Stiff crank arm

[Ball]

Hello all,

I know how knowledgeable and helpful you all are on here, so I'm returning to the well...

I'm just trying to fit a crankset to a square taper BB, but every time I tighten the crank bolt, the cranks seize up and don't spin properly. The only way they spin is if I loosen the crank bolts, but I mean really loosen, so they're not even finger tight, which cannot be right at all.

Any idea why this is and how to solve it?

Thanks,
Tom

 

[Rickshaw Phil]

What crank set & bottom bracket?

My first thought without further information is that the bottom bracket spindle is too short for that crankset so tightening the bolt is clamping the crankset against the body of the bottom bracket.

This could easily be completely wrong so don't quote me.

 

[Ball]

Really not sure to be honest Phil. The crank set is whatever came with the Carrera Virtuoso I stripped it off a few years ago. The BB is whatever came with the frameset I just bought, which is a Peugeot Carbolite 103.

If I took a photo of the crank set on the bottom bracket would it help?

 

[HovR]

Tighten the crankset back on to the point where it binds, and see if the rings/crank are rubbing against the frame anywhere, including the area directly around the BB axle/spindle.

Photos would be good.

 

[Ball]

I'll take some photos but actually, looking at it again I think you're almost certainly right. The drive side crank is fine, there's about 5mm clearance, but the non drive side crank is rubbing against the BB. Bearing in mind that the chainring was initially a compact, and I've taken the small chainring off to convert it into a single, that makes perfect sense. If the small chainring was on, it would probably be rubbing the BB too.

So, I need a BB with a longer spindle... ugh, more money

 

[Rickshaw Phil]

Yes, photo's may help. If possible, measuring the length of the spindle will be useful too. Do you have the old bottom bracket from the Carrera to compare it to?

The fact you are mixing bits from two bikes makes me think it probably is an incompatibility between the parts and the solution will most likely be to source a bottom bracket suitable for that crankset.

Here is a link to Sheldon Brown on the subject of bottom brackets which may be useful.

Edit: posted too slow.

 

[Ball]

No need for photos. I've just found the old BB from the Carrera and it has a sort of cup shape, so that the crank arm doesn't rub, which the current BB doesn't have. Problem solved.

New problem, I don't have the right tool to remove the BB currently in the frame

 

[MontyVeda]

No need for photos. I've just found the old BB from the Carrera and it has a sort of cup shape, so that the crank arm doesn't rub, which the current BB doesn't have. Problem solved.

New problem, I don't have the right tool to remove the BB currently in the frame

hammer, big flat screwdriver.

 

[HovR]

hammer, big flat screwdriver.

Whilst I've been known to use this approach on older cup & cone style BB's, I'm not sure I'd recommend this on more modern splined BB's (which I'm assuming this is).

Sounds like a good way to damage the splines, when the appropriate tool could be bought fairly cheaply online.

 

[Ball]

hammer, big flat screwdriver.

Ye that worked :-p

Having some trouble screwing the Carrera BB into the frame now. Could the thread just need a bit of greasing or what? It is so so stiff

 

[MontyVeda]

try to clean the threads out with a small wire brush/suede brush type thing. A good squirt of WD should help clean the threads out too. Try not to go for a bigger spanner or more leverage as you could cause serious damage if you cross the thread (easily done). It should go on relatively easily and by hand providing the threads are clean, and it's the right size.

 

[Rickshaw Phil]

How old is this frame? If it is pre 1986 it is possible that the bottom bracket is threaded to the French standard or possibly the Swiss one. If it is pre 1980 it will certainly be French threaded. More info here.

If this should be the case then the Carrera BB (British threaded) won't fit.

 

[Ball]

How old is this frame? If it is pre 1986 it is possible that the bottom bracket is threaded to the French standard or possibly the Swiss one. If it is pre 1980 it will certainly be French threaded. More info here.

If this should be the case then the Carrera BB (British threaded) won't fit.

OK that is what's the problem then.

I've been recommended a threadless bottom bracket, for example this one http://www.ebay.co.uk/itm/YST-125mm...keparts_SR&hash=item4d04440d51#ht_1193wt_1163

What I'd like to be sure of is that the crankset won't rub against this BB like it was against the old French one?

Also, out of curiosity, how do these BBs secure to the frame if they aren't screwed in?

 

[compo]

OK that is what's the problem then.

I've been recommended a threadless bottom bracket, for example this one http://www.ebay.co.uk/itm/YST-125mm...keparts_SR&hash=item4d04440d51#ht_1193wt_1163

What I'd like to be sure of is that the crankset won't rub against this BB like it was against the old French one?

Also, out of curiosity, how do these BBs secure to the frame if they aren't screwed in?

As far as I know, and I am prepared to be corrected, the BB cups screw onto the BB itself rather than threading into the BB frame shell. Some are slightly tapered so they centre properly. I guess to be pedantic they are not really threadless but they are as far as the frame is concerned.

 

[Rickshaw Phil]

I agree with what Compo said about the threadless BB^^^^^

To be sure the crankset won't rub, the best bet is to check the length of the Carrera BB spindle and get the same size seeing as you know they were a matched set. The bottom bracket may have the size written on it (most likely in the format 68x???) or measure it using a vernier caliper if you have one.

Measure the width of the BB housing on the frame as well to make sure you get the right BB. There are a couple of different widths. 68mm and 73mm are most common but it'll probably be 68mm.