by F. W. Stiles,
late Managing Director of Alfa-Romeo British Sales, Ltd.
Part II —
The Single O.H.C. 1 1/2-litre Model
My introduction to the then-new o.h.camshaft Alfa-Romeo followed the arrival of a cable from the works in Milan in the early part of 1927, requesting me to go out there to inspect the new model when it was in the experimental stage. I accepted this invitation with a feeling of excitement, for I had already met the quietly enthusiastic Sig. V. Jano, who was responsible for this and several later models of the famous Italian marque, and in the course of earlier visits to Milan I had come to appreciate the clean layout of the chassis, and the beautifully finished castings, in the design and production of which Italian engineers, undoubtedly, are artists. Clearly, there were possibilities of its sale to enthusiasts in this country.
The Alfa-Romeo factory covered a large area and they operated their own foundry and gear-cutting shops, machined their own crankshafts and pressed their own chassis-frames. Their products cannot by any stretch of imagination be classed as merely assembled from other manufacturers’ components, for, with the exception of such items as electrical equipment, wheels and tyres, practically the whole chassis was made in the Alfa-Romeo factory.
I already knew the 3-litre push-rod o.h.v. six-cylinder models described in Part I of this article, and now it was obvious that Alfa-Romeo had in mind the production of a small chassis of very high quality, and that no expense was to be spared in attaining this object. I may say that by the time I arrived at the chassis-erecting shop I already coveted one of the new o.h.c. 1 1/2-litres as a personal car. Unfortunately, it was very slow getting into production, for motor cars formed only a small part of the total output of the Milan factory which, even in 1927, was busy with such things as air-compressors, aeroplane engines, and many and varied engineering components.
When, later, I was permitted to try one of the first of the new models on the road, piloted by Guilio Ramponi, who is now well known in this country, I was amazed at the smoothness of the small, six-cylinder engine, coupled with a remarkable ability to go from idling speed to 5,000 r.p.m. with a minimum of effort, and the lightness of the steering and the fine roadholding capabilities.
The first of the 1 1/2-litre series was known as the “Turismo” and had a wheelbase of 9 ft. 6 in., a track of 4 ft. 6 in. and a chassis weight of 1,554 lb.
The engine was a monobloc six-cylinder of 62 by 82 mm. (1,487-c.c.) with a crankshaft running in five bronze bearings lined with white metal, and slightly offset H-section connecting rods having their bearing caps secured by a single split-pinned bolt. Lubrication was by a gear-type pump on the near side, driven from a cross-shaft at the rear of the crankshaft, which drove the water pump from its opposite end.
The overhead camshaft was driven by by a vertical shaft and bevel gears from the rear of the crankshaft and ran in four bronze bearings. The valves were vertical and had threaded stems on which were screwed the serrated tappet head, which was kept in contact with the tappet base by the valve spring. Adjustment was by means of a special toothed tool, which plugged into a hole in the head adjacent to each valve and rotated the tappet head while locating the tappet base, thereby varying the clearance between cam and tappet.
The pistons were aluminium-alloy with domed crowns, each carrying two compression rings and a bevelled ring and oil-control ring. The base chamber was of cast aluminium, holding 14 gallons of oil. The radiator was a honeycomb. The water pump had a flynut for draining it and the four-bladed aluminium cooling fan was driven via a friction clutch from the camshaft.
The carburetter was an Italian vertical Zenith, bolted to a short two-port aluminium manifold on the off side; a hot-air intake and cold-air intake were provided. Petrol fed by gravity from a nine-gallon tank on the cast-aluminium dash, a three-way tap giving “off,” “main” and “reserve” settings.
The clutch was of dry-plate type, with five friction-lined plates and five alternate steel plates, sliding on splines on the steel centre boss.
The four-speed and reverse gearbox had a central, exposed gate-change and was in unit with the engine, three-point mounting being employed. The drive went via an enclosed propeller shaft having a single universal joint at the rear of the engine and a splined sleeve engaging with pinion-shaft splines at the rear, to a spiral-bevel rear-axle, the casing of which was constructed of electrically-welded stamped sheet metal. A variety of ratios, including 9/46 and 10/46, were provided for use according to the type of bodywork fitted. When the half-shafts were drawn about 4 in. out of the axle the differential and drive unit could be withdrawn with the banjo cover-plate, after this was pulled out 1 1/2 in. and then rotated 90 degrees.
Suspension front and back was by 1/2-elliptic springs, damped by Italian-type Hartford friction shock-absorbers.
