Balancing Fans

[Steve Bryant]

I discovered that the aluminum fans I had are all badly out of balance. I had put them on the pulley and shaft and spun them by hand to see which one ran the most true only to discover the problem of poor balance they all had. Since I don't want to introduce a bad vibration  to the engine, I want to balance them.

Is there a preferred method to balancing these given that they are difficult to mount for this purpose?

Suggestions welcomed.
Stephen