Cylinder Head Description

The engine is fitted with an aluminium alloy cylinder head, which carries the camshafts, valves and spark plugs. The cylinder head is cast as a single entity and various components are permanently added after machining.

The camshafts run directly in the cylinder 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 drive chain, via a sprocket bolted to each of the camshafts, using slotted holes. The use of slotted holes allows the camshaft timing to be adjusted very accurately, to compensate for manufacturing tolerances in the camshaft drive system.

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 open sprays oil through a drilling in the tensioner blade onto the camshaft drive chain.

Oil is supplied to the cylinder head by a gallery in the crankcase. Once supplied to the head, the oil is distributed along internal drillings within the cylinder head casting and camshaft.

Single valve springs are used to close both the inlet valves 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). Both the tip and seating face of the 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.