Description
Engine
General
Operation of the engine is controlled by the ECM (engine control module). For additional information, refer to Electronic Engine Controls
Variable Valve Timing
When directed by the ECM (engine control module), the VVT (variable valve timing) unit will be set to the optimum position between full advance and retard for a particular engine speed and load. This is achieved when the ECM (engine control module) sends the energizing signal to the oil control solenoid until the target position is met. At this point, the energizing signal is reduced to hold the solenoid position, and as a result the position of the shuttle valve. This function is under closed-loop control, where the ECM (engine control module) will alter the energizing signal, when required, to maintain the desired position.
Engine oil properties and temperature can affect the ability of the VVT (variable valve timing) mechanism to follow demand changes to the cam phase angle. At very low oil-temperatures, movement of the VVT (variable valve timing) mechanism is sluggish due to increased viscosity, and at high oil-temperatures the reduced viscosity may impair operation if the oil pressure is too low. To maintain satisfactory VVT (variable valve timing) performance, an increased capacity oil pump is installed, plus an engine oil temperature sensor to enable monitoring by the ECM (engine control module). The VVT (variable valve timing) system is normally under closed-loop control except in extreme temperature conditions, such as cold starts below 0 °C (32 °F). At extremely high oil-temperatures, the
ECM (engine control module) may limit the amount of VVT (variable valve timing) advance to prevent the engine from stalling when returning to idle speed.
The VVT (variable valve timing) does not operate when engine oil-pressure is below 1.25 bar (18.1 lbf/in2), as there is insufficient pressure to release the VVT (variable valve timing) unit's internal stopper pin. This usually occurs when the engine is shutting-down and the VVT (variable valve timing) has returned to the retarded position. The stopper pin locks the camshaft to the VVT (variable valve timing) unit to ensure camshaft stability during the next engine start-up.
Engine Structure
Cylinder Block Components
The cylinder block is of a cast aluminum alloy construction with cast iron liners. The 90 degree 'V' configuration provides a rigid structure with good vibration levels. A low volume coolant jacket improves warm-up times and piston noise levels; the longitudinal flow design of the jacket, with a single cylinder head coolant transfer port in each bank, improves rigidity and head gasket sealing. The RH (right-hand) cylinder bank is designated as bank 1, and the LH (left-hand) as bank 2, viewed from the front of the engine.
Data Locations
Engine data is marked at 3 locations, 2 on the cylinder block (shown) and 1 on the engine front cover, which consists of a label displaying the engine number. Component diameters are represented by alpha and numeric codes. For additional information, refer to Crankshaft Main Bearing Journal Clearance - 4.2L Crankshaft Main Bearing Journal Clearance
Piston and Connecting Rod Assembly
The connecting rods are manufactured from sinter-forged steel and have fracture-split bearing caps. The bearing caps are produced by fracturing the opposing sides of the connecting rod at the bearing horizontal centre line. As well as being easier to manufacture, when reassembled the fractured surfaces interlock to form a strong seamless joint. The cylinder position is marked on adjoining sides of the joint to identify matching connecting rods and bearing caps. The connecting rod bearings are aluminum/tin split plain bearings.
The pistons are of the open-ended skirt design with a dished crown. Three piston rings, 2 compression and one 3-piece oil control ring, are installed on each piston. Each piston is installed on a gudgeon pin located in a bronze bushing in the connecting rod.
Connecting Rod Orientation
The piston grade number is stamped on the crown of the piston and must coincide with that for each cylinder bore. The piston must be assembled in the correct orientation for the designated cylinder bore:
- Bank 1 - piston grade number and the thick flange of the connecting rod must face the front of the engine.
- Bank 2 - piston grade number and the thin flange of the connecting rod must face the front of the engine.
Crankshaft and Structural Sump Components
Crankshaft and Main Bearings
Six counter-balance weights ensure good vibration levels from the 4 throw, 5 bearing crankshaft. Manufactured in cast iron, the crankshaft also has undercut and rolled fillets for improved strength.
The crankshaft rear oil seal is a press fit in the bedplate to cylinder block interface.
