Cycling UK Forum

Hi guys, I need help!

I just purchased a 1960Ks Mercian which came with a bottom bracket, it looked like it has been in the frames approx. 1 million years, the bottom bracket that is, it was quite damaged and old.

I've taken It out and measured the spindle so I could buy a sealed bottom bracket the correct size. I went out and got a Shimano UN54 which was relatively easy to install but I've come to realise that the left crank sticks out quite far with a large gap between the BB shell and the actual crank arm.

I've probably made some error along the way but have no idea what but after taking another look at the original spindle one side of it is longer than the other, maybe this is the problem?

Like I said the BB is Shimano UN54 and I have a SR Apex chainset

Any help would be great as I'm lost! Thanks Carley

Modern cranks generally are designed for symmetric bottom bracket axles (same length both sides). Previously, most cranks were designed for unsymmetric axles (longer in the drive side). Even though you got the same overall length, the length on each side might be different.

There are other possible complications (ISO v JIS sizing) that can be difficult to identify over the Internet.

Left hand cranks can be straight, or cranked to give clearance from the chainstay. Perhaps you can get hold of a left hand crank with little or no crank (can't think of another word for it ) which won't stick out so much.

I would always recommend getting a matching pair - BB and chainset. That way, you know they are right.
Sorry, but I have no advice as to the correction of your problem.

As for JIS vs ISO, I understand that SR Apex and Shimano UN54 are both JIS as they are both Japanese.

Thanks for the replies.

I'm pretty sure that although I've bought the same size spindle as the original, because of the unsymmetrical original I could actually get a much shorter modern one. So I'm guessing that is the problem.

Although I have absolutely no idea what length spindle I need now, it's all really confusing!

From my own experiences the only thing to watch out for is the clearance between the chainstay and chainrings. (chainline).
I try to get the distance between the back of each crank arm and the chainstays the same both sides, within reason.
Having said that I have at least one bike where the crankarms are offset to the right (by using a spacer - [big washer]) to give clearance for the granny gear.

Like you, I ordered a slightly longer BB but ended with too much aesthetically sticking out to the left.
It has had no adverse effect on the functioning but I would prefer it nearer the BB.
I would assume Shimano design their crank arms to cope with this but if you use some other make then that can be the reason.

I've just measured 2 old LH cranks, one straight and the other "bent". The bent one would clear the chainstay by around 1.5cm more than the straight one, quite significant.

The only technical stuff I can think of to help you understand it is this about chainline:

http://www.sheldonbrown.com/chainline.html

Unfortunately, I don't think it offers a practical solution because your problem is adapting old stuff to new. I suppose the main issue is one of clearance: if there's not enough the RH crank and or the inner chainwheel may foul the chainstay.

There is a discussion here which includes contributions about a similar problem to yours ie fitting an SR Apex chainset to a modern BB.

http://www.bikeforums.net/archive/index ... 73473.html

The only sealed cartridge asymmetric bottom bracket on the market is Phil Wood. Super expensive, the cups are sold separately from the cartridges so figure spending £100 and you'll most likely have to order it from the states.