How to Update a Folding Bike




Introduction: How to Update a Folding Bike

About: toolmaker turned sparky

This is my first instructable. Probably nothing new to most of you but i thought id give it a crack anyway.  I like the brompton fold up bikes but can no way justify the money for the amount i would use it. After reading sheldon browns article about his fold up raleigh twenty i decided to build my own but on the cheap. After a week or so i got this folder of ebay. If i were to do this again i would make sure i got one with a threaded bottom bracket. I have now got hold of a suitable bottom bracket from germany as these thompson bbs are popular there ( i also have an old bb tube i could turn down and braze in). The crank shown in the picture was one i had laying around. 

Step 1:

Modern folders are multispeed and i was looking for a way to replicate this and also i heard that the best modification was to replace the chromed steel wheels with alloy as these brake much better. I had an idea that a kids 20" wheeled mountain bike would answer both of these points at very little cost and a suitable donor was bought . The wheels and derailleur were quickly unbolted from the kids bike and offered up to the folder frame. Also at this time i removed  the mudguards and rack as i wont need them.

Step 2:

I thought that the frame looked a bit weak so i welded a piece of 1" conduit in as a brace. If nothing else i think it is more astheticaly pleasing but should give a firmer ride.

Step 3:

Next i brazed on some 5mm nuts for water bottle cage bosses . I could have used rivnuts but im going to repaint anyway and also as this is the only tube holding the head tube on, brazing will keep the tube stronger.

Step 4:

Next i turned my attention to brakes. At first i toyed with sticking with the origional sidepull calipers that came on the bike but they looked way past their best. I then decided to use the cantilever brakes that came "free" on my donor bike. I hacksawed the bosses for the brakes of the kids bike, shapped them with a round file and welded them to the folder frame. To work out the centre height for the bosses i set the brake blocks at their mid point then held it against the rim of the wheel showing roughly where the boss should go. Even if they are slightly out of position there is plenty of adjustment on the blocks latter. 

Step 5:

Then i repeated this on the forks. as the forks looked a bit on the flimsy side i decided to braze these on. I fitted each wheel then marked roughly where the brake bosses should go. I drilled two holes in a piece of scrap to hold them in place whilst brazing which wasnt a problem with the rear bosses as i tack welded before fully welding.

Step 6:

I got one of these twisted wire brushes to go in my angle grinder and it stripped the whole frame in about half an hour.
I wore a pair of safety goggles as these can "spit" bits of the wire out at you but nowhere nearly as bad as the untwisted variety.
I now  have a stripped frame hanging in my garage waiting for a free day to be painted. I use smooth finish hammerite spray cans as it dosnt need a primer and gives a good looking and rugged finish,

Step 7:

Next i spray painted the frame and forks. I had to wait for the weather to warm a bit but still used a heater in the garage. During coats i also managed to clean the wheels up.

Step 8:

I couldnt wait a week and got too carried away rebuilding to remember to take photos. The forks were greased using bike grease then refited. Then the wheels were bolted into place. The deraileur, seat post and handlebars were next. It went together really quickly and im well chuffed at the look of the bike. The adjustment levers (for the seat height,handlebar height and to fold the bike) havent come up very well and are a bit rusty but to replace or rechrome would cost too much, i suppose i could always paint them silver. 

Step 9:

Ive had to go down the route of getting an old bottom bracket to fit into the bb tube as the thompson one dosnt fit as the rear stays come through the tube. Fortunately i found a bottom bracket tube on an old rear suspension that was the same diameter as the tube on my folder with a bit of tweaking it fitted (using a mallet). I t was only when i tried to screw the bottom bracket cones in that i realised that the first end to be pushed into the frame had colapsed a bit ( it was a very tight fit). I thought about buying a tap and found that they are a fortune. I took an old shell and ground four slots then backed the relevant side away to produce my own tap. It may not be hard like a real tap but it worked. The shells and axle were then screwed into the frame and the crank arms fitted. 

Step 10:

I finally got a free afternoon to get the chain, brake cables and deraileur sorted. I bought a set of gear and brake cables for £4 and a chain at asda which seem ok quality (for my needs). The chain was wrapped around the rear cog then through the deraileur then back around the chainwheel where the spring link was fitted to join both ends together. I ran the cable outer casings into place through the brazons then when happy with the lenghts fed the inners through and trimmed them to length. A bit of adjustment to the deraileur and I was ready to ride. Im pleased with the speed and the chunky mountain bike tyres are great for going up kerbs!!!

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    5 years ago

    nice to see a Universal folder bike getting modded. Ive been after one. Not seen one in my price range. I got a Hawk Club frame, that was abandoned. Its similar. I don't have a welder tho. So it wont get many frame mods. Still looking for a new Thomson axle. I got one from China. But its takes a regular cottered crank. I did have a Polish Roadster that had cotterless cranks on, with a Thomson bb. So the axles were made. Just getting them in the UK.

    wavey davey
    wavey davey

    7 years ago

    Thanks for the comments. The bike was £10, seat post £14, paint £10, kids doner bike £8, cables £4, chain £4 so £50 all in. The bike was in a sorry state as one of the pedal arms had broken off but perfect for me!!! I rekon about two weeks of evenings here and there would do it. Cheers

    Nice job. I wish I had your mechanical skills. I bought an orange folder last year with a 3-speed hub. I live in Detroit so I wanted to get something cheap yet cool, but not so cool that someone would go out of their way to steal it. I bought it for $60, got a $50 tuneup at a bike shop and bought new handgrips and folding pedals for $25. How much money did you spend on yours and how many hours of work did you put into it? Thanks.


    8 years ago on Step 2

    In order to provide a smoother ride bikes with steel frames are sometimes designed with a tiny bit of controlled, directional flex in the frame. Not only comfort but the life of wheels may also be effected. I do not know if the bike in question had that feature or not.


    10 years ago on Step 8

    If the rusty bits are chromed steel, I would try using Oxalic Acid to clean them up. Just get a can of "barkeepers Friend" at the local grocery store, it's just OA powder. Get a plastic bowl, and shake in some Oxalic Acid, add water, mix it up, and soak your parts in it. Then make a paste of OA and water, and toothbrush the nasty bits on your parts. Wait an hour or so, and rinse. Repeat if needed. It works great for removing rust and grime from old steel, especially chrome.

    BTW, OA is an awesome non-abrasive kitchen and bath cleaner too!

    wavey davey
    wavey davey

    Reply 10 years ago on Introduction

    thanks for that . just ordered a bottle of ebay as i dont think ive ever seen that here in the shops. i will give it a go as soon as it arives, dave


    10 years ago on Introduction

    Nice job so far, looking forward to the finished bike. I have an old super-cycle folder that I plan to fix up in a similar way. No welder yet so I am going to go with coaster brakes. Fun to skid turn or stop anyway.

    Cheers zipperboy aka adventureboy7