The main bearings are aluminum/tin split plain bearings. An oil groove in the upper half of each bearing transfers the oil into the crankshaft for lubrication of the connecting rod bearings. An aluminum/tin thrust washer is installed each side of the top half of the center main bearing.
Bedplate
The bedplate is a structural casting bolted to the bottom of the cylinder block to retain the crankshaft. The use of a bedplate further improves rigidity. Iron inserts, cast into the main bearing supports of the bedplate, minimize main bearing clearance changes due to heat expansion.
Two hollow dowels align the bedplate with the cylinder block.
Beads of sealant seal the joint between the bedplate and the cylinder block.
Oil Pan
The aluminum alloy structural sump is bolted to the bedplate. A windage tray attached to the underside of the bedplate isolates the oil pan from the disturbed air produced by the rotation of the crankshaft, to prevent oil aeration and improve oil drainage. A rubber plug at the rear of the structural sump seals the port that provides access to the torque converter securing bolts. The engine oil drain plug is located in the pressed steel oil pan, which attaches to the underside of the aluminum alloy structural sump.
A bead of sealant seals the joint between the structural sump and the bedplate.
Oil Pump
The oil pump is installed on the crankshaft at the front of the engine. The pump outlet port aligns with oil passages in the bedplate (see Lubrication System for more information).
Starter Drive Plate
The starter drive plate is attached to the rear of the crankshaft. A timing disc, for the CKP (crankshaft position) sensor, is spot welded to the front face of the drive plate.
Camshaft Timing Components
Multiple link primary and single row secondary chains drive the camshafts of each cylinder bank. The primary chains transmit the drive from 2 sprockets on the crankshaft to variable valve timing units on the intake camshafts. The secondary chains transmit the drive from the variable valve-timing units to sprockets on the exhaust camshafts.
A key locates the 2 drive sprockets on the crankshaft. The crankshaft's torsional vibration damper retains the sprockets in position. The variable valve timing units and the exhaust camshaft sprockets are non-interference, non-keyed fits on their respective camshafts; the drive being transmitted by the face to face friction load produced by the valve timing unit/sprocket securing bolt.
Each chain has a hydraulic tensioner operated by engine oil. The primary chains are lubricated via oil squirt tubes located at the front of the engine block near the crankshaft drive sprockets. A jet of oil from the end of each secondary chain tensioner lubricates the secondary chains. The primary chain tensioners act on pivoting flexible tensioner blades. The secondary chain tensioners act directly on the chains. Guide rails are installed on the drive side of the primary chains.
Variable Valve Timing
The VVT (variable valve timing) unit is a hydraulic actuator mounted on the end of the intake camshaft, which advances or retards the intake camshaft timing and thereby alters the camshaft to crankshaft phasing. The oil control solenoid, controlled by the ECM (engine control module), routes oil pressure to either the advance or retard chambers located either side of the 3 vanes interspersed within the machined housing of the unit.
The VVT (variable valve timing) unit is driven by the primary chain and rotates relative to the exhaust camshaft sprocket. When the ECM (engine control module) requests the camshaft timing to advance, the oil control solenoid is energized moving the shuttle valve to the relevant position to allow engine oil pressure, via a filter, into the VVT (variable valve timing) unit's advance chambers. When the camshaft timing is requested to retard, the shuttle valve moves position to allow oil pressure to exit the advance chambers, while simultaneously routing the oil pressure into the retard chambers.
Timing Cover
The aluminum alloy timing cover accommodates the crankshaft front oil seal (a PTFE (polytetrafluoroethylene) lip seal). Silicon rubber in-groove gaskets seal the joint between the timing cover and the front face of the engine.
Cylinder Head Components
The cylinder heads are unique to each cylinder bank. Deep-seated bolts, to reduce distortion, secure the cylinder heads to the cylinder block. Two hollow dowels align each cylinder head with the cylinder block. The multi-layered steel cylinder head gasket has cylinder specific coolant flow cross-sections for uniform coolant flow.
The 14 mm (0.55 in) spark plugs, 1 per cylinder, locate in recesses down the centre line of each cylinder head.
The engine-lifting eyes are bolted to the cylinder heads, 2 on the rear (1 per head) and 1 at the front.
