The new Jaguar V12

The Jaguar V12 engine
Technical description

For some considerable time rumour implied that Jaguar were working on a vee engine to supplement or succeed their illustrious twin-cam XK six-cylinder power unit. It was not at first known whether this would be a V8 or a V12, but the truth is out—the new engine is a 5.3-litre V12 with two (not twin) oh. camshafts, for installation alongside the famous XK six in a revised E-type and ultimately, but not necessarily this year, in the fast-selling XJ saloons—one hesitates to say it at the present time, but a 12-cylinder XJ Jaguar, if sold at Sir William Lyons' traditional competitive price, might well constitute a tough rival for the V8 Rolls-Royce Silver Shadow. However, that is for the future...

Work began on an experimental racing-type 4-cam V12 designed by W. M. Heynes and C. W. L. Baily in the early 1960s, this 5-litre fuel-injection engine producing over 500 b.h.p. at 8,000 r.p.m. after only limited development. But it would have been unduly bulky for the E-type, and costly to produce, the latter being the reason for terminating production of the Turner 2 1/2-litre and 4 1/2-litre V8 Daimler engines by British Leyland.

Instead, Messrs. Hassan and Mundy were asked to prepare another V12, easier to make in quantity and giving the sort of power output available from the 4.2-litre XK engine in competition guise, while providing new parameters of smoothness, mid-range torque and quiet running. The outcome is the new 90 x 70-mm. (5,343-c.c.) engine, developing 272 (DIN) b.h.p. at 5,850 r.p.m. and 314 gross b.h.p. at 6,200 r.p.m. on a 9-to-1 c.r. Maximum torque of 349 lb./ft. (304 DIN) is achieved at 3,600 (3,800) r.p.m. Maximum BMEP is 141 lb./sq. in. (DIN), 161 lb./sq. in. SAE, at 3,600 r.p.m.

The new V12 has several outstanding design and construction features, of which the most notable are: (a) The use of Lucas "Opus" Mk. II transistorised ignition; (b) the use of aluminium for the cylinder blocks, cylinder heads, tappet blocks and cam-covers, etc.; (c) camshafts and tappets running directly in the alloy tappet blocks; (d) oil-cooling achieved by passing water from the cooling system through a heat-exchanger; and (e) a Jaguar oil pump of "crescent" gear-type.

In evolving this engine experiments on single-cylinder rigs showed that a single o.h. camshaft actuating in-line vertical valves offered cost, space and weight saving over a twin-cam layout and it was adopted after much research, and has some similarity to Coventry-Climax racing engines, with which both Hassan and Mundy were well acquainted. This valve layout was tried initially with a 10.6-to-1 c.r., and the engine ran happily on 99-octane fuel. This was reduced, first to 10 to 1, then to 9 to 1 for the production engine, enabling 97-octane petrol to be used. After fairly deep bowl-in-piston combustion chambers had been tried, more power was obtained with shallower chambers of greater diameter. Single cylinder experiments also showed that with this head the sparking plug was best located near to the centre, firing from the inlet side, which multi-cylinder research confirmed.

While in the experimental stage exhaust emission for the USA, Canadian and Swedish markets was taken into account, the Lucas transistorised ignition being favoured largely for its benefits in this connection of consistent timing over big mileages, which two-phased six-cylinder distributors did not maintain on the 4-cam racing engine. Carburetters were also better than fuel injection in respect of a cleaner exhaust. The air-injection method of oxidising unburnt gas has been adopted for the Jaguar V12.

To enlarge on the significant aspects of the new engine outlined as (a) to (b) above, the Lucas transistorised ignition features for the first time on a volume-production car. Developed from F1 racing practice, it copes with the V12's demand for 600 sparks per second at 6,000 r.p.m., with a capacity of up to 700 a second, while dispensing with conventional contact-breakers, so that timing is constant for the life of the engine. The light-alloy construction saves 116 lb. over a similar c.i. cylinder block and the V12 weighs only 80 lb. more than a 4.2 XK engine in similar rig. Jaguar say they expected noise problems but installed in the car no difference is detectable—implying that both iron and alloy V12s were built. The cylinder block is an alloy casting, with wet c.i. liners. The heads are sand-cast alloy with 40° inlet ports; the valve guides are c.i. and the 90° valve seat inserts of sintered iron. The tappet blocks are of diecast alloy, and include the seven camshaft bearings, which have die-cast alloy caps. The bucket-tappets are chilled c.i., working directly in the tappet blocks. It is claimed that, apart from compactness, the single oh. heads save 22 lb. each over twin-cam heads. The oil heat-exchanger is of cast aluminium, beneath the shallow front portion of the sump, cooling water from the radiator passing over its fins, in an integrally-cast 1 3/4 in. dia-tunnel. This oil-to-water system drops oil temperature by 22°C. for a rise in water temperature of just over 1°C. The oil pump is like those often used in automatic transmissions and permits a less critical end-clearance than the normal gear-type pump, nor does it require an extra drive, as it is keyed to the crankshaft.

