On Sun, 2 May 2010 20:46:54 -0400, "Stormin Mormon"
wrote:

Sure. And then when you run over a rock or survey stake, the
machine will bend the crankshaft instead of shearing the
flywheel key. F'ing brilliant, you think?

Hint for Clare only: Some devices have a reason for
existance.
The shear pin on the TOP of the engine gives minimal protection to
the shaft on the BOTTOM of the engine. By shearing at the flywheel end
it shuts the engine off immediately upon hitting something - limiting
the amount of damage it will do to the crank - but certainly not
eliminating damage.

And did you also know that trying to start the average vertical shaft
lawn mower engine without a blade attached CAN shear the flywheel
key?? This is because the "flywheel" on most current vertical shaft
engines designed for direct blade attachment is way too light to allow
the engine to run without the blade and the torsional reversals are
strong enough to shear the key. The BLADE is the actual "flywheel"
that provides the required inertia on these engines.
Older engines with cast iron flywheels and horizontal shaft engines do
not have this issue.