I would like to upgrade the spindle and reuse the cups on my Twenty's bottom bracket. Has anyone one done this? What spindle works? I delved into the Twenty info on Sheldon's site but it does not give exact replacement part numbers. This seems like the least expensive way of getting rid of the cottered cranks. Any help would be appreciated.

I haven't done what you describe but since this is quite the recurring topic on here if you want to have a scan back through the archives, I can offer some alternatives. Apologies if you've already considered them.

Put briefly - the simplest way to upgrade is to get the shell rethreaded from 26tpi threading (english raleigh threading) to 24tpi (I may have the numbers back to front here but you get the idea); From what I've read - a good bike shop with a leaning towards the upkeep of older bikes should be happy to do this, and then you'll have the full gamut of modern bb cartridges to choose from. One anecdotal version I heard was that you can rethread with brute force and some old 24 cups though I wouldn't recommend it.
Another way is to source a plastic-shelled bottom bracket from the humourously named manufacturer ***. (Info on that installation here: https://www.rhizomes.nl/twenty.html)

My own Twenty has the 'uber cheap' (not) Phil Wood / Shimano UN72 conversion a la Sheldon's site, but if I was doing it again I'd go the rethreaded route for definite.

Thanks for the help. Is the UN73 a direct replacement for the UN72? I have not been able to locate a UN72 on the web and all references seem to direct me to the UN73. I would think that there would be a spindle replacement for the Twenty's BB. I seem to remember a bike shop taking a shimano 105 sealed cartridge BB and threaded it into a 60's Raleigh Gran Prix I have. It worked but I don't rember if the threading was the same as the Twenty.

'72 superbe,

When I was building up my Twenty, I actually went down the list of crank/BB upgrades that Sheldon listed and eventually ended up rethreading. It is near impossible to source a long enough spindle...I even contacted Harris Cyclery. They sent me their longest one and it was not long enough. I tried the un72, but as you've found out, they are no longer made and it is difficult to find one in the proper length. My rethreaded BB works great, and even better, it was a cheap fix. Save yourself a headache and either rethread or source a *** bb,

Juan

After having the bottom bracket re-threaded, what would be the right bb cartridge to get? Maybe better, how long of a spindle should I be looking for? The spindle I have is 144mm end to end. Considering going from a cottered spindle to a tapered one what difference in spindle length should there be?

Looks like the default recommendation by most people will continue to be, find a cartridge bottom bracket, and either use the 26 tpi rings or re-thread the BB.

But please, if anybody *does* find an ordinary non-cottered spindle that works, post the exact model number, and a source for it if possible. I'm still using the original cottered unit on mine, and it's still fine for now. At the end of this year, though, I'm going to have to bite the bullet and overhaul it. I have some spare crank cotters, or I can find a cartridge solution. I'd just as soon go with replacing the axle, though.

Problem with the un73 is that one end of the actual cartridge is threaded so it can't be swapped out for the phil wood item. on the un72 it's a removable (eventually!) ring hence the need for it if you aim to keep the english threading.

I too have been thinking about tapping a 26 tpi Raleigh BB to 24 tpi BSA threads, and I'm not sure I like the idea at all. Some members have posted remarks such as "the difference between 26 tpi and 24 tpi is only two per inch, so it's no big deal..." or some such thing that doen't make sense to me, so I made the graphics below.

The first graphic represents a 1/2" section of metal with 13 threads cut into it, followed by the same section of metal with 12 threads cut into it, and finally what's left if you first cut 13 and then 12. This represents 1/2" of thread. So in an inch of thread, you are going to have two strong threads, four to eight weaker ones, and a bunch of very weak ones. Since ALL the new valleys will be a little thicker than the old ones, ALL the remaining ridges will be thinner than the old ones.

The second graphic shows what happens when you thread your new 24 tpi cup into the BB, and thread your new 24 tpi lockring onto the cup, and tighten the cup against the re-faced BB shell.

In this graphic, anywhere you see white between the threads, the threads are not in contact.

When you tighten the lockring, it pulls the cup to the left, so the left sides of the cup ridges press on the right sides of the BB shell ridges. At first, the load will be held by the right sides of about six ridges; as you put more pressure between the lockring and the cup, the steel of the BB shell may deflect a little, gradually spreading the load to other ridges. But you risk shearing all the ridges off. Sounds a bit risky to me.

These are not engineer-grade drawings, obviously; they are intended only to illustrate my thinking about the problem. Needless to say, if there are flaws in my thinking, I hope someone will point them out to me.

Would it make more sense to leave the BB threads alone, and grind off all but maybe 1/4" of the threads on the cup? That way, if it fails, you only ruin a cup and a small portion of your BB.

Alternately, could you melt some brass into the threads of the BB before you cut the new thread into it? I'm sure it's not a perfect solution, but it must be better than nothing.

A very nice thought in deed, but the edges of BB shell of the R20 are threaded only 15 mm. Modern BB cartridge cups have at least 20 mm of therading, so the new 24 tpi "retread" will be longer than the original thread.

Fellas

And if we use a BB cartridge with alloy cups, can't we force the entrance of the cups inside the BB shell of the R20?

Sheldon Brown the man himself says:
''The bottom bracket threading on Raleigh Twentys is Raleigh's proprietary 26 tpi size. The shells are also rather wider than standard, approximately 76 mm. If you wish to upgrade a Raleigh Twenty for modern cotterless cranks, you have 3 options:
1.
Have the bottom bracket shell re-threaded to take an ISO standard 24 tpi bottom bracket. This works, but the threads are not terribly strong, because the diameter is the same, so there will be some missing threads. (The shells are not thick enough to tap out to the larger Italian size.)

2.
Re-use the original 26 tpi cups with a long cotterless axle. "7" series bottom bracket axles are made to work with 73 mm "oversized" shells, and some of them can be made to work in the Raleigh cups.

3.
Use a cartridge bottom bracket with Phil Wood 26 tpi retaining rings. I'm told that it is possible to use Shimano UN72 bottom-bracket cartridges with the Phil Wood rings, if a Phil Wood bottom bracket is beyond your budget.
If you order a Phil bottom bracket for a Twenty, you should be careful to order a long-barrel bracket (made for a 71-75 mm BB shell), or tightening down the mounting rings may not be possible."

He claims re-tapping will leave you with some weak threads...

This is exactly the 3 suggestions I tried, and I ended up with #1. It works great, and I don't think Sheldon would have listed it as a possible fix if it was a bad idea. If it were a bad idea, I think he would have said so, and suggested not doing it. In the end, you have to make your own decision, but I finally made mine and will never look back...I've put aobut 3,000 miles on this set up so far and haven't had a problem. I can also attest to the fact that the original threading is only 15mm deep, so you will have at least 5mm of completely new threading,

Juan

After rethreading my Raleigh Sport, I needed a magnifying glass to tell the threads weren't cut into new metal. 20mm is one heck of a lot of engagement, I wouldn't worry about steel threads being a bit compromised. After all the cartridges work in aluminum, and the left side threads are plastic.

On my Sport, I faced 1mm off each side of a 70mm shell to use a 68mm BB. The shell on my Twenty measures 77mm so I'd need to face 2mm off each side and use a 73mm BB. Shouldn't be a big deal as the shells are thin and probably just 1020 steel. 15mm of original threads, minus 2 for shortening means you would have 7mm in new, steel threads and you should get at least 50% strength out of the old ones. Sounds like "Plan A" to me.