BBS02 Fat bike conversion kit from California E-bikes

After much anticipation I purchased the new tap kit and 3 axle kits from Doug at California E-bike. After doing my first BBS02 conversion I was not disappointed. The BBS02 is a fantastic drive unit and the 750W unit designed for the US market fits a wide range of 68-73mm Bottom bracket bikes. Since the bottom bracket is the strongest part of the frame there is no need for torque arms or reinforcing brackets. This unit is quiet and stealthy due to its small size and barely perceptible hum. The only drawback is the weak controller and the fact that you can’t mount it on anything much bigger than 73mm without grinding away the bottom bracket and installing crankarms that are massively offset. Even if you do all these things, the BBS02 chainline will most likely still rub against the tire in the lower gears. Doug designed the BBS02 conversion kit several months ago and many customers complained because while there was a HUGE pent-up demand for the design he had created, no one wanted to pay to have the machining done to the BBS02. Doug scratched his head for a while and in the end came up with an ingeniously designed tap kit which could be shipped out with the tap kit and then returned when people were done installing their own axles. While the tap kit looks a little intimidating, with the right tequnique and some high quality tap oil most any do it yourselfer can tap their own BBS02 and install a new axle themselves. From start to finish I estimate my first shop conversion took about 2 hours. The tap oil I used was called Tap Magic and a small bottle of it can be had on ebay for about $7 with shipping. Everything you need is included in the toolkit with the exception of some lockring plyers to ease removal of the lockring. You can get a cheap pair of these on ebay for less than $10.


Three conversion kits for the BBS02 to 100mm axle and the tap kit. You can also see two adapter rings that California E-bikes sells for 4 bolt and 5 bolt chainwheels

I recommend laying out a large piece of cardboard to work on as once you pull the axle out grease will get everywhere. I use the blue nitrate gloves ($5 a box at walmart) to keep my hands clean, if I have to use a tool I will take one of the gloves off and use the tool with the ungloved hand so my tools do not get greasy. Grease control is huge when working with bikes,if you ignore it then everytime you touch anything bike related your hands turn black and will stink for days.


The original crankarms weighed in at 424, these were a bit heavier so I stayed with the originals.

The kit came with high-offset crank arms that would probably be necessary for fatbikes with 5″ wheels. I didn’t need them and they ended up weighing it at 112grams more than the stock crankarms from Bafang. It was nice to have them if I needed them, and they are not included in the picture of the modification package that is sent, but Doug still sends them out. Everything in the modification package was top knotch and high quality. The chainring adapters were the nicest ones I have seen yet. The needle bearings came pre-greased and already installed in the extension. Taking apart the axle was very easy and took about 20 minutes. I put each piece down in order of removal and made sure to keep the orientation of the bearings the same. There is an excellent video of how to do it located here which is mandatory watching for anyone attempting this process. When attacking the 5 large Philips screws on the flywheel casing make sure to use blue locktite and tighten them down as hard as you can without stripping them. Once the new axle is put together it’s time to tap the BBS02. I inserted it into my 2″ hitch on my Dodge Sprinter but any shop table clamp would work too. Tap oil must be liberally applied to the inside of the BBS02 as well as the tap itself (don’t use motor oil). Don’t forget to install the rubber stopper so it butts up against the needlebearing. If should not take much pressure to turn the tap, if there is too much pressure then the threads are probably clogged. Back off the entire tap, remove it, clean the threads and start again. It’s totally OK to do this a couple of times, especially if it is your first time tapping. Take your time, do it right. If you try to tap the unit with the threads clogged you can make deeper cuts than you should and the threads won’t work right. Turn 16 half turns or until you hit the rubber stopper. Cleaning the chips out with compressed air is the best way to do it. Clean them out before you remove the rubber stopper. The last thing you want is those metal chips inside your BBS02 unit. They will wreak havoc on your bearings. When cleaning out the unit make sure you get every single chip out before your start putting the axle back in. I recommend cleaning off the axle and re-greasing it before inserting it to make sure there is not dirt or grime that got picked up in handling. Be careful when screwing on the black plastic cover as it can break VERY easily if the tiny screws are put in too tight. Once you install the axle it is time for a test fit. When I removed the BB from by Deadeye Monster I found that the BBS02 would not slide in due to protrusions into the BB area by the aluminum frame. A dremel with a tiny grinding head is perfect for wearing away protrusions into the BB area. Once I grinded enough to fit the BBS02 I found that one of the dog ears was bumping against the frame. I ground off one side of the nub that the unit threads into as well as cutting off the rubber pad with a mat knife and re-siliconing it so it would pad the downtube. With a steel frame I probably wouldn’t bother but with aluminum frames once they become dented they lose a lot of their integrity. When the motor turns the torque pushes the motor into the downtube so over time it could scratch or dent the frame.


Cut and move the rubber pad and grind down one of the mounting ears

When you install the mounting triangle on the non-drive side of the BB make sure that the rough ‘teeth’ face toward the BB. Once you tighten this down these teeth keep the BBS02 from dropping down when you go off drops or jump over things. In the end I’ve had several days of riding with my new converted unit and I honestly can say I couldn’t be happier. The new axle runs cool, everything seems to just work. For anyone who is used to dealing with shady chinese ebike parts dealers they will immediately realize the value in american workmanship and the excellent craftmanship of this product. In my opinion it is worth every penny. You can purchase a modification package and the tool package from Doug at California E-bike and modify your own BBS02 to 100mm. This modification package does not require any special milling tools and can be done in any decent bike shop. The modification package is $499 plus $35 S/H available here and the tool package for doing the conversion is $345 plus $35 S/H found here. If you only want to do one conversion you can return the tool package for a $300 credit, but you must specify that when ordering the tool package. The video for how this is done is found here.

For a follow up article on mistakes I’ve made with my last 3 axle swaps and how to not make these mistakes yourself check out this article.


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