HORIZONTAL OPPOSEDThis engine is
designed to fit into compartments where height
is a consideration. It is used for air-cooled
RADIALThis engine is designed almost
exclusively for an aircraft engine.
The cylinders are numbered. The cylinder nearest
the front of an in-line engine is number 1. The others are
numbered 2, 3, 4, and so on, from front to rear. In V-type
engines, the numbering sequence varies by
You should always consult the
manufacturer's manual for the correct order.
The FIRING ORDER (which is different from the
NUMBERING ORDER) of the cylinders of most
engines is stamped on the cylinder block or on the
manufacturers nameplate. If you are unable to locate
the firing order and no operation or instruction manual
is available, turn the engine over by the crankshaft and
watch the order in which the intake valves open.
ARRANGEMENT OF VALVES
The majority of internal combustion engines also
are classified according to the position and arrangement
of the intake and exhaust valves, whether the valves are
located in the cylinder head or cylinder block. The
following are types of valve arrangements with which
you may come in contact:
L-HEAD (fig. 2-11)The intake and the
exhaust valves are both located on the same side
of the piston and cylinder. The valve operating
mechanism is located directly below the valves,
and one camshaft actuates both the intake and the
Figure 2-11.L-head engine.
Figure 2-12.I-head engine.
I-HEAD (fig. 2-12)The intake and the
exhaust valves are both mounted in a cylinder
head directly above the cylinder. This
arrangement requires a tappet, a pushrod, and a
rocker arm above the cylinder to reverse the
direction of valve movement. Although this
configuration is the most popular for current
gasoline and diesel engines, it is rapidly being
superseded by the overhead camshaft.
F-HEAD (fig. 2-13)The intake valves are
normally located in the head, while the exhaust
Figure 2-13.F-head engine.