Sometimes, especially with engines that have had a lot of use, the piston / conrod ball socket joint is very loose and will adversely affect performance. A Cox “reset” tool, available for the.010, 020, 049/051 and the 09 series engines, is used to tighten the ball joint back up again. The correct free play is.001 to.003 inches. The.15 engines use a wrist pin so a socket reset tool is not required for these.