TD5 Defender
12
ENGINE
28
DESCRIPTION AND OPERATION
Inlet and exhaust valves
The inlet and exhaust valves are mounted directly above the engine block cylinders.
Each valve is a forged and ground solid one-piece head and stem which is hardened by heat treatment. The
stems are chrome-plated then ground for improved heat transfer, wear resistance and smooth operation. It is not
possible to recut the valve’s face angle, but the valves can be lapped to their seats using grinding paste.
The valve springs are made from spring steel and are of the parallel single-coil type. The bottom end of the spring
rests on the flange of a spring seal which has a centre bore that locates on a recess ground into the lower valve
stem. The top end of the spring is held in place by a spring cap which is held in position at the top end of the valve
stem by split taper collets. The taper collets have grooves on the internal bore that locate in grooves ground into
the upper stems of the valves.
The valve seats and valve guides are sintered and are an interference fit into the cylinder head. The valve seats
and guides are non-serviceable.
Finger followers and lash adjusters
1. Valve stem
2. Finger follower
3. Lash adjuster plunger
4. Oil supply hole
5. Lash adjuster body
The valves are operated through finger followers and lash adjusters, actuated by the camshaft lobes. When the
camshaft lobe presses down on the top of a finger follower roller mechanism, the respective valve is forced down
opening the inlet or exhaust port.
The lash adjuster body contains a plunger and two chambers for oil feed and pressurised oil. Pressurised oil is
supplied to the lash adjusters via the oil galleries in the cylinder head and through a hole in the side of the lash
adjuster body. The oil passes into a feed chamber in the lash adjuster then through to a separate pressure
chamber via a one way ball valve. Oil flow from the pressure chamber is determined by the amount of clearance
between the lash adjuster outer body and the centre plunger, oil escapes up the side of the plunger every time the
lash adjuster is operated, the downward pressure on the plunger forcing a corresponding amount of oil in the lash
adjuster body to be displaced. When the downward pressure from the camshaft and finger follower is removed
(i.e. after the trailing flank of the camshaft lobe has passed), oil pressure forces the lash adjuster’s plunger up
again. This pressure is not sufficient to effect the valve operation, but eliminates the clearance between the finger
follower and top of the valve stem.
