The Evolution of Modern Small Car Engines
Last year the Automobile Division of the Institution of Mechanical Engineers instituted a Symposium on the Design of Small Mass-Produced Motor Car Engines. The following is a summary of these.
Ford: Mr. R. A. S. Worters, Assistant Chief Engineer, Engine and Transmission Engineering, of Ford Motor Company Ltd., Dagenham; Essex, commenced his paper by saying that the Ford Anglias and Prefects of the immediate postwar period were powered by the well-known 1,172-c.c. s.v. engine which was basically a 1932 design, although the 100E of 1953 incorporated such design changes as larger bearings, revisions to the valve layout and cooling system, and the addition of a water pump. Even so, it was apparent by 1954 that a new design was needed.
Market studies predicted cars in this class of substantially the same overall dimensions and at least equal performance to existing models. Overall weight could be reduced only by extensive use of aluminium, unfavourable on cost, and styling was unlikely to appreciably lower air drag. So equal power and torque with unproved specific economy was sought, As Ford had plans for an additional, smaller car, new engines of 835 c.c. and 1,097 c.c. were laid down. Prototype 835-c.c. engines were built but a change of concept called for performance equal to the s.v. 1,172-c.c. engine from the new small engine and a larger version to power what became the Consul Classic. The production engines were based on the 835/1,097-c.c. design but with a capacity of 997 to 1,390 c.c., later increased to 1,500 c.c. The design of this new Ford range was simplified because new manufacturing equipment was used throughout.
The two-stroke was rejected because of its poor specific economy. although attractive for its power/weight ratio. Weight saving by using air-cooling was found to be small when the cylinder finning, fan and ducting were taken into account, and cost advantages were also relatively small. Water cooling provided an inherently quieter engine and facilitated adequate car heating. Various cylinder arrangements were studied and an in-line four was found to be the cheapest to produce and was entirely suited to an orthodox vehicle if bore and stroke were carefully chosen. A target of 40 b.h.p./litre and 130 lb./sq. in. b.m.e.p. at maximum torque were considered practical, and on this basis capacities were fixed at 997 and 1,276 c.c., the latter increased to 1,340 c.c. before production commenced. A weight target of 190 lb. was agreed, for a complete engine with all accessories and flywheel but less clutch and engine mounting This was based on the known weight of 223 lb. for the s.v. engine but was not achieved by production versions of the new o.h.v. engine. The o.h.v. layout added cost and weight. Today, Ford's Engineering Division control all components of new engines on a cost/weight basis, making it possible to identify areas which will prevent the overall target being achieved and providing opportunity of rectification before it is too late; this was not so in 1954.
At that time it was considered that to make economic use of transfer machines for blocks and heads, volumes should be between 500 and 1,000 units per day. Anglia/Prefect sales were then about 850 per day, so it was essential that the two capacities of engine should form part of a family and use as many common components as possible. Where this wasn't possible, similar components must be made on the same equipment. especially blocks and heads, thus no undue penalties could be tolerated on one engine size for the sake of the other, if both were to be fully competitive.
To reduce manufacturing costs a single bore size was specified, which also simplified dealers' stocks of one size of piston and rings, apart from oversizes. The transfer machining line for the new engines alone cost in the region of £750,000 and extensive foundry equipment was also needed. Varying the stroke to alter swept volumes was less costly than machining different bore sizes; time lost in changing over the boring and honing tools becomes complicated. The different crankshafts needed presented relatively small problems with Ford's cast shafts and the volume production envisaged necessitated multiple turning and grinding machines in any case. Similarly, different-length con.-rods presented no serious difficulties.
By 1954 the mildly "oversquare" engine had been successful in the Mk.1 Consul/Zephyr. Theories that a long stroke was needed for "slogging" power was proved false by developing torque curves, proving that short-stroke engines peaked no higher in the speed range than long-stroke power units. Successful tests with the prototype 1,097-c.c. engine of 0.84 stroke/bore ratio encouraged a decision to make the new 997-c.c. engine extremely "oversquare" (0.60) and thus have available a considerable capacity range without alteration of bore.
