The camshafts run directly in the head without separate bearings. Valve clearances are adjusted by changing variable thickness shims which sit between the valve tappet bucket and the valves.
The camshafts are driven by a silent-type chain. The chain is guided by two blades and is tensioned by a hydraulic tensioner.
The Hydraulic tensioner is fed oil via a gallery in the cylinder head. The combination of oil pressure and spring pressure pushes the plunger against the tensioner blade which tensions the camshaft drive chain. The hydraulic tensioner has an oil pressure relief valve located in the plunger that is set to open between 12-16 bar and when opens sprays oil through a drilling in the tensioner blade onto the camshaft drive chain.
Oil is supplied to the head by an internal gallery. Once supplied to the head, the oil is distributed along internal drillings within the head casting and camshaft.
Single valve springs are used to close both the inlet and exhaust valves. These valve springs have close wound coils at one end to assist in the prevention of valve bounce at high engine speed and to give a smooth valve actuation. When assembling the cylinder head it is important that the close wound, colour coded ends of the springs are fitted downwards (towards the piston). The tip of the inlet and exhaust valves are hardened to give a long service life.
Due to the methods used to assemble the valve seat and valve guides to the head, these parts cannot be replaced.
Caution: In any of the following operations which necessitate the removal or disconnection of the camshaft drive chain, NEVER tum the engine without the camshaft drive chain and tensioner correctly fitted and adjusted. In the disassembled condition, the pistons will contact the valves if the crankshaft is turned, causing severe engine damage.