Excessive piston/cylinder clearance can also let the piston rock back and forth in the cylinder on each revolution. If this happens too much it will crack and break skirts. I would slap whoever had you put a spacer plate on the top of the cylinder. The spacer plates go on the bottom, or you get a set of custom cut domes for the stroke you have and the deck height you end up with, with whatever gasket you are using. Most 4mil setups are not just a bolt and go setup with stock cylinders. There are a few critical measurements that you have to find and adjust before you ever fire the engine. Piston/cylinder wall clearance (which is something you do on any top end rebuild, not just strokers), deck height, gasket thickness, what porting you have, port durations in relation to the thickness gasket you have or that your builder recommends, squish clearance, squish angle, dome size... Anyone who builds these engines can tell you that you don't just bolt on a spacer plate and let her rip down the track.