Quick bb fitting question

ishaw · May 9, 2016

It's been a while since I dabbled with square taper. I've refitted the same BB that came off the clockwork, a Un 71 in 113 axle size.

I threaded on the loose cup first on the drive side, the fitted the rest but it doesn't seem quite right to me as there are a few mms of thread on the nds out of the frame and the tapers don't look symmetrical (slightly more tapee on the nds).

I read a few threads on here about Shimano bbs being asymmetric so perhaps all is well, just wanted to get confirmation from some folk as to whether this sounds right or not.

Benmac · May 9, 2016

Was the NDS sleeve flush in the frame before? Is it a 73mm BB in a 68mm shell?

As far as BBs being slightly asymetric, yes, I think they can be although I am not sure why (or even if I am correct). I suppose for clearance and chainline on the DS.

Thias · May 9, 2016

On those BB-UN-71 you should be able to take off both caps, IIRC. But with used units, one side usually is stuck.
I always try to take off both sides, clean and grease the inside with that special mounting paste.
If the drive side did slide completely in, you should be good though.
Assymetric or not depents on the lenght of the drive side. iirc. NDS always has the same length? Not sure actually.

The History Man · May 9, 2016

I tend to get them both on loose so that everything threads up nicely, then drive side flush to get the line right, then NDS nice and tight. If there's a little thread showing on NDS not so critical.

ishaw · May 9, 2016

Drive side is flush and the bearing is now fitted snugly against the inside of the cup. There was about the same amount of thread showing before I removed it so it's gone back on as it came off, just want to make sure nothing untoward is going on.

ishaw · May 9, 2016

A quick measure seems to slugged that the previous owner was running a 73bb in a 68 shell. Luckily I have a spare one in 68 so looks like I'll be swapping that over.

Thanks for the responses.

ishaw · May 9, 2016

A more accurate measure and also confirmed by the bb markings and comparison with another bb I had confirms that it is actually the right size bb at 68mm. As it's all fitted OK on the drive side I can only assume it's right. I'll get round to fitting the cranks and see how they measure up.

Quick bb fitting question

ishaw

Benmac

Old School Hero

Thias

The History Man

ishaw

ishaw

ishaw

Similar threads

Latest posts