Bottom bracket shell the wrong way around, or bike workshop mistake?

[hulver]

I've been building up a frame from scratch into a new bike for myself. This has been a learning experience for me, but the one thing I didn't want to do was spend a fortune on tools that I'm not going to use a great deal. A bottom bracket chasing and facing tool was one of these, so I took my new frame into a bike shop to get the bottom bracket shell chased and faced (as well as the disk caliper mounts)

This was done, I built the bike up and had a couple of rides. All was sort of well, except the left crank came loose while I was riding. I didn't think much of it, except that I must not have torqued it up correctly when I installed it. When I did install the cranks, I managed to bugger up the bottom bracket by knocking the seal out when I was pushing the crank through (hollowtech II cranks).

So I got a new bottom bracket and I've just fitted it.

In doing this I noticed something that I missed last time. The threads on the bottom bracket shell are the wrong way around. The bottom bracket is helpfully labeled "L" and "R" as well as the direction you need to tighten them in.

However, the L is on the Right side of the bike, and the R is on the left.




The old bottom bracket was also loose, and I think this contributed towards the crank getting loose.

There are three things I think could have gone wrong.

1. The bottom bracket shell was put in the frame up side down when the frame was made.
2. The bike workshop used the chasing / thread cutting tool the wrong way around. (Surely they would have noticed the shell being wrong when they chased it?)
3. I somehow managed to fuck up installing the original bottom bracket so badly that I cut new threads into the shell

Now, I'm not discounting 3. It was a bit stiff when I installed it, in that I couldn't run it all the way in by hand, but I'm sure that I got it a lot more than 1/2 a turn in before I started using tools.

So I'm thinking that 2, the bike workshop messing it up might be the most likely explanation. Surely if you were chasing threads in a BB shell you'd notice that they were the wrong way around? Would I see it if I looked at the threads? Could you tell that new threads had been cut on top of the old.

Regardless, what can I do to fix this? I'm really down about this, I spent a lot of time putting this bike together and now I want to ride it, I can't do that if the BB is going to keep coming undone.

[LittleWheelsandBig]

The LH side of an English-threaded BB has a RH (clockwise to tighten) thread. The RH side has a LH (anticlockwise to tighten) thread.

The reason is https://en.m.wikipedia.org/wiki/Precession_(mechanical)

If the threads have been recut the wrong way over the correct threads, you will see both thread directions in the shell. Is that what you see when you pull the cups? Look closely.

If the BB shell was put in backwards, the threads will be clean and the cups easy to put in.

If the swapped around BB has been forced in over the top of a correctly threaded BB shell, it is nearly impossible to install or remove aluminium cups.

My guess is that the shop recut the threads the wrong way round...

[hulver]

The LH side of an English-threaded BB has a RH (clockwise to tighten) thread. The RH side has a LH (anticlockwise to tighten) thread.

The reason is https://en.m.wikipedia.org/wiki/Precession_(mechanical)

If the threads have been recut the wrong way over the correct threads, you will see both thread directions in the shell. Is that what you see when you pull the cups?

If the BB shell was put in backwards, the threads will be clean and easy to put in.

If the BB has been forced in over the top of a correctly threaded BB shell, it is nearly impossible to install or remove aluminium cups.

I'm pretty sure there's only one thread direction in the shell. They looked clean, and this time I could run the BB cups almost all the way in by hand, and the old ones came out easily enough. In fact they'd undone themselves a fair way when I replaced it.

So, looks like the BB shell was put in backwards then?

I really don't want to send this frame back, mess about getting it changed then build it all back up again.

Is that the best option though? Given it's quite an expensive frame.

[LittleWheelsandBig]

If the threads were recut the wrong way, the newest thread direction would be clean and bright and easy to thread the cups into. No difference to cleaning out the thread correctly, except there is less metal left to hold the cups in place.

If so, you could see the intersecting threads by looking for regions parallel with the axis a few mm wide that look ‘different’ (threads would have to be completely clean/ degreased though). The two threads intersect perfectly for a portion of the circumference. Everywhere else, the new thread would be cut into the original thread by a different amount, leaving evidence of differences in remnant thread around the circumference. You may be able to feel the difference in thread height around the circumference.

If the shop did this, it is entirely up to them to fix it. Probably by replacing the frame. If the BB shell was installed the wrong way at the factory, the shop should have picked that up when they recut the threads in the correct direction. If there are threads cut both ways, you may be able to tell which was the last cut direction by how shiny the threads are but that is less certain since the cups have been fitted, come loose and been tightened again.

[grams]

Hollowtech BB cups are made of soft aluminium. If you successfully cut new threads with them you deserve some sort of prize.

[LittleWheelsandBig]

It is an aluminium frame but even so, cutting opposite threads even with steel BB cups would take real muscle, so seems the least likely.

A competent bike shop that had in a bike with an opposite threaded BB shell should have talked to you before going any further. Cleaning out or correctly retapping a wrong threaded BB and not talking to the owner about it before or after tapping the threads is worse.

My guess is that the shop apprentice put the taps in the wrong sides, ‘cleaned them out’ (actually cutting new threads) and didn’t even notice.

[Brucey]

I double-checked what  the labelling on the BB should be

   

and the cups are indeed labelled L and R by position (rather than by thread type).

So my money is on hypothesis #2.  In any event the dealers that did the work or supplied it like that are responsible; there is no way you would be able to screw the cups in wrongly, not without an almighty struggle.

In practical terms you might be able to bond the cups into the frame so that they will stay put, but it is hardly an ideal solution;  regarding   precession, it is exactly twice as bad as having an Italian threaded BB, because both cups will tend to work loose, not just one.....

