Cox Model Engine - Pistons

Pistons

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 favour of a hardened steel rod which 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.

The engines that used the early-style three-piece piston are any engines produced prior to 1957, i.e. Space Bug, Space Bug Jnr, Thermal Hopper and Strato Bug. Since the Space Bug, Space Bug Jr and Thermal Hopper where produced up until 1958 you will find versions of these early engines around with the later-style pistons. (and cylinders)

The post-1957 piston is coated with copper on the inside and top. This was done to prevent the nitrile hardening process from hardening the ball socket joint area. The outside wall of the piston was then finely machined and polished to produce a chromed appearance.