Krov9

So, I may well have ruined my cassette bottom bracket and / or the threads on my frame, but the thing is, both look just fine :S

I think I tightened the left cup too much (~55nm, 5,5 mKg?), and it ended up just turning freely without getting any tighter.

However, I took it apart and neither the threads on the aluminum alloy cup nor the threads on the steel BB shell seem damaged? The left cup came out and went back in without a problem, it just won't tighten against the bb cassette.

This is actually like the third time this has happened to me, so I guess I should have learned by now...

What should I do next to get this bike rideable?

Andrew R Stewart 

What kind of BB, brand/model? What material is that LH cup made of?

" it just won't tighten against the bb cassette." OP Please explain. Is the cup moving inside the BB shell as you turn it (as in it is threading in but won't stop if you continue to thread it in) or does the cup stop moving inwards but will still be able to be turned?

Was this BB in this frame before and was working well? If so than why did you take it out (and there are good reasons to do so if all is still OK). If you did remove it did you note how the cup outer edge related to the shell's face? Is that not the same now?

You have enough posts to paste a photo or three here. Andy

AeroGut

I think perhaps you mean “cartridge” BB?

Krov9

Yep that's the word, sorry.

It's the cheapest no-name cartridge I could find and ITA threaded by the way, so both sides are supposed to turn clockwise..

I'm building up the frame with a new crankset.
The LH cup is made from some kind of soft aluminum alloy. It threads in to a certain point, and then seems to just "skip" if I try to tighten it, meaning there is a slight resistance, and if I turn past that point, there is again close to no resistance... Repeat. It will turn endlessly, but not move any deeper. However, if I start turning it in the opposite direction, it comes out neatly.

Crankycrank

Perhaps you have an old French treaded BB. Made for slightly smaller BB shell but has same direction threading as Italian. Sheldon Brown's Bicycle Glossary Bo - Bz

Andrew R Stewart 

This is pretty common with threads that are not fully ruined but have some function. Not enough to overcome resistance but OK to run in or out.

Have you let someone with experience take a look? I wonder about the thread condition. What material is the frame? Andy

Krov9

Could be, but no. It says 24tx36mm on the BB cartridge.

This sounds plausible, I was working on the bike at a "bike kitchen" kinda space, and I had a volunteer take a look, but they thought it looked fine too. Just wondering maybe the threads on either side are not "high" enough to engage fully?

As far as I know, the frame is Columbus Aelle which I think is cro-mo. The BB lug seems to be cast.

What do you think, should I

1. Re-trace the threads on the BB shell
2. Find another BB cartridge (and install it with less force)
3. Just throw in some thread lock and call it a day

- or all of the above?

Thanks for the advice so far

dedhed

Honestly the NDS cup on a cartridge bottom bracket does nothing but center and support the BB radially.

JohnDThompson 

Chasing the threads removes material. Your problem is that the fit is already too loose; removing more material will only make it worse.

There's a chance the problem is due to sloppy manufacturing tolerances (you did say you got the cheapest cartridge you could find), but I suspect a different cartridge would show the same problem. If there's a local bike co-op where you could try different cartridges, that could be worthwhile. Otherwise, you could be throwing good money after bad.

Another option would be a threadless cartridge. These are available from Velo-Orange, YST and others.

Bearing mount adhesive, like Loctite #609 would be a better choice. Less aggressive and possibly worth a try would be to wrap a few turns of teflon plumber's tape around the cup threads to see if that snugs things up.

Good luck!

JohnDThompson 

It also maintains proper chainline, and an Italian thread bottom bracket, as the OP states is the case, will have a tendency to loosen with pedalling unless snugly installed, which is the basic problem here.

Hondo6

Don't think Velo-Orange offers a threadless BB anymore, JDT - I haven't seen one even listed on their website in quite a while, much less in stock and for sale.

Sunlite and YST (may be the same BB) and Olympia (if I recall correctly) do still seem to make a square-taper threadless bottom bracket. But all I've ever seen offered for sale made by those firms were for 68mm shells. The OP's bike is an Italian thread BB with a 70mm shell having larger ID than a 68mm shell. I don't know if any of those are going to work for him.

At one point, I've read that some company made sleeves for converting Italian BBs to English thread. If the threads on the OPs BB are trashed AND that product is still available, that may be a viable option.

70sSanO

There is a sure fire way to see if your BB shell threads are damaged. Since both DS and NDS have right hand threads, flip the BB around and thread the DS into the NDS.

If you can torque it, properly, just get another BB. If it won’t torque, you most likely damaged the threads in the BB shell.

John

jccaclimber

This sounds an awful lot like a stripped thread. TBD if it’s on the frame, or more likely BB side.

I echo the above to try a different cup in that side.

Thread chasing won’t help. With some BB taps you can run them backwards and do some mild thread forming, but it’s a little tricky to do, bad for the tap, and I suspect won’t help your problem anyways.

