TurbineBlade

I have a square taper shimano BB with the little white-colored plastic piece that threads in the normal way on the non-drive side. I noticed that when I install it tightly I am actually getting binding of the spindle..? The bottom bracket has some miles on it, but not enough that I would think it'd be worn out.

What the heck is that all about? I don't remember it doing that when I installed it new, and I am pretty sure I tightened it to about the same torque.

I thought that with cartridge units you basically install them extremely tightly, put the cranks on, and go!

Thanks,

furballi

There should be some resistance at the bearing at the proper pre-load, but excessive binding/grinding may be sign of worn bearing. If you don't have a torque wrench, then attach the appropriate weight to the wrench to simulate the recommended ft-lb.

operator

The plastic cup has MUCH lower torque spec than the main unit. Something like < 20 ft lb. That being said. You should *not* get a dramatic increase in bearing resistance upon installation - this usually indicates a BB facing issue.

joejack951

I've never seen an official Shimano spec for this. Can you point me to a source?

ValVal

Barnett says 350 in.lbs for plastic cup of shimano cartridge BB

furballi

I'd limit the torque on the plastic part to 25 ft-lb. Make sure there is no play at the crank arm.

Garthr

I know what you're referring to. On a used aluminum cupped UN-72 if I torque the cup to Shimnao spec, the bearings feels very stiff. I just back off some. On the plastic cupped ones, just make it snug, not too much torque. Shimano is nuts spec'ing both side the same torque! ... don't do it.

On these BB's the left cup really serves as a stabilizer in the shell for the enclosed unit. It has no real function for the bearings themselves .... or at least it shouldn't ..... unless as you found out you tighten it too much. I've tried other brands of cartridge BB's that you can torque the left side all you want and the bearings remain free and smooth. Maybe it's a Shimano/Tange thing. Don't worry about the cup not being very tight, it's not going anywhere. I've tested mine by marking them on the outside of the shell to see if it would move despite the lower torque .... it does not. It's not the best of designs really, but it is what it is!

TurbineBlade

Yeah, I was reading Lennard Zinn's book and he was saying that the plastic cup should be torqued the same as the drive side! As you said, doing this seems to tighten the bearings and additionally feels like you could break the plastic at any time!

I backed it off a bit and was just worried it would loosen, but I'll just keep an eye on it. Thanks for all the replies!