Rotor / Flywheel

Rotor/Flywheel

The engine rotates counterclockwise when viewed from the alternator side.  The required flywheel puller has an M27 x 1.0 RH thread (same as used by GasGas with Kokusan Denki flywheel).

As you can see, there are only 5 flywheel “trigger teeth” (locations highlighted with a Sharpie pen), one of which is longer to allow determination of absolute position.

Even with the head off, the engine does not spin easily.  There are 12 distinct “detents” in one complete crank revolution.  This is due to 12 powerful permanent magnets (locations highlighted with “X”) in the flywheel.  I've heard this called “magnetic drag.”  “Cogging position” is the term used with brushless DC motors.   It takes a fair amount of electrical energy to run an EFI system, and this alternator is much more powerful than one on a carburated trials bike.  I also think the engine's primary compression ratio must be quite high, as I feel a lot of “pumping resistance” in addition to the magnetic drag.  A high primary compression ratio makes sense to me as the simple exhaust system is not at all like a 2T expansion chamber.