Jamestyle

Hello everyone,

Thanks for any information provided in advance.

I recently installed a new bottom bracket into my bike and it seemed to go well but I am wondering if there would be anything observable that would suggest that I did any cross threading.

the reason I ask is because of all the warnings I have read online about cross threading and I am looking for some clarity that I did not actually do this. The threads went in smooth for about 4 turns then they required more force on the non-drive side. Is this normal?

Andrew R Stewart 

Differing amounts of thread cutting/chasing and grit/grime build up can be common enough reasons to feel different efforts on either side.

What brand/type of BB did you install? Some have plastic non drive side cups that have fairly rough molded threads, some cups have a thread locking compound that makes their insertion harder. Some cups have longer/deeper skirts that thread deeper into the shell than the previous one did.

Usually a cross threaded cup will look (and be able to be measured) askew WRT the BB face. Either measuring the face to cup feature (like its end or flange) or tracking the threads as they enter the shell should show cross threading. Andy

Duragrouch

I installed a new hollowtech II style crank with external bearings, and they were difficult to get started. So I put the drive-side bearing on the shaft, put the shaft through the BB shell and placed the non-drive-side bearing on the shaft, held the bearings against their respective threads, and got each started without problem; The shaft kept both bearings in much better alignment, for easier starting and less chance of cross-threading.

I recommend silver (aluminum) anti-seize on bottom bracket threads; It's doesn't change friction and torque as much as grease, but will prevent the bearing housings from freezing in place in the BB shell, whether steel, aluminum, titanium, or carbon, though I'd check to see if carbon requires anything special. With proper torque on the BB of whatever style, the anti-seize should not cause it to loosen. The threading direction also is intended to help in this regard, intended to tighten and not loosen each side, but it's counterintuitive; Left side is right-hand-thread, right side is left-hand-thread. This is opposite from pedal rotation. I can't recall the geometric term (EDIT: Precession*), but on the right side, as you pedal forward (right-hand), because the bearing is not perfectly tight in the shell threads, it will "roll" inside the shell, slowly, in reverse direction (left hand).

* https://en.m.wikipedia.org/wiki/Precession_(mechanical)

grumpus

That's the way to do it. With the axle and cups aligned, turn the cup backwards while maintaining gentle inward pressure until you feel it drop into the start of the bbkt shell thread, then you should be able to start screwing it in by hand. Once it's started, check alignment visually (it may help to place a straight edge against the face of the bbkt shell to sight against the cup) before you start winding it in hard. With cartridge bearings the threads are a lot less stressed than they were with CCB bearings so you don't need as much metal to hold them in place - if you cross-thread a bbkt you can often just chase it out and use it without any remedial work beyond a splash of thread-locking compound

mpetry912 

if it went in 3-4 turns smoothly and then seemed to tighten up then it's pretty likely not cross threaded, but you may have some crud in the threads.

I'd suggest take the cups out and wire brush the threads, make sure everything is as clean as you can get it.

There are a few older Raleighs that have a BB thread that will not take a 1.370X24 cup (I think it is 26 tpi ?) but that's an edge case.

/markp

Iride01 

If you aren't having issues, I wouldn't worry about it till the next time you have to change the BB. If that ever happens during the time you have the bike.

While you can take it apart and check, sometimes the damage done makes the fix worse than just living with the cross threaded BB that so far is working properly enough not to cause you noticeable issues.

What you describe for threading the BB in isn't unusual for things that aren't precision built. Bicycles are not the precision built machines some want to believe they are.

ScottCommutes

I like this perspective. Iride01 is saying that your original question doesn't matter. If it works, it works - whether it is cross threaded or not. The threads are not necessarily made to the highest precision. Attempting a fix might make things worse. You can always try again down the road when you re-replace the bottom bracket.

KerryIrons

Not really. If it is cross threaded that means the BB won't be square with the frame and the result will be "not good." That said, unless the OP sees the cup faces as not square with the BB faces, there is very little chance that a BB would thread in 4 runs and be cross-threaded unless the BB was already seriously messed up. If it were me, I would unscrew the BB, clean and regrease the threads, and screw it back in. I bet it goes in easier the next time.

Iride01 

Are we really worried about a 18 - $25 BB that might wear out at 20,000 miles instead of 25,000 miles? (sure I pulled those out of my you know where!)

How many vintage bikes have we taken apart with tens of thousands of miles on them and found the BB shell faces are not quite square to each other?


But I do agree that from how the OP describes the installation, it sounds like cross-threading isn't even a concern.

FBinNY 

If you got it on and it's working, that's compelling evidence that it's not cross threaded.

Anyway, whatever damage might have be done already has been done. Since it's working enjoy the bike until it's not, and deal with it then.

choddo

Unless it’s so skewed the crank can’t turn cleanly of course

FBinNY 

FWIW, given the length of thread involved, it's highly unlikely that you could thread a cross threaded cup in more than a few turns, and EXTREMELY unlikely you could ever turn it in all the way is. If by some miracle you did manage to get it all the way in, there would be a wedge shaped gap running from about 1mm at the widest point.

