TD5 Defender
EMISSION CONTROL
7
DESCRIPTION AND OPERATION
CRANKCASE EMISSION CONTROL
All internal combustion engines generate oil vapour and smoke in the crankcase as a result of high crankcase
temperatures and piston ring and valve stem blow-by. A closed crankcase ventilation system is used to vent
crankcase gases back to the air induction system and so reduce the emission of hydrocarbons.
Gases from the crankcase are drawn into the inlet manifold to be burnt in the combustion chambers with the fresh
air/fuel mixture. The system provides effective emission control under all engine operating conditions.
Crankcase gases are drawn through the breather port in the top of the camshaft cover and routed through the
breather hose and breather valve on the flexible air intake duct to be drawn into the turbocharger intake for
delivery to the air inlet manifold via the intercooler.
An oil separator plate is included in the camshaft cover which removes the heavy particles of oil before the
crankcase gas leaves via the camshaft cover port. The rocker cover features circular chambers which promote
swirl in the oil mist emanating from the cylinder head and camshaft carrier. As the mist passes through the series
of chambers between the rocker cover and oil separator plate, oil particles are thrown against the separator walls
where they condense and fall back into the cylinder head via two air inlet holes located at each end of the rocker
cover.
The breather valve is a pressure depression limiting valve which progressively closes as engine speed increases,
thereby limiting the depression in the crankcase. The valve is of moulded plastic construction and has a port on
the underside which plugs into a port in the flexible air duct. A port on the side of the breather valve connects to
the camshaft cover port by means of a breather hose which is constructed from a heavy duty braided rubber hose
which is held in place by hose clips. A corrugated plastic sleeve is used to give further protection to the breather
hose. The breather valve is orientation sensitive, and ’TOP’ is marked on the upper surface to ensure it is
mounted correctly.
It is important that the system is air tight. Hose connections to ports should be checked and the condition of the
breather hose should be periodically inspected to ensure it is in good condition.