To continue with a general description of the engine, it is a conventional 60° V12 with a 3-plane forged-steel crankshaft running in seven 3-in. journals, with c.i. four-bolt bearing caps. The centre and rear mains are 1.2-in. wide, the remainder 1-in. wide. The con-rods are paired, on 2.3-in. diam journals, all bearings being of copper-lead. The Tuft rided crankshaft is balanced statitically and dynamically and has a rubber/steel vibration damper. The front seal is a lip-type, the rear seal of asbestos rope. The forged-steel I-section con-rods have bronze-bushed little-ends. The Hepworth and Grandage pressure die-cast alloy pistons each have three rings, and the combustion chamber is in the crown surface, bore surface between piston and head, and the area of head defined by the bore periphery.

Each head is attached to the block by 26 studs. The camshafts operate the valves direct through bucket tappets, with shim adjustment. The camshafts are driven by a single-stage duplex 9.5-mm. pitch endless chain, tensioned by a new type of Morse tensioner incorporating a Nylatron GS blade and anti-backlash device, from a 21-tooth crankshaft sprocket. Jaguar contemplated belt-drive but considered the pulleys required too wide for the V12's installation clearances and preferred a drive they are familiar with, especially in conjunction with the latest Morse control of the chain (which exceeds a 5 1/2-ft. run), this using the "creep" properties of thermoplastic polymers and having a rod to take care of "back-drive" when the engine stops rotating—it is used also for the VW K.70, one believes. There is vernier adjustment of the camshaft timing. Valve crash speed is 7,840 r.p.m.

The lubrication system works at up to 70 lb./sq. in. (the oil gauges of the two E-types I drove never came off maximum readings) supplied by the pump on the front main bearing housing. Delivery is approximately 16 gallons a minute at 6,000 r.p.m., when some eight gallons are fed to the heat-exchanger every minute. The valve-gear is supplied at approximately 15 lb./sq. in. with spillage to the tappets. A Tecalemit full-flow filter is incorporated in the system. At the front of the engine a jack-shaft is driven by both sides of the timing chain. It runs in white-metal bearings. Auxiliaries are belt-driven from the nose of the crankshaft, twin vee-belts being used for the Butec A7/1A alternator, which has a 60-amp capacity at 10,000 r.p.m., equal to 4,800 engine r.p.m.

The centrifugal impeller-type water pump feeds both banks of cylinders, its maximum output being 90 gallons per minute at 6,500 r.p.m., reducing to 18 g.p.m. at 1,000 r.p.m., in each case with the thermostats fully open.

Carburation is by four Zenith 175CDSE carburetters, two on the outside of each block, a position necessitated by scarcity of space between the vee, although the inlet ports are on the insides of the blocks, the resultant long inlet manifolds being welcomed as contributing to effective torque in the middle speed ranges. Air filtering is by AC Delco, in Jaguar casings. The four 3-branch inlet manifolds are water heated, at about 100°C. Fuel feed is by SU AVF 106 electric pumps, at 1.5 lb./sq. in. The exhaust manifolds are on the outside of the cylinder blocks, with paired pipes per bank to two main exhaust pipes.

The engine weighs 680 lb. with ancilliaries and full exhaust emission equipment and measures 44 in. x 39 in. x 27 in. or 38 in. x 33 in. x 26 in. without emission pump, in both cases without gearbox. The firing order is 1A-6B-5A-2B-3A-4B-6A-1B-2A-5B-4A-3B, reading "A" as the o/s bank, front. The valve timing is inlet: 17° BTDC, 59° ABDC; exhaust: 59° BBDC, 17° ATDC. The inlet valves are of EN52 silicon chrome steel, the exhaust valves of 21-4WS austenitic steel, both having a dia. of 7.74 mm., the lift being inlets 4.18 cm., exhausts 3.46 cm. Tappet clearances are 0.30 to 0.35 mm., cold. The distributor for the Lucas "Opus" ignition is a 36DE12, the coil a Lucas oil-filled 13C 12, and the engine is started by a Lucas pre-engaged M45G starter fed from a Lucas RXCA 55/8 battery. The sparking plugs are 14 mm. Champion N9Y and the lubricating oil specified is SAE 20W50 in hot climates, SAE 10 W 50 in cold climates. There is a normal carburetter enrichment. The engine idle is 650 r.p.m. or 750 r.p.m. with automatic gearbox.

From the foregoing it will be appreciated that Walter Hassan, OBE, A.M.I. Mech. E, and Harry Mundy, A.M.I. Mech. E, MSAE, MSIA, have produced a significant engine. Clearly the need for maximum power has been balanced against volume-production facilities and it has been borne in mind that the day of the complex production engine is perhaps numbered, even when having an extravagant number of cylinders—Lamborghini went to a V8 with belt-driven o.h. camshafts when introducing a 2 1/2-litre car, and Ferrari has a six in the Dino.

