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.

A-O-RING GASKET

B-EXHAUST VALVE

C-INTAKE VALVE

D-CYLINDER

E-CYLINDER BARREL NUT

F-LOCK NUT

G-DOME FIN DEFLECTOR (LH)

H-BOLT

J-LOCK WASHER

K-PRIMER NOZZLE ASSEMBLY

L-INTAKE VALVE GUIDE

M-EXHAUST VALVE GUIDE

N-CAMSHAFT BEARING CAP

P-ROCKER SHAFT

Q-ROCKER

R-ROCKER SUPPORT BRACKET

S-WASHER

T-SLOTTED NUT

U-ROCKER BOX COVER PLATE

V-TAB WASHER

W-VALVE ROCKER COVER

X-BOLT

Y-LOCK WASHER

Z-WASHER

AA-VALVE LOCK

BB-VALVE SPRING RETAINER

CC-OUTER VALVE SPRING

DD-INTERMEDIATE VALVE SPRING

EE-INNER VALVE SPRING

FF-VALVE RING SEAT

GG-DOME FIN DEFLECTOR (RH)

Figure 3-3. - Air-cooled cylinder.

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