The big bore meant a long engine, so it was desirable to keep height to a minimum. As a con.-rod length/throw ratio of about 3.4 has been accepted as the minimum if secondary out-of-balance forces are not, to become objectionable, Ford decided not to go below 3.35. It was then possible to achieve a 1,340-c.c. engine with a block height of only 7.125 in. A prototype of 1,390 c.c. was later built for durability testing and was not noticeably rougher, but did give greater mounting problems than the 997-c.c. engine.
The bores were spaced equally with 0.18 in. thick walls and a nominal space between them of 0.25 in. Equal spacing of the main bearings was then possible and sufficient length was available to use micro-Babbit liners on the smaller engine in place of more costly copper-lead. The low stroke/bore ratio gave these benefits but the large bore required a correspondingly large bearing area, because gas loads on bearings increase as the square of bore diameter.
Partly due to the low height of the block, the conventional pocket above the camshaft for the push-rods, requiring a separate core in the casting and a cover to close the opening (which is a potential oil-leak area) was replaced by tunnels drilled up the water-jacket wall. Lengthwise drillings above the tappets collect oil from the rocker gear and vertical drillings pass it down to the sump, modern techniques and the low block height making light of all these drillings. Cast in grey iron, the fully machined block for the 997/1,340-c.c. engine weighs exactly 60 lb.
Ford Motor Company has proved cast crankshafts to be fully reliable, and considerably cheaper than forgings. Formerly of a cast steel peculiar to Ford, the new engines used nodular iron, which was just becoming known. It has adequate properties if close control of the degree of nodularity during casting can be maintained, and the Ford foundry maintains without difficulty the specified minimum nodularity of 80%.
The very short strokes gave a generous overlap and made possible a fully cored-out 3-bearing shaft, very stiff, especially in the flying webs and overlap areas, which concentrates the bending and torsion stresses into the crankpins. The early prototype 997-c.c. crankshafts with a pin diameter of 1.75 in. produced unusual failures running vertically through the crankpin. An increase in diameter to 1.937 in. gave an adequate safety margin. The shell moulding technique gave an accurate casting with consistent wall thicknesses and a minimum of metal to be removed in machining - another big advantage over a forging. The low inertia forces made it possible to dispense with balance weights but bosses had to be added to the hollow "flying webs" for final static and dynamic balancing, which is controlled to 0.2 oz./in. The finished weight of the 997-c.c. crankshaft is 17.56 lb., compared to 24.2 lb. of the solid shaft of the s.v. 1,172-c.c. engine with smaller bearing journals. Thrust washers were reduced to two Babbit-faced upper half segments, which have ample capacity for clutch loads.
Orthodox bearing shells are used for mains and big-ends - micro-Babbit lined on 997/1,200-c.c. engines, copper-lead on the 1,340-c.c. engine. All mains measure 2.125 in. dia. x 0.995 in. wide. Big-end shells are common, lined with copper-lead or aluminium-tin.
Various head shapes were investigated and the "bath-tub" with large vertical valves found to give excellent all-round results. Early decisions were made to use individual inlet and exhaust ports and fully-machined combustion chambers. For both 1,340-c.c. and 997-c.c. engines inlet and exhaust-valve diameters of 1.267 in. and 1.188 in., respectively, were adopted, with corresponding port sizes, with no significant disadvantage to the smaller engine. The combustion chamber is machined in four simple milling operations, each applied to all four chambers simultaneously, and controlled to within 1-c.c. Each size of engine is available with two compression-ratios and combustion chamber volumes are varied by changes in overall head depth. Cost was reduced by threading all the port cores simultaneously into a one-piece water space core instead of conventionally splitting the water-space core horizontally.