The rear springs were underslung, those at the front passed through the tubular axle, and the front shock-absorbers were mounted inboard of the springs. Four-wheel-brakes with ribbed drums were rod-operated, via a complex system of bell-cranks at the front, where the cam-lever was pushed up by a rod running up the steering king-pin. There was a compensating device beneath the gearbox and a central hand-lever actuated all four brakes via the pedal operating linkages. At the rear the cam-shafts continued inwards to bearings on the axle casing. The facia carried Bosch ignition lock, ignition warning light, speedometer, oil gauge, clock and a dash lamp. Lighting and starting were by Bosch single-pole system and the Bosch coil ignition distributor, driven by a vertical shaft from the camshaft-drive shaft, was set at an angle at the rear off side of the engine. The oil filler was a screw-capped orifice on the centre. near side of the base chamber and behind this was a float oil-level indicator. The exhaust manifold, on the near side, had a forward off-take pipe. A typically Italian advance and retard lever was situated above the pleasant four-spoke steering wheel. The tyre size was 28-5.25, 29-5.25 or 30-5.25. Steering was screw and wormwheel type. Fuel consumption was 19-23 m.p.g. according to body-style and the open cars would exceed 65 m.p.h.
So far as servicing is concerned, the following data may be of use to the many owners who still proudly run 1 1/2-litre single-cam cars. Oil pressure should be 25 lb./sq. in. normally, or 5 lb./sq. in. when idling. Castrol XL for winter and XXL for summer was recommended and the sump should be drained every 1,500 miles and the base filter, at the rear off side of the sump, removed for thorough cleaning before replenishing. The pressure regulator valve is located near the water hose at the rear off side of the crankcase. Firing order is 1, 5, 3, 6, 2, 4, and the distributor rotor runs clockwise. T.d.c. is indicated by three lines, marked 1-4, 6-3, 5-2, on the flywheel and when these are central, as seen through the peep hole when the clutch inspection plate is removed, the pistons concerned are at t.d.c. Tappets should be set with 0.006 in. clearance inlet, 0.008 in. clearance exhaust when the engine is cold. A check should. be made every 1,500 miles. The valve timing is: 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. To re-time, the teeth marked 00 on the camshaft crown-wheel mesh with the tooth marked of the pinion. The clutch should have about 1 1/2 in. to 1 1/4 in. free movement before pushing on the thrust bearings. The dampers on the brake cross-shaft should have 0.004 in. clearance from both lever and pins. The front brakes should do slightly more work than the back brakes. Tyre pressure should be in the region of 40 lb./sq. in. if the sizes aforementioned are used. The plugs originally recommended were Champion 13 or Bosch V12 f.r.a., set with 0.0016 in. gaps and 0.0012 in. to 0.0016 in. contact-breaker gap. Castrol S gear oil was advocated for all chassis parts.
The following notes may be of assistance when undertaking an engine overhaul, these remarks being applicable to each of the several models.
Assuming the engine has been removed from the chassis and completely dismantled, say after a mileage of approximately 40,000 and with the object of obtaining quietness, it would be important to carefully examine the train of vertical gears for wear and, in the event of it being necessary to replace the crown-wheel mounted on the crankshaft with its respective pinion and possibly the upper crown-wheel and pinion, the latter being affixed to the camshaft, the procedure which was found to be the most successful was to commence by having the crankshaft reground, bearings remetalled (preferably die-cast) and having fitted these, to build-up the engine in skeleton form, using shims of various thicknesses for obtaining the correct meshing of the timing gears. Mesh the gears closely and endeavour to eliminate all slack between the teeth; afterwards run-in the engine-gears by means of a belt-rig until freed off, dismantle, clean off all parts, and remove high spots on the teeth of the gears before finally assembling.
Pistons of various makes which have been fitted and have given good results include Specialloid and Wellworthy.
It is important that the camshaft bearings are a really first-class fit, that the oil pipe which feeds the camshaft bearings is correctly bedded-in, also that the spring clip is locating the oil pipe, otherwise a smoky exhaust will result regardless of the care taken in fitting pistons and piston rings as the surplus oil will be pumped via the valve guides into the combustion chamber. Examine carefully the oil pipe located at the front end of the cylinder block and, if necessary, replace the original oil pipe with a copper pipe; the early models were fitted with a steel pipe which became porous in a few instances, with the result that the camshaft bearings did not receive an adequate supply of lubricant and in such cases oil was discovered in the cooling water.