Bottom bracket woes

[rjb]

The Tandem rear bottom bracket had developed some play and as it was approx 20,000 miles old I set to to replace it. The installed unit was a Kinex XD square taper. Left cup came out easily. Right cup was a bit stiffer but started to move and came out a couple of turns before the shoulder parted company with the cup and came off in the removal tool.

Kinex XD bottom bracket.

Bit of head scratching then a brainwave. Using a freewheel dog removal tool I put it over the axle and tightened up into the remains of the right hand cup using a couple of washers acting as spacers and used the crank Allen bolt to hold it all tightly together. Suitable adjustable spanner then removed the whole unit relatively easily. Phew.

When I came to fit the replacement Shimano un26 unit I found to my dismay that Shimano have fitted a sleeve on the axle which makes It impossible to use their own un72 installation tool. why did Shimano do this! I can see no obvious reason for the collar, it doesn't even but up to the cup.
Fortunately I have access to a lathe so machined off enough of the collar to enable the tool to fit. Not fully but enough purchase to screw it in and out. I made sure I used plenty of copper grease on the drive side. The left side has a plastic cup and the fitting instructions say fit dry no grease, so I used PTFE tape as a precaution.

Shimano UN 26

So what should have been an hour's job took me all afternoon.

[Brucey]

shimano have this habit of making slight revisions to their tools etc without always making it clear that they have done so. There are various versions of TL-UN72 and the later TL-UN74, including;


TL-UN72 first version; fits metal cups only


TL-UN72 second version, with deeper splines to fit plastic cups too


TL-UN74-S

my guess is that you have the second version of TL-UN72, since it has the deep splines (that fit plastic cups) but has an internal shoulder which means that BBs with the collar can be problematic. I think TL-UN74-S fits everything. Not sure what the collar on some BB spindles is for BTW; it seems that some (cheaper) cranksets do butt up against the collar, but to what purpose is not clear.

Nice improvisation with the freewheel remover BTW!

cheers

[rjb]

Thanks Brucy,
I have the first version of the un72, fits metal cups but not ones with collars evidently. It fitted the plastic cup fine but not sure if the splines go full depth.
Won't be looking again until I remove it. BTW I managed to prise open the seal on the UN26 and squirt some semi fluid grease inside. . Hoping not to remove it again for several thousand more miles. I thought that was a good hack with the freewheel remover. Hope it helps others with a similar problem.
I suspect the old bottom bracket had been overtightened when installed weakening the collar.

[Brucey]

I have the first version of the un72, fits metal cups but not ones with collars evidently. It fitted the plastic cup fine but not sure if the splines go full depth....

I don't think you can have TL-UN72 first version; that only fits metal cups, and doesn't fit plastic cups at all.

cheers

[rjb]

Just checked with a spare plastic cup. It does go full depth so it must be the 2nd version. Nothing on the tool to identify it as a revised tool, just states UN72. I wonder if the collar is fired during manufacture to hold and align the axle during machining.

[Brucey]

the original spline has the same major diameter but also has a larger minor diameter than the later spline. This means the original spline tool doesn't fit plastic cups at all; no part engagement. The only part engagement is if you fit a new tool into a metal splined cup; in theory the tool might be more likely to break but in practice this is rare.

cheers