The attraction of o.h.c. valve gear in terms of quietness and freedom of valve bounce did not outweigh the costly drive arrangements, so push-rods and rockers were used, the short stroke permitting short, light push-rods of EN8C steel, valve bounce with single valve springs being above 6,000 r.p.m. The camshaft was positioned as high as possible, subject to keeping down the length of the timing chain. The camshaft was of alloy cast iron, running in three Babbit-lined bearings, with cams hardened to Brinell 427. A single roller chain was provided with a simple hydraulic damper similar to that on Consul/Zephyr engines but some early production 997-c.c. engines developed noisy timing chains at low mileages due to insufficient tensioner control, cured by substituting a mechanical tensioner of the spring-loaded snail-cam and very fine ratchet variety. Cast-iron tappets with chilled faces were known to work well with the chosen camshaft material, from previous experience. The rockers were of nodular iron, running direct on an EN43B tubular rocker shaft, their valve ends induction hardened.
During prototype testing excellent reports were received from America of 21-4NS steel for exhaust valves but its high co-efficient of expansion required large stem-to-guide clearances with one-piece valves, so Dagenham adopted a two-piece valve with an EN18D stem butt welded to a 21-4NS head, which also reduced cost. Following Ford practice, EN18D was used for inlet valves, running direct in the head without separate guides. The smaller engine's timing and valve lift restricted performance of the 1,340-c.c. engine until a wider valve opening was developed.
The oil-pump layout was unique, as pump, full-flow filter, main relief valve and filter by-pass valve were combined, and mounted externally on the cylinder block. The pump has to lift oil some 6 1/2 in. but a rotor-type pump was found to prime effectively if designed to trap some oil in the rotor pocket. Separate oil pipes are obviated in favour of drilled galleries in the block, even for the rocker feed.
The new 997-c.c. engine went into production in September 1959. The 1,276-c.c. version was discarded in favour of the 1,340-c.c. engine in April 1961. By mid-1960 it was seen that an engine between these sizes would be wanted for the Cortina and 1,200-c.c. was chosen for adequate performance with good economy. All that was needed was a new crankshaft, rods and head. A 1,500-c.c. version was then required for the Classic and an option in the Cortina, work starting in September 1960. Using the 3.187-in, bore, a stroke of 2.864 in. gave 1,498 c.c. The stroke/bore ratio of 0.90 was fully satisfactory but 0.62 in. was added to block height. To avoid harsh, noisy running a 5-bearing crankshaft was specified but the position of the oil and fuel pumps made it necessary to retain the 3-bearing camshaft.
Both 3 and 5-bearing prototype engines were built and compared for noise and harshness. The most obtrusive part of the crankshaft noise originated when No. 4 cylinder fired, vibration being transmitted to the body via the rear engine mounting. The taller block for the 1,498-c.c. engine was acceptable as increased production had necessitated an additional transfer machine, which was able to handle both 3 and 5-bearing blocks. The 5-bearing layout costs more but the lower individual bearing loadings made it possible to revert to micro-Babbit, which more than offset the cost of the additional bearing shells. For the 5-bearing shaft a hollowed design wasn't feasible but nodular cast iron was used, with balance weights added to the end and centre webs to offset the increased inertia loads of the longer stroke. Otherwise the 1,498-c.c. engine only called for longer (4.8 in.) con.-rods, different thickness head, inlet valves of 1.437 in. dia., a 4 lb. heavier flywheel and increased capacity sump.
Thus even this 1 1/2-litre engine met the original requirements of using common components or common manufacturing methods.
More recently the GT version of 1,498-c.c. engine went into production, using a head with larger exhaust valves and higher c.r., special manifolds with compound Weber carburetter, and a new camshaft with wider timing. The basic design proved able to accept the 31% power increase with no change other than copper-lead main bearings and heavier section pistons. Competition versions of the GT engine were soon running reliably at twice the output of the standard 1,498-c.c. engine. - W. B. (To be continued)
Continued on page 644
Auto-Union cars, which have been shipped from Zeebrugge and brought by M.A.T. transports to London, their pre-delivery inspection. The heavy wax coat they wear for shipment is removed by steam hoses at 80/10o lb./sq. in. pressure and the chromium parts untaped. Dealers are, however, expected to carry out a second pre-delivery check before handing a car to the customer. in one month, earlier this year, soo cars were brought in. so dealers now receive a bonus, starting at tos. a day, to collect cars they have ordered on schedule, to relieve congestion at this new clearing depot.
Every care k taken to ensure the maintenance of the traditional Daimler-BenZ quality and high finish, at Brentford. A new body shop looks after the crash-repairs. The front and rear .sub-framcs, designed to cushion impacts, not only make Mercedes-Benz cars preferable to .many others if you intend to indulge in an accident, but this form of construction reduces repair charges, while replacement doors, etc. are not much, if any, more expensive than those for mass-produced vehicles.
A Heenan & Fronde dynamometer has been installed for power testing, engines ranging from 3-cylinder D.K.W. two-stroke's to Daimler-Benz lorry engines. There is also a roller dynamometer for checking power at the driven wheels, carburation, etc., being checked against temperature and barometric pressure, while the ingenious DB automatic gearbox has its own elaborate test and demonstration rigs, energised by a 2•20SE power unit. In a separate bay, 2.3oSL. .sports models are attended to by skilled operatives Who also hold special driving permits, which ensures safe and sympathetic test driving of these fast cars. There is a paint shop with drying oven to take one car and soon a new paintoven plant, capable of quick-drying at a temperature just below that which would be detrimental to tyres and electrics, will be instaned. Across the busy Gt. West Road the Auto-Union premises have been revised, priority going to a comprehensive spare parts store for all Daimler-Benz products, commercial vehicles included. I was told that spares to the value of some are held, with another /A-million-worth spread amongst the dealers and distributors. A simple but effective system serves to prevent stocks of any parts failing, additional Supplies being ordered from the Acton warehouse when required. There was even a 300SL space-frame SOME ADDITIONAL TECHNICAL ASPECTS OF THE MERCEDES-BENZ 300SE /:!flgine Capitals' : pint, Coaling system eaPacav ITicith heater) : 29 pints
Furl tank capacity : IS gallons range approx 315 miles., Valve clearances 'calt.11? : Inlet. 0.004 in.: eshatiq, 0.00S Furl infection pressureApprox. 213 lb. ",,t. in.. 15 ;nu). l'ucl iniectiart pinup : BoSch 6 plunger-type 2 KL 75 It /
/ /t/fel/i0/1 linseh type liPil),ES. .0inpression ratio : 8.8 to t
Brakes : German Dunlop discs :9.96 in. front. 0.04 in. rear). ATE vacum servo.
( ;car toxins: 10-33. (,-45.
noperoron : Phoenix SF suspension elements. three Bosch regulating valves. 7-litre ait stnrage sank.
'hcellmse ! ft. 0: in. Tracks : From, 4 ft. o!, in rear. 4 It. 9 I! in. 'high3) : 16 ft. 13/64 in. • 5 I.!, to 3/6.1 4 14. it?, in. (iligb Turnim : 31; ft. Dry weight : 3,18o lb. Kerb yverlehr : 3,395 lb. Permissible total xeight : 4.450
Alaker's jr nil and petrol cpmtimptiOn 14ISi'7I3 miles per pint : 175:25,9 m.p.g. /.4rbrieurron : 22 points needing attention every 1,00o miles Fuses : 12
chassis in stock, and gull-wing doors, etc., for this now obsolete model. An emergency spares service operates and Mercedes-Benz (Gt. Britain) Ltd. claim to be able to dispatch any part by trait within six hours of it being called for, even if this costs the dealer concerned a discount penalty for not stocking it himself. Orders are booming and the popularity of the various MercedesBenz models in this country call be summarised as:— 2.2oSE saloon 31% 2051.3 ti.:: :no and inoD 21% 22051: coupc' and convertible 2205 IS% 100...i)l s:jloon including long wheelbase saloon 2.20B6'':, iooSE coupe and cnnvert iblc
Automatic transmission—and how nice that Daimler-Benz designed and make their own!—is ordered for about 25"„ of al cars supplied and the demand for it is expected to increase at a rate of approximately to-15", per year.—W. B.
4th ANNUAL SLOGGIN & CLATTER (June 26th) "
The Hants & Berks M.C.s " Sloggin & clatter," organised by Nancy Cawthorne, is not as ominous as its title—it merely implies that as many unusual and interesting vehieles as possible shall slog and clatter their way to EverSley Cross for tither members to gaze on them, and perhaps admire them. This year the clatter was provided by D. Fowler's solid-tyred Burrell 5-ton steam crane-tractor, a rare engine, the only one surviving of seven built at the Thetford works. It delighted everyone by towing a Mini pick-up which filled the role of coal bunker and communications dinghy! Steam was also represented by Fisher's well-known and really entirely docile 1922 Foden steam waggon. At the other extreme, Gahagan brought his Type 37 Bugatti and Morgan-J.A.P., George Cooper a 1927 Austin 1214 and Earles a 1929 Alvis Silver Eagle coup& Baby Warrior came with her mother in a baby Austin of 1931 vintage; her father, a leg in plaster, needed something larger, which was provided by new member D. Steynor, in the form of .a P2 Rolls-Royce. This was driven by W-ll--m B y, reputed to be in heavy disguise in view of the make of the car factually I merely wore my second-best suit.—En.). Rolls-Royces were also brought by J. Hawthorne (1933, 20/25) and 0. Lockee Bayne (1937, 25/30). Jenkinson dazzled us with the pure whiteness of his ex-team 328 B.M.W., Wood came in his 47,-litre low-chassis Invicta, Michael Burn
.11 his .mmaculate 1951 prop-shaft-driven Frazer Nash, while the Morgan Plus Four was represented by Dr. Nelms' car.
C. Conway spent the evening very enthusiastically demonstrating how ho Citroen 2 C.V. takes to pieces and goes together again (it is the actual 375-e.e_ car road-rested by Mount Smar tell years ago). Modern exotics included two Lotus Elans, a Lancia Aurelia GT, a Deep Sanderson icti coupe and Dick Casythorne!s Rochdale Olympic Mk. I. Jolm Holford showed that the Turner Alexander he races is also a road car, Mike Eyre nonchalantly drove into the pub car-park in an enormous pontiac Parisienne and as if that wasn't enough, had on behind a cage-trailer containing the V8 B.R.M. that finished 9th at Syracuse, driven by Jackie Epstein.
Scragg had his H.W.M.-Jaguar, Bert Fountain his Jaguar E-type, Peter Walker an ex-works rally Mini-Cooper, Bill Tanner •a Jensen 541k and Wennerdahl one of the only two Saab Sports in this country. Then there were a tuned Simca moo, a Panhard PIA 7, Peugeot 403, Volvo Estate car, and a Porsche. Nan certainly ropes 'em in. There were some nice-looking girls there, too. They tund it hard to compete with the cars!
DON'T STAMPE ON THE STOMP
In reporting the Blackbushe Air Display last month we took liberties with the Stampe acrobatic biplane, spelling its name phonetically. But please do not Stampe On the Stomp or, for that matter, don't Stomp on the Star»pe!
A DISCERNING READER
,Simon Gough, who played the part of the son George in the ur.v. channel Nine play " Valentina " was reading a copy of Morog Swat. in one of the scenes. We congratulate him on his discerning choice of motoring literature, hoping that it was his own property and not lust something he found in the studio!
SONOSY STEM AT BEAULIEU
It is now possible to hire a Sonnsystem tape-recorder which give-s a running commentary on the exhibits in the Montagu Motor Museum as the visitorwalks round. This hire charge is 2s. (d., or ;s. Ad. if wired for two persons, and both general and technical recordings arc available. The Sonosystem dispenses with :a guide and adds greatly to the enjoyment :of touring the luse.urn. Palace I louse is similarly served, the commentary ill this case being by Lord Montagu himself.