Sometimes you search on the internet and simply do not find the info you need to solve your problem. Bummer. You then need to think about it yourself and figure out a solution. I think this is what people did before Google and the encyclopedic internet came along. I wanted to learn to ride a bicycle backwards and possibly fab up a giraffe uni, but did not have the money. Central to both endeavours is the fixed rear hub, one that when you pedal backwards it goes backwards, and when you pedal forwards it goes forwards. This is how I converted a 20″ bmx bicycle freewheel hub into a fixie hub.
Your typical and cheap 20 inch bmx freewheel hub. Note the two holes on the top cover, which are used to remove the cover. Toronto, Canada. Photo by Don Tai
People in my neighbourhood throw away a lot of old bikes. I think they just like the new and shiny ones for their kids, so there is no market for the old ones. These bikes are great for parts and projects. I had two old bmx bikes that have freewheel hubs. These were ideal for the conversion. Freewheel hubs are those hubs that when you pedal forwards they move the tire forwards and when you pedal backwards they make that clicky sound and you coast. This is called “freewheeling”. Other bike hubs are not suitable or I could not find out how to easily make them fixed. Coaster hubs are those wheels that when you pedal forwards they propel you forwards but when you backpedal they brake. These are very common on small kid’s bikes. Their hub mechanism is not easily converted into a fixie. If you find a way, please let me know.
There are two ways to convert a BMX freewheel hub into a fixie. The first way, I found out from my buddy Darren Bedford, is to remove the freewheeling mechanism and attach a locking ring in its place. Between the hub that attaches to the spokes and the locking mechanism you install a chainring. These chainrings are rare and come from 1970s kids bikes. There are two flat but shallow indentations on the hub that are used to remove the freewheel mechanism, and you can get a specialized tool to do this. I tried hitting these indentations with a screwdriver and hammer but could not get it to budge. Since I could not find a way to remove the freewheel mechanism I would have to go to a bike shop and pay them to remove it. Total cost: $20 to the bike shop to remove the freewheel mechanism, $25 for the chainring, $20 for the locking ring, for a total of $65. He also recommended I weld the locking ring into place so it would never move. This would add another $20. This expense got me thinking about alternate solutions.
I chanced upon an Instructible from Gael – Tim, an American who said he welded his bmx freewheel to fixed but did not give any details on how he did this. I then decided to explore. My method is to remove the ball bearings and weld the hub to the wheel.
Take your 20″ bmx freewheel hub and crack it open. Mine had two holes on the top surface of the hub, one on either side. I am sure you can buy the proper tool to open this type of hub, but I did not have it and was not going to buy it. Take a pin punch, a nail or any other strong but thin cylinder and insert it into one of the holes. Position the pin punch on an angle and hit it with a hammer so that the top cover will rotate clockwise. After a couple of hits I was able to remove the top cover.
Bmx Freewheel Hub with cover removed. Note the ball bearings, and two black pawls. Toronto, Canada. Photo by Don Tai
Once the freewheel hub cover is removed this exposes the ball bearings and pawls. When you pedal forward the pawls interlock with the gear teeth inside the hub and propel your wheel forward. Pedal backwards and they glide over the gear teeth and make the characteristic “clicky” sound. Remove all the ball bearings, two pawls, and an inner washer, and remove the grease from the hub, the cleaner the better. The pawls are held in place with an indentation in the hub and can be removed without tools.
Bmx freewheel hub, closeup of the ball bearings and one pawl. Remove and clean the hub very well. Toronto, Canada. Photo by Don Tai
Bmx freewheel hub: ball bearings, pawls and inner washer removed. Toronto, Canada. Photo by Don Tai
Your hub is a pretty slick place. This is to reduce as much friction as possible so as to increase the glide on your bike. Grease inhibits a good weld. After you scrape out as much of the solid grease as possible then get some degreaser and wash the area well to remove any oily residue. I used aerosol automotive brake cleaner, which comes with a small straw to direct the cleaner into small areas. Spray the whole area with brake cleaner, which will flush out all the gunk. The brake cleaner dries quickly and does not leave a residue.
I am not a good welder, as you can clearly see from my welds. While I am a perfectionist on many fronts, I have not the skill in welding. I also use a stick and though this is not an excuse, it makes it a little challenging. Ugly, yes, but my welds do hold. Set up your welding table and clamp down the wheel. You will need to position the hub in the exact middle of the wheel. Once the ball bearings and grease are removed there will be some extra play in there. I used some spare wire to wire up my desired position before I welded, bending the wire between the spokes.
