Bottom Bracket Thread Clean-up
 

Quick question. I lightly rebuild about 50 bikes a year, (for donation), and try to do all repairs myself. I have always avoided loose bottom brackets since I did not have the tools for removal. Simply, they intimidated me. I have removed and reinstalled 2 in the last couple of months and feel better about the task. The only thing that I see a problem with is finding threads that are not in good condition. I don't want to spend $450.00 for a Park thread chaser. I see cheap $60.00 ones online, but is this a case of you get what you pay for? I also see right and left taps for around $90.00. a pair. Any advice on what to buy for thread clean-up.

Thanks

A small rotary steel brush and a drill. Spin the brush around in the threads of the bottom bracket with the drill running at about half speed. The brush will clean about 85% of any old grease and debris out of the threads. Same for the threads on the cups and you should see marked improvement in your work. HTH, Smiles, MH

Take an old cup and cut slots across the threads to create your own thread cleanup die.

Most older bike don't have BB threads that are buggered enough to need a real chasing with a tap. Some do, but this is part of doing business. Either you invest in tooling (whether home made of bought) or you learn to be good with walking away from a project and that bike becomes a donor for other projects or a lesson in the cost of doing what you do.

If mere corrosion is needed to be removed the wire wheel on a drill works pretty well for little cost.

This is but one reason that shops that have to pay employees and rent shy away from used bikes. Andy

Go to a hardware store that sell welding supplies. Buy one of the smaller stiff wire brushes used for cleaning up welds. Should only cost a couple bucks. Dip brush in penetrating oil. Work it around inside bottom bracket in the direction of threads. Let the tool do the work. Carefully comb the threads with the wire bristles. Presto. All cleaned up. Good to go. That's it that's all. Done deal.

I was trying to clean some large diameter internal threads once. An old machinist told me to find a smaller diameter tap with the same pitch, and use it as a scraper. Worked wonders. You could probably even get away with a right hand tap on the left hand threads for this purpose.

That’s a BINGO

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Works like a charm. In the video, the BB shell in question is the PERFECT candidate for the wire brush technique. I've used this technique for many years and it's the way to go. His threads still had residual paint on them as well; the wire brush will remove pretty much everything. And one more thing: the wire brush to get has a larger OD than the BB ID, so it takes some effort to get the bristles into the BB shell. This is good as they're forced as deeply as possible into the threads. Don't get one so small it isn't a tight fit.

Now as far as the home-made thread chaser goes.... Looks like a cool project. However, note that the tool you create (and hopefully from a set of steel BB cups, not Al) will not be actual tool steel, so it will dull quickly and not cut very well. Also, his cuts with the ceramic wheel seemed to leave the slot somewhat rounded. If I were cutting, I'd want the edges either vertical, or even undercut a bit so the tool can pull material away instead of just mash. This is how taps are cut in many cases. Oh, and use oil when you're using it, preferably cutting oil.

I volunteer at a couple of non-profits where we lightly refurbish many hundreds of bikes a year, and I've never run into a case where a BB tap has been needed. Wire brush and cloth always work.

A far more likely "fatal error" is a crank arm (or seat post or stem) seized.

Yes it's not a tool steel proper tap, but for a chase here and there it's better than nothing. You can just cut a new set of slots every time or two you use it and it'll last quite a few BB.

I've had the same question, but when I really needed chasing I took it out to the LBS. Until the recent loss of several local LBSs and the COVID business closures, One of my local shops had some excellent young craftsmen - the owner did a great job of training his employees, as well as hiring good ones. The best one is now a contract wheel builder at another shop, but only wants to make wheels in between operating his own tool and die shop.

If I set up to go it alone, a few questions: In cleaning threads, you don't want to change anything about the original threads, except perhaps to remove any threads that have broken loose. So tool steel as in a tap is not the best choice. The set of grooved BB cups should be a decent choice - properly threaded it should shear out dirt on the surface of the existing threads, but not down to bare metal.

Similarly, would a small brass rotary brush be a better choice than one with steel bristles?

Yes, I would want shearing action at the interface between the BB cup-turned-chaser and the BB shell, and if it could lift the crud away from the cutting area, that would be great!

One of the challenges (perhaps the biggest) is getting whatever type of thread chaser to engage the initial few threads as the original were done. Of the more then a few thread repairs I've done it's the couple/four threads at the shell's face that are the ones needing the corrections, don't remember when on a used bike I had to clean up the threads beyond these first few. (Well, this excludes the few that needed more threads inside the shell to allow deeper cups to fully thread in, but that's not a repair job. It's modifying to fit other then OEM parts, a different job motivation IMO).

Why is this, the first few threads, an important detail? Because if these first few threads are not coaxial to the shell any "corrections" will only better allow the cup to cross thread and then the deeper ones will be damaged. Especially if the deeper threads are also crossed (and this is from an assembly gone bad) when those first few are properly cleaned up and the cup is run in 5-6mm it will pretty much every time act as a chaser for those deeper threads. Cross threaded cups are far less common then wallowed out threads from either seriously loose/backed out cups (and the bike is continued to be ridden) or from a buggered up insertion.

