Lift Fan Post Morten

I took it all apart, and found out why I got such a different sound.

Damage to the lock nuts

With the slightly shorter collet mounting meant that the locknuts holding the fan to the housing impacted the screen housing before the mounting bolts impacted the bottom of the engine.

The nuts before fully removed. 

Doing some research I've found that the B&S engine shaft appears to have 2 woodruff keys slots as well as a standard keyway. And the end of the shaft is tapped with 3/8-24 and is about 1.3" deep. 

I will use the end cap plate, to hold the assembly to the end. 

End cap plate, which will need to be drilled out in the middle.

And I've ordered keys to go into the keyways and stainless bolts to secure the plate to the bottom of the shaft. The plate will keep it from riding up, and the bolt will keep it from dropping down. And the keys will keep it from spinning.