There are two basic types of cylinder heads used on today's automobiles, The two are Overhead Valve (OHV) and Overhead Camshaft (OHC), with the OHC having further subtypes known as Single Overhead Camshaft (SOHC) and Dual Overhead Camshaft (DOHC). Most of the cylinder heads are manufactured from the aluminum alloy due to its strength and lightweight with cast iron also being commonly used. Valves and seats are present in all cylinder heads, with number that may vary between two per cylinder to more complicated multi-valve designs. Always ensure there is play by increasing or decreasing the valve stem in relation to the guide to avoid the consumption of oil and spoiling the engine. Valve springs are designed to keep the valves in place and closed when not in use and to then open the valves when required. Remachining a cylinder head, as a rule, means the replacement of all the components; however, this may not be the case regarding the engine maintenance. Disassembly is less complex than assembly and entails stripping of parts, where the heads with the two camshafts call for orderliness; the removal of the rocker arms, springs, and the valves using the tools. Thorough check for the components for wearing or any damage is required, and it necessary to use measuring instruments such as micrometers, and gauges. The valve parts have to be inspected for crack and wear whereas spring as well as retainers for breaks and squareness. Cylinder heads are another part of the engine that have to be checked for the guide condition, seat wear, flatness, and there should always be a check for the presence of any crack; while refinishing of these or repair works are usually done at the machine shop. Assembly includes greasing and fitting of valves, application of spring and sealing and positioning of the parts.
