AC's missing-link

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Bill Boddy

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The AC made in Thames Ditton as luxury light-cars in both four and six-cylinder versions in the 1920s and well-publicised by none other than S F Edge, previously of Napier fame, did well in racing and record-breaking at Brooklands and Montlhery. So it was not exactly surprising when sprint exponent Raymond Mays turned to this make of car when his notable successes with his two Brescia Bugattis, Cordon Rouge and Cordon Bleu, terminated at the close of the 1924 season, because Mays had to sell them to settle outstanding accounts.

Mays was a great “persuader”. He persuaded the astute Mr Edge that he and his engineering friend Amherst Villiers, who had supercharged one of the Bugattis until the engine of this 04 cwt car developed nearly 80 bhp, could perform similar wonders for the AC Company. Mays also persuaded the Memini carburettor people to let him use one of their carburettors, with a financial bonus as well, and to use their London depot in which to construct a new supercharged racing AC. He further persuaded the manager of London’s Grosvenor Hotel to let his equipe have a room therein on special terms, after he had persuaded his father to release him from the family business at Bourne for the time it took to build and race the new car. I suspect that Mays also persuaded his mother to book seats for the theatres he liked to attend at that time. . .

The AC was a development of the earlier four-cylinder 1 1/2-litre racing cars, to which Villiers was to apply a supercharger. Thus the 69 x 100mm (1496cc) engine had a wet-liner aluminium cylinder block, a onepiece alloy crankcase, and a bronze head.

The single overhead camshaft was chaindriven from the back of the crankshaft, but Villiers tickled up the valve timing, as he had on the Bugattis. A more substantial twobearing crankshaft was made by Vickers, who also supplied the high-tensile steel forgings for the blower blades. William Mills of Birmingham supplied heat-treated Y-alloy pistons and the new aluminium castings. Lubrication was dry-sump, using pumps beneath the supercharger, which projected through the shapely new Serck radiator. The supercharger had a blow-off valve, also a by-pass, enabling Mays to control the blower pressure from the car’s cockpit. It sucked from the carburettor, of course. Ignition was by two Bosch magnetos, mounted transversely on a platform on the under-bonnet side of the dashboard and driven from the back of the oh camshaft, supplying two plugs per cylinder. The aim was 5500 rpm at 10 lb/sq in boost.

The chassis followed established AC practice, the lightweight differential-less back axle having exposed drive-shafts. But better stability was sought by using splayed-out springs, clamped at each leaf. Woodhead supplied these and the tubular Alford & Alder front axle was provided with Rubery brakes. Steering was Manes with a bell crank linking drop-arm and steering arm. While Amherst Villiers, who had several other important jobs to oversee as well, toiled, Mays played tennis at Queen’s Club, frequented also by Parry Thomas, and enjoyed plays at the Drury Lane theatre, where he became friendly with Ivor Novello, and nights at Mrs Meyrick’s 43 Club. But that is getting ahead of this story; back to the AC and the 1925 racing season.

Mays had done a spot more persuading, obtaining from Edge the loan of a new 2-litre AC sports two-seater, and behind this the engine of the racing AC was towed on a trailer (borrowed from Memini’s), to a Chalk Farm engineering-shop where Mays had arranged for the engine to be put on their water-brake. With the help of a mechanic (borrowed from Memini’s) and watched by Edge and Sydney Smith of AC, tests were conducted. Alas, with the “hot” Lodge plugs installed, after five minutes running at maximum revs, with over 100bhp on the dial, water filled the cylinders.

This trouble persisted. But after fitting revised waterseals and trying the car out on Toft hill near Bourne, Mays set off for Shelsley Walsh, the AC towed behind a lorry lent by his father and driven by the faithful Ayliffe of the Bugatti days. Mays, his mother, Villiers and Mays’s girl cousin rode in the sports AC. A neat single-seater body had been fitted to the racing car, which weighed 14 1/2 cwt. Running sans bonnet, after last-minute work in the paddock, the ignition apparently retarded itself after the Esses, and the AC’s time was 57.0s, putting it fourth in the 1 1/2-litre class, two seconds slower than A Joyce’s AC.

