crankpin 12 pistons 1 and 5 and cylinder housing 11 are specifically designed so as to provide running clearance for yoke 3 lever 8 and crankpin 12 fig2 shows the same mechanism during the power stroke after crankshaft 13 has moved 90 u00b0 in its direction of travel it is worth noting that the inverted yoke produces a direction of rotation opposite that of a conventional yoke drive mechanism hot piston 1 is about halfway along its expansion stroke while cool piston 5 is at nearly the same position as in fig1 relieved portions of waist 14 and bottom guide flange 15 of hot piston 1 provide running clearance for yoke 3 and crankpin 12 hot piston 1 is longer than cool piston 5 because in an actual engine the hot piston would carry a cantilevered insulation dome above it and therefore requires guide flanges 15 and 16 that are spaced farther apart than those of the cool piston for good mechanical efficiency fig3 shows the mechanism at its point of maximum volume with the crankshaft advanced 180 u00b0 from fig1 while pistons 1 and 5 appear to be in the same position cool piston 5 is actually moving up while hot piston 1 is continuing down to complete its expansion stroke fig4 shows the mechanism during its compression stroke with the crankshaft advanced 270 u00b0 from its position in fig1 in this position it is the relieved portions of waist 17 and bottom.