Bromptons -what to look for when buying a used one

[Brianjeff50]

I want to buy a Brompton. Need rather than want TBF. I want a compact folder to keep on our canal boat. I’m not one of these people who wants to ride up Alps or do Audaxes on them. An ordinary bike is work enough for me. Mrs will probably ride it a bit too.
I know virtually nothing about them except that they seem madly expensive. I’ve done basic research into the current range - six gears seems essential to me.
Info on older versions and what to look for mechanically would be a great help.

[Slowroad]

Do you actually need a Brompton - or a half-decent folding bike? There are cheaper options if you're not cycling far, and some fold down nearly as well.

[Brianjeff50]

Do you actually need a Brompton - or a half-decent folding bike? There are cheaper options if you're not cycling far, and some fold down nearly as well.

I do really. Space is tight on our boat and I’ve already had a folder which was just too big and cumbersome for the space.

[djnotts]

^"Info on older versions and what to look for mechanically would be a great help."

Post-c.2017 for the newer, better, brake levers and calipers and spider cranks rather than 1 piece chainset. Check for play in the rear frame/rear triangle hinge pin. A difficult DIY replacement job IME and very few bike shops will take it on.

Prices high - but not like they were a few years ago! Good 2nd hand 6 speed for c. 500-750 quid.

[colin54]

This is a good video about what to look out for - 21min 30 long.
https://www.youtube.com/watch?v=2vaTsEmu1RI
There are others if you search on youtube no doubt.
Personally I'd avoid a Brompton that's been used for commuting to any great extent, due to some of the wear issues mentioned in the above video.
It may be worth your while buying a copy of the Brompton Bicycle book by David Henshaw before you start looking, the latest 4th edition 2024 is the one to get - it covers all the alterations to the bikes over the previous years, a well written and researched book in my opinion.
I bought mine here (£13.28), there may be cheaper elsewhere.
https://www.ebay.co.uk/itm/396511908756

Good luck.
edit , book link added

[deeferdonk]

Looks like folks have mentioned what I would, about checking for play in hinges. Just to add as they are small wheeled rim brake bikes, if you buy one that has seen frequent use, I would keep an eye on wear of the wheel rims.

Best thing would be to find one that's hardly been used but most things are easily maintainable/upgradable and available. Watch a video on how to adjust the hub gears if you are not familiar with the sturmey archer gears.

Modifications i have found useful as a larger rider, are bigger folding pedals - (mks fd-7 ) I also replaced the narrow S type handlebar with a Joseph Kuosac brand ergonomic one that is a bit wider. Still folds up fine but feels like riding a larger bike.

[Brucey]

there's plenty to look out for, and part of the reason why it folds so small is that it is festooned with (expensive) Brompton-specific parts. Thus a used bike can easily cost more to fix (at dealer rates) than it is worth. It doesn't really help that Brompton adopt something of a 'closed shop' approach.This means that brompton will only supply (typically 1 per town) a registered dealer with bikes and parts at trade prices, often leaving others out in the cold. Even DIY repairs can be pricey, owing to the relatively high price of Brompton-specific parts. It is thus not unusual to find used bikes which have the following problems;

1) bad paint. At one time, bromptons were not usually well-painted, so it isn't exactly unusual to see one with rust developing, especially in the swinging arm.

2) SRAM rear hub in need of repair. Largely because they had no other choice for a while, SRAM rear hubs were fitted in the noughties. SACHS/SRAM no longer make IGHs, thus arguably rampant capitalism did what the RAF could not.do, decades earlier. The SRAM hubs fitted to bromptons are closely-related to the popular 'SACHS/SRAM torpedo' hub, so repair is usually possible even when new spare parts cannot be obtained.

3) New cables required. Despite the use of some proprietary fittings, it is usually possible to re-cable a brompton using mostly standard parts, re-using any brompton-specific parts where necessary.

4) Worn rims. Having quite small wheels and rim brakes, the spectre of worn rims is never far away. In fact, it is probably fair to say that they get through them at a rate of knots. Brompton changed to a new style of rim a few years ago; whilst the 'new' style of rim is probably an improvement in many respects it does use a different spoke length, so re-rimming older machines isn't quite as straightforward as it might be. Fortunately rims that are a close match for older brompton single-walled rims are available, just not from brompton. They are usually a lot cheaper, too.

5) Worn LH pedal. This costs about fifty quid, and because it folds so small, it has a major impact on the folded size. I'm not going to say 'you can't do without it' because many do; but it is usually at the expense of the folded size. The pedal contains a single large cartridge bearing, held in place by the aluminium pedal body being crimped around it. Commonly, this bearing wears, and replacing it (which is no mean feat, since it means undoing the crimping) has been the main focus of attention. I have a rather different idea; IME worn cartridge bearings usually have most wear in the balls, and least wear in the outer race. Therefore if the inner raceway of a 'worn' bearing is changed for new, along with the balls, any signs of wear will be significantly reduced or even eliminated. Thus a DFC conversion can work wonders, especially if the inner raceway is changed at the same time. Even if you have to purchase two bearings in order to have enough balls of the correct size, it is still considerably less money than a new pedal.

If ever there was a bearing crying out to be DFC converted, this is it. Once converted, the bearing is expected to be almost twice as strong, because it has almost twice as many balls inside it; no bad thing, in this application. Not only is the bearing strengthened, it is likely to have a more benign failure mode too, largely because there is no longer a clip, only balls inside. Doubtless there is an optimal alignment for the loading slots, but I'm not at all sure I'm clever enough to think of it. Until the optimal arrangement is clear, you might have to make do with my best effort so far. This is (more or less, with the left crank pointing vertically upwards, the loading slots on the left side of the bearing, and the left pedal in the usual orientation) to have the outer loading slot in the 3 o'clock position, and the inner loading slot in the 1.30 position. This should be enough to ensure that the bearing always wants to stay in one piece, unless you pedal backwards whilst twisting your foot in a peculiar fashion.

6) Worn swinging arm bearings. Conventional 'wisdom' (which is much more like a form of insanity to me) is to replicate exactly the same thing as they do in the factory. This sends you off down a rabbit hole full of expensive reamers etc. and makes out that bushing replacement is some kind of a big deal. Well, it isn't, not by a long chalk. I can categorically state that you should be able to do a much better job for much less money. You see, the bushings fit the shaft perfectly until they are fitted in the swinging arm, whereupon they deform, necessitating reaming to correct this. Any reaming is arguably counterproductive, in that it is likely to remove infused PTFE, something the bushing could always use. It also generates swarf. The solution is to reduce the OD of the bushings very slightly (eg. via SG), then to adhesively bond them into into place. This way perfect fit and alignment with the shaft is assured, since it can be present when the adhesive cures. Yes, the adhesive bond strength is likely to be low, but that is OK; if the adhesive did little more than fill the space it would probably still work OK. If you are making bicycles by the thousand, using a reamer is probably very slightly less expensive, but for a repair it makes no sense at all.

[Brianjeff50]

Thanks for all that Brucey (and to everyone else too)
Can you just explain a couple of acronyms - ‘DFC’ bearings and ‘SG’ in bushing.
Ta.

[Brucey]

DFC = directional full complement

and

SG = spin grind

you can find more by reading 'how to SG'
viewtopic.php?p=1851917
and my post in the 'cheap bearings' thread
viewtopic.php?p=1821606

[pjclinch]

- six gears seems essential to me.

Not really: I ride my old 3 speed happily round Dundee which has plenty of brown lines on the map.

What I would say is that the standard gearing option on the 3 speed bikes was stoopidly high. Mine has the -18% gearing option (15 tooth sprocket and smaller chain wheel) and that makes it a useful bike where there are hills. The -12% option useful too but I wouldn't use the standard gearing (changing the sprocket not exactly rocket surgery though). It does make it relatively easy to spin out with a brisk tailwind or downhill, but if I'm on the Brom that's in the realm of non-problem. If I was touring on it, yes, I'd want more.

Mine was one of the first with the frame extras to take the 6 speed and I went to try a 6 with money burning a hole in my pocket for the retro-fit... but having tried it decided to keep things simpler.

Pete.

[Brucey]

some (myself included) might get the 6s just to have the gears closer together....