Working on the VCT Unit

When the engine is switched off the VCT unit is nonpressurized 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.

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.

Installation Position-Oil Feed Ring/Camshaft:

The triple oil bore of the oil feed ring and the camshaft 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 seats into the oil feed flange in the positions shown.

A new oil feed flange gasket needs to be installed every time the oil feed flange is disassembled. Correct seating of the gasket make sure that the oil feed flange seals correctly and lies correctly on the scaling face (incorrect seating can cause tilting).