Did some filing on the Surly forks to deepen the fit of the flatted axle today, was able to get the Ebikes.ca stainless "C" washers to seat behind the chrome-moly steel fork's lawyer lips on both sides, and install the torque arm on the non-wire side. To fit the second torque arm will require removing hall sensor connector pins and passing wires through the torque arm hole. I need to find my bag of NordLock washers before I do that.
One thing I really like about these torque arms is the resultant force is straight up into the dropout. In this left side view the wheel rotates counterclockwise and the resulting torque is clockwise. They are also very thick stainless steel to avoid cutting the soft axle steel, and very nicely made without being too bulky and heavy. From Ebikes.ca. At 1300W the BMC might not need torque arms with a Chrome Moly Steel fork, but I'm going to use one on each side, plus the "C" washers and NordLock wedge locking washers. Front wheel failures are ugly.
I need to take a better photo, but the "C" washers sit behind the so called "lawyer lips" on the fork dropouts insuring that the axle cannot come out of the dropouts until the nuts are loose and backed out some distance. Combined with the torque arms it will be very unlikely to ever fall out, and the lockwashers guarantee the nuts will stay tight.
The NordLock wedge lock washers create a condition where, to loosen the nut the tension goes up first, due to the ramped wedges between the two washers. So vibration can't loosen the nuts. To work properly the teeth on the outside surfaces of the washers must bite into a nonrotating surface (the torque arm) on one side and the nut on the other side. No other washers can be adjacent to the lockwashers or the locking effect could be nullified. Installing the washers properly with the teeth and wedge surfaces in the correct orientation is critical.
When you go to remove a wedge lock washer you can feel the tension increase until a ramp drops into the next one, after that the tension drops off. So you can feel the locking effect. The washers are harder than the nut or torque arm so the teeth bite in and don't deform, so the washer is re-usable unlike most locking devices. In the photo above a conventional split ring lockwasher is still present, those are not very effective in retaining tension if there is any vibration or motion present. The rocking motion of acceleration / regen is particularly difficult, here there will be no regen on this geared hubmotor but on the Borg's CroMotor there is both lots of acceleration and large regen forces, and after 2 or 3 tightening cycles they don't move. This is very important on a regen setup hubmotor.