Log splitter questions

Just buy another spring. Take the pieces of the broken spring to a hardware store or a farming supplier and you should find something that will work. That bottle jack doesn't look special either.

You'd be foolish to try to conver that thing to powered hydraulics.

Faster action and higher ton capacity are sort of opposites. When one goes up, the other goes down. Unless you get a two stage hydraulic jack, like on the car jack I recently bought. With no load the jack goes up fast. With no load it takes two strokes to go all the way up. In normal use it takes less than one stroke until it hits the frame, then it changes to the slower but stronger stage. If it were one stage going up fast, when it hits the log you would need to gain a couple hundred pounds to push the lever for it to split.