Tests and Reports

ROVER SCARAB
First of a Series - "Cars, That Might Have Been"
by Edward Eves, The Autocar, 8th December 1961

It is typical of human nature that it finds the unknown, and the unseen, vastly more fascinating than the plan-to-view realities of life. In no sphere is this generalization more true than of motoring, and the development activities behind the closed doors of motor manufacturers’ experimental departments are the subject of endless speculation. Today the veil of secrecy can be lifted off some of the projects which might have been. In doing so, we hope to show that the conservatism of which our manufacturers are accused repeatedly is not so innate as enthusiasts for mechanical novelty would have us believe.

It is typical of human nature that it finds the unknown, and the unseen, vastly more fascinating than the plan-to-view realities of life. In no sphere is this generalization more true than of motoring, and the development activities behind the closed doors of motor manufacturers’ experimental departments are the subject of endless speculation. Today the veil of secrecy can be lifted off some of the projects which might have been. In doing so, we hope to show that the conservatism of which our manufacturers are accused repeatedly is not so innate as enthusiasts for mechanical novelty would have us believe.

At the end of the ‘twenties the British motor industry was in the melting pot of the great depression. Names, glorious and mundane, were disappearing from the lists, or the companies which bore them were being absorbed by more businesslike competitors. The Rover Company was perhaps feeling the draught like everyone else, but it was on sound foundations and it neither merged nor was absorbed. By the end of 1931 it had weathered the worst of the storm with the 10/25 model, the first Rover with a vee-radiator, and it faced 1932 with an improved version of this model, backed up by the six-cylinder Meteor and another new model, the Pilot, virtually the 10/25 with a 1.5-litre, six-cylinder engine.

On 1 September 1931, Rover dealers received a brochure describing these new models. Almost hidden at the back of the book was a fourth model, of which no mechanical details were revealed. All that the company was prepared to say was that this car would be called the Scarab, because, like the Egyptian stone of that name, it was “phenomenal and marvellous.”
The Rover publicity manager of the day must have been one of the earliest exponents of the “controlled leakage” method of publicity, because shortly afterwards a more detailed, but still tantalizing description of the car appeared in a contemporary magazine.

The engineers entrusted with the project were M. C. Wilkes and Robert Boyle, today managing director and chief engineer of the company. In the interests of secrecy they set up a self-contained engineering department, complete with draughtsmen and machine shop, at Braunston Hall, near Rugby, the home of the then chairman, Colonel Seattle. Production of at least 30,000 cars a year was envisaged.

This revolutionary small car was to have an air-cooled twin-cy1inder engne at the rear, swing-axle rear suspcnsion, and sliding-pillar front suspension with coil springs. Moreover, the price was expected to be about £89, this figure being achieved by simplicity of design rather than by reduction of quality. It was aimed at that section of the market which has in recent years been exploited by Hans Glas, the economic no-man’s-land which lies between the motor-cycle combination and the conventional small car.

There was nothing out of the ordinary about the power unit of the Scarab. It was a simple 60-degree 75mm by 95mm o.h.v. pushrod vee-twin, with cast-iron cylinders and an aluminium crankcase. The cylinder heads were cast in one piece with the barrels and the generously proportioned, transversely placed valves were inclined and removed easily down the cylinder bore. A single Amal carburettor fed the mixture through a tee-shaped aluminium manifold on the inside of the vee. There was no hot-spot, and the two exhaust ports led the gas out sideways to the silencer.

Motor-cycle Practice

Pistons were of aluminium with fully floating gudgeon pins; they had two compression rings and one scraper. Following motor-cycle practice - it was intended that the motor-cyclists who were expected to buy the car should find nothing unfamiliar under the bonnet - the crankshaft revolved on roller bearings, with similar bearings for the big ends. However, wet sump lubrication was chosen, the oil pump being driven oil the lower end of the distributor drive shaft.

