Kurlon

You increased the stroke 4mm, but you didn't take into account that he rod length may have changed also. You need a longer rod as you increase the stroke to keep the rod angles in check. As the rod to stroke angle gets lower, the rod has to be at more and more extreme angles when the crank is around half way through a rotation, that in turn tries to drive the piston into the side of the cylinder, resulting in faster wear and more drag.

So, as long as both cranks are setup for the same pin height piston, in this case usually they expect 'short rod' pistons with 19.5mm pin heights, a 50mm crank will have the rod setup so the piston is near the deck with a 63mm tall cylinder, while a 54mm crank will have a longer rod to put the piston at the deck on a 69mm tall cylinder and help keep the rod ratio in check. That's why the import motors went to 78mm tall cylinders when they were only going to 55mm and 57.5mm strokes, they gained rod length to get some longevity. Lifan bumped to an 80-something mm tall cylinder for their first 59mm stroke motors for the same reason.