Engine noise at shutdown

[Constant Mesh]

Sometimes when I switch off my '04 FJR I hear a weird mechanical noise coming from the left side of the engine near the area where the starter motor meshes with the crankshaft. Is there anything about the starter clutch mechanism that could make unusual noises as the crankshaft comes to a stop? Also in the same general area is the balancing shaft on the left front of the crankcase.

If it made the same noise every time I'd be less suspicious.

 

[charismaticmegafauna]

The starter motor is in "constant mesh" with the crankshaft thru a gear train -- the only thing that prevents the starter motor from being turned by the c/shaft is a sprag over-running clutch mechanism. This, along with the permanent magnet alternator, is another one of the areas where motorcycle design & engineering are compromised (imo). The over-running clutch operates when the relative movement of one piece (the starter-driven gear is greater than its mating piece (crankshaft -- stopped). The motion causes pawls, rollers, etc. to reach-out and grab the non-rotating piece and turn it. When you stop the engine, there may be some backward rotation (pistons stopping at the top and pushing a bit back, for instance?) that catches the sprag rollers and then turn the starter motor. Heavy oils tend to exascerbate these symptoms by increasing the drag on the sprag rollers. In extreme cases, rollers will flatten and mating surfaces galled. The only cure I'm aware of is very careful operation of the starter button or replacement of the sprag assy. if it becomes a problem.