recovering stroke victim
Yet more on the Twenty BB...
So I thought I'd try the "so called" cheap route. I found a 7NL spindle. I can just get it to fit with the standard cups if I remove the locking ring. But even if that would work, I find the chainline is all wrong.
I also have a NOS shimano 68mm BB (came with the crankset I bought for this). I reconn that if I hack off about 8mm from the drive side, it will probably fit with a good chainline.
The problem is that will leave no thread for the cup. So if I had a 1-3/8" 26tpi, left hand thread tap everything would be good. But I don't. Does anybody?
One other posibility is to have it tapped 1-3/8" 24tpi and use the shimano cup. This would be good because it would almost all be new threads. Anybody any opinion on if that's possible without damaging the original thread on the other side?
If you retap the bracket with standard English threads and take 2 mm off each side of the BB shell, then you are ready for the 7NL and standard English cups. when you say Twenty, you mean the Raleigh Twenty retreau folder no?
Chainline will be dependent on crank selection and whether you use the inside or outside position for your chainring. r, G.R.
recovering stroke victim
Originally Posted by Guy Retreau
This is the folder Forum. What other kind of Twenty would I be talking about? :-)
Obviously, I'm going to have a closer look before commiting myself but, with the parts I have to hand, it looks like I should take more off the drive side than the adjustable side, in order to get the right chainline.
My point being that that would allow me to retain useage of the original threads on the adjustable side, and have "weakend" threads on only one side.
Or better still, if somebody knows where I can rent or buy a left hand 1-3/8" 26tpi tap then I could retain both cups.
The main point here is though that, before I started down this path, none of what I read indicated that to make the 7NL spindle work I would have to re-tap the threads anyway.
Do as you please, but retapping to standard threads opens up a world of alternatives. Finding a tap for the proprietary Raleigh threespeed BB is going to be a chore. I retapped and ran a 7NL for a period but like you have found it puts your chainline way outboard. Now I am running a 118mm cartridge BB with
the drive side spun in to give me the desired chainline, and used a headset spacer inside the leftside retrainer to take up the additional width in BB shell. I ground bothsides of the BB shell to keep the setup symetric. A 68mm cartridge and 4mm spacer gets me to the 72mm shell that I now have. Loctite after rethreading has accomodated any slack there may have been in the reworked threads.
Just another vote for retapping. As you have already found out, the original threading doesn't even run all that deep, so you will actually have quite a bit of new, strong threads even if you don't choose to cut it down,