ARBW

Hi Everyone,

It's my first post so I'll try and make it brief.

I bought a used 2006 Trek 1200 SL and I'm in the process of stripping it down, replacing any worn components and overhauling everything else.

I noticed that with the chain off, the cranks would only spin for about 1/4-1/2 a rotation before stopping, so I removed the cranks and the BB to check it, but when removed it seemed to spin freely with no noise and there was no play that would indicate wear. When removing the BB cups, I noticed that they weren't done up with a huge amount of torque.

The BB is a 68/73mm Truvativ Giga Pipe SL which came installed with the supplied 2.5mm drive-side spacer and the rubber o-ring on the non drive-side as my frame takes a 68mm BB.

I cleaned the frame and the BB, applying new bearing grease to the internal non drive-side cup and copper grease to the frame and BB threads. I then installed the drive-side of the BB with the 2.5mm spacer finger tight (reverse-threaded as it is English drive), then installed the non drive-side cup finger tight (normal RH thread). I then attempted to torque up the drive-side cup to 40Nm, the value stated on the BB, however I encountered an issue.

I found that if I tighten the BB cup to just-tight by hand the spindle spins freely, however if I tighten it any more the spindle gets tight and won't spin unless forced. If I did it up to 40Nm the spindle wouldn't turn at all.

I've loosened it and re-tightened it a few times, each with the same effect. Both side's threads are sitting fine and the BB is centred perfectly, so I can't for the life of me figure out why the spindle should become tough to turn when the BB cup is only done up to a fraction of the recommended torque value.

As a workaround, I've tightened the LH and RH side cups bit by bit and the spindle is now slower that when the BB is free from the frame (about how it was to begin with), however both sides are only just tight, so I don't really want to re-install my cranks and ride it with a BB that could easily work itself loose.

Am I missing something or doing something wrong, or is there any reason you can think of as to why it would display this behaviour?

I'd greatly appreciate any help that you knowledgeable people could give me!

Thanks in advance.

Ben

Andrew R Stewart 

Ben- You are experiencing the preloading of bearings when in a fitting that supplies an inward force. The opposite is true with hubs that are a bit tight before lacing up a wheel and then loosen because of the spoke tension stretching the hub outward. When a bearing is new/unworn, the rolling surfaces are so smooth that even with a large pressure the balls still roll with no noticeable roughness. But after some wear and loss of lube the balls will roll roughly when under pressure. The last bit of the retaining cup's threading will place a pressure on the bearing outer race, compressing it slightly. Good design can and does reduce or eliminate this pressure BTW. good design can and often costs more either in actual $ or in time and care while manufacturing or installing. Andy.

HillRider

It's possible your bottom bracket shell has faces that are not parallel and trying to tighten both cups will distort the spindle.

dsbrantjr

This was my thought as well.

Andrew R Stewart 

While this is possible as the cartridge BBs tend to have a casing which contains and locates the bearings (and doesn't rely on the shell's faces to do so like a "classic" loose ball Bb does) this is far less an issue. In fact the LH retaining ring/cup really doesn't butt up against the shell's face at all. So maybe a threading that's not coaxial between the two sides... A RH face that's not square might tend to cock the whole BB unit but not distort the bearings much still. Andy.

ARBW

Thanks everyone.

As Andrew said, it's a cartridge-type BB, so facing shouldn't be an issue, but my frame isn't bad either, with facing registering 68mm around all measurable points.

I've just removed and refitted the BB again, this time without fitting the LH cup. When just the drive side is tightened up, there is still heavy resistance when turning the spindle.

The threads are all clean and the BB went in smoothly without catching, and looking from the LH side, the BB appears to be sitting perfectly centred.

Has anyone got any suggestions for things I could try? I'm considering just taking it to my LBS and having them fit a new BB, but I don't want to admit defeat just yet.

Thanks in advance.

HillRider

If just tightening the cartridge in the shell with no nds cup at all and it binds, there has to be something defective in the cartridge itself. I've installed numerous square taper and Octalink cartridge bottom brackets and never had anything like what you are experiencing happen to me.

techsensei

If you're tightening the non-drive side removable ring all the way in before torquing the drive side, you may not be able to fully seat the drive side against the face of the bottom bracket shell. Back off on the removable ring, torque the drive side down, and then secure the removable ring.

ARBW

Thanks for your replies everyone.

I bought a new BB which installed correctly and is working well.

Cheers!

Andrew R Stewart 

Nothing defective about a part wearing out. Andy