Motor Mounting Plate
Once you have your motor selected and in-hand, you need some way to physically mount the motor where you need it to go in the motorcycle.
To do this build an “Adapter Plate” or “Motor Mounting Plate”.
I built mine from a piece of scrap 1/4″ aluminum plate that I had around. The plate needs to have a hole in the middle of it for the driveshaft to pass through and four holes in the appropriate locations for the bolts to mount the motor to the plate.
The plate also needs mounting points to connect it to the frame of the motorcycle. On this project, I re-used the existing mounting points in the frame of the cycle where the engine and transmission originally bolted in place. Those holes are already just about where I needed them and it meant I didn’t have to make any new holes in the frame.
MAKE IT REAL
Rather than making a template from scratch, or drilling holes based on careful measurements of the motor, I simply made my own paper template based on the PDF file that I already had of the mechanical drawing of the motor. In a graphic design program, I simply made sure that the measurements on the diagram matched up to 100% actual scale, and printed it out on paper. The motor is compact enough that the whole image fit on one 8.5×11″ sheet.
I cut out the piece of paper and then glued it (rubber cement) to the aluminum plate. Using a drill press, I simply drilled holes of the appropriate size (the size is marked right on the diagram!) right through the crosshairs on the piece of paper. That gave me a plate of aluminum with a central hole for the driveshaft, and four holes to mount the motor to the plate. I test-fit the plate in place on the motorcycle, with the drive-shaft hole lining up with the marks on the frame indicating where the chain originally went. I then sketched right on the plate “tabs” of where the plate would extend to the existing mounting points on the frame – one on the bottom and one on the high side of the back. I will later add another attachment point on the front with an angle bracket.
At that point, I could just put the motor and plate together to confirm that all the holes lined up. I also traced the outline of the motor on the plate.
Once I rounded off all the edges, I put the plate in the motorcycle, and ran threaded rods (3/8″ and 5/16″, which matched the holes in the frame) through the frame attachment points, through the plate, and through the matching attachment point. Stainless steel nylock nuts and washers went on both sides of the adapter plate and on the outsides of the motorcycle frame. If I ever need to adjust the position of the motor side-to-side, I can loosen the nuts on either side of the plate and move it one direction or the other.