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