CYLINDER HEAD COMPONENTS: PURPOSE AND DESIGN

1. Cylinder Head Design

Cylinder-head design depends on the valve arrangement of the engine it is used on. The cylinder head is of two designs, flat-head and valve-in-head. The flat-head is designed for use with the L-head engine and the valve-in-head is designed for use with the I-head and F-head engines. Remember, some diesel engines have the combustion chamber located in the top of the piston. You may have heard of an engine referred to as a flat-head six, a flat-head V-8, an

over-head-valve six, or an over-head-valve V-8. These are common terms referring to the valve arrangement and the cylinder block. Therefore, you might say that engines are not only classified by cylinder arrangement and numbers, but also by valve arrangement. Let's take a look at the technical terms which refer to valves and valve arrangements.

2. Valves

Three of the more common valve designs are the mushroom, the tulip and the semi-tulip. With the exception of the top of the valve head and the valve-lock grooves, all poppet valves have basically the same design, though sizes will vary. The design of the top of the valve, in conjunction with materials used by the manufacturer, will determine the temperature range of the valve during operation.

Three of the more common valve designs

3. I-head, L-head, and F-head Valve Arrangements

An engine's valves may be located either in the cylinder head, the cylinder block, or both. If the valves are located in the head, which is the most common arrangement found today, the engine is known as an I-head engine. The valves are positioned upside-down and directly above the piston in the cylinder head. On the cross-sectional view, an imaginary line has been drawn.

I-head valve arrangement

For the camshaft to operate the valve, a pushrod and a rocker arm must be incorporated between the valve lifter (tappet) and the valve stem. The I-head valve arrangement is often referred to as overhead valves, probably more often than its technical term.

The I-head valve train

The flat-head arrangement of the valves is technically termed as the L-head. In the L-head engine, the valves are located in the cylinder block alongside the cylinder. Draw an imaginary line across the valve head of the cross-section of this engine and continue the line over to the center of the piston head. You should be able to see an inverted "L" dotted line.

The L-head valve arrangement

The F-head arrangement is sometimes termed valve-in-head/valve-in-block. However, you will almost always hear it referred to by its more technical name, the F-head. This valve arrangement is actually a combination of the two we just covered. One valve, usually the intake valve, is located in the cylinder head and the exhaust valve is in the cylinder block. Again, draw imaginary lines to help you remember the valve arrangement. Draw an imaginary line across the exhaust valve and continue it across to the center of the piston head. Now, draw another line across the intake valve head. Continue this line until it is the same length as the first.

Now draw another line down the center of the piston, joining the ends of both the previous lines. You should find that you have drawn a distorted "F" dotted line.

F-head valve arrangement