The F-head layout (not to be confused with flathead) can be thought of as a combination of L-head and I-head: the intake manifold and its valves are located atop the cylinders (in the cylinder head, as in an I-head design) and are operated by pushrods, but the exhaust manifold and its valves are located beside the cylinders (in the block, as in an L-head design). The exhaust valves are either roughly or exactly parallel with the pistons; their faces point upwards and they are not operated by pushrods, but by direct contact with a lifter contacting the camshaft. Reverse variation of F-head with side intake and in head exhaust were also made- the Ford V8 overhead exhaust valve conversions to flathead engines were to decrease the overheating under load problems in commercial service. The Indian/Henderson 4-cylinder motorcycle engine family used both designs- the overhead exhaust was again an overheating consideration design.