What a nightmare!

cheers

[hulver]

So my money is on hypothesis #2.  In any event the dealers that did the work or supplied it like that are responsible; there is no way you would be able to screw the cups in wrongly, not without an almighty struggle.

In practical terms you might be able to bond the cups into the frame so that they will stay put, but it is hardly an ideal solution;  regarding   precession, it is exactly twice as bad as having an Italian threaded BB, because both cups will tend to work loose, not just one.....

What a nightmare!

cheers

That's my worry. The workshop (who did not supply the frame) will say "The threads were already like that" and the frame supplier will say "The workshop messed it up" leaving me holding the crap.

[LittleWheelsandBig]

No. The thread height and profile will vary around the circumference as the interference between the original and recut threads varies. It would be pretty easy to prove with a thread gauge on a degreased BB shell and a bright light. As I said, you may be able to see and feel the difference around the circumference without tools and possibly which thread direction was last cut.

[Brucey]

I agree that you should be able to tell with some certainty what has happened to the threads in the  BB shell, if they are examined carefully.  Getting someone to take responsibility for it might be another matter though.

In the event that you can't get satisfaction, or you don't think it will be resolved in a timely fashion, you may be able to make the frame work by using epoxy resin to bond the cups in.  This would not be a good solution in that you would need to have bottomed out the origin of the problem (and if someone else is going to carry the can) before using the glue; afterwards, proving anything will be kind of tricky.

At times like this n+1 seems appealing....?

cheers

[LittleWheelsandBig]

Alternatively recut to Italian thread (and Loctite anyway) but in reality, it is the bike shop’s problem to replace the frame. Let us know how it goes.

[quixoticgeek]

My money is on factory screw up over shop screw up. Just cos the shop would have to be really fscking useless to screw up that much. Whereas fitting a tube in the jig the wrong way round... Well Friday afternoon happens every week...

J

[LittleWheelsandBig]

But the shop should have noticed that before starting work or at worst while recutting the thread the right way and immediately talked to the OP. Didn’t happen, so they didn’t know. The most recently cut thread should be the cleanest. I bet that will be the incorrect thread direction, given how easy it was to thread in the wrong cups.

[rogerzilla]

It is easy for a numpty, or even a vaguely intelligent person, to use BB taps the wrong way around.  Cyclus taps and, I believe, Park taps, are labelled according to their thread-handedness, NOT the side of the shell they are to be used in*.  Taps are so hard compared to shells that they will happily go in the wrong side anyway and bugger up the threads that were there.

I avoided this mistake by taking extreme care and spinning the tool in my fingers to see which way the threads went.  A right-hand thread appears to move away from the workpiece when spun clockwise (like a drill bit does) but a LH thread appears to move into the workpiece.

*to add a layer of confusion, Cyclus Italian taps are not both labelled R, even though they could be.

[Brucey]

this is a welded aluminium frame, right?  It occurs to me that the normal arrangement in a frame of this sort is that the BB shell is drilled with vents in four places, where each of the tubes intersects, before it is welded into the frame. If so, that would make it practically impossible to install the BB shell the wrong way round.

By contrast it is very easy for a dozy person to tap an aluminium BB shell the wrong way....

cheers

[LittleWheelsandBig]

I have cut reverse threads in a steel BB shell in the past (deliberately, for a homebuilt recumbent) and it was easy enough. Echoing the posters above, if the bike shop bloke (as is usually the case) has the frame inverted and/or is asleep and/or doesn’t know left from right, he could recut an Al frame without noticing. Still an idiot regardless.

[hulver]

this is a welded aluminium frame, right?  It occurs to me that the normal arrangement in a frame of this sort is that the BB shell is drilled with vents in four places, where each of the tubes intersects, before it is welded into the frame. If so, that would make it practically impossible to install the BB shell the wrong way round.

By contrast it is very easy for a dozy person to tap an aluminium BB shell the wrong way....

cheers

From the pictures I've just taken, all the internal holes are in the right place.

[hulver]

Full load of pictures here if anybody wants the full size uncropped pictures.

To me, it looks like it's been recut. On the right side the thread angle seems to change at the back where it's not as clean.

[LittleWheelsandBig]

I think you are right.

[quixoticgeek]

Ouch.

That is rather ugly. Hope the shop are reasonable. Looks like I was wrong.

J

[zigzag]

yep, lbs screwed up and should offer replacement/compensation.

[arabella]

Threadless bottom bracket as a last resort?

[rogerzilla]

New frame as a first resort.  At the very least, a proper ream and retap to Italian standard*, plus a new Italian threaded BB.  Would invalidate any frame warranty, of course.

*Highly unlikely that the LBS has the tools and skills for this, although they might have Italian taps if they're road-oriented.

[hulver]

New frame as a first resort.  At the very least, a proper ream and retap to Italian standard*, plus a new Italian threaded BB.  Would invalidate any frame warranty, of course.

*Highly unlikely that the LBS has the tools and skills for this, although they might have Italian taps if they're road-oriented.

Why Italian? So they only have to do one side?

Would retapping the frame to English standard on both sides not work? I have a blingy Hope bottom bracket that I'm reluctant to not use.

Frame warranty is a good point. I'm meeting the workshop manager at the LBS tomorrow, so I'll make sure that anything they do either they'll cover the frame warranty or just supply a new frame.

[grams]

Why Italian? So they only have to do one side?

Italian is a slightly large diameter, so you'd be starting by obliterating the current mess. It'd leave a bit less meat on the shell though, and I think factory Italian BBs start with a larger shell.

Recutting to English means cutting into threads that have already been messed about once. Might be ok, might not.