The liners are inserted into a hole in the block with
The air-cooled engine differs from the
either a press fit or a slip fit. Liners are further
liquid-cooled engine in that the cylinders have closely
designated as wet-type or dry-type. The wet-type liner
spaced fins surrounding the barrel. (See fig. 3-18.)
comes in direct contact with the coolant and is sealed at
These fins provide a greatly increased surface area from
the top by the use of a metallic sealing ring and at the
which heat can be dissipated. This is in contrast to the
bottom by a rubber sealing ring; the dry-type liner does
liquid-cooled engine, which has a water jacket around
not contact the coolant. Special precautions must be
its cylinders.
taken with the seals when installing a wet-type liner.
The cylinder block is cast from gray iron or iron
Use a lubricant on the seals to prevent them from rolling
alloyed with other metals such as nickel, chromium, or
or twisting. Soap or brake fluid is recommended for this
molybdenum. Some lightweight engine blocks are
purpose. Continued overheating of an engine during
made from aluminum alloy. Cylinders are machined by
operation or improperly installed seals will allow the
grinding or boring to give them the desired true inner
coolant to enter the crankcase and contaminate the
surface. During normal engine operation, cylinder
engine oil. To determine which seals are leaking, it is
walls will wear out-of-round, or they may become
necessary to remove the engine oil pan or inspection
cracked and scored if not properly lubricated or cooled.
covers on the crankcase and pressurize the cooling
Liners (fig. 3-19) made of metal alloys resistant to wear
system, observing the liners through the crankcase for
are used in many gasoline engines and practically all
leakage.
diesel engines to lessen wear. Liners for 4-stroke cycle
Cylinder wear is caused by dirt getting through the
engines do not have air inlet ports, as shown in figure
air cleaner and acting as a grinding compound, by side
3-20. After they have been worn beyond the maximum
thrust of the piston, and by pressure of the piston rings
oversize, the liners can be replaced individually,
against the cylinder walls. Liners, therefore, do not
permitting the use of standard pistons and rings. Thus,
completely prevent wear. To check on wear and to
you can avoid replacing the entire cylinder block.
determine how much overhaul is required, use special
N
ASf03018
Y. Lock washer
M.
Exhaust valve guide
A.
O-ring gasket
Z. Washer
N.
Rocker support bracket
B.
Exhaust valve
AA. Valve lock
P.
Rocker shaft
C.
Intake valve
BB. Valve spring retainer
Q.
Rocker
D.
Cylinder
CC. Outer valve spring
R.
Rocker support bracket
E.
Cylinder barrel nut
DD. Intermediate valve spring
S.
Washer
F.
Lock nut
EE. Inner valve spring
T.
Slotted nut
G.
Dome fin deflector (LH)
FF. Valve spring seat
U.
Rocker box cover plate bolt
H.
Bolt
GG. Dome fin deflector (RH)
V.
Tab washer
J.
Lock washer
W.
Valve rocker cover
K.
Primer nozzle assembly
X.
Bolt
L.
Intake valve guide
Figure 3-18.--Cylinder of an air-cooled engine.
3-16