Bmx freewheel hub welded to become a fixed hub. Welds are ugly but deep and they hold. Do not damage the inner bearing housing. Toronto, Canada. Photo by Don Tai
Tack the hub down in four opposing directions first, so you get a good position for the hub on the wheel. Alternate in all four directions so you do not heat up any specific area and warp the hub. Chip off the slag and then reweld. I did multiple passes of welding and chipping, changing areas frequently. Note that I melted some metal on the edges when I was not careful. Though this does not impact the function of the hub it does not look as pretty. Maybe next time I could cover the edges with masking or duct tape so that when my electrode touches the area I would not have electrical contact. I suspect the tape would melt due to heat in the surrounding area. You do not need to weld all areas of the hub, just enough to ensure the welds will never break free. Do not damage the inner bearing housing, where your ball bearing race for your wheel is installed, or your race will either not fit or fit badly. I actually covered the housing in grease to guarantee I did not damage it. I have that much confidence in the accuracy of my welding.
Bmx freewheel hub welded to become a fixed hub. Welds are ugly but deep and they hold. Do not damage the inner bearing housing. Note damage to the threads of the hub cover, so the cover cannot be reinstalled. Toronto, Canada. Photo by Don Tai
Bmx Freewheel to fixie conversion completed. Reinstaill axle ball bearing races, install wheel on bike, and go. Toronto, Canada. Photo by Don Tai
Overall I am pleased with my fixie bmx hub. It is strong and I have not broken it. The hub did not warp due to over heating. The bearing installed easily and the wheel turns very smoothly. Though it still needs testing, even if it does break I am confident I can repair it. Backwards riding is not easy to learn and will need significantly more time.
Thank you. This is a really clear explanation.
I was just wondering about the welding part though. Have you considered using a different method, specifically epoxy adhesive? It is very strong, but not sure if it is strong enough for this job. It would definitely be more esthetic. What do you think?
[Don: Hi Bart, and thank you for looking at my very crappy welding. Strong but ugly. I am pretty bad but hope, with my new welding mask, to improve.
I had thought about epoxy resin but the wheel and specifically the hub is under a tremendous amount of stress and compression. All wheels flex a great deal, and this one of the reasons why we have spokes and not a solid wheel. I would guess that with all the flex that the epoxy would eventually break. If your epoxy weld did break while you were riding you would not have brakes, unless you also installed hand brakes. This is a safety issue. As I am using this fixie wheel to learn to ride a bicycle backwards, this is not so much of an issue for me.
There is also JB-Weld, epoxy for metal. You can try it. I would like to know if it does work. Good luck.]
Hi Don. Thank you for the quick reply. Your welding is not that bad. As long as it holds anyway.
The reason why I mentioned a different method was that I have never welded anything in my life nor I know anyone with the equipment. Epoxy seemed a much better option for me at least, but you are perfectly right – it may not be good enough. However, I will try to find JB-Weld. The only thing is that I am in Japan and not sure if anything like that is available here. Actually, I am sure it is, but Japanese like to change names of the products imported from abroad and it could have totally different name here. Anyway, I will try both methods and let you know.
[Don: Hi Bart, I lived in Miyakonojo, Miyazaki ken, for a year. It was very interesting! You should be able to go to an auto repair place and have it welded. I am sure that they have welding somewhere as it is very common to need some metal securely joined. I would not recommend trying welding yourself without come assistance as Japan’s 220v voltage is high and can be deadly. Welding with a stick can also be deadly and can permanently blind you without the right eye protection. Please be very cautious.
Still, if you did convert a BMX freewheel to a fixie you’d be the only one in town as this is very uncommon type of hub. Good Luck!]
Yes, you are absolutely right. It [welding] is highly dangerous and I would not attempt it myself without the supervision of someone experienced in welding.
Apparently, the JB-Weld as well as Epoxy are sold here and they are both called exactly the same, so no problems there.
The other good news is that this kind hub is found on millions and millions of Japanese shopping bikes (mama-chari), so I can try different methods and see what works best. So many of these bikes lay around abandoned and there are plenty of hubs to test :)
Anyway, I will let you know if either JB-Weld or Epoxy work as soon as I locate a store carrying these products. I will have a brake attached to the bike just in case.
Thanks once again for the page you’ve created. It was really helpful.
Hi there i did this on my bike some time ago and i have a question for you,when u stop pedaling like trying to skid the cog doesn’t go off? this is my biggest question i can’t fix it there tried to weld it on the hub but didn’t least.
[Don: Hi Andrei. I have never had my gear come off. This would require breaking the weld to the wheel. To ensure you get a good weld between the wheel and the hub you need to really clean the hub and gear of all grease before you weld. If there is any grease on the surfaces you wish to weld, the weld will not hold. To ensure I got off all grease I used automotive disk brake cleaner. This chemical is quite nasty and toxic but works very well. If you weld at many different areas around the wheel you will get a much better weld and therefore the gear not coming off. Just weld alternately on opposite sides of the hub as you go, or your hub will warp due to excessive heat. Do you have a photo of your hub and gear?]