Your ever-expanding web resource for the Raleigh Twenty
and other classic small-wheel bicycles.

The Bottom Bracket

The Raleigh Twenty has an unusual proprietary bottom bracket shell. It is nominally 76mm wide, although I have heard reports of it sometimes being closer to 78mm. The shell is the same internal diameter as the ISO standard, but the ISO provided for two widths of 68mm or 73mm. As far as I can tell, the wider 73mm dimension is going out of use and manufacturers are gradually settling on 68mm shell width.

Quite a few people have wanted to upgrade their Raleigh Twenty with new cotterless cranks. Over the years, we have found that there are four main ways to do this.

1.) Get a new Bottom Bracket and 26tpi rings from Phil Wood & Co.:

The easiest, but most expensive option. Phil Wood & Co make top-end bottom brackets and parts. It shows in their pricing too! They made specific 26tpi rings for fitting their bottom brackets, which are for the old Raleigh Standard threading. A very expensive option, but chances are that a Phil Wood bottom bracket will outlast the owner and it requires absolutely no modifications to the bottom bracket. You will also need to acquire the special tool for fitting these rings, supplied by Phil Wood & Co.

The Shimano UN52 and UN72 cartridge bottom brackets used to fit in using the Phil Wood 26tpi rings, but there appears to have been a recent change in the design of these cartridge units which no longer makes them suitable. (Click here for gallery album)

2.) Find a suitable cotterless spindle and retain original bottom bracket cups:

(right) Easiest and cheapest replacement for the cottered spindle. Kurt from The Headbadge had a small supply of these which are now out of stock. He's looking around for more. If he finds any we'll advertise it here, but since it is an old stock item, it is hard to find. All reports are that it is a perfect retro-fit, but it does not necessarily work well with all cranksets.

Sadly, it seems that as the supply of these spindles dried up in 2012 and they are now more-or-less "unobtainium."

3.) Modify the Bottom Bracket Shell to take a threadless bottom bracket:

"One advantage of threadless bottom bracket is that you don't need to be particularly accurate - the shell is currently between 68.5mm and 68.8mm I didn't bother with facing other than some judicious filing - I think a less than perfect face allows the cups on a threadless to 'bite' and tighten up easier, which is just as well as i've only one BB tool. When I can borrow another i'll tighten it some more - but as it is it's fine. If it all goes wrong I can still get the shell re-cut to 24tpi." - Heavyweather

(left) For the Raleigh Twenty, you will need to remove 4mm from each side of the bottom-bracket shell. (The Raleigh Twenty has an unusually-wide 76mm shell). If you mark it out properly and work carefully you can use a hack-saw to remove the unwanted sections of the bottom bracket shell. Be careful, and leave plenty of room to use a file to dress the shell down to size. The best way to get it down to precise width is to use a bottom-bracket facing tool.

This option is less expensive than Option 1, but does require 8mm width reduction of the bottom bracket. Careful use of a hacksaw, file and a facing tool should be able to achieve this. 

There are a few threadless self-tightening bottom brackets on the market. Perhaps one of the best is the Grand-Cru from Velo-Orange

If you intend to have the frame work done professionally, it is worth jumping to option 4:

Here is a photo set from flickr showing how someone used a threadless cartidge bottom bracket in 73mm wide frame.

4.) Have the bottom bracket narrowed to 68mm and re-threaded to 24tpi:

One of our site members, Luke, had this work done by Alex Meade Bikeworks, showing us a full example of how a bottom bracket shell is modified. Click here to see all the gallery images and his comments. Here is a brief summary showing what he has done:

(right) Whilst a milling machine has been used to remove most of the excess width of the bottom bracket, a bottom bracket facing tool is used to remove small amounts of metal until you get down to exactly 68mm. Again, not a cheap tool for DIY people. If you can get your hands on one for this purpose, consider yourself very lucky! The tools for this work will be held by a frame builder, so consult them to see if they are willing to do the work for you. Chances are it will be much cheaper than buying the tools!

(left) The bottom bracket shell has been narrowed with a milling machine and now new threads are being cut into the bottom bracket shell. The new threads will go much deeper than the original 26tpi ones, so plenty of cutting lubricant is needed and the threads are quite strong. The taps being used are professional tools found in bicycle frame-builders shops. Probably too expensive to be worth buying for a home builder, and unlikely to be loaned out by a bicycle shop.

(left) Here is the complete bottom bracket with a newly-fitted Shimano UN52 catridge. PERFECT FIT! He makes it look so easy doesn't he? I've emailed him about advertising this service here - will get back to you on the price of this work.

Luke informs me that this whole job was done by Alex Meade Bicycle works for $85 US (price at of Feb 2012)