Campy BB fixed cup damaged threads
 

Hi,
I got a ‘70s Campagnolo Record steel bottom bracket but later on I realized threads on the fixed cup were damaged, mostly cross threaded on the three first. Although not expecting much, I tried anyway to reshape them with a thin metal handsaw, then cleaned and greased everything and tried to install the cup on a useless frame. I went by small steps, back and forth, did have to apply some force, not excessively, at the end but eventually got it in. After removal, a couple of small shavings came out. My suspect was that I damaged the frame shell threads, so tried a well functioning cup to check and it also went all in without problems. Tried the damaged cup again a few times and it went in easily to the end, but once not straight. I therefore decided to proceed the same way on another (nicer) frame, but again had to apply some reasonable force before getting to the same situation: damaged and non-damaged cups eventually screwing in easily and tightening. I find it puzzling that both can work, so my question here is: is it more likely the damaged cup threads got to work more or less properly, or that I rather deformed (damaged ?) the frame shell threads? Here are pictures on the four sides of the damaged cup.
Many thanks.
PS: it’s French threading, so unlikely I can retap the BB just the same

https://cimg0.ibsrv.net/gimg/bikefor...cacb8a5bf.jpeg
https://cimg1.ibsrv.net/gimg/bikefor...09dd5367d.jpeg
https://cimg2.ibsrv.net/gimg/bikefor...7a3fb5602.jpeg
https://cimg3.ibsrv.net/gimg/bikefor...d3d4d57d4.jpeg

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you show the threads on the cup but what about those in the shell?

you could test fit another metric thread fixed cup as a diagnostic

if shell threads slightly damaged you can make a chasing tap by cutting slots into an old metric fixed cup with a bench grinder/die grinder/Dremel tool

https://www.bikeforums.net/attachmen...1&d=1637938312
such a chaser is not capable of making new threads but can reform damaged ones

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a) the cup is likely harder than the bb shell, if so the shell threads will yield before the cup ones do;
b) the cup htreads already look distorted so I'd not be putting it into any other frames before c), below;
c) grind or file a flat where the threads are damaged - keep the good ones closer to the flange and anywhere around the inner edge that they are not distorted.

Inspecting the BB threads should be done closely and thoroughly.
If that was my fixed cup (heh, heh) I would bin it.

Thanks guys! Yes, I can make a chaser if the bb shell is not too damaged, as said I tested another bb cup and worked fine, hence my puzzling, if the the shell was damaged that wouldn’t have worked.
In the end, my aim is to understand if I can still use that Campy bb cup or if the risk of damaging the frame shell is high, from my experiment above it’s not clear, your answers are clearer on that ;)
oneclick in point c) do you mean completely removing the damaged threads and have a flat surface instead? Will the cup have enough threads to hold tight?

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appears from photos that if damaged thread area on cup is ground away there would still be plenty of engagement for a secure seating of the cup


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If a damaged cup damages the shell threads it is likely to remove material. The good cup will still fit, but the fit will be looser.

I'd get rid of any thread sections that were bad, down to the thread roots - a part-circle of thread is worth keeping, though it may make initial alignment a bit tricky.

And likely yes, rule of thumb is that most of the load of a threaded fastener is taken by the first three threads.

ok, I see, thanks!

This is one reason to prefer aluminum BB cups -- vanishingly small chance of damaging the BB shell itself.

An update: before going for the solution suggested earlier, i.e. grinding flat the damaged threads, I tried one last thing mainly out of curiosity. Could freewheels be used as die proxies and help reshaping threads a little if they’re harder than the bb cup? Had spare ISO and French for the job, the former with same diameter as the 34.9mm French cup, the latter slightly smaller. I stuck the FW remover in a bench vise, put the FW on top of it and screwed the bb cup in. First gently into the 34.92mm large ISO FW with a different pitch, then switching to the narrower French 34.7mm FW but with the right pitch and pushing harder to engage the damaged threads. Did some back and forth using oil and removing some shavings coming off the cup. After repeating a few times I cleaned and checked, this time on my nice frame where I would take no risks… the cup threaded easily by hand until the bottom! Tried another undamaged Campy cup and had the same result. With one exception: the damaged cup is a bit looser through halfway, then engages increasingly firmer; the good cup stays firm all the time.

Some help to understand what happened here? I suppose that the damaged threads still provide little grip but at least screw in without damaging the shell, shouldn’t this be better than grinding them flat? Or did I damage good threads as well? Is it still safe to use this cup? Maybe adding some blue loctite?

Here are pictures of the four sides of the cup after the operation, to compare with the initial ones (of course they are magnified, with bare eye you can’t see much of the damage).

