30 AB Volvo Penta / Diesel Engine TAMD71B
7.6 Timing gears
The camshaft, oil pump, injection pump, circula-
tion pump and raw water pump are driven by
the crankshaft via helical spur gears.
Helical spur gear wheels are used in order to
keep engine noise to a minimum.
Fig. 7.2 Timing gears
1. Crankshaft gear
2. Carrier for oil pump
3. Drive gear for oil pump
4. Carrier
5. Drive gear for injection pump
6. Drive gear for engine coolant pump
7. Drive gear for camshaft
8. Drive gear for raw water pump/power take-off/servo pump
7.7 Crankcase ventilation
The engines have ventilation devices to prevent
overpressure and to run off diesel fumes, steam
and other gaseous products of combustion.
These are fitted on the right side of the engine in
connection to the air cleaner (ACL).
The gases from the crankcase pass through a
disposable paper filter which separates off any
oil mist before the gases are led away. Any oil is
returned to the oil sump via a drainage hose. On
the filter casing is also a relief valve which
opens if the pressure in the crankcase becomes
too high due to a blocked filter.
7.5 Pistons
The pistons, which are made of an aluminum al-
loy, have two compression rings and one oil ring.
The upper compression ring is coated with mo-
lybdenum, which helps reduce oil consump-
tion and the risk of ring seizing.
The pistons are oil-cooled to reduce the risk of
coking at high load. Piston cooling increases the
service life of pistons, piston rings and cylinder
liners and reduces oil consumption.
The engine’s combustion chambers are entirely
confined to the piston crowns.
Fig. 7.1 Piston cooling
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