It seems like every time I check up on the rear bottom bracket of my tandem, it has come loose. I'm thinking I should just replace it with a good quality (SKF?) cartridge but I'm wondering about how to deal with the fixed cup side of the old bottom bracket when installing the cartridge. Is there a way to unfix that cup or does the cartridge somehow install without removing it? Much thanks in advance for sharing your experience.

You'll need to remove the fixed cup. If you have an asymmetrical crank set you may want to use spacers to equalize L&R tread width.

Brad

Thanks, Brad. Now I just have to figure out how to remove the cup, whether the crank set is assymetrical enough to warrant spacers, and if so what kind of spacers to use and how, and what you mean by equalizing L&R thread width.

Most cartridge BBs are symmetrical and many cup and cone BBs aren't. Tread width is the distance between the L&R crank arms, sometimes referred to a Q factor. While tread width won't change, you may need to equalize the L&R spacing of the crank arms with shims on the drive side. I could've worded my previous answer better.

Brad

One factor unique to tandem BB choices is the need to have both cranks' LH rings end up pretty much the same distance from the frame (in other wards be in line with each other). So when changing out the rear Bb not only does the usual RH side need to be paid attention to but also the LH side. If the OE BB was asymmetrical then have fun finding the correct current cartridge one, for a reasonable price, that matches up. Of course there's always Phil BBs that can be had in asymmetrical and custom off sets. This also would solve any loosening up issues, what with their retaining rings being Locktighted in place. Andy

On a tandem stoker crankset both sides are usually made with the same casting so the BB spindle is usually symmetrical.

No worries. Discussing technical details can be difficult. I also worried that my thanks to you sounded sarcastic but it wasn't meant that way. I was just thinking ahead to the next step of figuring out what you were talking about exactly and how to proceed.

Quote:

Originally Posted by Andrew R Stewart

One factor unique to tandem BB choices is the need to have both cranks' LH rings end up pretty much the same distance from the frame (in other wards be in line with each other). So when changing out the rear Bb not only does the usual RH side need to be paid attention to but also the LH side. If the OE BB was asymmetrical then have fun finding the correct current cartridge one, for a reasonable price, that matches up. Of course there's always Phil BBs that can be had in asymmetrical and custom off sets. This also would solve any loosening up issues, what with their retaining rings being Locktighted in place. Andy

Quote:

Originally Posted by Bezalel

On a tandem stoker crankset both sides are usually made with the same casting so the BB spindle is usually symmetrical.

Andrew and Bezalel, thanks for mentioning the typical symmetry of tandem stoker BBs. I had a feeling it would be more symmetrical than a bike with chainrings only on the drive side but I really don't know how much of a factor it is for the drive side to have 3 rings and the other side to have only one. I assumed that with a standard British ISO type BB, it would just be a question of getting the old BB off and screwing in the new one.


What about any thoughts on whether to go with SKF or IRD Defiant for the tandem? I've heard these are heavier duty BBs but I just spoke with a local shop and they only carry Shimano, which the mechanic claimed wouldn't be any worse than the SKF and/or IRD Defiant but since I tour on this bike, I'd be willing to invest the extra $$$ if it will be worth it in the long run.

Two questions occur to me:

Why does your present BB keep coming loose? Will a new one solve this problem; if not why replace it?

Good question. I think it is either because of the large combined torque of two riders on the tandem or maybe because I ride it alone when the stoker is not with me so the rear BB has to function as a power-transfer axel between the tandem chain and the drive train chain (try saying "drive train chain" ten times fast).

I was assuming a cartridge would not come loose as easily as the current BB does but maybe I'm wrong. I was thinking of putting locktite on the current BB and seeing what it does but I'm afraid I would have trouble loosening it again later (I haven't used locktite much and I don't know how tightly it locks - usually I'm more concerned with greasing things to prevent them from getting too locked to loosen later).

Another option I've started considering is putting a lock-washer between the lock-ring of the BB and the frame. I've never seen that done, though, so I'm not sure how good an idea it will turn out to be if I go with that.

Do you think the cartridge BB is just as likely to loosen as the current BB?

Have you used a torque wrench to tighten the BB? It takes a surprising amount of force and I am sure I would under-torque them without using one.

I am not sure a cartridge BB will hold any better (why would it?) but YMMV.

You mean putting a lot of torque on the spanner wrench when tightening the ring after adjusting the bottom bracket? It's a short wrench so I assumed it wasn't supposed to be torqued too much but I suppose I could put a pipe on it and torque it harder. It concerns me a bit that the spanner wrench will slip while tightening it or when trying to loosen it again later, though. It only has one tooth that hooks into the notch on the side of the ring. Is that really suitable for hard torquing?

update: I have gone ahead and tightened it a bit more just by hand and it occurred to me how funny it is if the whole problem all along was that I just haven't been torquing it up to spec.

How the heck to you use a torque wrench on a cup and cone bottom bracket?

May be indicative of damaged threads, so first step is to disassemble and inspect.