A. Above the pistons the cylinder head is machined completely flat rather than slightly domed. The combustion chamber is confined to the upper end of the cylinder.
B. The valve covers are made of cast iron which gives them a flat appearance compared to stamped metal valve covers. Sturdy cast iron (or alloy) is necessary because the rocker arm shafts are bolted to the valve cover rather than the cylinder head.
C. The exhaust and intake valves are located beside the piston in the engine block. The cylinder heads appear flat because they only contain combustion chamber space rather than all the valve train gear (rocker arms, valves, springs, valve covers, etc.) found on overhead valve (OHV) engine cylinder heads.
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