I recently picked up a used CF Logo 600. I noticed there's no C clamp at the end of the shaft unlike my Logo 600 3D. In fact, the shaft only extends halfway through the lower bearing block, so there's no place to put one because of this.

This implies that all of the load (in a vertical climb-out, for example) is carried by the pin in the tail rotor drive pully.

That seems like a lot of load to be going through a plastic part. Does it hold or is there something I'm missing about how the load is distributed in this thing?

At a minimum, I would expect the plastic part to deform over time, resulting in vertical play in the main shaft.

It has not been a issue with any of my Logo's as of yet. Some are over a year old and flown quite often.
There is a aluminum belt pulley available at ReadyHeli, That may give you more piece of mind.

Bill Whittaker