Engine: Description and Operation
5.3 V-12:
GENERAL DESCRIPTION
Set in a 60 degree 'Vee' formation, the engine has twelve cylinders - six in each bank- each with a bore of 90 mm and a stroke of 70 mm, giving an overall capacity of 5343 cubic centimeters. On each cylinder bank, a single overhead camshaft actuates two valves per cylinder Fuel is supplied to each cylinder via an injector, fed from a regulated fuel rail. Clean air is supplied via paper element air cleaners, on each cylinder bank. To comply with statutory regulations in some countries and to reduce emissions during the warm up period, secondary air is delivered to the exhaust manifolds via an air rail to improve oxidation, until the catalytic converters are fully effective.
CONSTRUCTION
The skirted design crankcase is manufactured in aluminium alloy and its open top deck houses slip fit wet cast iron cylinder liners.
Housed in the crankcase is the forged steel crankshaft, which is nitro-carburize treated to permit the attainment of a very high quality finish on bearing surfaces and help increase the life of the bearing journals. The crankshaft is supported by seven main bearing caps, which have bearings of lead bronze on split steel backed shells with a lead indium overlay. Any crankshaft endfloat is controlled by half thrust washers fitted on each side of the center main bearing. The gears and pulleys which drive the timing chain and external drive belts are keyed on to the crankshaft nose and held captive by a single bolt fitted into the end of the crankshaft.
The 'H' section connecting rods are of forged steel and have small end bushes of lead bronze with steel backing, which are machined to size after being pressed into the connecting rod. Big end bearings are made from lead bronze on split steel backed shells with lead indium overlay.
Pistons are manufactured from aluminium alloy and have varying degrees of dished crown to suit high or standard compression ratios depending upon market requirements. Three rings are fitted to each piston, two upper compression rings and one lower oil control scraper ring. The pistons run on hardened steel wrist pins, which are offset from the center line of the piston towards the thrust face.
A major feature of this engine is the design of the aluminium alloy cylinder heads. The heads utilize the 'May Fireball' combustion chamber which by virtue of its design gives better fuel lair mixing and controlled, even burning. These 'lean burn' combustion qualities aid fuel economy and help to meet increasingly stringent emission regulations. The cylinder heads carry the tappet block (cam carrier) in which the single camshaft per cylinder bank runs directly, with two steel in-line valves per cylinder which run in cast iron guides. Each valve has two valve springs and is operated by the camshaft via a chilled cast iron bucket tappet and clearance-adjustment shim.
Manufactured in cast iron with chilled cams, the camshafts are retained by machined aluminium caps. The tappet block is manufactured in cast aluminium alloy and is topped by a cover of the same material.
Camshaft drive is by a single 'duplex' chain, which also incorporates the auxiliary shaft in its drive line. Drive for the chain is provided by the crankshaft and chain tension is controlled by a tensioner blade and three damper blades. The distributor is driven by the auxiliary shaft via a set of spiral reduction gears.
Four external drive belts situated at the front of the engine are operated by a pulley on the crankshaft nose. The four belts drive the following:
1. Alternator.
2. Air conditioning compressor and air pump.
3. Water pump and power steering pump.
4. Cooling fan.
Two windage trays are fitted below the crankcase and prevent oil being sucked up and thrown into the crankcase, thereby alleviating windage and power loss. Bolted on to the bottom of the crankcase is the aluminium sandwich plate, the front part of which forms the base of the engine, with the rear part opening out to let oil reach the pressed steel oil pan. The oil pan is bolted to the sandwich plate.
LUBRICATION SYSTEM
RELIEF FLOW OIL COOLER SYSTEM
Oil is drawn from the oil pan via a gauze filter fitted in the suction hose. Oil is fed under pressure via internal galleries in the cylinder block to the filter head. Here the oil is regulated by a relief valve fitted in the filter head. Any relief oil is returned to the suction side of the oil pump via a cooler, with a balance valve to return it direct to the oil pan in the event of a cooler blockage. After the relief valve, the main oil flow is filtered, is again regulated and in the event of a blockage, the filter is by-passed. Oil is then fed into the main oil gallery for distribution to various parts of the engine.
FULL FLOW OIL COOLER SYSTEM
This system is the same as the relief flow oil cooler system up to the regulation by the relief valve. At this point any relief oil is returned directly to the suction side of the oil pump. The main oil flow is then directed to the oil filter, is again regulated and in the event of a blockage the system is by-passed. After filtration, the main oil flow passes through a cooler, via a regulator, to guard against blockage. After cooling, the main oil is fed into the main oil gallery for distribution to various parts of the engine.
FEED TO ENGINE (BOTH SYSTEMS)
Filtered oil is directed under pressure from the main oil gallery to the seven main bearings and then by oilways drilled in the crankshaft, to the big end bearings. An oil feed pipe connected to the rear of the block feeds the camshaft bearings, drawing oil from the main gallery. The auxiliary shaft is lubricated with oil drawn from the main gallery by oilways drilled at the front of block.
CRANKCASE BREATHER
'Blow-by' gases are recycled through the induction system to maintain a crankcase depression and in so doing, prevent their escape to the atmosphere. These gases are led from the crankcase by a ventilation pipe, which is attached to the front of the left hand tappet block and fed into a positive crankcase ventilation (PCV) valve housed in the left hand air cleaner. At closed or part throttle openings, blow-by gases are drawn into the plenum chamber of the inlet manifold. With a wide open throttle, the blow-by gases are drawn into the clean side of the left hand air cleaner. The purpose of the PCV valve is to protect the crankcase against too high a depression being generated by either the induction manifold or the air cleaner and will restrict any such depression accordingly. In this way, a suitable depression is maintained at all throttle settings, ranging from closed to fully open.
COOLANT SYSTEM
The engine is cooled in a conventional manner, by the circulation of and cooling by a solution of good quality anti-freeze and water. The water pump is mounted directly above the crankshaft and is driven from the crankshaft nose by a three point drive, (which also drives the power steering pump). The coolant is fed into the cylinder block by external pipes and is drawn from the engine via two thermostats to the radiator or directly returned to the engine if the coolant temperature is too low.