Folding Bikes - Raleigh Twenty & Shimano UN72

I'm thinking about buying the Shimano UN72 with Phil Wood retaining rings.
Before making the order, does the BB shell on the Raleigh Twenty must be milled (or cut ?) to accomodate the UN72 ?

I'm thinking about buying the Shimano UN72 with Phil Wood retaining rings.
Before making the order, does the BB shell on the Raleigh Twenty must be milled (or cut ?) to accomodate the UN72 ?

No, the Phil rings screw all the way in so it doesn't matter that the BB shell is longer than the bearing. I have used a 68 mm shell UN72 but you really have to crank the rings in there, maybe cutting a new thread or two in the frame. A 73 mm shell bearing works better. The axle length should be 110 or greater to clear the stock frame. As Sheldon Brown says, you can cut the end of the BB shell off to reduce the axle length requirement.

best to cut on both sides though...as the cranks might be over to one side if you cut just one

No, the Phil rings screw all the way in so it doesn't matter that the BB shell is longer than the bearing. I have used a 68 mm shell UN72 but you really have to crank the rings in there, maybe cutting a new thread or two in the frame. A 73 mm shell bearing works better. The axle length should be 110 or greater to clear the stock frame. As Sheldon Brown says, you can cut the end of the BB shell off to reduce the axle length requirement.

UN72 bottom brackets are not different for 73 or 68mm width. Only the retaining rings are different, and you aren't using them. I've converted 68mm UN72s to 73mm and visa-versa a few times.

alex

Just a heads up that UN72s are getting hard to come by these days as they've been discontinued and replaced with the incompatible UN73 which doesn't have removable rings; Great if you've sourced one already - just letting you know if you didn't.

FYI my UN 72 had a 114mm axle which gave a good chainline on a SRAM Spectro 7 planetary hub. The black rings (which are glued on in some cases) were a pig to remove on mine, needing a good going over with a hacksaw on opposing sides before they came off. Some people have just had to pop them off with a rubber mallet but mine was the ring that got all the glue!

R20 BBs are 77mm wide. At least both of mine are.

Other Raleigh 3 speeds only have as many threads as are needed for their shallow cups. Can anyone confirm that this is also true for the R20? If so there won't be enough threads to screw in Phil rings far enough to hold the cartridge. Are you in England? If so, you *might* find someone with 26mm BB taps to cut more threads. If not you are SOL.

IMHO the ONLY way that makes sense to put a modern crank in a 26tpi BB is to have it tapped to 24tpi. Anything you do to make it work with 26tpi, like using a UN-72, will be fine till you need to replace the BB several years down the road.

In the case of a Twenty I would remove enough from the ends of the BB that it can be faced to 73 or 68mm.

When I had my Raleigh Sport re-tapped, the gent doing the work just faced 1mm off each side to give me a 68mm shell. The R20 shell is thinner, so facing off 2mm would be feasible if the cutters are sharp.

Hey Guy Yinon,

check this link out... I just put it together and it should help if you plan to use a UN72 with the Phil Wood rings. The Un 72 in the picts is a 113mm. I have two more UN72's, but they are 127mm's. I think Stevegor told me he used a 127mm on "The Wasp".

http://web.mac.com/phatatude/Green_Space/Raleigh_Twenty_Blog/Raleigh_Twenty_Blog.html
www.web.mac.com/phatatude/Green_Space/Raleigh_Twenty_Blog/Raleigh_Twenty_Blog.html

click on the entry "Phil Wood ring Install (With Ben “the Man”)"...

And Littlepixel and Vince, thanx for all the help so far... Im in the Middle of the U.S., and there are NO R-20's around here. When I finally get to ride my R-20s, I will be as Rare as a Black Man in Nebraska... Wait, I am a Black man in Nebraska... Hmm, I'll get back to ya with a better comparison :)

Phatatude- "Always measure using metric... The higher number sounds more impressive, Ya dig :)"

Yes I did use a 127mm...damn thing is too long as the chainline isn't as straight as I would like it, but it works well so far and that's with some hard riding. But I've conceived a secret solution to this problem........steal the shorter un72 bb I have set aside for my wife's R-20 and when she's not looking, swap them over......but shhh, nobody tell her ;)