When the piston moves, {TAIL ~ the power transfer shaft moves} in or out as {HEAD ~ the case} may be 
When the piston moves , { TAIL ~ the power transfer shaft moves } in or out as { HEAD ~ the case } may be
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH