auchencrow

I would like to install a square drive cotterless crank on and old Raleigh Grand Prix, and I noted that that BB shell is 71mm instead of the usual 68. I know I need to use a longer spindle, so that the lock-ring will still engage the threads on the adjustable cup.

Supposedly Italian bottom bracket spindles are longer, but are expensive and only marginally longer.

I understand that old MTB bike spindles are longer – long enough to accommodate a 73mm shell.

Q - Can I assume that any junky MTB I find would have such a suitable spindle?

cny-bikeman

https://www.bikeforums.net/archive/in.../t-362857.html

What you use partly depends on the chainline you will have on the back of the bike. It's not just length but how far out the chainwheel will be.

auchencrow

Hi cny-bikeman!

Indeed, I have a 42mm chain line to maintain, and a Sugino JIS sq taper crank. I never know what this means for exactly how far out the spindle needs to be, but past experiece tells me it's better to err a little on the wide side. I am assuming a MTB JIS bottom bracket made for a triple would do just that.

Right? Wrong?

duckforcover

Generally, if the chainline of the front rings are a few mm's further out than the rear chainline... it's no problem. Matter of fact, a lot of bikes are built this way. It depends on the shape of the crank arms, meaning how offset they are from the square taper.

MTB triple BB's are not necessarily any wider, the cranks are completely different.

Bezalel

What you have is a Raleigh BB. Velo Orange has a threadless BB that may work for you. You also might want to check with a frame builder to determine if it would make sence to mill the BB shell to 68mm.

Jeff Wills

No. You're confusing spindle length with bottom bracket shell width. Spindles made for a 73mm width shell have the bearing races further apart than those made for 68mm BB. Both were available in a variety of overall spindle lengths, although spindles for 68mm width shells were much more common than those for 73mm width shells. Complicating matters is that different grade BB cups will be different thicknesses, so the way we did it back in the day is by grabbing a selection of BB spindles and keep trying until something worked.

auchencrow

I'm familiar with the VO and milling options, and I knew that either would be cost prohibitive, so I think I'm going to have to take a chance with a No5 spindle, or search vainly for a No7. Every one I have is a No3. . .
I can't remember where I read it, but once I saw something about MTB spindles being made for wider shells, and if they're JIS taper I was thinking it would go. Ah well.
Apart from paying through the nose on eBay for an Italian bb, I may just stop by the coop and nose around, or alternatively, just stick with cottered. (I'm doing this for a flip and already I won't see $25 margin on it, even in the spring.)
Thanks very much all.

larry_llama

what was wrong with the cottered crank? just wondering...

HillRider

I assume your Raleigh has Raleigh's proprietary 26tpi threading. When we converted a friend's '73 Super Course from the OEM Stronglight (which was neither strong nor light) cottered crank to a Suguino square taper crank, we kept the old Raleigh cups and just replaced the spindle. The cups were deep enough that we were able to use the lockring with the spindle intended for a 68 mm bb shell.

auchencrow

It's missing a chain ring bolt and I have extra alloy cranks doing nothing. An alloy crank would facilitate maintenance for its future owner.

auchencrow

Your 26tpi assumption is corect.
It sounds like you and your friend really lucked out. The replacement spindles I cuerently have allow the adjustable cup to go flush with the shell.

larry_llama

for a flipper, i'd just keep the cottered cranks and spend the money saved on a bikesmith cotter press :-)

Mr IGH

I did this mod in the eighties, we always used a old fashion spindle with the thread for the crank fixing nuts , not bolts. A 3T was the right size if I remember correctly.