I saw some walls like that in a Boss 302 engine once----the pistons were press fit on the pins and when it was put together the piston boss was squashed on one side from the pressing in of the pins----it was so tight that the piston did not want to wiggle on the rod, in fact they were so tight that the engine was hard to turn over by hand---I took the piston/rod assemblies apart for the guy and honed the pistons to remove the squash area and reassembled with my sunnen electric pin deallie and the engine was then fine