Lesson 1/Learning Event 1
The camshaft extends the full length of the engine and has a cam for each valve, except in a few cases where
one cam is used to operate more than one valve. The location of the camshaft, tappets, and other valve
operating parts depends on the design of the engine they are used in.
In the in-line, L-head engine, the valve mechanism is located in the cylinder block. An adjusting screw is
threaded into the top of the tappet to allow an adjustment of the operating clearance between the tappet and
the valve stem. One or two covers with gaskets are bolted to the side of the cylinder block to cover the
mechanism, protecting it from dirt and preventing oil leakage.
FIGURE 33. OVERHEAD VALVES.
The valves of the in-line, overhead valve (I-head) engine may be operated by either one of two different
methods. In one method the camshaft and tappets are located in the cylinder block. Rocker arms that pivot on
a shaft are located on the head. The valves are forced open when the rocker arms pivot. Tappet movements
are transferred to the rocker arms through a pushrod