QD and Sportwin motors are famous for excessive wrist pin bushing wear so starting in ’59 the small end bushing was made a bit wider than the earlier models. The real fix was on the 61-63 motors which used rods and pistons which accepted a larger diameter wrist pin with needle bearings instead of bushings. If you are going to rebuild one of these motors, it’s a good idea to replace the rods and pistons with ones from a ’61-’63 donor motor to avoid any wrist pin wear. The crankshafts are the same thru the years.
’57 rod on the left with the standard bushing, ’59 rod in the middle with the wider bushing, ’61 and later rod on the right with the improved wrist pin design.
