The fly wheel key serves a duel purpose.
(1) It insures that the engine will remain on the correct timing
position.(main purpose)
(2) The weighted fly wheel is spinning at a high rate of speed. Should the
mower hit a permanent object and not have the ability to shear off a 50 cent
key, the flywheel, having the tendency to keep moving, will probably cause
serious damage, such as a broken or bent crank. (secondary purpose)

Even with a key in place, if it is not the proper one, damage can and does
occur.
I used to have a repair shop in my younger days and replacing flywheel keys
was a large part of our summer business. Very rarely did we see the key on
the blade end of the crank shear off.





wrote in message
...
On Sun, 25 Jun 2006 15:01:49 GMT, "Pop"
wrote:

...

Just curious. Why would they use such a soft metal for
that key? I guess it's intended to shear if the flywheel
jams up, but I cant see why the flywheel would jam. If
anything will jam, it will be the blade, but not the
flywheel.

Mark

If the blade hits an immovable object, the shear pin will go
rather than the crank and many other parts, plus it'd probably
bend the shaft in the process. You really should get the right
pin back in it. Same as the shear pin on an outboard motor if
you're familiar with that.

Pop


Thanks for the reply.

If the shear pin was on the blade or blade mounting attachment I'd
agree with you. But this shear pin is on the flywheel, (located on
the top of the engine). Unless someone was to intentionally stick an
object thru the plastic cover over the flywheel, there is no reason
the flywheel will jam up. I do intend to get the correct part since I
need other parts anyhow, but I just can not understand why they have a
soft metal pin up there......

If anyone knows of a website that has an exploded view and parts list,
or tuneup instructions for Tecumseh engines, please post the website.
I cant seem to find any. Briggs has all of them, but Tecumseh has a
website that's pretty much useless.

Mark