I’d use thread lock as a last resort as it can be a real bear to remove later. I don’t think PTFE is going to provide much help once at proper torque, and the lower thread friction won’t make it any harder for the cup to back out later.

dedhed

The way I'm reading the OP the "left cup" means NDS. Every cartridge I've used the DS cup is "fixed" on the cartridge. Tighten the cartridge down snug in the shell on the DS and install the separate NDS cup to "tight". The chainline isn't controlled at all by the NDS cup. If the "right" DS threads are good a little locktite will help with the Italian tendency to loosen.

Krov9

Thanks John, you are not the first to suggest that, actually. In fact, I bought two similar BB cartridges with different axle lengths, because I wasn't sure which cranks I was going to use, so luckily I have a matching set of pristine cups at my disposal.

This is correct, 'guess I'm not too savvy on the acronyms.

I'd rather not remove the driveside-cup nor the rest of the cartridge assembly mounted on it, as I got it tightened to around 55 nm to avoid said loosening in use (no thread lock), and based on my experience with the so-called "NDS" cup, it'd be scary to do that again!

I'll try my best to snag a pic of the bare NDS threads tomorrow...

Thanks all for your kind advice and great suggestions!

What I'm planning to do next is: if I manage to find some "non-permanent" kind of thread lock, I'll try to carefully install the unused NDS cup I have from the other similar BB cartridge using a slightly less ham-fisted approach 😁
and leave it be, unless it somehow fails, or I need to switch out the cartridge due to chainline issues... wish me luck 😬

Ps.

I actually uninstalled the drive side cup and bearing from the spindle with a vice and a gentle tap on the spindle head. The "sealed" machine bearing came out with the cup, as it was held on to the axle by friction only. I didn't try to remove it from the cup due to fear of damaging the unit in the process.

I dissassemble the cartridge, because I hoped to fit a spacer in between the cup and the sealed machine bearing, the reason being that the cartridge was apparently made 68mm wide (says so on the label!) instead of the ITA-spec 70mm! I guess that's why they were so cheap while ITA cartridges seem to be few and far between everywhere else! The thread markings, as mentioned, are correct to ITA spec, So bbasically what I've got in my hands is a bottom bracket that's not supposed to even exist: a 68mm wide cartridge BB with ITA thread. Must be some kind of manufacturing fault or maybe pure miscommunication somewhere in the supply chain...?

If you happened, for example, to have removed a little too much material while facing the BB shell and found yourself in a need of one of these, I can guide you to my source 😁 The brand is "Bonin" and it's sold very cheap by the pan-European(?) TradeInn conglomerate. I remember the box being labeled something else, have to check once I get home.

dedhed

Spacers, if needed, are usually installed between the BB DS flange and the frame shell.
https://velosolo.co.uk/bbspcano.html

70sSanO

Probably be a good idea to back this whole thing up and find out exactly what type of BB you have.

Is this an internal bearing or external bearing BB?

Typically internal cartridge BB are sealed with an integrated bearings/spindle. The DS is threaded in and torqued and that sets the chainline and the primary interface with the BB shell. The NDS is used for support to keep everything straight. There are some cartridge BB that have individual cups, each with a lockring, and separate bearings, but these are typically on the expensive end.

An external BB are basically two separate bearings/cups that thread in from each side and spacers are used to maintain the proper chainline and preload, in some designs. There are a number of different types that generally use either an integrated spindle on the DS crankarm or even a separate spindle. The big difference is that both the DS and NDS equally support the spindle and are equally torqued.

John

Jeff Wills

One thing to double-double check: Is the non-drive side (left side) "cup" also Italian thread? If you are working in a "bike kitchen" it's possible that someone put an English thread left-side cup with a cartridge that's marked Italian without knowing the difference. I had it happen to me and it drove me crazy before I figured this out.

Hondo6

Bingo. That info - preferably, in the form of photos showing any info printed/stamped/embossed on the BB itself by the manufacturer - along with a photo of the BB shell threads in question would be a big help.

Krov9

I think I know what I have 😊 this cartridge was sold as Bonin, but the box reads Teckno and made in China for Bematrix.it

The spacers were installed so that the left cup wouldn't sink too deep into the shell. I switched over to the never-threaded-in NDS cup and put it in with some threadlock. It wouldn't tighten any better, although I used *very* little force and turned it just to the verge where it would have hopped off the threads once more. We'll see how long this fix will last 😬

the threads on the shell too look pretty sharp and straight to me?

Most likely explanation at this point would be the combination of slightly too large shell and slightly too small cup? Threading in the cup, it felt like it could "shake around" a bit during the first few turns...

Crankycrank

I'm seeing a big gouge in the BB Shell threads above in the last photo. That could easily have ruined the BB threads to some extent. A photo of your NDS loose cup threads would be helpful too.

himespau 

I once got a BB from a brand new package this way.

Krov9

what you are seeing is not damage to the threads, but missing material (brazing) between the seatstay and the BB shell lug. So that hole was there before the threads were made at the frame factory

mitchmellow62

In the second photo the shell threading at the approximate 7 o'clock position don't look the best.