How the Jaguar V12 engine is made
One of the most encouraging aspects of the Jaguar V12 story was to find a half-dozen or so of the new power unit running on the production test-beds and a great many more complete at the Radford factory well over a month before announcement date. The new engine is being made in a new machine shop equipped at a cost of nearly £3-million. The output target is 170 to 180 V12 engines per week of single-shift working, with a future optimum of 1,000 per 80-hour (two shift) week. Cylinder blocks are machined on three Archdale 57-station transfer machines, cylinder heads on a 42-station Huller transfer machine, costing nearly £700,000. Five special purpose Cincinnati machines do the initial milling of the blocks. The three previously-mentioned Archdales, with 18, 6, and 33 stations respectively, drill, seam, tap, mill and bore the blocks. A Weatherly horizontal broacher is used for sump face and bearing-cap locations and Desoutter and Ingersoll-Rand stud insertion and nut runners fit bearing cups. Cylinder liners are bored to a location tolerance of 1 1/2-thou. in. Cylinder liner seating faces are given + or — 1/2-thou. in. An electric oven heats the heads to 180°C for fitting the valve inserts. Much final machining is done on Huller borers, valve guide locations being to + 0.0005 in. to —0.0002 in., on a six-spindle borer.

Crank-pin milling is done in one operation on a GFM twin-headed miller and oil-ways are drilled to a pre-set feed rates on a 16-station Kearney and Trecker transfer machine. Crankshafts are stress-annealed and shot-blasted and then ground on multi-wheel machines to a + or — 0.0005 in. Tolerance, balancing by web in-drilling to a tolerance equivalent to 0.5 oz. in. being done with a four-spindle drilling unit and Avery balancer. Landis grinders give a bearing surface finish to 0.0003 in. limits. The final crankshaft balance tolerance is approximately 0.15 oz. in. Tappet block machinery include a special-purpose Archdale rotary transfer unit and a Boncham and Turner fine borer.

Engine assembly takes place adjacent to the new machine shop. The mechanised track has 52 stages, and consists of tubular pedestals mounted on six-wheeled trolleys running in underfloor guides. Each pedestal has a face plate which can be locked in any position hydraulically. The cylinder block, when its sub-assembly stages are complete, is attached to a fixture on this plate by three "slave" studs and nuts. Grouped around the track are the sub-assembly stages which—in the case of cylinder blocks, heads and crankshafts—are fed from the machine shop by overhead storage conveyors.

On the main engine assembly track, the ability to rotate and lock the pedestal-mounted cylinder block in any position eases the whole process considerably. For example, at the touch of a lever, the unit can be inverted for crankshaft and sump fitting, and turned on end for the installation of the cylinder liner-piston-connecting rod assembly. When assembly is complete, the engine receives its gearbox and is filled with oil, prior to testing. Each V12 unit is subjected to bench testing before it is transported to the Jaguar assembly plant at Browns Lane, Allesley (some three miles from the Radford factory). A section of the engine test shop at Radford has been adapted to take the V12. Indeed, comparatively little modification to existing test beds has been necessary. When the unit is installed, exhaust, oil and petrol pipes are fitted; water hoses, throttle cable, and an oil-pressure gauge are connected. Blanking plugs are fitted to the vacuum and heater hoses, and a "slave" jockey pulley and fan belt are attached, the fan being shielded for safety. In the case of automatic transmission models, oil cooler pipes are also fitted, and a line-pressure pipe (with gauge) is screwed into the gearbox. The engine is first run on "no load", whilst oil flow, noise and leak checks are made.

Idle speed is set at 500 to 600 r.p.m. and, with the vacuum advance pipe disconnected, the ignition timing is set; the vacuum pipe is then replaced and the engine idle speed re-set. Manual gearboxes have already passed noise and operational tests, and a check is now made to ensure that the gear-lever movement is functioning correctly. The engine/gearbox unit is then coupled to a dynamometer and run at quarter-load for 20 minutes at 2,000 r.p.m. and for 20 minutes at 2,500 r.p.m.; a further run at half-load (still at 2,500 r.p.m.) occupies another 15 minutes. The carburetter dashpots are topped up after these tests, and the carburetters are set for their correct idle speed. An automatic transmission test is carried out at 1,200 r.p.m. in "Drive", and here the line pressure is set. Manifold depression is also checked under these conditions. The automatic box is then checked for operation in all ratios. In a final power-output check, the engine is taken up to 3,000 r.p.m. under full load. Test reports are completed, temporary attachments are removed, and the unit is taken from the test shop and sprayed with protective material before being transported to the Browns Lane assembly plant by special trailer. Final detail engine adjustments are made during the two road tests to which all completed Jaguar cars are subjected.

From the foregoing it will be appreciated that Messrs. Hassan and Mundy, directed originally by Heynes and Baily, have evolved for Jaguar a significantly compact, 300-b.h.p. V12 engine which is well contrived for volume output on modern transfer machinery. I wish it well.—W. B.