K301 flywheel to drive flange "discovery"
 

I am in the process of getting my $200 127 up and running.
Need to do that this weekend before the lawn weeds require a brush hog.

First time tearing into the 12hp K301 and I am flabbergasted to discover that the drive shaft is turned via a mere 1/4" dia. pin into the flywheel.

The 1/4" pin you refer to is a hardened dowel pin which is extremely tough. It would take one butt load of torque to break. The 125 I used to have that pin was worn almost in half and still held up. And trust me I do not take it easy on any of my cubs. Prolly you will see some wear inside the drive hub.:beerchug:

Yep they only last about 40 years :biggrin2:

I am not talking about the cross pin in the end of the driveshaft you can see in the hub from outside.
I am talking about the 1/4" (might even be 3/16) stub of a pin going into the flywheel, parallel to the crank.
Which is embedded in an aluminum diecast hub.

P.S. the hub that drives the driveshaft cross pin was wore about 1/4" or more so I welded the wear and ground the slot back to original shape.

I think you are talking about a woodruff key, you would be surprised at how much force it takes to break one. To fail it would have to shear the pin the entire length. Very unlikely failure, usually when something like that goes, something else failed first.

Or maybe that's not it either?

The torque of the nut/washer on the end of the crank, and the tight fit of the cup on it is what does the job. I think the pin he is referring to is just a locating pin to assure proper centering on the crank. At least that's the way in looks on a AQS engine.

You have the right one.
But the nut (the original 127 engine) or the bolt in a newer black painted replacement K301 really only holds the cup/hub up against the flywheel hub and keeps the flywheel from coming off of the crank.
All torque is transferred thru that little pin in between the flywheel and cup/hub.

You would go no where without that little pin and even a slightly under torqued crank nut/bolt.

If I were you I would worry more about the flywheel breaking, than I would worry about that 1/4" pin. I've had more than one flywheel break where the pin goes into it and the pin looked fine in all cases.

The taper of the crank and flywheel is what does the lion's share of "holding". The key is primarily to index the flywheel to crank.

I'm going to respectfully disagree. It's to keep it (even though it shouldn't) from spinning. There is no reason it needs "indexed". The flywheel and shaft are not balanced together. There is no particular reason to index them.