Usually, the Tecumseh allignment key is soft metal, and is
sacrificial. You hit a rock, the flywheel is now out of time
with the cylinder stroke. On the points ignitions, you lose
spark. On the electronics, you still have spark, but it's
way out of time.

Maybe you need a softer flywheel key?

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"RS at work" wrote in message
...
I am thinking about making a blade adaptor for my lawn mower
that has
a sacrificial shear pin so when I am out mowing down the
tall weeds
and find that chunk of concrete or stump that someone tossed
into the
field it will reduce the stress on the mower engine.

On my mower with a Tecumseh 195cc motor, I have had to
replace the
flywheel as the shaft is steel and the spline key is steel
but the
flywheel itself is cast aluminum. Although I found a new
one on e-bay
for $30 if I had to get one from a dealer it would have run
$60 or so,
and added to the cost of a new blade ($10-20) and a new
blade adaptor
this gets really pricey.

My design is about the same as the factory set up except the
torque
will be transmitted through the shear pin(s).

My question is how to size the pin or pins? I want them to
be the
weakest link, but to hold up when mowing down the big nasty
weeds.

My gut feeling says that two 3/16 brass pins ought to do the
trick,
but I figured that some one here might have some experience
with this
kind of calculation.

Roger Shoaf