Cooling was by an uncowled fan revolving on the forward end of a belt-driven jackshaft carried on a bracket in the vee of the cylinders. One of the reasons for choosing a vee engine was that the cylinder arrangement fitted into the circle swept by a fan. Unfortunately, no account seems to have been taken of the fact that the exhaust ports were out of the draught, most of the output of the fan going where it was least needed ... to the inlet ports. This fundamental error rnust have contributed to rhe overheating problems which were among the eventual reasons for abandoning the project.

A single plate, inserted cork clutch, running in oil, conveyed the drive to the gearbox; thereafter convention was thrown to the winds. Measuring no more than 9in. overall, this unusual three-speed gearbox had gear selection by sliding dogs, and the bevel pinion was concentric with the rnainshaft. Moreover, the push-pull selector rod passed through the centre of the bevel pinion, circumventing the axle shaft by means of a yoke. Thus gear selection was by a simple quadrant gate in the middle of the driving compartment floor. Reverse gear was selected by a sideways movement of the lever at the end of the gate.

On the experimental cars - six were built to speed up development - a conventional star-wheel diflerential was employed, but designs existed for both free-wheel and slipping clutch units. Inboard drum brakes were carried on extensions of the differential cross shaft, the drive to the exposed half-shafts being through Hardy Spicer Hooke-type universal joints.
The frame was of simple ladder pattern, built up from inverted U channels with rolled-under flanges. At the rear it was braced by the engine and gearbox assembly, while at the front the bolted-on tubular front axle beam acted also as a cross-member.

Nor did convention play a part in the layout of the front suspension. Bearing a vague outward resemblance to the sliding pillar suspension pioneered by Morgan, it overcame lubrication problems by making the king-pin slide in a vertical housing in the end of the axle. This housing was of cast-iron, incorporating an oil reservoir. The king-pin ran directly in this housing, and there were no air vents, the pneumatic effect thereby set up acting as a crude shock absorber. Springing was by two coil springs per side, in tension. Since they were fixed relative to the chassis at their lower ends and swivelled with the wheels at the top, they had a strong centring effect on the steering. This feature was considered desirable on a rear-engined car and is still to be found on the Renault Dauphine. The steering box was a simple affair embodying a pinion and quadrant, and front-wheel brakes were fitted.

Up to a point, the rear suspension was the forerunner of swing-axle suspension as we know it today, channel section A-brackets, swinging about the U-ioint centre line, locating the driving wheels. The suspension-arm joints themselves were interesting, being in effect conical friction shock absorbers with Ferodo facings, spring loaded to compensate for wear. Coils were the springing medium, bearing at their upper end on a transverse member mounted on top of the gearbox casting.

Prophetic Solution

Here Wilkes and Boyle unwittingly produced a layout which has only recently been accepted as an answer to the handling peculiarities of swing-axle cars; instead of bolting their transverse member rigidly to the top of the gearbox, they pivoted it, thus reducing the rear roll moment of the car to nil. In combination with rather stiff front suspension, this arrangement gave the car pronounced understeer, in keeping with conventional models of the period. It is amusing to relate that Porsche and Nibcl, who were both working on rear-engined projects at the time, came over to Coventry to see and drive the Scarab. Both commented on the exceptionally good handling, this aspect of their designs apparently being somewhat problematic, and went away scratching their heads.

The open two-door four-seater bodywork of the car was of sheet steel on an ash frame. double curvatures on the panels being eschewed to avoid expensive panel beating or presswork. To salve popular opinion, a dummy Rover radiator with blank slats adorned the from of the car. For its day, the weather equipment was very complete, consisting of celluloid side curtains and a canvas hood.

It is difficult to pinpoint just why this prophetic design did not reach production. Difficulties with cooling have been mentioned, but these would not have been insuperable had there been a determination to go ahead. Perhaps the company decided that the dmign was too avant-garde for the times; or perhaps their more conventional models were selling well enough to render the financial risk in launching an unconventional model less tempting. More likely the decision not to proceed coincided with the decision to forswear the popular market and to work towards the place in the quality market which Rover hold today.

© The Autocar

Note: The technical images of the article were transferred to the ⇒ technology - page .