Entomological Dissection

Harold Biggs reveals, we believe for the first time, what makes the “Grasshopper” Austin Seven such a desirable little car.

Ever since the Austin “Grasshoppers” made their debut in trials, I, as an Austin enthusiast, had been anxious to obtain some genuine detaiIs of their amazing little engines.

When my friend George Symonds purchased the ex-Scriven car, it appeared that a source of information was to hand, but it was not until the car was destroyed by fire that the engine was removed. or, in fact dismantled in any way, and my long-delayed wish was gratified. To commence with, the crankshaft is of the 3-bearing type, with 1 3/16-in. big-end journals, although the crank cheeks are more robust than those of’ the standard 3-bearing crank, beina more like those of the 2-bearing “Ulster” shaft. There are two oil feeds, one to the centre main as standard. and one by external pipe from the main gallery to a nose piece, as fitted to pressure-fed. 2-bearing engines.

As the shaft was still mounted in the crankcase I was unable to tell the exact distribution of the oil. Possibly the centre main feed also looked after numbers three and four big-ends, and the nose feed catered for the needs of numbers one and two big-ends, or the nose feed might feed supply all big-ends and the centre main feed only the main bearing. Symonds informs me that the running pressure is over 30 lb./sq. in.

Oil is drawn from a “Nippy” 1-gallon, ribbed aluminium sump. The connecting rods are offset, as on the standard 3-bearing engine, but are of a deep “H” section, machined all over and relieved at the sides of the big-end bolt lugs, as in the “Nippy.” The big-end liners are of the thin-wall pattern and the pistons are a very light, slipper type with one stiffening rib on the underside of the crown, two very narrow compression rings and one slotted scraper. The gudgeon pins are fully floating in unbushed little ends, with aluminium end-pads.

Looking at the cylinder block one can at once see that it is quite special. Water passages around the valves and ports are larger, the connecting passages between block and head are in the form of elongated slots, and the internal sweep of the ports differs from those of any other Austin.

Each cylinder has two external ribs on its bore sides running from water jacket to base flange, and the block is held to the crankcase by 3/8-in. studs, with the usual special pair at front and rear.

The cylinder head is of aluminium with a long, cast water-outlet passage along the centre; it is retained by the standard number of studs, but these are of 3/8-in. diameter; 14 mm. plugs are arranged over the exhaust valves.

The valves are about 3/8 in. longer than “Ulster” valves, and the inlet is slightly larger than the exhaust: they are closed by very long, double springs retained by split taper cotters and standard collars. To accommodate these very long valves the tappets are short, as are the cast bosses in the base flange which carry the tappet guides. Clearance is set by ground buttons.

The camshaft is a very high lift type, with split-bush centre bearing and steel gear. This gear meshes with another in the special dynamo housing and the dynamo spindle carries the pulley from which the blower is driven, this pulley revolving at engine speed. The pulley on the blower is of similar size. The blower, a Type 125 Centric, is mounted by means of its outlet port studs on the inlet port of the separate induction manifold, which port is situated on the top forward end of the main horizontal trunk of the aluminium manifold. The blow-off valve is at the rear, and blower pressure is 6 lb./sq. in. at peak.

The actual drive is by vee belt, this belt passing over the fan pulley, which can be swung in an arc giving the required adjustment range; to resist the belt tension load on the blower shaft a strut is fixed between the supercharger casing and the timing case cover bolts.

Austins apparently find that a very thin (about 1/32-in.) copper and asbestos gasket stands up well as a cylinder head-to-block seal. The exhaust manifold is very similar to that used on the “Nippy,” pairing with the inlet manifold in a similar manner. A vertical updraught Stromberg carburetter is used. Passing on to ignition, it was interesting to observe that an apparently standard Lucas distributor, possibly fitted with an automatic advance range to suit the engine, and also with a manual over-riding control, was fitted. I understand that, on this particular car, when the contact point gap was fixed it was locked by soldering in addition to the usual nut. A revolution-counter drive was taken from the base of the distributor shaft, the outer casing being anchored to the drive casing. Normal “Ulster” cast-iron clutch linings are used, with a standard steel floater plate as on the earlier Austins.

Symonds informed me that he obtained excellent results by using Champion NA 14 plugs, and that a standard Lucas coil stood up to its work admirably.

However, I still retain my enthusiasm for the Austin Seven.