I've noticed some creaking coming from the front BB area on our tandem so decided to have a look at it. I pulled the cranks off and noticed that the BB axle was a bit tight. I removed the Shimano UN55 unit to examine it more closely. To my surprise the axle turned freely with the unit removed from the bike. I cleaned it up and reinstalled it from the r/h side and immediately once tightened into the frame (without the l/h cup yet) the axle became tight again. Backing off the unit a bit resolved the problem. I then refitted the l/h cup and the same thing happened. With the cup tightened up the axle tightened up and backing off the cup freed up the axle again. I have fitted many Shimano sealed BB units over the years and never had this happen. I can't figure out what's going on here. Has anyone else ever experienced this? Any ideas what's going on?
Cheers, Ian
Sealed BB - rotation tight when installed
Re: Sealed BB
It could be misaligned due to the eccentric shell faces not being square. You may need to have it refaced. Try inserting the left cup to full depth first so that when you fit the main body you know it's going in square and not cross threaded. Don't forget to back off the left cup as you proceed. 
How is the front eccentric shell clamped? Does it have a double clamp like a seat bolt lug or does it rely on a pair of protruding screwed set bolts? I found my eccentric was fitted the wrong way around.
and the installer had stripped the bolt thread, drilled an extra hole and used a new bolt which didn't actually clamp the eccentric. I solved this by using an oversize Allen bolt and tapping a one size larger thread in the original fixing.
My front bottom bracket still creaks but i think the problem is the eccentric clamp arrangement isn't ideal and it is not a tight fit in the bottom bracket. I have used a coke can shim to improve the fit and greased it all. Not had any problems with the sealed bottom bracket unit.
How is the front eccentric shell clamped? Does it have a double clamp like a seat bolt lug or does it rely on a pair of protruding screwed set bolts? I found my eccentric was fitted the wrong way around.
and the installer had stripped the bolt thread, drilled an extra hole and used a new bolt which didn't actually clamp the eccentric. I solved this by using an oversize Allen bolt and tapping a one size larger thread in the original fixing. My front bottom bracket still creaks but i think the problem is the eccentric clamp arrangement isn't ideal and it is not a tight fit in the bottom bracket. I have used a coke can shim to improve the fit and greased it all. Not had any problems with the sealed bottom bracket unit.
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X3, Raleigh 20 stowaway X2, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840 
Re: Sealed BB
the preload on the bearings is always affected by how tightly a shimano cartridge BB is fitted; if the threads in the BB shell are not perfect it can make things palpably worse at a lower torque.
Very often when refitting a well-used unit (which has a tiny amount of free play when the thing is out of the frame) the free play mysteriously disappears when the unit is tight in the frame.
When a new unit is fitted, the only reason you don't feel the preload is that the bearing surfaces are smooth. With a used unit, the bearing surfaces can be slightly rough and variations in preload are more easily felt.
Quite a few cartridge /sealed bearing BBs suffer quite badly with uncontrolled preload variations arising during installation. Such units might be better fitted using low torque and strong threadlock, rather than high torque and low strength threadlock.
cheers
Very often when refitting a well-used unit (which has a tiny amount of free play when the thing is out of the frame) the free play mysteriously disappears when the unit is tight in the frame.
When a new unit is fitted, the only reason you don't feel the preload is that the bearing surfaces are smooth. With a used unit, the bearing surfaces can be slightly rough and variations in preload are more easily felt.
Quite a few cartridge /sealed bearing BBs suffer quite badly with uncontrolled preload variations arising during installation. Such units might be better fitted using low torque and strong threadlock, rather than high torque and low strength threadlock.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Sealed BB - rotation tight when installed
Thanks for the replies chaps.
RJB: I don't think it's an issues with the faces of the eccentric BB as the problem manifests itself even when only fitting the unit without the l/h cup. The eccentric is fixed with a pair of set screws, which I'm not sure is a great arrangement, for whilst it prevents the eccentric from rotating I'm not convinced is allows for a good fit in the shell, and I do wonder if this is where the noise is coming from.
Brucey: I had come to the same conclusion as you with regard to preload and the precision of the BB threads. But I have never come across this before. I think I'll adopt your idea of using less torque and threadlock.
Cheers, Ian
RJB: I don't think it's an issues with the faces of the eccentric BB as the problem manifests itself even when only fitting the unit without the l/h cup. The eccentric is fixed with a pair of set screws, which I'm not sure is a great arrangement, for whilst it prevents the eccentric from rotating I'm not convinced is allows for a good fit in the shell, and I do wonder if this is where the noise is coming from.
Brucey: I had come to the same conclusion as you with regard to preload and the precision of the BB threads. But I have never come across this before. I think I'll adopt your idea of using less torque and threadlock.
Cheers, Ian