Ben clegg

Hi
Does anyone have any tips on how to rethread the BB?
I've had the frame resprayed and the thread is now clogged with paint, i've managed to get the right side in but am struggling getting a straight start to the thread on the left (none drive side).
The frame is aluminum .
Any ideas out there?

CliffordK

Paint or powdercoat?

Many older bike shops should have thread taps, and chasing the threads should be relatively easy if there is enough to catch the original threads.

You can also "face" the bottom bracket which will clean any paint off of the outside edges, and get yourself a nice square face to work with.

Unca_Sam

Clifford has the best choice. If you're strapped for cash, try a brass brush rotated along the threads to expose more of them, then chase with a well lubricated cup a few times.

AnkleWork

Paint stripper, carefully applied.

ign1te

Use a power drill + wire brush wheel of appropriate size inserted directly into BB shell. If your drill is even moderately powerful, the paint will come off.

Crankycrank

I would avoid any power tools on aluminum threads. It will destroy them pretty quickly.

Reynolds 

You can make thread cleaning taps with old steel cups and a Dremel.

CliffordK

Probably.

Although a real tap kit will hold the tap into alignment as long as it can catch the first thread.

Bill Kapaun

And use them as "plugs" before painting-

Unca_Sam

Yeah, masking off important threads shouldn't be overlooked. An ounce of prevention...

dedhed

Are you first turning it in the wrong direction and feeling for it to "drop" and align? I realize with the fine threads of a BB feeling the drop isn't like coarse threads.

CliffordK

The other point, of course, is that:

For standard English/ISO threading, pedals are right/right, left/left

Bottom brackets are just the opposite.

Right hand side, left threads.
Left hand side, right threads.

So, if the OP has already gotten the right hand side in, then that shouldn't be an issue. But, it is always worth considering.

3alarmer 

.
...find someone with a set of piloted taps. Takes 5 minutes with the right tool, and the repair costs if you genuinely cross thread it the entire length of one side will far exceed whatever someone charges you to do it. We have a set of piloted taps at the bike co-op here, (both English and Italian). See if there's a similar bicycle co-op near you. If you already have one side working well, the pilot shaft will make short work of getting the other side started properly.

squirtdad

+1 for the win

Mad Honk 

Triple alarmer,
Those taps aren't cheap! the last set I bought were $160, so any bike shop doing thread chasing is gonna want some compensation for the tools and the job.
But the best way to do a thread cleaning is with the piloted threading tools. I have a number of vintage bikes that were sent out for recovering with powder coatings and the best option was to use the piloted taps for cleaning the threads after the painting. My advice to anyone with this problem is to look to a professional for help. The cost are just too high for the home mechanic. Smiles, MH

3alarmer 

.
...I bought some Cyclus ones through an online Dutch website about 8-10 years ago (for about 100 bucks a set, with the handles) when I got tired of always dragging my projects over to the co-op. In my case, they've more than paid for themselves, but I have a lot of projects.

I see they're up to 118 bucks American now. But unless you have some other stuff to order at the same time, the shipping costs are another 30 bucks. Nonetheless, they seem to be pretty solid tools based on my experience with them. I wish I could get a set of French threaded ones somewhere, instead of using my trusty single tapered tap in that size, one side very carefully at a time.

Gresp15C

Sometimes, if just one or two threads are dinged up, you can use a hand tap of the same pitch but a smaller diameter, as a scraper to clean internal threads. An old machinist taught me that.

79pmooney

If these are English taps and they cannot be saved and you want to keep this frame there is always the Italian thread option. Italian BBs are enough bigger that any English, French or Swiss BB shell threads at any state of disrepair can be drilled and tapped to Italian and basically be like new. (But care for them. There is no place to go if you mess them up.) You will have to find the shop that has the taps and they will want real money to do this.

I've never had to do this but have known of this for the past 40 somethng years.

Ben

wheelreason

Greedy LBS! I live for roadies coming in with stuff where they bit off too much, the algorithm says CHARGE!
And yes, it takes longer to take the tool out of the case, clean it, and put it away that the job itself, but hey, the only tool I like more than taps (grinder doesn't count) is my Abbey HAG.

Ronsonic 

On a recent build my favorite shop gave the new-to-me frame a full inspection and did a needed "chase and face" on the BB shell for $35.

I cannot tell you how much better a build goes together with this sort of treatment. I used to just work with what I got and then after a couple of builds with properly serviced Headtubes and Bottom Brackets and aligned Drop-Outs, etc. I am not going to skip this stuff again.

I am cheap, would rather DIY whenever I can, but ...

Really, it's worth it.

hokiefyd 

I have done this, and it's worked great on a few occasions. This video should help you (or anyone) out, if all you truly have to do is clean paint or other garbage out of otherwise good threads:

AnkleWork

OP: Is it cross-threaded or just clogged with paint?
Some in this forum default to the most destructive methods first and forget that taps only remove metal, not "restore" it. Using a tap should follow after some other (nondestructive) methods have been tried, and only when proven necessary. Also as mentioned above, even brass wire brushing will damage aluminum threads if not done gently. Excessive brushing work-hardens and distorts the surface making subsequent remediation much more difficult.

Ben clegg

Hi People
Thanks for all the advice , I didn't want to take it to the shop nor buy a special tool that I would only use once in a blue moon, as I wanted to see if I could do this myself. So this is what I eventually ended up doing.

Faced the edge with a packing knife blade, this made it easier for me to see what I was up against.
I then used the packing knife in the grooves of the thread, I was surprised how easy this was to get out a lot of the paint.
Eventually I used the "RJ guys" method (thanks hokiefyd) of using an old square type bottom bracket to re-cut the rest of the threads . Did this on both sides and now I can screw the new bottom bracket all the way in and out with my fingers.

Thanks to everyone for all the suggestions, really appreciated