Cut to the chase and change it to a flat belt. While you are at it, eliminate the speed reducer, it is way too slow to do any work at all. 350-400 blows per minute.
I would also rearrange the geometry of the entire top of the hammer, balance out the spring so it has a chance to whip. The spring should come near the bottom of the stroke and still have 1-2" of free space between the dies.