The YZ-EMX, Electric YZ250 Build

The YZ-EMX, Electric YZ250 Build

There aren’t many topics as polarizing in the motorcycle world as electric bikes, especially when it comes to racing.  At 3DP we’re clearly fans of this new breed of motorcycle, and after spending quite a bit of time racing and refining the Electro & Co EMX14 pitbike we began to wonder what it would be like racing a full sized electric dirtbike against a field of gas powered machines.  What would the advantages be, where would the bike struggle, and perhaps most importantly what type of racing would suit the characteristics of electric the best?  After some thought, the answer became clear, Endurocross.  The idea of not having to worry about a clutch or stalling the bike on the tight and technical Endurocross tracks was very appealing, and the races would be short enough that battery life would not be of any concern.  As it so happened our friends over at Electro & Co were already planning on building a full sized bike using a 96 YZ250 as the donor chassis, and just like that the YZ-EMX project was born.


Plenty of challenges await on every Endurocross track

Upon receiving the bike from E&C the challenges of converting this chassis to electric became readily apparent.  Because of the single backbone design of the frame, fitting enough battery capacity without having the box be too cumbersome was going to be a difficult task.  We started by getting the electric motor in place, a QS138 72V available directly from .  The biggest consideration was ensuring that the front sprocket was in the same location as the stock gas motor, which is critical not only for chain alignment but also for handling.  We designed two custom brackets to interface the existing motor mounts on the frame, as well as a third bracket to interface the rear swingarm pivot just like the gas motor would.  This allowed for easy assembly that required no modification of the stock frame, a goal we were able to achieve throughout the entire project. 


The electric motor mounted in its final location

The next task was to design the battery box.  As mentioned above, jamming as much battery capacity into the relatively small frame was a major challenge.  A modern perimeter frame would have been a much better candidate for this type of conversion, but after a lot a trial and error we were able to come up with a design that would fit nearly 5kWh of capacity from a total of 320 21700 cells, which is almost equivalent to an Alta MXR.  In order to hold the box securely in place we designed a tray that would interface the top mount of the QS138 motor, as well as two brackets up above that connected to the stock head stay mounts on the frame.  This box was so large that we couldn’t even fit in onto the bed of our larger printer, but luckily E&C came through and were able to print it on their monstrous Modix Big 6 printer that boasts a massive build volume of 8 cubic feet!


We weren't kidding when we said there wasn't a lot of room. . .

The final major component to be mounted was the controller.  We wanted this bike to look as close to a stock gas bike as possible from the outside, and with this goal in mind we set about figuring out a way to hide the controller in the stock airbox.  As it turns out the controller BARELY fit inside, and we designed a sheet metal bracket that interfaced stock mounting holes on the subframe and held it securely in place.  Out of all of the parts on this bike we’re most proud of our hidden controller mount; to bad nobody can see it!  We also printed up a custom cover to mount in place of the stock airboot, hiding the controller completely from view once the number plates and seat were installed.


Nobody seems to be as excited about this controller mount as we are. . .

With the major electrical components and their associated mounting brackets set and ready to go, attention was turned to freshening up the chassis itself.  Although in good shape for a 25+ year old bike, all of the bearings and other miscellaneous items needed either attention or replacement.  We also swapped the long and vulnerable from brake line for a CR style unit to help avoid any potential damage from rocks and other hard objects littered about the EX course.  Finally, we added a SXS Slide plate to protect the bottom of the frame and linkage from damage, as well as help us glide over obstacles without hanging up. 


Full skid plates are a necessity in Endurocross

After freshening up the chassis and performing a bit of trimming on the stock gas tank to make sure it cleared the battery box, the YZ-EMX was finally ready for final assembly.  When building up one of these bikes you really begin to appreciate just how simple the electric powered machines really are from a mechanical perspective.  Bolting the motor, controller, and battery box in place was relatively straight forward, and once the plastics were installed the bike was complete!  No heavy engine to deal with, no coolant or oil to fill, no air filter to oil and install, just a very simple and clean system that was ready to run. 


The YZ-EMX finally assembled just days before the race.

The bike’s maiden voyage was the final round of the 2022 Endurocross series in Reno, NV, and overall the day was a huge success.  We were successfully able to put the bike in the night show in the EX Intermediate class, and it ran flawlessly all day long with no controller faults or issues of any kind.  We ended up 12th in the main event after some struggles in the matrix section, but overall the bike felt great around the entire track and simplified riding experience without gears or a clutch was much appreciated on the demanding and technical track.  Footage from the race can be found HERE . The bike drew a lot of attentions from fans and other racers, and it was really a cool experience to show up with something completely out of the box to try to tackle this unique and challenging form of racing.


With the YZ-EMX project completed we’re very optimistic about the future of electric conversions.  With the success of this project Electro&Co are considering offering a full kit that would include everything you need to convert a steel frame YZ250/YZ125 to electric, and we’re really excited about the prospect of having a kit like this available to the consumer.  If this is something you would be interested in please send us an email using the “Contact” page and we can provide a bit more detail regarding projected cost and battery range.