wherein the crankcase acts as a third working chamber by {HEAD ~ virtue} of {TAIL ~ the pressure} from the working medium acting on the underside of the pistons, 
of
wherein the crankcase acts as a third working chamber by { HEAD ~ virtue } of { TAIL ~ the pressure } from the working medium acting on the underside of the pistons ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH