Details of the valve timing adjustment mechanism (Discovery 3)

Item name	Spare part number	Description
1	-	Secondary chain tensioner
2	-	secondary circuit
3	-	The mechanism for changing the valve timing
4	-	primary circuit
5	-	Primary chain tensioner

Timing gear

Multi-link primary and single-row secondary chains drive the camshafts of each bank of cylinders. The primary chains transmit torque from the two sprockets on the crankshaft to the variable valve timing mechanisms on the intake camshafts. Secondary chains transmit torque from the variable valve timing mechanisms to sprockets on the exhaust camshafts.

Both drive sprockets are keyed to the crankshaft. The crankshaft vibration damper holds the sprockets in place. The camshaft timing mechanisms and exhaust camshaft sprockets are anti-collision design and are mounted on the shaft without a key; torque is transmitted through the connection "end to end", in which the friction load is provided by the bolt of the fastening mechanism for changing the valve timing / sprocket.

Each chain has a hydraulic tensioner powered by engine oil. Lubrication of the primary circuits is carried out by means of syringe tubes located in the front of the cylinder block near the camshaft drive sprockets. A jet of oil from each secondary chain tensioner lubricates these chains. Primary chain tensioners act on pivoting flexible tensioner plates. The secondary chain tensioners act directly on the chains. The guides are installed on the drive side of the primary circuits.

Timing cover

Aluminum alloy timing cover covers front crankshaft oil seal (cuff made of PTFE). Between the timing cover and the front wall of the engine, silicone rubber gaskets are located in the recess.