The early engines that were produced before 1957 had a light alloy piston rod which is retained in its socket by a slotted steel retaining cup which in turn is held in place by a steel circlip located in a shallow groove in the interior piston wall. This arrangement (known as a three-piece piston) was abandoned as of 1957 in favor of a hardened steel rod that was swaged into a bearing cup formed integrally in the piston interior. The advantage of this latter set-up was that it simplified assembly and the bearing could be re-set to take up play using a suitable "reset" tool to re-swage the cup.