Many thanks.
https://cimg8.ibsrv.net/gimg/bikefor...299b42c5e.jpeg
https://cimg9.ibsrv.net/gimg/bikefor...b53a95253.jpeg
https://cimg0.ibsrv.net/gimg/bikefor...4932d689e.jpeg
https://cimg1.ibsrv.net/gimg/bikefor...47b7e74c3.jpeg

agree… when possible ;)

I found a NOS 35 x 1 fixed cup from the mid-70's in my parts stash.
I don't believe I will ever use it to replace the circa-'71 one on my Gitane.
Some brief research on value shows that $25 shipped would be a fair price, if you're interested.

https://cimg7.ibsrv.net/gimg/bikefor...7bd69d9ae0.jpg
https://cimg8.ibsrv.net/gimg/bikefor...38ffeddebc.jpg

Thanks, unlike yours I need the thin cups version, so I will still try to use mine if possible…

Anyone willing to comment on my thread repair experiment using a freewheel?
thanks!

Threads look good in the pics - could you use the BB lockring to check how they engage?

sure, the lockring engages and threads smoothly, although a bit looser on the first threads than on a proper cup

Bottom bracket cups are hardened steel, while the bottom bracket shell is not hardened, so it's easier for a misthreaded cup to damage the shell threads. Still, your pictures show a good number of undamaged threads on the cup, so as long as you can install it straight and secure, it should be useable.

As mentioned above, a sacrificial cup can be converted into a thread chaser tool. But if the shell threads are too badly damaged to securely hold the cup, you still have a couple options: 1) a threadless bottom bracket cartridge as from Edco, Mavic, YST, Velo-Orange, etc. or, 2) reaming the shell and tapping fresh Italian threads into the shell to use a standard Italian thread bottom bracket or cartridge.

You need french thread bottom bracket taps with a pilot to keep all straight.

Ditch that cup. lone French thread cups are around, note if it has the reverse spiral or the earlier "thin" cup dimensions.

Too late now, but there is a tool called a thread file. For next time.

If they are for sure the exact same threads when new, then a good strategy and you could also make a chaser out of a FW body by cutting groove/slots in it but as already stated, you needed a thread file when you started this or a very good small triangle file. Have saved many cups and BB's with a right angle pick to scribe all threads very clean and better to start the process. From there it takes a very light touch and anti seize to get compromised threads started, very hard to feel the first thread "catch" and know if its aligned perfectly without causing more damage as you found.

I imagine French thread files to be pretty hard to come by but a good, small, sharp triangle or single thread one.

I know you're past this so like Mr. Thompson said, if the cup goes in all the way and can be tightened well, you should be good to go.

On this I would use super glue or at least red loctite with clean dry threads and get it good and tight. ;)

excellent… and reassuring!

It’s the thin cup, would like to use it for a triple spindle and crank, couldn’t find so many around and not at reasonable price for now…

A thread file tool… I didn’t know about and used a hand saw, that says all about my knowledge of the matter :foo:

the French cup pitch is 1mm, so I searched for a metric thread file, is it something like the one in the picture below I should have used?

happy to read the FW method was not so wacky, the result doesn’t seem so bad given how the cup goes in but I needed better trained eyes to confirm. I will try to go with it and use some loctite as suggested, isn’t the red one too strong? I never used it but how likely is that the cup will stay there forever and be impossible to remove if need be…?

in any case, many thanks to all of you !!!

https://cimg5.ibsrv.net/gimg/bikefor...ac2f654de.jpeg

Thats the best kind to use and they have single bade ones kind of like a knife blade, as we know a hacksaw isn't tapered like a file. Well my hacking inclination is pretty strong having been a mech/tech all my life, drag racing mc's for 25 years and plenty else, many here don't agree with some of my methods but if you proceed with an abundance of caution and patience, you can succeed with some pretty unorthodox workarounds.

In general, any "loctite" other than red is an oxymoron, its not loctite if it doesn't hold semi permanent.

In this situation it seems likely to come loose more easily when already prone to do so.

Never had anything put up much of a fight, even with red, I would get this completely clean and dry and lock it down good. these are where I use my removal method setup to tighten these when I think they won't stay tight and it always gets them apart afterwards too.

This has never failed to remove a cup without any damage to the tools, parts, frames, paint or flesh.

The oldschool Sugino wrench is the key but others work with this when you trap them in place so you can really lean on them, adding a pipe when necessary. ;)

https://cimg8.ibsrv.net/gimg/bikefor...99673e2e1c.jpg
https://cimg9.ibsrv.net/gimg/bikefor...dd2f27db0d.jpg

Go backwards - if a right-threaded cup, place it in the shell and turn anti-clockwise with light pressure. When the cup gets to a point it will drop inwards one thread and that's when you know you have the start.

For damaged threads there may be more than one point where the cup drops. Check the cup visually as most often the original threads will still be there, and hopefully they are still deeper and better formed than whatever damage there is. Go around several times and decide which point has the best-feeling drop - size, and at the moment after the drop look at the alignment. Use that.