Land Rover Discovery: Camshaft Carrier

1. Fuel rail
2. Fuel injector (4 off)
3. Oil filler and cap assembly
4. Engine vent module
5. Engine breather pipe
6. Camshaft carrier
7. Exhaust camshaft and Variable Camshaft Timing (VCT) actuator
8. Inlet camshaft
9. Camshaft cap (9 off)
10. Bolts (20 off)

The structural camshaft carrier is cast from aluminium alloy using a high pressure die cast process. The camshaft carrier is located on two dowels in the cylinder head and secured with bolts. A gasket seals the camshaft carrier to the cylinder head.

The primary function of the camshaft carrier is to house and secure the inlet and exhaust camshafts. The camshaft bore geometry is bored in a single machining operation to ensure optimum friction reduction and each camshaft cap is uniquely identified and must be matched to its related bore.

The camshaft carrier also provides locations for the Camshaft Position (CMP) sensor, the oil filler pipe and the engine vent module. The camshaft carrier has high pressure oil galleries feeding the Variable Camshaft Timing (VCT) actuator and provides thrust face lubrication. A low pressure oil gallery returns oil from the engine vent module back to the cylinder block and oil pan.

The camshaft carrier also provides the locations for the fuel rail, engine breather and the oil filler cap.

VALVES AND ROLLER FINGER CAM FOLLOWERS

1. Hydraulic lash adjuster (16 off)
2. Roller finger cam follower (16 off)
3. Valve spring collets (32 off)
4. Valve spring retainer (16 off)
5. Valve spring (16 off)
6. Valve spring seat (16 off)
7. Valves (8 off inlet, 8 off exhaust)

The engine uses sixteen chrome plated steel valves; eight intake and eight exhaust. The intake valves are 27.3mm diameter and the exhaust valves are 25.7mm diameter. The larger the intake valve size, the more the engine can breathe. This will enhance more engine power output at higher Revolutions Per Minute (RPM). The intake valve stems are 5.47 mm diameter and exhaust valve stems are 5.463mm diameter. These allow reduced flow interruption through the intake and exhaust ports, improving performance and emissions.

The valves are located in conventional, non-serviceable valve guides in the cylinder head. A valve stem seal with integral spring seat is located in the cylinder head. The valve spring is retained in a compressed state on the valve stem by a valve spring retainer and a pair of valve spring collets. The valves are opened mechanically by a roller finger cam follower design which is operated directly with roller to camshaft lobe rolling contact. The clearance between the roller and camshaft lobe is compensated with the use of a hydraulic lash adjuster. This ensures that all roller finger cam followers are in contact with the camshaft lobes throughout engine operation.

The valves are located in conventional, non-serviceable valve guides in the cylinder head. A valve stem seal with integral spring seat is located in the cylinder head. The valve spring is retained in a compressed state on the valve stem by a valve spring retainer and a pair of valve spring collets. The valves are opened mechanically by a roller finger cam follower design which is operated directly with roller to camshaft lobe rolling contact. The clearance between the roller and camshaft lobe is compensated with the use of a hydraulic lash adjuster. This ensures that all roller finger cam followers are in contact with the camshaft lobes throughout engine operation.

CAMSHAFTS

1. Needle roller bearings
2. Camshaft lobes
3. Reluctor ring - CMP sensor
4. Exhaust camshaft
5. Inlet camshaft

The engine is fitted with a Double OverHead Camshaft (DOHC) configuration which uses two camshafts; one inlet and one exhaust. The lobes on the camshafts control the opening and closing of the valves via a roller finger cam follower valve train system.

The camshafts run on needle roller bearings to reduce friction and minimise the breakaway torque on engine start-up. The needle roller bearings are housed in the camshaft carrier and the camshaft caps are marked with 'I' and E' to denote inlet and exhaust. The camshaft caps are also numbered to ensure assembly in the correct position in the camshaft carrier; for example 'I4' or 'E1'.

The camshafts are of a hollow steel tube construction, with pressed on sintered lobes and needle roller bearings. The hollow tube design provides reduced weight for increased engine performance. Each camshaft has a pressed on drive adapter which locates a drive sprocket on the inlet camshaft and the Variable Camshaft Timing (VCT) actuator on the exhaust camshaft. The drive adapter on each camshaft is fitted with a timing pin to locate the drive sprocket and the VCT actuator on the camshaft relative to the lobe positions. The exhaust camshaft has a pressed on reluctor ring for use with the Camshaft Position (CMP) sensor.

The exhaust camshaft is fitted with a Variable Camshaft Timing (VCT) actuator. The actuator contains a sprocket which drives the camshaft via a timing chain, driven from the crankshaft. The VCT actuator adjusts the timing of the exhaust camshaft, increasing engine efficiency and performance as required. A reluctor wheel is pressed on to the opposite end of the exhaust camshaft which is monitored by the CMP sensor. The CMP sensor signal is used by the ECM and enables the ECM to determine the position of the exhaust camshaft. The exhaust camshaft can then be phased by the VCT actuator to provide increased performance and efficiency.

CAMSHAFT TIMING CHAIN

1. Secondary chain guide
2. Inlet camshaft
3. Timing mark link plate
4. Sprocket
5. Exhaust camshaft
6. Variable Camshaft Timing (VCT) actuator
7. Secondary chain tensioner guide
8. Secondary chain tensioner
9. Primary chain tensioner
10. Primary chain tensioner guide
11. Crankshaft
12. Primary chain guide
13. High pressure fuel pump sprocket
14. Primary chain guide
15. Idler sprocket

Two bushed timing chains are used to drive the camshafts via an intermediate idler sprocket. The primary camshaft chain is driven by a sprocket on the crankshaft which in turn drives the fuel pump and the intermediate idler sprocket. The fuel pump sprocket is a non-round sprocket that is timed to the crankshaft to reduce chain loads. The secondary camshaft chain is driven by the intermediate idler sprocket and then passed over the sprockets on the inlet and exhaust camshafts. The camshaft sprocket is integral with the VCT actuator assembly.

Each timing chain has a fixed timing chain guide which is secured to the cylinder block. A chain tensioner is fitted to each timing chain which can rotate around a pivot bolt. The primary timing chain has a mechanical tensioner operated by spring tension to apply a controlled tension to the timing chain. The secondary timing chain has a hydraulic secondary chain tensioner which receives pressurized engine oil from the variable flow oil pump with integral vacuum pump. The tensioners maintain the timing chains at the correct tension and allows for and dampens backlash in the chain tension due to engine deceleration. The timing chains and tensioners are maintenance free components.

A procedure and special tools are required to ensure that the correct crankshaft to camshaft timing is achieved. Both the primary and secondary timing chains have gold coloured links which are aligned with timing marks on the sprockets.

Oil PanVariable Сamshaft Еiming (VCT) - Exhaust Camshaft Only

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