Running tap through Raleigh BB shell
I had a customer come by with an old Raleigh frame, and he wants me to run my tap through the BB shell to convert it to stardard English threading (rather than the unique Raleigh threading). He insists that this is indeed possible, and works every time.
Is this true?
Anything I should be aware of?
I am using a Park tap.
I don't know if the right person is going to come through here, someone in Classic and Vintage knows. Raleigh is 24 tpi and English is 36 tpi.
Correction: English is 1.37" x 24TPI, Raleigh is 1-3/8" (1.375") x 26TPI, so it might work. If the BB shell is wider than 70mm, it will probably use 26TPI; the 68mm shells generally use 24TPI.
Originally Posted by unterhausen
Right... so can I run my Park tap through it to convert it?
I wouldn't do it myself. Taps are worth more than the frame, and you will basically be cutting a new thread. The threading depth is enough that you will be across two threads by the end. It should start running in then end up with all new threads on the other end. Sounds like more wear than I want on my tools. The point of the BB tool for a framebuilder is to create perfect factory new fits in possibly heat distorted BBS. Not re-thread pottentially gritty, and nasty old junker parts. And at that level it's your call. Sounds like a job for someone wielding the bosses tools at a local cycle emporium. But hey, I'm cheap. My local shop isn't and they would charge me 50 Canadian to do that in a fresh frame (stuff up here i soo expensive).
wow, I have reading comprehension problems sometimes
That's a pretty small difference. I don't remember ever having done this, but
I don't remember seeing all that many Raleighs either. Sheldon Brown says go for it, but
the shell needs to be faced down to a reasonable size. That may actually be more
damaging to your tools than the tapping operation
Bicycle Repair Man !!!
You can re-thread Raleigh 26 tpi bottom brackets to a standard 24 tpi... it is a common fix for those of us who ride old Raleigh's (especially folders) that want to upgrade our bottom brackets and cranks.
Because the bottom bracket has already been threaded there will be less stress on the tap than what you would find if you were tapping new threads and after this is done one can use a cartridge bb and a modern crank on an old Raleigh.
It is not a difficult job when you have the right tools.
PM me if you need more info.
Bicycle Repair Man !!!
I will move this to the mechanic's forum so it gets more attention.
I thought this was the mechanic's forum? If there's another please let me know.
So there's two extra threads per inch on the raleigh bb. I haven't had to do this, but it should be ok. However, it doesn't solve the problem of the longer bb shell, and you will have visibly crossed threads. If you have a facing tool round you can face it down. Or you can use a 72mm mtb cartridge bb and have a few exposed threads on the non drive side. Put a lockring on there if you like to cover them up.
If you have an Italian tap around that you can afford to use, you can tap the thing italian. The shell diameter of Italian is 26mm, larger than any other, and in the words of a friend of mine: "Its the standard sex change." Italian bb shell length is 70, matching the old raleigh, and cartridge bbs are readily available. This is possibly the best option sans facing tool.
Don't worry about cutting threads. That's what these tools are made to do. There are tools made specifically for cleaning or "chasing" threads, but bona fide bb taps are made to cut threads, just like any other tap.
Bicycle Repair Man !!!
As always, I can save myself a lot of typing but posting a link to Sheldon's Brown article on Raleigh threading and BB conversion options... of which there are many.
Park taps work well for this as they are piloted. Be sure to start both sides at the same time and work the taps in together.
Originally Posted by calikid2006
Other single side taps are not a good idea as the variation in thread pitch will cause an unguided tap to cant with the result that the bb cups will not screw in straight when you are done.
Also- I wouldn't use a cup'n'ball bottom bracket anymore after tapping from 26 TPI to 24 TPI- there will only be 3 good rows of threads left, and a cartridge style will have better chance of staying put.
A couple of items: Italian bb shell threads are 36 mm diameter, not 26. I've also seen the recommendation to use Blue (Grade 242) Loctite on the threads afrer changing a Raleigh to ISO/English threading.
Whoops, I must have been thinking of the raliegh thread pitch.
Originally Posted by HillRider
Anyway, 36mm = 1.42 inches = about 0.5mm larger than the standard 1.37mm English shell diameter, which is shared by Raleigh.
If what you're doing requires you to use loctite on your bottom bracket afterwards, I would avoid doing it. If the threads are going to be any good after tapping English (note I said if, though I'm really not worried), they should be good enough to hold the bracket. Clean the threads well after tapping, grease heavily, and tighten the bracket in securely. You should be able to feel it gripping well... or not. You'll probably be fine, seriously. But then again, tapping italian will give you a fresher start.
Last edited by krems81; 02-26-09 at 09:47 PM.