Each cylinder head incorporates dual overhead camshafts operating 4 valves per cylinder via solid shim-less valve lifters.
The lightweight valve gear provides good fuel economy and noise levels. Valve head diameters are 31 mm (1.220 in) for the exhaust and 35 mm (1.378 in) for the intake. All valves have 5 mm (0.197 in) diameter stems supported in sintered metal seats and guide inserts. Collets, valve collars and spring seats locate single valve springs on both intake and exhaust valves. Valve stem seals are integrated into the spring seats.
Camshafts
The camshafts are manufactured in chilled cast iron. Five aluminum alloy caps retain each camshaft. Location numbers, 0 to 4 for the intake camshaft and 5 to 9 for the exhaust camshaft, are marked on the outer faces of the caps.
Sensor Timing Ring
A camshaft position sensor timing ring is located at the rear of both intake camshafts. A flat, machined near the front of each camshaft, enables the camshafts to be locked during the valve timing procedure.
Camshaft Covers
The camshaft covers are manufactured from thermoplastic. Bank 1 camshaft cover incorporates an outlet for the part load engine breather and the pressure control valve. Bank 2 camshaft cover incorporates an outlet for the full load engine breather and the engine oil filler cap. Identical oil separators are incorporated below the breather outlet in each cover. For additional information, refer to Engine Emission Control Description
NOTE:
LH (left-hand) exhaust manifold shown, RH (right-hand) exhaust manifold similar.
Exhaust Manifolds
The cast stainless steel exhaust manifolds are unique for each cylinder bank. Each exhaust manifold installation includes two metal gaskets and two heat shields. Spacers on the securing bolts allow the manifolds to expand and contract with changes of temperature while maintaining the clamping loads.
Each exhaust manifold incorporates a connector for the AIR (secondary air injection) system (where fitted). Where an AIR (secondary air injection) system is not fitted, each connector is sealed with a cap nut. The RH (right-hand) exhaust manifold incorporates a connection flange for the EGR (exhaust gas recirculation) system. For additional information, refer to Engine Emission Control Description
Lubrication System
Oil is drawn from the reservoir in the oil pan and pressurized by the oil pump. The output from the oil pump is then filtered, cooled and distributed through internal oil passages.
All moving parts are lubricated by pressure or splash oil. Pressurized oil is also provided for operation of the variable valve timing units and the timing gear chain tensioners.
The oil returns to the oil pan under gravity. Large drain holes through the cylinder heads and cylinder block ensure the quick return of the oil, reducing the volume of oil required and enabling an accurate check of the contents soon after the engine stops.
System replenishment is through the oil filler cap on the LH (left-hand) camshaft cover.
With the exception of the pump, all oil system components are installed on the structural sump.
Oil Pick-up
The fabricated steel oil pick-up is immersed in the oil reservoir to provide a supply to the oil pump during all normal vehicle attitudes. A mesh screen in the inlet prevents debris from entering the oil system.
Oil Pump
The oil pump is installed on the crankshaft at the front of the engine. The pump inlet and outlet ports align with oil passages in the bedplate.
The pumping element is an eccentric rotor, which is directly driven by flats on the crankshaft. An integral pressure relief valve regulates pump outlet pressure at 4.5 bar (65.25 lbf/in2).
Oil Filter Assembly
The oil filter is a replaceable cartridge with an internal bypass facility that permits full flow bypass if the filter is blocked. The oil filter is attached to the engine oil cooler, which is attached to a filter head installed on the front of the structural sump. The filter head also incorporates:
- An oil pressure switch. For additional information, refer to Instrument Cluster Description
- An oil temperature sensor. For additional information, refer to Electronic Engine Controls Description
The engine oil cooler is a liquid-to-liquid heat exchanger cooled by engine coolant. The coolant feed and return hoses for the engine oil cooler are connected to the radiator lower hose. For additional information, refer to Engine Cooling Description
Oil Level Gage
The oil level gage locates along the left side of the oil pan, supported in a tube installed in the bedplate. Two holes in the end of the gage indicate the minimum and maximum oil levels. There is a difference of approximately 1.0 liter (1.0 US quart) between the two levels.