Brompton rear frame hinge rod?

[drossall]

They can get corroded in and an M10, or even 7/16", tap rips out. Same problem.

The frame is not scrap as long as some bush is left. They are actually steel with brass facings and an acetal inner liner, so quite hard in the core. You have two options:

1. Get a bearing puller that will expand behind the bush and can then be used to drift it out. This is how Kinetics do it.

2. Carefully cut a slot in the bush with a junior hacksaw blade and then collapse it inwards with a punch (or awl). As soon as it loses most of its grip, it will knock out easily from behind. I did this two weeks ago where the bushes had been in for 16 years.

I'm currently working on my own Brompton and having this issue. The Brompton tap is not ripping out, but the old bushes just won't shift. So it's likely to be the hacksaw method? Anyone tried soaking the things in GT85 or something?

When I did this on a friend's bike, the bushes fell out!

[Brucey]

if loose bushings fit over the pin OK then the only reason you need to ream at all is that the swingarm isn't quite straight and/or the bush collapses slightly when it is installed. So there could be a whole different solution here; by either machining the swingarm or the bushing OD the whole shooting match could be made a self-aligning adhesively bonded assembly instead. IME epoxy resin is more than strong enough for this kind of job. If this approach is viable, no reaming will be required.

[rogerzilla]

If you've ever done the job with the Brompton reamer (I have) quite a lot of plastic can be removed. The local dealer said he occasionally gets away without reaming, though. It may be that the ID of the hinge tube is inconsistent, paint gets in there, or the recesses are not quite coaxial. I doubt there is much manufacturing error in the bushes themselves.

Moulton pivots are similar and I find they normally also need a reamer once fitted - although very, very little material gets removed.

[Brucey]

I would suggest SGing about 0.1 mm from the bushing OD and then adhesively bonding them in position, using the hinge pin itself to ensure the correct alignment. In reaming, you may actually be shortening the working life of the part, by removing more of the plastic. It is surely a much better idea to machine the bushing OD.