Another BB question

[Mick F]

Cards on the table .....

Raleigh Chopper (again!) BB has a cottered crank set with 140mm cranks.
I want to install multi-gears, and want to have a triple cog set on the SA hub.

I want 170mm cranks, and thought I could get a long enough BB spindle with square section ends, but I can't find one long enough for the Old Raleigh BB shell. The shell is 73 mm with 26tpi threads, and I don't want to modify anything in any way.

I bought a new spindle, as long as my LBS could order, and although it will go in, both BB cups have to go all the way in, rather than leaving a tight one and one on a lock-ring.

This spindle, I gave to my engineering mate complete with the original spindle, and asked him if he could cut the new one in half, add a short length of tube, and weld up so the distance between the spindle bearings was right.

He got back to me this evening to tell me that the new spindle is so hard that he can't cut and weld it! Perhaps he can cut it with a grinder, but it wouldn't weld as it's so hard. Normal tools won't even touch it.

All I wanted was something simple!

Any ideas about my way ahead?

[rjb]

Tried to turn a bb axle down in a lathe to fit some sealed bearings. Like your welder mate found it was so hard the lathe tools wouldn't touch it. I decided it was probably case hardened so as a last resort i left it in the dying embers after a summer bar-B-Q. The next day it was soft enough to work ok and i managed to turn it down and fit the bearings. It was then perfectly ok in use ie not soft enough to twist etc under load.

I am sure some metallurgist may enlighten you further on this issue!

[rjb]

Forgot to say this was a square taper BB axle. But another thought, you may be able to bodge it by fitting a suitably sized sealed bearing to one side to make up the difference!

Best of luck,

[hubgearfreak]

I want 170mm cranks

you'll have to grind off the stand i think?

[hubgearfreak]

The shell is 73 mm with 26tpi threads

really. if i've read sheldons table properly, it's either old raleigh and a different width, or it's standard english and 24tpi? is the BB you bought from you LBS standard thread? and the threads go in no trouble?

my LBS could order

poor old chaps. imagine what they say when you've left

if the original BB is in good order, could you fit a chainset off another (old) bike to it, that has cotterpins and 170mm cranks*? or is the issue of 1/8 chainweel going to mess with you rear hub mod plans? if so, could your friend with the engineering shop not grind the other chainset down to 3/32?

is that enough questions? is your engineering friend called peter?

* if you want one, i'll have a look in resource corner for you

[Mick F]

Answers:
Thanks guys.

The BB shell is 76mm wide. Just measured again to make sure.
The BB cups/threads are 26tpi
The spindle/shell couldn't take a different bearing system than cup-and-cone.
Plenty room for longer cranks with the stand in place.
My mate is Paul Pridham www.rkpridhamengineering.co.uk
I'll chat again, and see whether annealing the spindle would allow modification. It could be re-hardened afterwards.
Paul suggested that he could manufacture a spindle from scratch, but it would be one heck of a lot of work as the accuracy of the tapers are paramount both in taper angle and radial accuracy, let alone the bearing surfaces. As a one-off it's a no-no.
Other than the above, the way ahead is to source 170mm cottered cranks and trim the chainwheel teeth to fit an 8sp chain.
Still, I could just forget the whole idea!

[pioneer]

If you use a cottered 170 crank with 1/8" chainwheel and have either a double sprocket back to back or a Cyclo triple freewheel,a 1/8" chain will run through the derailleur.Not one of the modern one's possibly but an older Simplex type definitely works.
You might have to open up the cage a bit and/or grind the sideplates slightly.

I've got a few old cottered spindles in a box. If you need a longer one, remind me what size/lenght you're after,if one of them is any use,you're welcome to it.

[Mick F]

Thanks, Pioneer, but the original cottered spindle is fine. It was just that if I could get a square section spindle to fit, a whole new world of cranksets and rings would open. Indeed, I have a Stonglight 99 with a variety of rings available. All I need is a suitable spindle.

Hubbers.
Further to my last about stand clearance. Just measured up again, and it COULD be a problem. I wouldn't want to grind anything on this precious frame, but I know the stand can be removed by releasing the clip?
http://homepage.ntlworld.com/catfoodrob ... stand.html

[hubgearfreak]

I wouldn't want to grind anything on this precious frame

if it can be removed, then that's fine. overpriced maybe, precious i don't think so

if you want a cottered crank to skim on the grinder...i think there's one here