The next appointment was the Brooklands Summer meeting, where the regulation silencer recently insisted upon would increase back pressure in the AC’s delicate engine. Mays entered for the 100mph Short and 90mph Long Handicaps. Although he did not start in the first of these races he suffered an almost unprecedented rehandicap in the second, a penalty normally inflicted only on those who had gone exceptionally quickly in an earlier race. Indeed, he had to concede four seconds to the winner, Parry Thomas in the big Lanchester 40 single-seater who lapped at 106.42mph.

Presumably the AC’s supercharger had frightened the handicappers; the only other car so endowed was, I think. the Halford Special; so rare was forced induction in 1925 that it wasn’t noted on the Race Card. But yet again the AC failed, unable to complete a full lap, although before water again entered all its cylinders Mays had apparently seen 4000rpm, equal to 107mph. However, Mays extracted a little more money from Edge, and Amherst, Villiers designed a new bronze head with three valves per cylinder, cast by Brotherhood’s, extra holding-down studs were used, and the boost was reduced to five lb/sq in. All then seemed ready for the two-day Skegness race meeting. But when in the lead in a half-mile sprint clutch slip intervened.

The next day bent gearbox selectors ruined Mays’ chances. There remained the ICC 200 Mile Race, for which a two-seater body was made, by Brainsby’s of Peterborough, for which the chassis had to be extended, at a cost of some £1000. The weight went up to 21cwt. In the meantime Mays had hoped to break the 1 1/2-litre Hour record held by the Eldridge Special at 107.62mph, with the AC. But the steering column broke, and he had a close shave, after covering the Brooklands’ half-mile at II6mph. In practice for the “200”, the boost up to 11 lb and on Englebert balloon tyres, overheating was the problem and Richards of Croydon had to hastily increase the radiator area. In the race, over the artificial road-circuit, the header tank was punctured and Mays was out early, the crankcase already bound up with wire-rope. The AC was towed in. Mays then gave up, transferring his allegiance to Mercedes for 1926. (Tim Birkin put the AC’s engine into his racing boat.) Now comes that missing link. In spite of AC Cars having apparently run out of money, they had a new racing engine ready very early in 1926, It was a six-cylinder 60 x 88mm (1493cc) power-unit of all-aluminium construction, using wet cast iron cylinder liners.

There were two overhead valves per cylinder (instead of the earlier four valves per cylinder), in typical AC form, with floating valve guides, volute valve springs and conical cotters. The crankshaft was a built-up circular web one, running in eight ballbearings. Ingenious tapered pegs secured the crank webs, obviating the use of nuts. The inclined valves were operated by twin overhead camshafts chain-driven from the back of the engine, with the famous Weller chaintensioner. (Note: All previous AC engines had used a single oh-camshaft). There were rockers between cams and valves, the rocker bearings being pressure-lubricated, through hollow axis-pins. The sparking plugs were central in the hemispherical combustion chambers, fired through a double Delco distributor driven from the front of the o/s camshaft. From the front of the nis camshaft the vane-type water pump was actuated. The big-ends were of roller-bearing type and the crankcase was of circular section, the wide sump below it possessing copper cooling tubes.

Thus this new engine had wet-sump lubrication, with a pressure filter. The supercharger was driven from the nose of the crankshaft, and had triple alloy blades. There was a by-pass to enable blower pressure to be varied in the inlet pipe. Would it have used the chassis of the Mays’ AC? Nothing more was heard of this racing engine. But had AC contemplated joining Alvis in Grand Prix and other longdistance events in 1926, if finance had not evaporated? Mr T G John may unwittingly have offered a pointer to this when he said that while the Alvis Company could only spare £3000 a year from its 1926 advertising budget for racing, Continental teams (he may have had Salmson in mind, or perhaps STD) were spending £87,000. W B

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