by F. W. STILES
late Managing Director of Alfa-Romeo British Sales. Ltd.
Part IV — The Supercharged and Non-supercharged Single- and Twin-o.h.c. 1 3/4-litre Models.
As outlined in the previous articles in this series, in 1929 the Alfa-Romeo range comprised the single o.h. camshaft, twin o.h. camshaft and supercharged twin o.h. camshaft 1 3/4-litre cars.
At the 1929 Show the first of the Tipo 6C 1 3/4-litre models was exhibited. This was the long-chassis “Turismo” which had a single o.h. camshaft engine but differed from its 1 1/2-litre counterpart in having the bore increased from 62 to 65 mm. (65 by 88 mm., 1,750 c.c.), a double-port Solex carburetter in place of the Zenith, a rear fuel tank in lieu of the dash tank, an exhaust-heated inlet manifold on the off side and 18-in, in place of 19-in. wheels. This chassis weighed 15 cwt., and with closed coachwork the weight varied between 21 and 23 cwt., in which form a speed of 70 m.p.h. could be attained.
Early in 1930 deliveries commenced of the “Gran Turismo” twin-cam 1 3/4-litre “17/85” cars, which superseded the equivalent 1 1/2-litre model. The chassis cost £650. Again a Solex carburetter was used, while the rear springs were 2 in. shorter than on the 1 1/2-litre car and all the springs had an increased number of thinner leaves, which materially improved comfort and roadholding. Heavier, ribbed brake drums and 18-in. wellbase wheels were used. The “Gran Turismo” had a wheelbase of 9 ft. 6 in. and a track of 4 ft. 7 in. Oil and fuel capacities were two and 12 gallons respectively. Both it and the afore-mentioned single-cam 1 3/4-litre came over as bare chassis and were equipped with instruments and coachwork in this country. Four-door, four/five-seater saloons and two-door drophead close-coupled coupés were the most popular, but a few open four-seaters were made. The “Gran Turismo” was unquestionably the more popular and was capable of 80 m.p.h. and 20 m.p.g. at normal cruising speed, with very brisk acceleration, the reliability being of a high order if the cars were properly serviced. Early examples of both models had a wire-mesh radiator stoneguard, replaced on later cars by a vertical slatted stoneguard.
A few short-chassis, 9-ft. wheelbase “Gran Turismo” cars were also imported, these having a somewhat higher compression-ratio, giving 85 m.p.h. and better acceleration, and the engine mounted approximately 15 in. farther back as on the supercharged if “Gran Sport” cars. Indeed, a supercharger could be fitted if desired. These and the blown cars were distinguishable by their sloping radiator and slatted stoneguard.
The supercharged, twin-cam 1,750-c.c. “17/95” model (chassis £1,075) retained this 9-ft. wheelbase and had a Roots blower driven at 1 1/2 engine speed from the front of the crankshaft and drawing from a two-port Memini carburetter which was supplied from a large pear-shaped rear tank mounted above the frame, via an auxiliary dash tank. The standard jet settings were: choke 21, jets 115, but in some instances one main 115 jet in conjunction with a 114 or a 110 jet, and careful regulation of the air-adjustment screw, gave better results. The correct fuel was 75/25 petrol/benzole with the addition of 2 per cent. light-grade mineral oil for the supercharger on later versions. On the earlier cars it was necessary to remove the front cover-plate from the supercharger every 1,000 miles and pack it with petroleum jelly in order to lubricate the bearings. The blown cars normally had a 12:49 (4.1 to 1) axle ratio, giving 20 m.p.h. per 1,000 r.p.m., with 18-5.25 tyres. The constant-mesh gears were 17:27. A speed of 95 m.p.h. was attainable in either light two-seater or T.T. four-seater form and in some cases higher speeds were obtained. A special version of this model was used by G. E. T. Eyston when he took the hour-record at some 115 m.p.h.
It has often been reported that factory teams of 1 3/4-litre Alfa-Romeos competed in races in this country, but this can be contradicted as such cars were purchased from the factory, in most cases fitted with bodies in this country, being entered, prepared and raced under my sole jurisdiction, a process involving considerable financial embarrassment as a result of the capital involved as well as much effort and many sleepless nights.
For example I ordered three chassis early in 1930 and these arrived, destined for the 1930 T.T., with no equipment and requiring numerous modifications. I had to journey backwards and forwards between England and Italy to engage drivers who regularly handled these cars, the only help Alfa-Romeos offered being one or two mechanics who arrived a few days before the race to assist in the final preparation. The “Gran Sport” was designed essentially for two-seater bodywork and on no account could the works be persuaded to provide specially-designed four-seater bodies, as required in our over-1 1/2-litre sports car races, or the full touring equipment also called for by the race regulations.
6C “Turismo”: Maximum engine speed 4,000 r.p.m.; h.p., 45; firing order, 1, 5, 3, 6, 2, 4.
6C “Gran Turismo”: Maximum engine speed 4,400 r.p.m.; h.p., 55; firing order, 1, 5, 3, 6, 2, 4.
6C “Gran Sport,” s/c: Maximum engine speed 4,400 r.p.m.; h.p., 85; firing order, 1, 5, 3, 6, 2, 4.
“Gran Turismo,” maker’s servicing data: Normal oil pressure: warm, 20 lb./sq. in.; Castrol XL in winter, XXL in summer. Timing: inlet opens 5 deg. before t.d.c., closes 35 deg. after b.d.c.; exhaust opens 45 deg. before b.d.c., closes 13 deg. after t.d.c. Tappet clearance: .006 in.-.007 in., cold. Contact-breaker points: .012 in.-.016 in. Plug points: .0016 in. Timing: 2 deg. on crankshaft = about 3/16 in. on flywheel rim. Ignition: 2 deg. after t.d.c. at full retard. Check compression every 1,500 miles; decoke every 8,000 miles. Replace cooling water every 1,500 miles. Clutch free movement: 1 1/8-1 1/4 in. Lubricate with petrol. Oil thrust-bearing (a few drops) every 1,500 miles. Top up gearbox with Castrol S every 1,500 miles and ditto axle every 2,500 miles. Fill front hubs with Castrol S every 2,500 miles. Clearance of brake pin and lever by gearbox: .004 in. Lubricate steering box with Castro! S every 2,500 miles and road springs with Castrolese G every 2,000 miles. Normal tyre pressure (28-5.00): 28 lb./sq. in.
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