Technical > Transmission
Nomad BB bolts
Bippers:
I was doing some fine tweaking of my BB this morning. I had slackened off the two pinch bolts did my adjustment and was re-torqueing a bit at the time the two bolts, using a torque wrench. One of the threads then stripped...whoops!
Now, I'm an engineer, so like to think I know what I'm doing. Why do Thorn use such a fine thread rate for. I have ordered two new bolts, I think I will get away with it, but tempted to tap out to a coarse 8.0m thread and fit new appropriate bolts. Has anyone done this before?
Danneaux:
--- Quote ---One of the threads then stripped...whoops!
--- End quote ---
Oh, dear. :o :'(
--- Quote ---Why do Thorn use such a fine thread rate for.
--- End quote ---
Most likely to facilitate fine adjustment and the tighter, more shallow pitch discourages the bolts from backing out. As I recall, it is a 0.75mm pitch.
--- Quote ---tempted to tap out to a coarse 8.0m thread and fit new appropriate bolts. Has anyone done this before?
--- End quote ---
I would resist for the reasons cited above. The coarser bolts will drive home more quickly and it will be difficult to get them to hold as well.
I would suggest drilling out and heli-coiling the threads. Have you checked...are the bolt threads stripped, the BB posts, or both? If it is a faulty bolt or threads, a replacement bolt of the same size may well do the trick.
A general caution, not aimed at you 'cos you used a torque wrench: I have seen eccentric BBs with grub screws of this design ovalized by overzealous tightening. It can happen, sadly.
Best and sympathetically,
Dan.
Bippers:
after the screw stripped out I ran the better of the two screws through and feels ok but I'm not sure I will ever be happy
Danneaux:
--- Quote ---after the screw stripped out I ran the better of the two screws through and feels ok but I'm not sure I will ever be happy
--- End quote ---
There's a couple alternatives. One is a thread-insert kit, example here:
https://www.amazon.co.uk/PowerCoil-3523-8-00K-0-75-Thread-Repair/dp/B00MV1PE02
The other is to use a thread-repair compound, essentially an etching polyamide/polyamine epoxy resin -- and retap through it. I would avoid it in preference for the helicoil insert. Reviews here: https://www.amazon.com/product-reviews/B000WSEUII
Even better would be if the new bolts were a good match and you could achieve a nice, sound fit in the existing bosses. Fingers crossed for your good luck.
Best,
Dan.
Bippers:
Hi Dan. I think the heli coil idea is good. Still don't like this fine thread malarkey, just feels bad to me. Never stripped a thread in my life, so a warning out there to anyone torqueing up these bolts.
I love my Nomad but this eccentric boss is the downside of a brilliant bike.
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