now you are in the problem all us DIY'rs face, is it cheaper to pay a professional to do the job right first time, or muddle along ourselves and end up paying out more for a half good job?
Still, you live and learn!!

A friend did something very similar, he was determined to replace his chainset himself and ended up ruining it so he couldn't exchange it, even though the lbs had told him he was buying the wrong one, but they would exchange it if undamaged.
(07-19-2010, 08:32 AM)buono Wrote:  Hopefully I will get better luck with this:


Are you happy with the tooth count of the rings - 36 / 22 ?

Is this similar to your existing one?
Ride hard or ride home alone!

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