{HEAD ~ The pistons} are connected to {TAIL ~ a crankshaft} via two connecting rods which are pivotally connected to the same crank pin 
are connected to
{ HEAD ~ The pistons } are connected to { TAIL ~ a crankshaft } via two connecting rods which are pivotally connected to the same crank pin
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH