CQP Cook Bros Chainset & Front Mech Clearance Problems

[julesg007]

Hi All,

Setting up the drive train and have run into an issue that is giving me a headache :?

I am running a CQP chainset with 48/36/24 rings with 181mm crank arms but with the chain engaged on the 48 chain ring I get no clearance between the outside of the front mech cage and the back of the crank arm.

I am using a 122mm spindle length and this gives the following approx clearances; 7mm between the crank arms and rear stays on the drive side, 5mm on the non drive side and 4-5mm clearance between chainring teeth and rear stays.

I have tried using 2 different types of front mech, both high clamp and low clamp being XT FD-M737 and XTR FD-M950 respectively - picture hows the M737 but the same is for the M950.

Any help in resolving would be fantastic.

My own view seems to suggest using a bigger chainring to increase the clearance between the back of the arm as it tapered and the mech cage. Also I'm not sure as I don't know a great deal about the chainset if I should be running a larger anyhow.

Thanks all

Jules

 

[Splatter Paint]

Try a 127.5 mm Axle maybe? Failing that is the spider fitted incorrectly?

SP

 

[scant]

earlier era front mechs should be narrower. if not move the f.mech up the seattube slightly?

 

[mynchiboy]

Hmm...I've had this problem also, right pain it is too :x

As scant suggests it may be worth trying to move the front mech slightly upwards. Otherwise maybe look at switching the top chainring for something with a lower profile (long shot...)

 

[dyna-ti]

Is the cage of the mech parallel to the chainring? and 2mm above it?
You could try twisting the mech slightly

Try a 127.5 mm Axle maybe? Failing that is the spider fitted incorrectly?

SP

I think 122.5mm is the standard, with some applications needing the 127.5mm

 

[julesg007]

Hi all,

Thanks for the info.

Just to let you know the chain rings fitted are actually fairly new being TA Specialities Zephyr 9/10 speed.

I will try moving the mech up the seat post to see what happens, hopefully that'll sort the problem but the M737 is off a bike that had first generation XTR M900 gear on it so I'd have thought it'd be as narrow as its XTR equivalent - M901.

That said I have a M901 on it's way to me as we talk so will also try that, but I'd have thought that a newer mech say M953 which uses a narrower 9 speed chain would also have had a narrower cage?

This is the thing that is really confusing me, the mech is parallel and clears the top ring by 2-3mm and set to avoid chain rub, which as far as I'm aware is about right.

I thought about a longer bb but the movement of the mech and the relative position of the crank on the spindle wouldn't change so at this stage I'm thinking messing around with the mech would seem to be the answer.

Any other comments or help would be grateful.

Thanks again

Jules




1) The [/quote]

 

[mikesnowdon]

.....Failing that is the spider fitted incorrectly?

SP

+1 Something is definately wrong with the crank/spider if the arm dosent clear the front mech cage.

The spider could be on back to front. If its back to front you would then have the problem of the C'Rings fouling the frame once its flipped over and re-installed, so a longer BB would be in order too. Check the spider is on the right way first.

 

[raymondluxuryyacht]

Hmmm that crank really does not look right. The only time I ever had the clearance problem was with ritchey logic cranks that have a low q factor. My solution was finding a mech with a very flat outer cage and raising the mech position. Be aware that 9 speed mechs are not neccessarily narrower than 7 or 8 speed mechs. In fact I would have thought earlier 7 speed setups would have narrower cage as there is less of a range of angles and heights to cope with on 7 speed cassettes. Also the curve of the mech plates (parallel to rings) may be different on older and newer mechs. I'm not quite sure of your exact setup but on an MTB with 48 tooth ring you really need an older style mech e.g. 7 or 8 speed era. I am intirgued why you seem to be aiming for a 9 speed setup as the size chainrings you mentioned seem mor appropriate to an earlier setup. You may end up with some funny gear ratios if you go for a 9 speed cassette unless you find one that has the smallest sprocket as 12 teeth instead of 11.

 

[julesg007]

Hi,

Thank you for the further information and help.

I'm actually going to be running a 8 speed set up. I have an early set of XTR M900 hubbed wheels with corresponding XTR M900 12 - 28 cassette and the bike will spend most of it's time on the road (am building a modern full susser for the off road stuff) hence having a 48 chain ring rather than the more usual 42/44 for MTB's.

I was wondering about the chainset as being honest I don't know a huge deal about CQP cranks; as the crank arms are slightly longer than normal could it just be the case that they were designed to be running a larger ring in the first place say a 50 or 52 as perhaps this version was designed for road use rather than MTB use. Using larger rings would increase the clearance due to the taper on the back of the crank arm.

As for the crank spider being on the wrong way round (am using the chainset as it arrived) looking at it, it does seem to be correctly fitted. As you see from the pictures it still has an original CQP sticker on it and that is to the outside and on the inside it is recessed for the fitting of a circlip. There is, however, some wear to the crank arm which indicates a clearance issue in the past.

When I have the M901 front mech (dependant on PO) I will compare to the other front mechs I have and will give that a go to see if problem is resolved and report back.

Please keep the suggestions and help coming.

Happy retro riding to you all.

Jules

 

[legrandefromage]

tapers looked buggered forcing the chainset a couple of mm onto the bb spindle further than it should.

your xt mech is designed for compact drive rings and may have trouble with rings over 46t


allegedly of course.