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.