Slowly proceeding with my old Raleigh Super Course project, and I want to switch to a square taper BB. The bottom bracket on this SC is 70mm and 26tpi, so most replacement bottom brackets won’t work. Sheldon recommends using the original cups and adding an appropriate spindle. He recommends a square taper spindle with the designation “7” (as opposed to a “3” or “5”) on it as well as using 6mm bearings. The “7” spindles are scarce, but the Dura Ace BB-7400 Spindle is listed for a 70mm BB shell. Will this work for me? Or will I need a “7” sized spindle as Sheldon says?

.
...I have done this conversion a couple of times, and I have no idea whether a DA 7400spindle will work for this. Nor do I know where you would buy an old DA 7400 loose ball spindle nowadays. I did mine by sorting through a bin of spindles at the bike co-op, and one worked.......out of maybe a hundred in the parts bin.

I think, but am not entirely sure, that the "7" spindles were more commonly found on the mountain bikes of that time.

You might also check out old loose ball Italian standard spindles, which are about the right length between the bearing shoulders, but I don't know what you'll run into in terms of the bearing curvatures.


Mostly, this is one of those things you just have to try out in dry mock ups until you find something that works.

I have heard of people using sealed unit BB's with nylon cups on both sides, and just forcing them into the Raleigh proprietary threads, because they are nylon and will deform somewhat to fit. I have never tried this myself, and while it sounds possible in theory, I wonder if it's a lasting solution.

If you're not committed to replacing it per St. Sheldon's approach, Sunlite/YST and Velo Orange make threadless cartridges that tighten nicely into the shell. I've use them both, one in a Super Course.

And Phil Wood could supply 1-3/8" x 26tpi mounting rings for a Phil cartridge of your choice.

Thanks! I checked out the threadless ones - pretty interesting. I’ll keep researching.

Above, 3Alarmer wrote "... and while it sounds possible in theory, I wonder if it's a lasting solution."
It is, at least in my experience. I used a Sunrace cartridge for cottered cranks in a Raleigh Sport with badly worn BB threads.
The plastic adjustable cup misthreaded in smoothly and it has been fine for over 5 years of daily winter use.

I got a generic italian cartridge with aluminium cups and put them on a lathe and made them 26 tpi. Works a treat, the bottom of the 36mm thread is just about the same as the top of the 1.375 thread.

Can do it again, pm me if interested.

This is exactly what I did. Maybe OP could carefully measure the existing spindle and post it here. Someone might have one that would work.

This is exactly how I’m approaching the same problem, to weight-weenie the chain set on my ‘52 Rudge. Same Raleigh proprietary BB threading. I took the old cottered spindle and measured the “B” distance, which is 55 mm. So any other steel spindle with B=55 mm and shaft diameter not too large for the British cups should fit the frame. Right now we’re not taking about other compatibility points. I’ve looked at three sets of cups for these frames, I’ve found the original races to have pretty smooth bearing tracks, certainly re-usable. Same for the cups on a 1970 Peugeot UO-8.

If you’re looking to minimize Q, nail the chainline, and not have any bolt (think Specialitee TA, Rene Herse or Stronglight 49d) or crank arm interference with the frame or the BB cups, you need to meet these requirements AND find and satisfy the constraints on the two spindle stub lengths. This is not always a problem that can be solved. One of the issues is that the English BB shells are 70 mm wide, not the 68 mm you find on the more modern Standard British stuff.

The Raleigh system (cups, spindles, cotter-pinned arm attachments, and BB shells fit together and still (!) work quite well! Too bad they weigh so darned much!