bad bb threads

[dollar]

The philistine who worked on this bb previously, cross threaded the rhs threads and mangled them pretty badly. I have cleaned them up as best I can, but I am not sure the cup is going to stay put (tighten up?). I am reaching for the loktite.... Has anyone got any better ideas?

[Sammajoor]

PM Johan Bornman............... he will have an answer

[Johan Bornman]

I assume you're afraid of tightening it properly in case it strips.

 

You don't say if it is an alu or steel bike - I assume Alu thread since most bikes are nowadays carbon (with alu thread inserts) or Alu. You also don't tell us whether the frame's threads were damaged or the cup's threads. This could have a bearing on your your approcah.

 

BB cups on English-threaded BBs are made so that pedal rotations keep them tight. The mechanisms or that is precession, if you care about technical stuff (Wikipedia has a nice description). They will therefore not work themselves loose and if you can get away with a loose-ish BB cup without the BB clicking, you're OK.

 

Loctite is OK, it just makes removal a bit more difficult but, there are weak Loctite versions just for that.

 

 

[Slave]

I would stay away from Loctite. It is pretty good stuff and I use it often for other applications.

 

In this case though I would not use loctite. I think you will be creating more problems than you solve.

 

If you thread th new cups in correctly, the thread should hold without having to resort to artificial means. 

[Jules]

Have you rethreaded them already?

[GoLefty!!]

which type of bike and what type of BB?

[dollar]

I have cleaned them up but they are pretty munched. The bb cup screws in but I am scared to tighten - it's close to pulling out the few "good" threads left. I heard that you can tap the bb oversize?

[dollar]

Johan - its steel. Old racer. It't the frames threads. Half of them are gone! Its on the chain side - lh thread. Scared to tighten because the threads that are left dont look too good either 

[Johan Bornman]

Johan - its steel. Old racer. It't the frames threads. Half of them are gone! Its on the chain side - lh thread. Scared to tighten because the threads that are left dont look too good either 

 

You have three options.

 

1) Rethread the frame as is and hope for the best.  Do this in anyway and proceed to points two and three if this fails.

 

2) Mill it out to Italian size and live with an Italian BB for the rest of your life.

 

3) Have a competent welder braze a filler layer on the inside of your BB and then find a machinist to mill the BB out so that you can rethread it with English threads. This was often done in the old days to save frames. Steel BB threads have a finite life (about 30 years) and eventually from fretting and corrosion, nothing is left. The drawback of this is that it ruinns the BB's paint.

[dollar]

Thanks Johan. Will Loktite, then fit Italian BB then throw the frame away 

 

I thought about doing the brazing myself then remembered that the whole bloody thing is held together with braze....

 

[Guest Big H]

Thanks Johan. Will Loktite' date=' then fit Italian BB then throw the frame away 

I thought about doing the brazing myself then remembered that the whole bloody thing is held together with braze....
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Loctite Blue - Medium Strength. Keep it away from the bearings. I use it on all metal to metal screws and bolts on my E-Flite Blade 400 3D Electric RC Heli.