The eccentrics and {HEAD ~ cranks} associated with {TAIL ~ each piston} and cylinder maintain their parallel relationship while they are rotating 
The eccentrics and { HEAD ~ cranks } associated with { TAIL ~ each piston } and cylinder maintain their parallel relationship while they are rotating
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH