gitaneusa.com :: View topic - Bottom Bracket Help

stealwhereyoucan

I have a 1984 Kilo that came with Nervar cranks/BB. I want to replace the bottom bracket, but am having trouble with the threads. I know it's english, not french threaded, because the right-hand cup unscrews backwards. But when I tried to screw in an English BB, it was super, super hard and I stripped the threads. What did I do wrong? Should I not be using english cups?

Thanks everyone!

-william
New York

vanhelmont

I don't know if it is a lot of help now, but parts on a bike usually shouldn't be very hard to put together. If they are, my first guess is either the thread is slightly damaged, or I'm doing something wrong. If it really is an English BB, a shop should be able to chase the threads for you. I've had the threads in cranks for pedals chased a couple of times. It looks like very little metal that comes out, but the pedals go on easy afterwards.

sandranian · Site Admin

My (Lofter's) Kilo was (is) English threaded. I never had those types of problems, but it may be swiss threaded?

stealwhereyoucan

I don't think it's Swiss - looking at them up close, the Nervar BB cups' threads were identical to those on the English BB I tried (and failed) to install. But could I be wrong about that? Were some '84 Kilos Swiss threaded? (I know most were English... right?)

sandranian · Site Admin

As far as I know, most were British/standard.

That doesn't mean that there weren't oddities. Did you see if the threads were the same on the Nervar BB and the one you are attempting to install? Did you run the original cups back through it?

stealwhereyoucan

Yeah, like I said, the threads on both cups (the original Nervar and the new English cups) look identical. Would I notice if one was Swiss? Would the difference be visible?

I'm thinking something happened to the threads a while back when the Nervar cups were first installed that made them wonky, and that I should just take it to a shop and get the threads chased, like vanhelmont recommended. If they are indeed Swiss threads, and not English, I'm hoping the LBS will notice.

sandranian · Site Admin

Another possibility:

Is the "depth" of the threads on the new and old cups identical? A lot of the frames were made with a certain production cup in mind...and they were only tapped to that distance. For example: On a bike that was factory built to take a Stronglight BB, they might only tap/thread the BB to a depth of 10mm. However, for a Campagnolo cup, 15mm is required (those numbers are just guesses for purposes of illustrating a point!).

Could that be the issue?

stealwhereyoucan

Ah-ha! Yes, the original Nervar cups are much shorter than the cups I tried to install... That must be the issue. So... now what? Am I stuck with the old cups? Or can I get the BB shell tapped to extend the existing threads deeper?

sandranian · Site Admin

A couple of different options:

(1) Recommended that you tap the BB. Make sure it is a good mechanic.

(2) Not Recommended, but works: File off the threading on the last few mm of the replacement bottom bracket cups.

lofter

another option , mavic makes a bb that is for stripped bb's. its tappered on both sides and it actually doesnt thread in, it tightens up to the edge of the bb. i would try tapping it first. and see what happens then if all else fails use the mavic bb, and the mavic goes with the french theme Wink