Uneven crankarm clearance...

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TONY.M
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Uneven crankarm clearance...

Postby TONY.M » Fri Nov 23, 2012 18:49 pm

...or something like that. Pictures are worth 1000 words so here is what I mean.

Image
Image

The clearance is actually around 2mm closer than the ruler shows so about 8mm driveside and about 2.5mm left side. Highly frustrating as you can imagine and I am clueless as to what is the cause.

The frame is a brand new Dolan Pre Cursa bought from Dolan this week.

The cranks are Stronglight 2000 (165mm) and the bottom bracket is a Stronglight JP400 107mm. The BB is brand new and the cranks are from my PX track bike with light use and are undamaged. Planet X recommend a 107mm BB for a 42mm chainine which is what I bought.

I fitted the old BB (also a 107mm labelled JP400 though different - see photo below) and believe it or not the chainring was up against the driveside chainstay leaving scratches.

The old BB from last year is on the right with pink grease, as you can see they are clearly different.
Image

So I am basically after suggestions from folk who possess more knowledge than me on how to fix this very annoying issue.

Thanks in advance.

Tony

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nicklouse
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Re: Uneven crankarm clearance...

Postby nicklouse » Fri Nov 23, 2012 18:52 pm

buy another BB as there is nothing you can do with your new one.

or live with it.
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Fri Nov 23, 2012 18:59 pm

nicklouse wrote:buy another BB as there is nothing you can do with your new one.

or live with it.

You recon that the BB is the culprit?

Tony

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nicklouse
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Re: Uneven crankarm clearance...

Postby nicklouse » Fri Nov 23, 2012 19:02 pm

yep just look at the thickness of the flange. it will do what it has done.

stand them on a flat surface and you will see the top of the axles will be the same but the flange face will be lower.
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Fri Nov 23, 2012 19:09 pm

nicklouse wrote:yep just look at the thickness of the flange. it will do what it has done.

stand them on a flat surface and you will see the top of the axles will be the same but the flange face will be lower.

OK thanks, I think I know what you mean now. Effectively it does not go as "far" into the bike as the flange stops it thus meaning the left crank arm is closer to the chainstay.

Any solutions to what would bring the clearance even on both sides?

Cheers

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nicklouse
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Re: Uneven crankarm clearance...

Postby nicklouse » Fri Nov 23, 2012 19:15 pm

a different BB that does not have such a fat flange.
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Fri Nov 23, 2012 19:21 pm

nicklouse wrote:a different BB that does not have such a fat flange.

Cheers Nick!

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sungod
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Re: Uneven crankarm clearance...

Postby sungod » Fri Nov 23, 2012 19:28 pm

just a thought, if you measure the width, face to face, of the bb shell of the bike, is it 68mm?

if it's wider (or narrower) then the bb is going to be off-centre vs. intended position

has the bb shell been faced? if the edges have paint on it probably hasn't been, if it is wider than 68mm then facing it would reduce it
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Fri Nov 23, 2012 19:34 pm

sungod wrote:just a thought, if you measure the width, face to face, of the bb shell of the bike, is it 68mm?

if it's wider (or narrower) then the bb is going to be off-centre vs. intended position

has the bb shell been faced? if the edges have paint on it probably hasn't been, if it is wider than 68mm then facing it would reduce it

Will head to the garage now to check.

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nicklouse
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Re: Uneven crankarm clearance...

Postby nicklouse » Fri Nov 23, 2012 19:48 pm

TONY.M wrote:
sungod wrote:just a thought, if you measure the width, face to face, of the bb shell of the bike, is it 68mm?

if it's wider (or narrower) then the bb is going to be off-centre vs. intended position

has the bb shell been faced? if the edges have paint on it probably hasn't been, if it is wider than 68mm then facing it would reduce it

Will head to the garage now to check.

and as it was fine before it will be in tolerance.

not the problem.
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Fri Nov 23, 2012 19:57 pm

nicklouse wrote:
TONY.M wrote:
sungod wrote:just a thought, if you measure the width, face to face, of the bb shell of the bike, is it 68mm?

if it's wider (or narrower) then the bb is going to be off-centre vs. intended position

has the bb shell been faced? if the edges have paint on it probably hasn't been, if it is wider than 68mm then facing it would reduce it

Will head to the garage now to check.

and as it was fine before it will be in tolerance.

not the problem.

The frame is brand new and never used before, the old bb was from another track bike.

