{TAIL ~ two pistons} connected via connecting rods to {HEAD ~ a single eccentric crank pin} of a crankshaft, 
{ TAIL ~ two pistons } connected via connecting rods to { HEAD ~ a single eccentric crank pin } of a crankshaft ,
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH