Cylinder Head Components
CYLINDER HEAD COMPONENTSThe main cylinder head components are:
^ Cylinder head
^ Cylinder head gasket
^ Oil separator
^ Camshaft housing
^ Camshafts
^ Intake and exhaust valve assemblies
^ Variable Camshaft Timing (VCT) solenoid and Camshaft Position (CMP) sensors
^ Spark plugs
^ Coils
^ Fuel rail and injectors
^ Vacuum pump
^ Intake manifold
^ Exhaust manifold
Cylinder Head
The chill cast cylinder head is of the cross-flow type, manufactured from a light-alloy metal. Deep-seated bolts, to reduce distortion, secure the cylinder head to the cylinder block. Two hollow locating dowels align the cylinder head with the cylinder block. The 2 camshafts are supported by 7 bearing caps each, directly in the cylinder head and camshaft cover.
Cylinder Head Gasket
The seal between the cylinder head and cylinder block is a conventional cylinder head gasket. The head gasket is made of steel and has multiple layers. For service, there is only 1 size of gasket available.
Oil Separation Housing
Crankcase gases are routed from the crankcase, engine block and cylinder head to the oil separation housing located on the camshaft cover. From the oil separation housing, the crankcase gases are routed via a pressure regulator, located at the rear edge of the housing, to the cylinder head and the intake ports for the intake valves.
Camshaft Housing
The chill cast camshaft housing is manufactured from a light-alloy metal and acts as a combined valve cover and camshaft bearing cap. The housing has cast oil ducts on it's underside, which ensure good oil supply to the camshafts and the valve lifters. The oil separation housing is located on the camshaft cover.
Camshafts
The camshafts are of a hollow steel tube construction, drilled to save weight. Each camshaft is retained in the cylinder head by the camshaft housing. The intake camshaft is equipped with a VCT unit and also drives the vacuum pump.
The intake camshaft has cam lobes with different profiles. One for a small lifting height of 3.6 mm, and 1 for larger lifting height of 10.0 mm. The transition between the lifting heights is controlled via the Camshaft Profile Switching (CPS) function.
The exhaust camshaft is conventional, i.e. only has a lifting height of 10.0 mm.
Intake and Exhaust Valve Assemblies
The cylinder head incorporates 2 overhead camshafts operating 4 valves per cylinder via hydraulic tappets for the intake camshaft and mechanical tappets for the exhaust camshaft.
Camshaft Profile Switching
CPS is a system where the intake valves, at engine speeds up to approximately 3000 rpm, have a small lifting height of 3.6 mm, and at speeds above approximately 3000 rpm, have a greater lifting height of 10.0 mm. CPS, in combination with the VCT function makes it possible to control the cylinders' incoming air quantity in such a way that the Electronic Throttle Actuator (ETA) can be fully open. A fully open ETA, during operation, reduces the pump losses considerably compared with when the amount of intake air is controlled by the ETA itself. Reduced pump losses, in turn, cause a reduction in fuel consumption.
The electrical hydraulic valves are seat valves.
The valves have 3 inputs/outputs:
^ Inlet, oil supply
^ To/from tappet
^ To return, i.e. oil pan
A solenoid is affected via an electro-magnet, which affects a valve that can assume 2 positions.
When the solenoid is not activated, the valve is only affected by the oil pressure on the intake side. The valve closes for intake but opens between the tappet and return.
The oil pressure is low at the tappet's outer locking pin and the valves lift a small amount.
When the solenoid is activated, the valve is affected from above by an electro-magnet that overpowers the force of the oil pressure.
The valve shifts position and closes between the tappet and return but opens the connections between intake and tappet.
The oil pressure is high at the tappet's outer locking pin that is lifted and affects the inner locking pin. Outer and inner tappet connect and the valves lift a greater amount.
The intake camshaft is equipped with 3 lobes for each valve. One centrally located with a small lifting height of 3.6 mm, and 2 outer lobes with greater (same) lifting heights of 10.0 mm.
At small lifting heights, only the centrally located lobe works on the valve, which occurs via the inner tappet. The outer lobes work on the outer tappet that follows the movement of the lobes. The return spring is compressed and ensures that the tappet is always in contact with the camshaft. When the centrally located tappet and the outer tappet are not joined, the outer tappet moves without affecting the valve. Thus the lifting height is small. At high lifting height, the inner tappet and the outer tappet are joined via the 2 lock pins.
The position of the lock pins is controlled hydraulically by 2 electro-hydraulic CPS solenoid valves. These valves are located in the camshaft housing.
One solenoid controls the valves for cylinders 1, 2 and 4 whilst the other controls the valves for cylinders 3, 5 and 6. The solenoids therefore control 6 valves each (when the engine has 2 intake valves and 2 exhaust valves per cylinder).
The position of the solenoids valves, on or off, are controlled by the ECM.
The inner tappet works like a hydraulic tappet, which compensates for any wear. The valve clearance is therefore '0'.
The exhaust camshaft is conventional and has a lifting height of 10.0 mm. The tappets are mechanical (i.e. have valve clearance).
Camshaft Data
Intake
^ Opening angle, 3.6, mm lifting height: Crankshaft degrees - 152° Crankshaft degrees - 76°
^ Crankshaft degrees - 152°
^ Crankshaft degrees - 76°
^ Opening angle, 10.0 mm lifting height: Crankshaft degrees - 240° Crankshaft degrees - 120°
^ Crankshaft degrees - 240°
^ Crankshaft degrees - 120°
Exhaust
^ Opening angle, 10.0 mm lifting height: Crankshaft degrees - 240° Crankshaft degrees - 120°
^ Crankshaft degrees - 240°
^ Crankshaft degrees - 120°
The intake camshaft has a VCT unit.
^ BTDC = Before Top Dead Center
^ ABDC = After Bottom Dead Center
^ BBDC = Before Bottom Dead Center
^ ATDC = After Top Dead Center
Camshaft Position in Relation to Load and RPM
By closing the intake valves early at low load and low engine speed, reduced fuel consumption is achieved.
The oil inlet, located on the front edge of the cylinder, supplies oil to the following:
^ The hydraulic tappets
^ The vacuum pump
^ The nozzle for cam chain lubrication
^ The intake camshaft's front bearing
^ The electro-hydraulic CPS solenoid valves, front and rear
^ The tappets with CPS function
There is a bleed valve (16) in the duct for the rear electro-hydraulic solenoid valves.
The duct is also equipped with 2 calibrated passages (3) to each tappet circuit (2) (i.e. the circuits after the CPS solenoid valves). A continuous flow through the circuit ensures the necessary stable pressure differences that are necessary for a stable transfer between the small and large tappet (or vice versa).
NOTE: In the event of a small lifting height, the tappet circuit, in principle, has no pressure when the CPS valves are open, which produces a return flow to the oil pan.
A filter is located in each passage.
The oil inlet, located on the rear edge of the cylinder, supplies oil to the following:
^ The camshaft chain's hydraulic tensioner
^ The intake camshaft VCT unit
^ The intake camshaft's bearings
^ The exhaust camshaft's bearings
To switch from low lift to high lift and vice versa as smoothly as possible, the transfer is only permitted when certain conditions are completed. These are:
^ That the oil temperature is above +40°C (104°F). Calculated internally in the ECM, from, amongst other things, the coolant temperature
^ Occasionally the volumetric efficiency is the same for low and high lift, which means that the air requirement is within a range where it can be managed initially by VCT control. This is to achieve as soft a transfer as possible.
^ It is possible to adjust ignition timing to prevent torque peaks during CPS control
Variable Camshaft Timing Solenoid and Camshaft Position Sensors
The profile, or position and shape of the camshaft lobes are optimized for a certain engine rpm, but this normally limits low-end torque or high-end power. At high engine speeds, an engine requires large amounts of air. However, the intake valves may close before all the air has been given a chance to flow in. On the other hand, if the camshaft keeps the valves open for longer periods of time, problems start to occur at the lower engine speeds. This will cause unburned fuel to exit the engine since the valves are still open.
To overcome this, VCT changes the valve timing by either advancing or retarding the camshafts to allow for optimum engine performance, reduced emissions, and increased fuel efficiency. This is achieved via an electronically controlled hydraulic solenoid valve located in the camshaft housing at the rear of the engine, behind the rear CPS solenoid. The ECM transmits a signal to the solenoid, which directs engine oil into the VCT unit. A valve spool in the VCT unit regulates the flow of oil.
There are 2 CMP sensors located in the camshaft housing. The CMP sensors monitor the position of the camshafts to establish ignition timing order, fuel injection triggering and for accurate VCT camshaft advance-retard timing feedback.
The CMP sensor is a Hall-effect sensor, which switches a battery fed supply on and off. The supply is switched when the teeth of the reluctor pass by the tip of the sensor. The 4 teeth are of differing shapes, so the ECM can determine the exact position of the camshaft at any time.
Spark Plugs
The spark plugs screw into the cylinder head through the camshaft housing and are controlled by the ECM via individual coils.
Ignition Coils
The ECM uses a separate ignition coil for each spark plug. The ignition coils are of the plug top design, which attach to the top of the spark plug. The coils are secured to the camshaft housing with a bolt.
The coil has a rubber seal, which seals the coil in the spark plug hole in the cylinder head, preventing the ingress of moisture and debris around the spark plug. These coils eliminate the requirement for HT leads, which in turn improves the ignition system reliability.
Each coil has a 3-pin female connector, which provide for a battery voltage ignition feed, an earth for the secondary winding and a primary winding negative (switch) terminal. The switch terminal of each coil is connected to a separate pin on the ECM to allow independent switching.
Fuel Rail and Injectors
The fuel rail maintains a fuel pressure of 3.8 bar (55 psi) above manifold depression under normal operating conditions, though this is programmed to rise to 4.2 bar (61 psi) in response to either:
^ Cold start conditions, to improve fuel vaporization
^ Cold fuel conditions, as the colder the fuel the higher viscosity
The fuel rail is attached to the intake side of the cylinder head with 3 bolts. Six fuel injectors are installed in the cylinder head and connected to the fuel rail. 'O' ring seals are used to seal the injectors in both the fuel rail and cylinder head. A connection for the fuel pressure pipe is located between injectors 1 and 2.
There is a fuel rail pressure and temperature sensor located at the end of the fuel rail, next to injector number 6. The pressure sensor continuously monitors the fuel pressure in the fuel rail, this value is used by the ECM to calculate the injector pulse-width required to deliver the correct mass of fuel per injection. The temperature sensor measures the temperature of the fuel in the fuel rail. This input is then used to deliver the correct quantity of fuel to the engine.
Vacuum Pump
The intake camshaft is equipped with the VCT unit. The intake camshaft also drives the vacuum pump.
NOTE: When installing the vacuum pump make sure the slot in the VCT unit and the vacuum pump coupling are in the vertical position to aid installation. The vertical position is marked on the vacuum pump housing by 2 raised lines.
Intake Manifold
The intake manifold attaches to the cylinder head with 6 bolts and the oil pan with 2 bolts.
The manifold is capable of varying both intake tract length and plenum volume by means of 2 separate valves.
At low engine speeds, long intake tracts are utilized to provide optimum engine torque. Shorter tracts are used at medium speeds, again, to optimize engine torque for the existing engine speed range.
At higher engine speeds the benefits of optimizing the tract lengths are outweighed by the necessity of maintaining an appropriate supply of air to meet the engines requirements. Therefore, the plenum valve is opened to create a single, large plenum volume to provide the maximum quantity of air to charge the engines cylinders.
Exhaust Manifold
The exhaust manifold comprises 2 separate manifold assemblies. One manifold is used for cylinders 1 to 3 and the second manifold is used for cylinders 4 to 6. The manifolds are sealed to the cylinder head with a gasket and secured with 14 bolts.
Each manifold comprises 3 fabricated branches, which merge into an integral catalytic converter. A threaded boss is positioned where the 3 branches merge and provides for the fitment of a pre-catalyst Heated Oxygen Sensor (HO2S).
The catalytic converter outlets have offset flanges which mate with corresponding flanges on the front section exhaust system.
A bracket on each outlet flange allows for the attachment of an exhaust manifold heat shield.