dominic18

Hello

I would like to replace my BBR60 24mm Ultegra bottom bracket (BSA 68) with a Rotor 30mm BSA 68mm so that I can install Rotor InPower cranks.

From the online shop I have the visual impression that the BSA thread on the Rotor BB is slightly longer than on the BBR60. Are all BSA threads the same depth/length or could it be that the Rotor BB would not fit?

I haven‘t visually checked how long the thread in my frame is…

Thanks!
Dominic

grumpus

If the thread isn't wide enough you can probably have it tapped some more. I've never seen any mention of how wide the thread should be, never even thought about it, I've tapped and fitted quite a few bottom brackets.

ThermionicScott 

I don't know of a standard for depth of threading in the shell. If your frame is an older steel one, it may not be threaded as deeply as a newer frame. The reason is that the steel cups of old-school bottom brackets didn't need to engage very many threads in the shell to get a good purchase. I've noticed that newer cartridge bottom brackets with aluminum cups sometimes have more threads, I think to spread out the load on the softer material.

If your Rotor BB cups can't thread all the way into the frame, the right thing to do is to have the bottom bracket shell tapped deeper. Alternately, I have ground off some of the leading threads on modern BB cups so they can thread all the way in.

Kontact

It shouldn't be an issue.

FBinNY 

Thread length isn't the issue because there's thread relief beyond the thread.

Since weight is always a consideration, BB aren't made with the same wall thickness all the way across. Obviously the outer half inch or so on each side has an ID based on the thread, but the middle can and does have a larger ID, typically larger than the thread OD.

dsaul

I'll second what FB said. I build bicycle frames and every bottom bracket I have used has a relief in the center of the bottom bracket that would allow you to thread something in past the end of the threaded portion.

grumpus

I disagree. A CCB BB axle exerts significant axial stress on the cups, trying to push them out, while a cassette BB exerts mostly radial forces on the shell.
You don't need much thread to hold a monobloc BB in place, which is why they can be made of plastic, or just fixed with a couple of lock rings and no thread at all engaging with the BB shell.

Kontact

"Disagree"!!!! You have to be kidding. Find a single instance of cup and cone BB pushing its way out off the frame threads. That's freakin' ridiculous to even suggest.


We can all pedal our pet engineering theories until the cows come home, but the answer to the OPs question is "It doesn't matter." Anything else is just really bad advice.

JohnDThompson 

While Cinelli and most other investment cast bottom bracket shells do have the relieved section past where the threads end, not all do. And bulge-formed shells tend not to have the relief.
In any case, if you encounter a shell that will not allow your cup or cartridge to fully seat, you can use bottom bracket taps to extend the threads.

N.B. I think the "unknown" shell above is probably Henry James, and does not have the relieved section.

grumpus

I didn't actually suggest that - I simply stated that the CCB arrangement causes axial forces to act on the cups.
I wasn't replying to the OP nor offering advice (that was in my earlier post in this thread).

ClydeClydeson

I have had older frames where the threads were too short to accommodate the cups on a Shimano cartridge bottom bracket. I used a dremel to grind away the protruding ends of the shoddily mitered tubes that protruded into the BB shell, then had a shop run the taps through to extend the threads a bit. For most modern-ish frames I doubt the protruding tube ends will be an issue, but the taps will likely be the correct solution.

JohnDThompson 

Was the problem that the threads were too short, or that the protruding tubes prevented installing a modern cartridge bottom bracket?

ClydeClydeson

JohnDThompson Both I think

JohnDThompson 

A Dremel with a grinding attachment can remove protruding tubes that prevent a cartridge from being installed, and bottom bracket taps can extend the thread as needed. Or a threadless cartridge from Velo-Orange or similar can be installed.

ClydeClydeson

This was the solution, yes.

Hondo6

FWIW: Velo-Orange no longer offers a threadless cartridge bottom bracket on their website. However, YST and Sunlight still offer them.

I believe I've also seen threadless BBs offered by a third manufacturer within the past few months (Olympia? Olympic?), but I can't say with certainty whether they're still available today.

JohnDThompson 

The YST threadless cartridge has a less-than-stellar reputation. Historically, threadless cartridges have also been offered by Mavic and Edco.

Hondo6

I'll defer to your opinion on the YST, since I haven't had to use a thradless BB - yet - and hopefully never will.

I knew about the Mavic threadless; not sure I'd run across references to the Edco version. Any idea if either of those are still made? I ask because I occasionally search for threadless BBs (personal interest, and in case of for possible future need). I don't remember seeing the Mavic version come up except as either used or vintage NOS. Would be nice to have other higher-quality options if needed.

JohnDThompson 

The YST bearings didn't last long, but it was inexpensive enough to simply replace at that point.

Both the Mavic and the Edco have been out of production for many years, but can still be found. The Mavic required chamfering the bottom bracket shell with a special tool prior to installation.


The Edco used eccentric cups to lock the cartridge in place.

Hondo6

Was afraid you were going to say that. Yeah, I've seen that they can still be found - but they aren't common or reasonably priced if NOS, either. And from what I've seen the spindle length selections are pretty sparse also.

Appreciate the info. Thanks.