After advice, Brompton folding bicycle frame repair

[Highway_Star]

An old mate of mine has a Brompton folding bike. Recently he noticed some corrosion on the frame so decided to strip the paint off to have a proper look. Firstly he noticed the damage to the tube cross member that supports the mudguard, then found something a little more serious.

I'm looking for advice as to a; if it is repairable and b; how?

I've never welded bike tubing before, this looks like it's brazed to me. Which I've also never done before!

 

[RonA]

Looks repairable to me, the brazing shouldn't be much of a problem, much easier than welding providing you get the area around the brazed joint properly clean first. I would have thought getting hold of the right thickness tubing might be the biggest problem, perhaps getting hold of a scrap bike frame with similar size tubing would solve that side of the repair.
RonA

 

[CRB]

If you think it is beyond you you could always try Ben http://www.kinetics-online.co.uk/framebuilding/frame-repairs-modifications/

More clever Bromptons than you can shake a rod at, and he is in Glasgow.

 

[julianthegypsy]

My friend Graham at tiller cycles specializes in bromptons. Google will find him and he can tell you everything you need to know. He also does neat gearbox conversions for them that are very popular apparently.

 

[Highway_Star]

Thanks chaps! This gives us a lot to go on.

I'm thinking that perhaps a good mates daily driver bike frame is not the place for me to be learning to braze, so it looks like it's going to be done 'in the trade'. The issue was finding somewhere as the local bike shops weren't interested.

 

[brightspark]

Thanks chaps! This gives us a lot to go on.

I'm thinking that perhaps a good mates daily driver bike frame is not the place for me to be learning to braze, so it looks like it's going to be done 'in the trade'. The issue was finding somewhere as the local bike shops weren't interested.

they wouldnt be and probably didnt have oxy acetylene gear to braze it. it looks a strait forward job to cut out and grind back and braze new part in

 

[Highway_Star]

That makes sense. And to be honest making the repair parts wasn't the bit that was concerning me, it was the process of attaching them to the frame. I've got MIG, TIG and arc readily at my disposal. I've got one of those wee 'Benzomatic' oxy sets but nothing bigger and zero brazing experience. I've only ever used it to apply heat to stuck threads.

Aren't bike frames often made of specialist alloys? Reynolds tubing rings a bell from my yoof. Doesn't sound like something one could be welding with my Clarke!

 

[MattF]

Aren't bike frames often made of specialist alloys? Reynolds tubing rings a bell from my yoof. Doesn't sound like something one could be welding with my Clarke!

I seem to recall Renold did/do have some weird alloys. Probably used normal stuff on a lot too though. It's amazing just where there gear crops up. I've seen Renold manufactured sprockets on stuff which ain't bike related.

 

[brightspark]

I seem to recall Renold did/do have some weird alloys. Probably used normal stuff on a lot too though. It's amazing just where there gear crops up. I've seen Renold manufactured sprockets on stuff which ain't bike related.

there used to be renolds chain factory just up the road from thornabythey make a multitude of power transmission products . the renolds tubing for motorbike and pushbikes was called renolds 531 tubing

 

[Highway_Star]

I've an old Coventry Eagle bike in the shed made of this stuff, had it since I was 16.

http://en.wikipedia.org/wiki/Reynolds_531

 

[julianthegypsy]

I just asked Graham, he says its a common problem and that often they twist too. You can tell if its twisted by folding it up. The wheel should stay in line with the frame. A new one is apparently £132. Hope that helps.

 

[CompoSimmonite]

Bromptons are a very expensive bike. Even secondhand they fetch eye watering amounts. My view therefore is £132 for a complete replacement frame section isn't excessive compared to what the whole machine is worth and even the rotten item will probably have a value if put on eBay !

 

[julianthegypsy]

Bromptons are a very expensive bike. Even secondhand they fetch eye watering amounts. My view therefore is £132 for a complete replacement frame section isn't excessive compared to what the whole machine is worth and even the rotten item will probably have a value if put on eBay !

I'm likewise amazed by how much those bikes cost, but seeing them regularly due to the workshop next door being a specialist, I can kind of see why. They do work very well. My mate lived on and had his shop on a narrowboat until his shop got too crowded with bikes, and they are perfect for the towpath, folding up to nothing for storage. It's also amazing how much people spend customizing them, Tiller cycles does all kinds of gearbox conversions, sprocket covers, special little widgets to upgrade standard components, the list is endless and so is the money you can spend but people do it I guess because the basic idea is so good.

 

[Cris B]

Ben at Kinetics is a top lad, worth talking to about the repair option.

 

[compositepro]

an aquaintence ben cooper is like the arch nemesis of brompton, (well ish) he kind of takes their product redesigns it manufactures upgrades and sells them ,if brompton werent brompton he would be mr brompton heres a link to his twitter site https://twitter.com/bencooper

 

[CRB]

I think he used to be a dealer but they got upset at the modifications he made. May be misremembered.

 

[Ben - Kinetics]

Thanks for pointing me to this, compositepro ;-)

That tube is a common failure point on older Bromptons - they put a vent hole facing the tyre, so the tube filled with water and rusted out. I repair by cutting back to bare metal and brazing in a new tube - I usually use stainless to prevent future problems.

The crack on the suspension block plate is something new to me, but I guess flexing without the chain stay bridge to reinforce it would cause that. I'd fix it with a brass fill on the back side of it.

The tubing Brompton use isn't especially sophisticated - it's just rolled chromoly steel, easy to weld or fillet braze. Only thing to be careful of is that the dropout and hinge plate positioning is important - best to clamp a dummy axle and pivot axle into the frame to keep everything straight.

Reynolds the bike tubing company aren't the same as Renolds the chain company, by the way.

 

[CRB]

Welcome Ben, I still want that Alligt but have got got a Bachetta in the meantime.

 

[Cris B]

Welcome on board Ben

 

[Ben - Kinetics]

Thanks