Duragrouch

CCB? I assume you mean old-style invidual parts? A search online says Constant Contact Bearing? Not sure I see the mechanical difference between a cartridge and individual parts in that regard. Do tell please, I'm getting tired of describing old style as "individual parts".

Regarding some saying could simply be "lack of precision" in the bottom bracket shell, I sort of disagree; The main reason for ease of cross-threading is a very fine thread pitch with respect to diameter, that makes it easier to misalign, because being one thread off is a smaller angle of misalignment, so harder to see by eye. BB shells are threaded fairly precisely, I would imagine the thread axis is very square with respect to the shell end faces, as I bet they were threaded and faced on the same lathe, or subsequent lathe stages, not using a large tap. If there is any "imprecision", my guess it would be slightly out of round, ovalized, due to distortion from welding heat, and that could manifest as increasing tightness when screwing in. But if the end cap is dead flat on the BB end face, or partly screwed in but absolutely equal in distance from the cap underside to the BB end face (within 0.1mm, that's 0.0039", which is 1/10 of the thread pitch (one thread)), it's screwed in straight. If it's off, it'll be by at least 1mm, which you will see visually.

Jamestyle

Thanks everyone. Super helpful responses. I think I’m good.

choddo

I think he means cup and cone bearings

Duragrouch

Thank you!! Yes, that's a much better term for me to use. Surprised in all my years, never heard it.

wheelreason

LOL. I can't say it's common, but it happens with some regularity that a guy will come in with a frame where a (or two) BB cup(s) are inserted from a few threads, half way in,and the "hey, hey, everyone check this out" all the way inserted ones. I've even seen the unicorn Italian/English "How in the world did you get that in there" one. Needless to say, lot$ of $ervice required...

2old

If the system seems tight and the parts don't mesh smoothly, have a good bike shop chase the threads, clean and lubricate the parts and reinstall.

grumpus

Cup and cone bearings, or cup cone balls, depending on who you ask. I'm undecided.

Duragrouch

Both make sense, though cup cone bearings makes even more sense when talking about tapered roller bearings.

For economy of rebuild and parts if not labor, CCB can't be beat, and I'll bet in parts of the world where there is not a local bike shop, amazon, nor much money, I'll bet CCB still rules.

For external BB bearings, what impresses me is not just the great function, but that they were able to make it retrofittable in a standard BSA (English) threaded shell, just fitting between the shell and the crank arms. That was a real stroke of genius. Anybody can make an entire new assembly design. But backward compatibility, that's something.

grumpus

OTOH that's great, but OTOH a larger bbkt shell makes sense and maybe it's time to move on - it would just require major manufacturers to agree on a new standard, or would be a great opportunity for making dozens of different adaptors 😧

Duragrouch

Totally agree, and no problem for older bikes as long as parts for them are still made.

I hate proprietary non-standard interfaces between parts. I'd love for a common standard, but there will be arguments about which one. Under the current market, probably one will tend to dominate and that will become the de facto standard. Hopefully, one using threads that can be installed with a cup wrench, and not pressed in, requiring a press or expensive hand tool to insert and remove. I suppose a press-fit could use standard industrial cartridge bearings, but the current ISO External threaded ones are same quality and dirt cheap, an aluminum housing containing a pressed-in cartridge bearing.

The current hollowtech II style in BSA threading and 24mm(?) shaft, has so far worked pretty darned good for me in smoothness, stiffness, durability, though I'm not a racer and it's not an e-bike. But for now, I'm just super happy with it. I'm a grouch for durability and standardized availability, took a lot to take me from square-taper, but this is something newfangled that works better and has stood the test of time. Other new stuff like carbon fiber, tubeless tires, brifters, electronic shifting, bikepacking seat racks, wheels with few spokes, I'm not yet sold on, for consumer bikes.

wheelreason

From a design and machining point of view, this is like not getting any crayon outside the lines. Check out some YT videos on guys machining watch parts...

Duragrouch

Oh I know. Before the advent of robots able to do micro-movements, such as computer chip internal wiring (dispensing gold wire if I recall), I wondered about that. Haven't seen it, but my guess was, a machine, for example, with the cutting tip 1cm from a pivot point, and the actuator controlling it, on a lever 1m or more from the pivot, to get the resolution needed at the tip. I'm sure it's different from that, modern machining (for over 50 years) with CNC control and zero-backlash controls, can move workpieces incredibly fast and precisely. But I wonder about techniques before complex machines, my guess is closer to the lever design for cutting teeth, and a similar arrangement for indexing the wheels to be cut.

Regarding the external bottom bracket, the issue isn't precision, but simply the creativity for someone to think of the design, that fits within existing envelopes. And it wasn't essential, the older designs worked. But this was better. Someone had the drive and creativity to think of that. Aheadset; Better design, compatible with existing bikes (though needed a longer steer tube on the fork). Adaptors to allow use of quick-release axles on thru-axle wheels (I found a huge deal on such wheels at the LBS, $5 each, gave to a friend, fit to his QR bike).