The BB shell is 68mm and still has paint on it though not very much and would not make a few millimeters so the BB must be the issue. Even with the cranks "even" the crank spider is very close to the chainstay so a BB with a larger axle may be needed, this will mean a larger than 42mm chainline though.

Thanks

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k-dog
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Re: Uneven crankarm clearance...

Postby k-dog » Fri Nov 23, 2012 21:19 pm

It might be making the crankset sit at a very slight angle though. Can you tell if the unevenness is the same with the cranks pointing forward?

Probably worth facing it for about £10. I didn't and my BB wore out sooner than expected. Just had it faced for a new one.
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mpdouglas
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Re: Uneven crankarm clearance...

Postby mpdouglas » Sat Nov 24, 2012 09:37 am

On the Dolan website, the BB sets they sell for track frames are 109mm spindle length. Those extra 2mm may well resolve your problems.

http://www.dolan-bikes.com/Dolan-Compon ... %20bracket

I'm convinced that your problem is the spindle being too short because you are suffering from the spider being too close and the non-drive side crank being too close. If it was a problem with the offset caused by e.g. the thicker flange on your new BB, one side would have too big a gap and the other too small.
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Sat Nov 24, 2012 09:46 am

k-dog wrote:It might be making the crankset sit at a very slight angle though. Can you tell if the unevenness is the same with the cranks pointing forward?

Probably worth facing it for about £10. I didn't and my BB wore out sooner than expected. Just had it faced for a new one.

I will check again a bit later on. Do frames have to be faced for cartridge BBs or is that only for external bearing BBs?

mpdouglas wrote:On the Dolan website, the BB sets they sell for track frames are 109mm spindle length. Those extra 2mm may well resolve your problems.

http://www.dolan-bikes.com/Dolan-Compon ... %20bracket

It might do and I will ask Dolan what they think.

Thanks

thescouselander
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Re: Uneven crankarm clearance...

Postby thescouselander » Sat Nov 24, 2012 10:27 am

I'm not sure if this is just the angle of the photo but the tyre / chain stay clearance looks uneven too. If so I suspect the problem is to do with the frame.

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sungod
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Re: Uneven crankarm clearance...

Postby sungod » Sat Nov 24, 2012 12:21 pm

TONY.M wrote:<...>
I will check again a bit later on. Do frames have to be faced for cartridge BBs or is that only for external bearing BBs?
<...>


it's possible it was faced by dolan before painting, some external bb systems specify a tight tolerance for width, but for a cartridge bb it's not critical as long as it's about 68mm, which you've verified

the 109mm bb suggested above sounds promising, definitely worth asking dolan
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Monty Dog
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Re: Uneven crankarm clearance...

Postby Monty Dog » Sat Nov 24, 2012 16:26 pm

The lack of chainring clearance would be my worry - it's unlikely you'd notice one crank being slightly closer than the other. Does suggest that rear triangle alignment could be out - worth getting it checked
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TONY.M
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Re: Uneven crankarm clearance...

Postby TONY.M » Sun Nov 25, 2012 10:49 am

There is no way a 42mm chainline is possible with this as the crank spiders are touching the chainstay... very frustrating and seems strange as a popular track crankset will not fit a popular frame. I am thinking that perhaps this batch of Pre Cursas have been altered but I'm speculating of course.

I would love to hear from anyone who has a Dolan Pre Cursa and if they had any issues.

Monty Dog wrote:The lack of chainring clearance would be my worry - it's unlikely you'd notice one crank being slightly closer than the other. Does suggest that rear triangle alignment could be out - worth getting it checked

Thanks Monty, it is actually the crank spider that touches the frame with a 42mm chainline although the a 48t chainring is also very close. There is no problem at all with my other track bike (Planet X carbon) with the same crank and BB.

Cheers

johnboy183
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Re: Uneven crankarm clearance...

Postby johnboy183 » Sun Nov 25, 2012 11:51 am

Just being curious because I have no knowledge. I'm assuming that the "chainline" you are talking about is the gap between the frame and the chain?

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nicklouse
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Re: Uneven crankarm clearance...

Postby nicklouse » Sun Nov 25, 2012 14:39 pm

johnboy183 wrote:Just being curious because I have no knowledge. I'm assuming that the "chainline" you are talking about is the gap between the frame and the chain?
nope distance between the center of the seat tube abd the center of the rings (ring).
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