Bicycle Mechanics - Shimano UN54 Collar on 113mm

Greetings,

I've recently bought 3 UN54's, a 110,113,and 115mm. Only the 113mm has this collar on the driveside. It's the correct size for my crank, but the collar prevents the crank from being able to fully torqued.

So .... for those that either work in the industry or see a lot of Shimano UN54's, do all the 113's have this collar?

http://farm5.static.flickr.com/4124/5023918812_7303b3bc45_z.jpg

Shimano made some square-taper cranks that are intended for full bottom-out, where the crank bottoms on that collar. That's why it's on there. Looking at the one we have in stock, yeah, it's got a collar.

Wait a minute, does that mean if you buy a Shimano BB-UN54 that your cranks won't be on fully tight? Because I have a Sora FC-3303 crankset and Nashbar touring frame and now wondering whether I should get the BB-UN26 instead.

By the way, I saw a bicycle with a bottom bracket that seemed to be fully exposed. I mean do bottom brackets like that come with some kind of cover for a more esthetic look?

My experience has been that the collar won't cause a problem in situations like yours, so you should be OK. If your crank's not designed to fully bottom out, it should end up with an air gap between the collar and the crank. So no harm, no foul.

The bottom brackets have seals or at least dust shields over the bearings, depending on the model. I've seen low-end ones where the bearings were visible after losing their dust shields, but that's not normal. Glad to hear you're getting the UN-54, they're worth it in the long run.

Shimano made some square-taper cranks that are intended for full bottom-out, where the crank bottoms on that collar. That's why it's on there. Looking at the one we have in stock, yeah, it's got a collar.

That's really weird. If the crank bottoms on the collar, it won't be properly tight on the tapers of the spindle. It's the tapers that keep the crank/spindle interface tight. If my crank bottomed on that collar, I'd try a different crank.

That's really weird. If the crank bottoms on the collar, it won't be properly tight on the tapers of the spindle. It's the tapers that keep the crank/spindle interface tight. If my crank bottomed on that collar, I'd try a different crank.

Shimano made those cranks to do some tightening on the taper before bottoming out (example, XT M737 crankset). Modern equivalents are ISIS and Octalink, both of which swedge on, then finish by bottoming (at least if they're sufficiently tightened).

how many times has the crank been installed before?
are the cranks JIS or ISO square taper?

I haven't had a problem with shimano 600 or sugino XD-600 cranks bottoming out on the collar.

I saw a bicycle with a bottom bracket that seemed to be fully exposed.

Sounds like BIKE PORN !!!

Pictures, please.
I'm starting to breathe faster already.

Sounds like BIKE PORN !!!

Pictures, please.
I'm starting to breathe faster already.

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