woodruff key sheared, wtf?

So today i got in my new/used stator, installed it took it for a hard road test, 3 miles from home its starts backfiring, acting like it wants to desiel. tried to kick for a while, every once it a while it would pop and spin a few times, and i also got the dreaded kick back multiple times which i have never once gotten before but just heard about. got a freind to pick me up with a truck, and found the woodruff key in the stator perfectly sheared off, no damage to any components, i specificaly remember tighting the reverse thread flywheel nut the same way i always do with a 3/8 impact on medium speed? why does this happened? lol i am baffled i didnt think this really happened just something people tell you to check for when they cant think of anything else to check? anyone know where to get one? both halves came out fine and doesnt seemd to have damaged the crank, flywheel or stator so i should be good to go when i get a new one i think....any thoughts? ever seen this before?

thanks as usual... :cheers: :cheers:

Update: $.45 cents at hardware store for new key, .5mm removed from said woodruff key, tap it into place, he kicks and its good :cheers:
maybe my compressor had low pressure or something when i tightened the flywheel nut and it loosened and thats why it broke? the nut was loose as a goose when i pulled the cover off but it looks like it sheared then the spinning crank did its part to loosen the nut and i only say this because the edges that hold the key in place are still perfect and sharp on the crank and flywheel, not rounded at all like i have seen on other cranks or shafts that shucked a key (thank god).... i can see a key breaking when it has a load on both sides like the big main crank sproket nut on other side of engine, but one with only a load on one side? stranger things have happened i suppose, this side of the engine better than the other side, and i cant remember the last time it cost me $.45 to fix this thing so i cant complain !!!

I would still like to get the proper key can a dealer get this? maybe my modified key is good enough as it fit in nice and tight to both sides, what would you do? leave it or get the proper key? i may not be so lucky time if it breaks again, or rolls....

I assume a dyno wrench is another way of saying what i would call a torque wrench? point taken ZAGA, its already done, 50 newton meters per spec. or as i would say it 37 foot pounds. locktight on the nut too....