Some of us (and I overlap with this tiny number only slightly) can retain the coaxial orientation while also applying enough force to move/cut metal. This is far easier with the slotted across it's threads cup then with a single faced tool like a tap. Sure the tap will remove the crud but to actually move metal that's a lot harder to do, most here have never had the chance to found this out. A slotted cup offers a reference surface, the cup's outer face, to try to keep parallel to the shell's face. A cup lock ring threaded onto the cup (pretty much RH threaded rings exist, but also pretty much most thread damage is found on the shell's LH side) will bring this reference face closer the that of the shell, making the visual easier to track.

A very big reason why a proper tap set made for BB shells is so nice to use is that they will be mounted on a pilot shaft. Thus both taps are kept pretty much coaxial at the start of any chasing. Thus the first few threads are cleaned up/chased coaxially. I consider this to be important.

So for mere cleaning the previously mentioned methods are fine and far less expensive then a proper bike intended and piloted tap set is. But for correcting damaged threads I'll want a true BB tool (pun intended true as in proper taps held true to each other).

I advise many budding frame builders in other forums and one question that repeats (sometimes it seems too often repeated:)) is that of tool needs. I suggest that only when one wants to control all aspects of their product will a BB tap set be a good value. Otherwise I suggest to partner with a shop/other builder who has them already. But in the building of a frame with a lugged/socketed shell the filler often flows through the sockets and into the threads so actual metal removal is the need. Andy

Bingo! I have seen a home made cup/chaser that had the cutting edge made from the cup's "skirt" and not across the threads. This will both allow a deeper cutting form and also tent to push the crud ahead of the cup and not have ther crus re crammed back into the threads as much. Funny how memory is activated and when it's not.Andy

If you need to cut threads, the home-made chaser isn't appropriate. You need an actual piloted tap set to do it properly. But the OP is only considering chasing threads, for which the home made tool can work quite well. You don't need tool steel (although BB cups are hardened steel) or sharp vertical edges on the slots. The chaser only needs to be able to push rust and debris out of the threads and into the slots.

Hello, found this old thread and bought some steel wire brushes as suggested but before proceeding I just want to double check, and triple check, that this isn't going to grind the threads into oblivion. I would rather try brass wire brushes and maybe I will but I could only find the disc type, these pipe cleaning brushes, I'm guessing for welding, seem perfect for this job (38mm and 28mm) except that they might be way too brutal, they are very stiff and very mean looking. Plan is to spray in some light oil, of course set the drill on low speed, give it just a few spins, and check the progress, slow and careful (maybe avoid back and forth motion?) but, honestly these brushes look like they'll grind the threads off in an instant. It's for a nice and otherwise clean Moser Deda Zero Tre frame, that I don't want to wreck.

BTW, the issue is rust in addition to hard grease, and crud, would kerosene be better than light oil? I also have a round p-tex brush for use with a drill, maybe I should try that first?

Maybe someone will chime in? All opinions and dire warnings welcome.

https://cimg8.ibsrv.net/gimg/bikefor...f3858b6e01.jpg

Which steel is harder? The brush or the BB shell? If you only run the brush for a second or two with light pressure you will likely do little. Except to start the learning process as to how hard to do this for real:) If you're really worried hold the brush in a Vice Grip and try it by hand. I've done this many times and while there's often some surface wear to the threads after it's not much and far better than rust. Andy

I bought a cheap bbkt tap set from AliExpress (maybe $80 three years ago) it's been fine for the few times I've used it, in both aluminium and steel. If you're not sure that a thread is straight, the tap holder aligns the two sides very accurately so you're sure it's not crossed, something that most DIY solutions aren't going to do. Used with a proper metal cutting lubricant, it's a quick and easy way to tidy the shell threads before fitting a new bottom bracket.
https://cimg5.ibsrv.net/gimg/bikefor...cb044dd0ec.gif

Reporting back as it may help others. I got up the courage and went at it, slow and careful using the brushes in the image above and a spray of cutting oil on the brushes and inside, worked a treat, threads are fine, the shell is as clean and shiny as the day it left the builder, or maybe better. I first tried the 28mm brush, slow and easy, not too much back and forth, checking after a few turns, checking that the cups still went in, wipe, and repeated. Then I got extra bold and forced in the 38mm brush worried it might not turn but it was fine, again a few quick turns at slow speed, worked from both sides not pushing it back and forth all the way through just to be safe, and the shell was left pristine.

Sadly, the drive side threads were cross threaded from some previous owner, I was hoping it was just gunk and rust, the facing is pretty raw too, looks like a hack with a file, now I know why I got the frame cheap. Now I need to find a shop with the tapping tool and the facing tool too. needs a headset pressed in and maybe the fork cut down a bit, could use a repaint, lots of serious flaking around the BB and the headtube that Moser diligently chromed and then painted over. Maybe there's a proper prep for chrome but they didn't do it.

I'm in a provincial part of Italy and tragically all the shops with such experience long closed up, only shops around me are "youngsters" with mostly carbon fiber press-fit experience, I know more than them regarding steel and just don't trust them even if they had the tools. This bike needs the fork cut down too, I'll probably have to ship it off to someone, somewhere, my cheap race commuter risks becoming my expensive race commuter.

A tap can only remove material, and may leave the threads too loose to secure the cup. Unless the shell is Italian thread (I did notice that you mentioned you were located in rural Italy), you can ream a metric or English thread shell and tap fresh Italian threads. If it is already Italian thread, your best bet is to use a threadless cartridge, which are offered by several manufacturers.