Would it be possible to build in a one-way rachet system?
I'm not understanding 100% how the crank handle works,
but what keeps it from spinning wildly?

From my understanding of old cars, it is basically cammed out when the
engine starts pushing the crank rather than the other way around. Look
at those one-way anti-vandalism screws used on public bathroom fixtures
for the principle (if not the actual scale)!

I think the rotary lawnmower starter cord is a good example of how to
do this perfectly right even in the presence of backfires, but the
crank isn't so bad.

Tim.