Camshaft Cover Components (Engine - Td4)

The four fuel injection nozzles are centrally mounted above each cylinder and each is fixed to the cylinder head by means of two stud bolts. The central position of the injectors provides a symmetrical spray pattern to the central combustion bowl of the piston. ENGINE MANAGEMENT SYSTEM - EDC, DESCRIPTION AND OPERATION, Description.

Glow plugs are arranged centrally on the inlet side of the cylinder head, between the tangential port and the swirl port of each cylinder. ENGINE MANAGEMENT SYSTEM - EDC, DESCRIPTION AND OPERATION, Description.

A support bracket for the camshaft driven vacuum pump is located at the rear RH side of the cylinder head.

Vacuum Pump The vacuum pump is located on a support bracket at the rear RH side of the cylinder head and is driven from the exhaust camshaft.

Camshafts There is one exhaust camshaft and one intake camshaft. Each of the camshafts are located in five bearings and maintained in position by five bearing caps. Each of the bearing caps are fixed to the cylinder head by two bolts. The camshafts are made using the clear chill casting process and are hollow cast. The cam lobes have a negative cam radius. The camshafts are driven from the crankshaft using a simplex chain and sprocket arrangement.

Each camshaft has eight machined lobes for operating the inlet and exhaust valves through lash adjusters and rollertype finger levers. The exhaust camshaft is machined at the rear end to provide a drive connection for the vacuum pump.

Inlet and Exhaust Valves The inlet and exhaust valves are identical and have ground, solid one-piece head and stems made from Nimonic alloy material.

The valve springs are made from spring steel and are of the parallel single-coil type. The bottom end of each spring rests on the flange of a spring retainer which has an integral valve stem seal. The top end of the spring is held in place by a spring retainer 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 to grooves ground into the upper stems of the valves.

Valve seats and valve guides are an interference fit in the cylinder head.

Hydraulic Tappets and Roller Finger Rockers The valves are operated through roller-type finger rockers and hydraulic tappets, actuated by the camshaft lobes. When the camshaft lobe presses down on the top of a finger rocker, roller mechanism, the respective valve is forced down, opening the effected inlet or exhaust port. The use of this type of actuation method helps reduce friction in the valve timing mechanism.

The body of the hydraulic tappets contains a plunger and two chambers for oil feed and pressurised oil. The pressurised oil is supplied to the tappets via the main oil galleries in the cylinder head and through a hole in the side of the tappet body. The oil passes into a feed chamber in the tappet and 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 tappet outer body and the centre plunger. Oil escapes up the side of the plunger every time the tappet is operated, the downward pressure on the plunger forcing a corresponding amount of oil in the tappet body to be displaced. When the downward pressure from the camshaft and finger rocker is removed (i.e. after the trailing flank of the camshaft lobe has passed), oil pressure forces the tappet's plunger up again. This pressure is not sufficient to effect the valve operation, but eliminates the clearance between the finger rocker and top of the valve stem.

Camshaft Cover Components

The camshaft cover and engine cover components are described below:

The cover is of moulded plastic construction and is used to seal off the oil chamber in the cylinder head. It shields the oil spray from the camshaft and the chain drive gear and provides the valve gear housing.

An oil separator for the crankcase ventilation system is mounted at the centre top of the cover, which provides preliminary oil separation by cyclone, and fine separation using an internal yarn wrap filter. The separator unit also contains a pressure control valve.