Page 130 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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114 Automobile mechanical and electrical systems

Oil Filter mounting Oil Pressure switch

Figure 2.60 Oilways

Figure 2.61 Piston features: 1, fi re land; 2, crown; 3, piston pin bore; 4, skirt diameter; 5, skirt;
6, piston rings

the oil supply system. The block is prepared, drilled and threaded to attach
Key fact
additional components such as the oil sump pan and oil pump assembly.
Pistons are generally manufactured
from an aluminium alloy which 2.1.3.2 Pistons and connecting rod
reduces weight and increases heat
dissipation. Pistons are generally manufactured from an aluminium alloy, which reduces
weight and increases heat dissipation. There are numerous designs to
accommodate thermal expansion according to engine type and application
( Fig. 2.61 ).
Aluminium has greater thermal expansion than cast iron used for the block and
cylinder liners. This means that the piston expands more than the block as the
engine temperature increases. When the engine is cold, the working tolerances
are greater to allow for expansion. The piston has design features to allow for
expansion and correct tolerances at running temperatures; for example, a cold
piston is slightly oval and tapered inwards towards the crown ( Fig. 2.62 ).

The piston pin or gudgeon pin has an offset by a small amount toward the thrust
face of the cylinder bore which allows the thrust forces at the piston crown to
maintain the piston against the cylinder wall ( Fig. 2.63 ). This has an effect when
the engine is cold by reducing piston movement due to excessive clearance,