Valve timing adjustment mechanism parts (Discovery 3)

Item name	Spare part catalog number	Description
1	-	Secondary chain tensioner
2	-	Secondary circuit
3	-	Variable valve timing mechanism
4	-	Primary chain
5	-	Primary chain tensioner

Timing gear

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

Both drive sprockets are keyed to the crankshaft. A crankshaft torsional vibration damper holds the sprockets in place. The variable valve timing mechanisms and exhaust camshaft sprockets are designed to eliminate collision and are keyless to the shaft.; torque is transmitted through an end-to-end connection where the friction load is provided by the variable valve timing mechanism/sprocket mounting bolt.

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Each chain has a hydraulic tensioner that operates on engine oil. The primary chains are lubricated by syringe tubes located at the front of the cylinder block near the camshaft drive sprockets. A jet of oil from each secondary chain tensioner lubricates these chains. The primary chain tensioners act on the pivoting flexible tensioner plates. The secondary chain tensioners act directly on the chains. The guides are mounted on the drive side of the primary chains.

Timing Belt Cover

The timing cover made of aluminum alloy covers the front crankshaft oil seal (pTFE cuff). Between the timing belt cover and the front wall of the engine, there are silicone rubber gaskets in the recess.