I’m not well versed in the mechanics of engines so bare with me if I have some of this wrong in asking my question. I want to understand what the value or advantage of the adjustable pushrod is, as compared to the fixed rod. As I se it, in the 883/1200 engine the crank shaft lobe moves the tappet up and down, on which the pushrod sits. The other end of the pushrod rides in the valve rocker arm and actuates the valve. The tappet/roller assembly has a feature where as it takes on amounts of oil to "pump up" the assembly and to remove any slack tolerance in the transfer of motion up the chain to the valve. If the tappet assembly removes the "play", what benefit is the adjustable feature on a pushrod?