Installing cranks on UN72 bb

[Captain Stupido]

Bought a 110mm UN72 BB for an LX M569 chainset on my current clockwork build. When I initially put it in it looked a little narrow / short on the drive side. There’s a kind of round spacer on the axle which would stop the cranks being pushed too far along it. You can see it in the library pic below. Most of the bbs I’ve used in the past don’t have this.

Anyway...Put the chainset on, and it seemed to work, tightened up and the chain line looks good.

Only thing is, whereas normally with square taper bbs they gradually tighten up to the specified torque (i.e. “bloody tight”) as the cranks push further up the taper, with this combination it seems like they tightened “suddenly” when the cranks butted up against the spacer thing on the axle.

All feels tight, chain line is good, nothing’s rubbing. I’m just slightly nervous of the cranks loosening and rounding off... Am I worrying unnecessarily? Obviously one solution is to ride them and see, just thought I’d ask, too.

 

[mattr]

Take the bolt out, see if the crank is drawn down onto the taper or not.
It'll either fall off (bad) or be solidly wedged on the taper (not bad).

 

[Captain Stupido]

Take the bolt out, see if the crank is drawn down onto the taper or not.
It'll either fall off (bad) or be solidly wedged on the taper (not bad).

Cool man, sounds sensible... and thanks for the speedy answer. Will give it a try.

 

[Woz]

I remove that stupid washer for exactly the reasoning you mentioned. It seems Shimano had a lapse
of reasoning if you wanted to use say 3rd party cranks or well used softer alloy cranks that may
have a slightly out of tolerance taper.

A 4mm drill to break one edge (being careful of course) and a flat blade screw driver to pry it off works.

BTW: The M569 crank works with a symmetric BB like the 107mm or 113mm depending on desired chain line. The asymmetric 110mm will mean the NDS crank will be 3mm slightly outboard compared to the DS crank. Alternatively a 1.5mm spacer on the DS cup
will center it all up.

 

[Captain Stupido]

Re:

I remove that stupid washer for exactly the reasoning you mentioned. It seems Shimano had a lapse
of reasoning if you wanted to use say 3rd party cranks or well used softer alloy cranks that may
have a slightly out of tolerance taper.

A 4mm drill to break one edge (being careful of course) and a flat blade screw driver to pry it off works.

BTW: The M569 crank works with a symmetric BB like the 107mm or 113mm depending on desired chain line. The asymmetric 110mm will mean the NDS crank will be 3mm slightly outboard compared to the DS crank. Alternatively a 1.5mm spacer on the DS cup
will center it all up.

Ah, ok, glad to hear I’m not going mad... maybe the sensible thing is just to stick a new BB in... for an easy life, would a brand new 107 or 113mm UN52 do the trick?

 

[Woz]

I generally only use UN72. From memory, all UN51 and UN71 did not have a silly washer, but like the UN72 at 107mm and 110mm
the UN52 did. Also, I believe there is no stupid washer on the 113mm and longer varieties, but I would need to rummage
in the attic to check. All Token BBs do not, even the mega short 103mm. Really Shimano had their head firmly up
their own arse on this one.

 

[hamster]

IIRC the spacer thingy was only on OE BBs to avoid factory overtightening. But agreed it's pretty pointless.

 

[Captain Stupido]

I've had a look through the odd BBs I have in my parts bin. Weirdly I have 3 (asymmetric) 110mm ones here. They also all have the spacer/washer - UN72, UN55 and LP26. Pretty useless selection, although I think I used this chainset with the (worn) LP26 on a different bike...

For some reason I also have 2 (symmetrical) 118mm ones here. One is a UN55 (with spacer) the other is TH industries, no spacer... But I think either is going to be too long for this chainset.

The M569 crank works with a symmetric BB like the 107mm or 113mm depending on desired chain line. The asymmetric 110mm will mean the NDS crank will be 3mm slightly outboard compared to the DS crank.

I hadn't really realised that different sizes were either symmetrical or asymmetric. I think I had assumed that longer BBs were longer on the drive side and shorter on the other. I'm confused about why they'd need to be shorter on the drive side when there's more "meat" on that side of the crankset. :|



Looking at it, I'm not sure that removing the washer is the right approach - things aren't really centred properly anyway and there's not much room to further tighten the right hand cranks - with the washer removed I might end up with clearance issues.

I'm inclined to go for a 113mm UN52 as they're decent enough and available new. A 107 might be tight and I could tweak the chainline with a spacer on freehub if required.

Is it a rule that 107 and 113 will always be symmetrical and 110 not? The Sheldon page recommends 107-113 for the M569 - I had assumed that 110 would be safe being slap bang between those figures!

:facepalm:

Thanks for your help guys - itching to get this build finished and as ever it's little things (and possibly a little bit of OCD/perfectionism) holding progress up!

 

[Woz]

Understand your frustration. Been there too. The Shimano 110mm asymmetric was intended for a handful of cranks, mainly
to center it all up due to the NDS crank profile - FC-M560 comes to mind. 110mm is an ugly duckling to be used with care - it does not alter the DS crank placement and thus chain line compared to the 107mm.

To make it worse still, a lot of STX / STX-RC cranks were specified with a 110.5mm which were symmetric and these BBs are virtually impossible to find. Retailers get confused too.

I would say if your cranks are sound (ie. not been on-and-off bikes as often as you change your U-Pants), go for 113mm. If it feels that they tighten up too suddenly, then I can't see any other way
than to remove the stupid washer. Otherwise, simply buy a Token or Tange BB.

More often than not, I use Middleburn cranks with the short 107mm. The stupid washer needs to be removed
and there is only 0.5mm between the crank arm and BB cup (measured with feeler gauge).

Good luck with the build!

 

[Captain Stupido]

Understand your frustration. Been there too. The Shimano 110mm asymmetric was intended for a handful of cranks, mainly
to center it all up due to the NDS crank profile - FC-M560 comes to mind. 110mm is an ugly duckling to be used with care - it does not alter the DS crank placement and thus chain line compared to the 107mm.

To make it worse still, a lot of STX / STX-RC cranks were specified with a 110.5mm which were symmetric and these BBs are virtually impossible to find. Retailers get confused too.

I would say if your cranks are sound (ie. not been on-and-off bikes as often as you change your U-Pants), go for 113mm. If it feels that they tighten up too suddenly, then I can't see any other way
than to remove the stupid washer. Otherwise, simply buy a Token or Tange BB.

More often than not, I use Middleburn cranks with the short 107mm. The stupid washer needs to be removed
and there is only 0.5mm between the crank arm and BB cup (measured with feeler gauge).

Good luck with the build!

Thanks dude... given the potential hassles with a shimano and my meagre means I’m actually tempted to just go for a bargain basement sunrace or FSA... I’ve used both on utility/touring bikes and found them to be fine, although I’ve never really used one in anger...

Token is new to me, a bit pricy though... I didn’t even know Tange made BBs. I like their headsets though... so for £18 or so maybe a better option. I’ll probably order something tomorrow...we’ll see...