Timing Components: Description and Operation
Ford does not provide camshaft gear timing marks, or information to perform timing belt service without the special tools shown in the timing belt service and repair procedure. Timing Belt
General
The use of the new variable camshaft timing optimizes the combustion procedure by improving gas exchange in the cylinders. As a result of this the exhaust emissions regulations can be met without the use of a pulse air system or an exhaust Gas Recirculation System (EGR system).
Mechanical Inspection
Mechanical Design Of The VCT Unit:
The mechanical principles behind Variable Camshaft Timing (VCT) are relatively simple. The valve timing for opening and closing of the exhaust valves is influenced by a hydraulic cylinder (3) which is riveted to the timing pulley (1). This cylinder connects the timing pulley (1) with the camshaft (8) through a hydraulic piston (4) and inner gear bushing (6). The hydraulic piston is guided along its axis by the helical gears (6,7) on the exhaust camshaft and the hydraulic cylinder. The helical gear transfers the up and down motion of the hydraulic piston into a rotary motion. As the timing pulley is fixed in place by the timing belt, the position of the exhaust camshaft i s rotated in relation to the timing pulley, and the exhaust. valve timing is therefore adjusted. The hydraulic piston is moved by supplying pressurized engine oil from the engine oil circuit to both pressure chambers of the hydraulic cylinder. The engine management system controls a solenoid valve which in turn supplies the pressurized oil to the pressure chambers.
When the engine is switched off, the hydraulic piston goes back towards its original position by means of the return spring (3).
Emergency mode:
- If oil pressure is to low, the VCT will be regulated to the "END-STOP" position.
- In cause of an electrical error, the solenoid will regulate to the "END-STOP" position.
VCT Unit In Original Position And At Maximum Extension:
Hydraulic operation
The VCT unit is supplied with engine oil (3) from the engine oil circuit and controlled by the engine management system. The engine management system regulates the solenoid valve (1) through a Pulse Wide Module (PWM) from 0 to 100 %.
With rising current (0-1 A) the displacement of the control piston (4) in relation to the return spring (6) increases, and vice versa. As a result of this motion the control edges and return bores (5) of the control piston open and close the oil flow to and from the two pressure chambers (11,12) of the hydraulic cylinder (9).
When the engine is switched off the return spring returns the control piston back to its original position. At the same time the return bores in the front pressure chamber (12) are opened, which allows the return spring (11) to slide back the piston in the hydraulic cylinder towards its original position.
Working on the VCT Unit
When the engine is switched off the VCT unit is non-pressurized and therefore has no function. However, the hydraulic piston usually only returns right back to the original position if the VCT unit has been removed or the engine management system caused this to happen just before the engine was switched off. A complete return to the original position is prevented by friction on the cams and the spring forces due to the valve springs.
Installation Position - Oil Feed Ring/Timing Pulley:
The VCT unit must be in its original position before the valve timing can be adjusted. Turn the exhaust camshaft in the normal direction of engine rotation to bring the VCT unit to its original position. When doing this the crankshaft must not be turned.
The triple oil bore of the oil feed ring and the timing pulley form a labyrinth on three levels. The oil bores of the oil feed ring and the two triple oil bores (1) on the hydraulic cylinder (one visible) are arranged at 120 degrees to each other. This prevents the hydraulic cylinder from running dry when the engine is switched off. This means that the VCT unit is ready to work shortly after starting the engine.
The lug (2) must be centered between the three oil bores (1) and the mark. If this is not the case install a new exhaust camshaft timing pulley and a new hydraulic cylinder. The lug (2) must locate in the bore when sliding the timing pulley onto the oil feed ring.
Oil Feed Flange Gasket (3 X O-Ring Seal):
NOTE: Use a thumb to press the positioning pins on the 3 x O-ring seals into the oil feed flange in the positions shown.
A new oil feed flange gasket must be installed every time the oil feed flange is disassembled. Correct seating of the gasket makes sure that the oil feed flange seals correctly and lies correctly on the sealing face (incorrect seating can cause tilting).