68's and 73's!

[Bear-Chan]

ello
i was wondering if anyone had any knowledge on whether there was any way to fit a 68 shell bb in a 73 frame?
ive been hunting for a nice 73/122 bottom bracket, but the only ones i can find are UN53s
theres loads of nice 68 shell ones but not 73 so i was wondering if it was possible to use one a 68 with a bit of fannying around?
taa very muchly for any help!
mike

 

[m1kesmith]

i guess you could machine 2.5mm off each side of the shell, but i'm sure theres a good reason not to

 

[Elev12k]

Yes, in 1 bike I do have a 68mm bb fitted. I think there is nothing wrong with it.

 

[rody]

Can it be done, yes.

Is it the best idea, no. Here's why...

Although a 68mm bb can be used in a 73 mm shell, it places the equipement at two distinct disadvantages.

The first is that the cartridge unit is not supported fully in the shell cup, allowing for potential lateral and vertical play which will be recognized through the cranks as exagerrated movement. This movement can eventually lead to deformity of the shell cups.

Secondly, frames are built around the bb width. Often chainstays are placed farther outboard from the bicycle centerline with the larger 73mm bb to allow for more tire clearance or a less extreme bend enroute to the rear dropouts. When using a bb spindle that is appropriately sized for a 68mm shell, your crank arms and chainrings will clear the right chainstay without issue. Place the same sized unit in a 73mm shell and you have reduced the intended clearance.

I would suggest taking a bit more time to find the correct unit rather than rig the 68mm to fit.

All projects take more time than our enthusiasm is willing to permit.

cheers,

rody

 

[Bear-Chan]

hi guys
thanks for the wise words rody! i think maybe i will just get a un53 for now then and keep my eyes peeled for something more snazzy!
cheers!
mike

 

[Max P]

I don't think they are made anymore - is a 127mm any good to you?

http://www.sjscycles.co.uk/product-...ealed-Cartridge-tapered-Bottom-Bracket-30.htm

 

[rody]

Bear-chan,

No need to wait. If you want the best bb for your ride, look here:

www.philwood.com/Price%20List/P11.pdf

Only $110 US for a bb that will last longer than your bike.

Comes in a standard JIS 73x123.

cheers,

rody

 

[Russell]

Or, for something a little less bling but a third of the price....

http://www.peterwhitecycles.com/bottombrackets.asp

$30 for a 122mm UN72

C'est parfait mon ami!

(he also does the Phil Wood one for $95 )

 

[Bear-Chan]

cheers guys!
russell thats brill! perfect!!
im gonna think long and hard about the wood one tho! its a very nice thing indeed!!

 

[scant]

older un71 & un51 BBs had removeable cups (not shimano intended). using a vice the cup could be tapped away from the main body. the main body was the same between 68&73 with different width outer threaded shells press fit over the body. newer shimano BBs dont allow this.