In {TAIL ~ a preferred example}, {HEAD ~ the engine} has a spark plug access well centrally located at the top of each cylinder 
In
In { TAIL ~ a preferred example } , { HEAD ~ the engine } has a spark plug access well centrally located at the top of each cylinder
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH