Clockwise thread on a bottom bracket?

hfidgen

Hiya,

Trying to fix my girlfriends BSO (bought from Halfords?) and on removing the bottom bracket found it was a truly old-skool cup-spindle type with ball races and the lot.

I'm trying to replace this all with a cartridge BB (Shimano UN26) but it appears that the setup is R-L not L-R!

IE the UN26 needs the main unit inserted from the left (when looking with the bike upright) and screwed in anticlockwise, but the frame is actually clockwise threaded! I can screw the cartridge in beautifully if I put it in the wrong way round, but then as soon as she does a few miles her BB will fall out

Can you get cheap BBs which are for insertion R-L rather than L-R? ParkToolsseems to suggest you can...

My other option is to replace the ballbearing cages and positively fill the frame with grease i suppose...

nicklouse

is the way it has always been done.

http://www.sheldonbrown.com/gloss_bo-z.html#bottom

right on the BB is the right (drive) side of the bike and is left hand thread.

hfidgen

But... that means that as the axle is turning... it's acting to unscrew the BB?

Surely that can't be right

nicklouse

it will be just the same on your bike (if not a press fit BB).

Berk Bonebonce

Reverse threading in the bb shell might at first glance seem counter-intuitive, but it is done to counteract a process called precession, where the direction of rotation of the inner part is opposite to the direction of rotation of the radial force. So as you pedal, it tightens and not loosens.

Note that the Italians never really understood this priciple.

hfidgen

Berk Bonebonce wrote:

Note that the Italians never really understood this priciple.

yeah I read that at Sheldon. So precession is actually that the force acting on the BB is the opposite to the direction the cranks are turning? I was assuming that as the cranks turned, the BB would try to turn with them...

Blue Meanie

He He, love the pics - makes it look so easy:
Clamp pristine frame in workstand and remove BB - simples

And when you try it, in the living room, with the bike's gubbings all attached. Bike upside down, bent over with your head upside down you can't even work out which way is clockwise.

I've broken shifters using shimano tools - why are the corners chamferd?
I famously broke the work's workshop vice.
I've tack-welded the tool into the cup.
I've blow torched the plastic cup to 'remove' it.

All good fun.

n.b. The 'old cup and cone' BB's lockring are good for making 'suicide' fixed wheels, same thread/diameter as the screw-on thread on hubs.