G'day Jeff and all
I wonder why the flywheel key shears? Seems like it's almost the furthest thing away from the impact. I guess the sudden stop combined with the weight of the flywheel.
Yes it's because of Inertia and Mass, Mass and speed determines how much Inertia an object has ,The blade, crankshaft, and flywheel are spinning at about 3000 rpm, so when the blade hits an immovable object, the crankshaft decelerates suddenly but the flywheel doesn't want to stop so fast. Thus it shears the flywheel key. Since the flywheel continues to rotate relative to the crankshaft, the ignition timing is advanced.
If the key didn't break the crankshaft could twist or break.
Inertia: the resistance an object has to a change in its state of motion. .
Cheers
Max.
