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