Operation

Operation

The V8 engine is an eight cylinder, water cooled unit comprising cast aluminium cylinder block and cylinder heads.

The cast iron cylinder liners are shrink fitted and located on stops in the cylinder block. The banks of cylinders are at 90 ° to each other. The crankshaft is carried in five main bearings, end-float being controlled by the thrust faces of the upper centre main bearing shell.







The centrally located camshaft is driven by the crankshaft via a chain. The valves are operated by rockers, pushrods and hydraulic tappets. Exhaust valves used on later engines are of the carbon break type which incorporate a machined undercut at the combustion chamber end of the valve. The design prevents carbon build-up on the valve stem which could lead to valves sticking. These valves are interchangeable with valves fitted to early engines.

Each of the aluminium alloy pistons has two compression rings and an oil control ring. The pistons are secured to the connecting rods by semi-floating gudgeon pins. The gudgeon pin is offset 0.5 mm (0.02 in), identified by an arrow mark on the piston crown, which must always point to the front of the engine. Plain, big-end bearing shells are fitted to each connecting rod.







Lubrication
The full flow lubrication system uses a gear type oil pump driven from the crankshaft. The assembly is integral with the timing cover which also carries the full flow oil filter, oil pressure switch and pressure relief valve.

Oil is drawn from the pressed steel sump through a strainer and into the oil pump, excess pressure being relieved by the pressure relief valve. The oil pressure warning light switch is screwed into the timing cover and registers the oil pressure in the main oil gallery on the outflow side of the filter.

Pressurized oil passes through an oil cooler mounted in front of the radiator to the full flow oil filter. The oil then passes through internal drillings to the crankshaft where it is directed to each main bearing and to the big end bearings via numbers 1, 3 and 5 main bearings.

An internal drilling in the cylinder block directs oil to the camshaft where it passes through further internal drillings to the hydraulic tappets, camshaft journals and rocker shaft. Lubrication to the thrust side of the cylinders is either by oil grooves machined in each connecting rod big end joint face or by splash.







The purpose of the hydraulic tappet is to provide maintenance free and quiet operation of valves. It achieves this by utilizing engine oil pressure to eliminate the mechanical clearance between the rockers and the valve stems.

During normal operation, engine oil pressure, present in the upper chamber, passes through the non-return ball valve and into the lower chamber.

When the cam begins to lift the outer sleeve, the resistance of the valve spring, felt through the push rod and seat, causes the tappet inner sleeve to move downwards inside the outer sleeve. This downward movement of the inner sleeve closes the ball valve and increases the pressure in the lower chamber sufficiently to ensure that the push rod opens the valve fully.

As the tappet moves off the peak of the cam, the ball valve opens to equalize the pressure in both chambers which ensures the valve closes when the tappet is on the back of the cam.