Pushrods 30 may be engaged with {HEAD ~ the camshaft} 26 to actuate the rocker arms 32 and selectively open {TAIL ~ the intake and exhaust valves} 18, 20 
to selectively open
Pushrods 30 may be engaged with { HEAD ~ the camshaft } 26 to actuate the rocker arms 32 and selectively open { TAIL ~ the intake and exhaust valves } 18 , 20
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH