Figure 3-2.Requirements of a cylinder.
Aluminum is more expensive than cast iron.
Aluminum is not as strong as cast iron.
Because of its softness, it cannot be used on any
surface of the block that is subject to wear. This
necessitates the pressing, or casting, of steel
sleeves into the cylinder bores. Threaded holes
must be deeper. This introduces extra design
considerations and increases production costs.
Aluminum has a much higher expansion rate
than iron when heated. This creates problems
with maintaining tolerances.
The CYLINDERS are bored right into the block. A
good cylinder must be round, not varying in diameter by
more than approximately 0.0005 inch (0.012 mm) (fig.
3-2). The diameter of the cylinder must be uniform
throughout its entire length. During normal engine
operation, cylinder walls wear out-of-round, or they
may become cracked and scored if not lubricated or
cooled properly. The cylinders on an AIR-COOLED
engine (fig. 3-3) are separate from the crankcase. They
are made of forged steel. This material is most suitable
for cylinders because of its excellent wearing qualities
and its ability to withstand high temperatures that air-
cooled cylinders obtain. The cylinders have rows of
deep fins cast into them to dissipate engine heat. The
cylinders are commonly mounted by securing the
cylinder head to the crankcase with long studs and
sandwiching the cylinders between the two. Another
way of mounting the cylinders is to bolt them to the
crankcase, and then secure the heads to the cylinders.
CYLINDER BARREL NUT
DOME FIN DEFLECTOR (LH)
PRIMER NOZZLE ASSEMBLY
INTAKE VALVE GUIDE
EXHAUST VALVE GUIDE
CAMSHAFT BEARING CAP
ROCKER SUPPORT BRACKET
ROCKER BOX COVER PLATE
VALVE ROCKER COVER
VALVE SPRING RETAINER
OUTER VALVE SPRING
INTERMEDIATE VALVE SPRING
INNER VALVE SPRING
VALVE RING SEAT
DOME FIN DEFLECTOR (RH)
Figure 3-3.Air-cooled cylinder.