ENGINE
The engine is centrally mounted at the rear of the tank with the flywheel end forward. Circular rubber mountings which surround the front and rear crankshaft bearings are used. Engine torque is transmitted through the forward mounting.

The aluminum crank case and cylinder block casting houses a circular web crank shaft in seven roller bearings. The cylinder liners are of the wet type having two rubber sealing rings, with the usual drain hole between them. At the top, a flange recessed into the cylinder block gives the necessary location and a slight spigot stands up into the combustion chamber. Pistons are of aluminum and are carried on steel connecting rods machined all over and forked to permit left and right banks to share the same journal. An interesting feature of design noted here is that the web of the “H” section of the forked connecting rod is in line with the crankshaft. The forked rod carries a bearing shell which bears on the full length of the crank pin and receives on its outside diameter the unforked rod from the opposite bank. The big-end nuts are serrated on their circumference instead of being hexagonal.

The unusual circular web crankshaft.

The camshaft and all auxiliaries are driven by straight spur timing wheels from the opposite end of the crank shaft to the flywheel, which is of steel, machined all over and with starter ring teeth machined on it. A normal torsional oscillation damper is fitted at the timing end of the crank shaft outside the crank case.

The cylinder heads, which are of cast iron, and one to each bank have hemispherical combustion chambers.

VALVES
Two valves, one inlet and one exhaust are provided for each cylinder. They are operated by a single overhead camshaft to each bank through the medium of rockers. Each rocker is a steel stamping and is mounted on an eccentric bush, the rotation of which enables tappet clearance to be adjusted. The bush is locked in the desired position by means of a slotted quadrant attached to it on a set screw and washer in the rocker pillar. The exhaust valves are sodium cooled, but there are no valve seat inserts.

CARBURETTORS
The aluminum inlet manifold of each cylinder head is mounted in the Vee between the banks. Each mounts two down draught Solex Duplex carburettors, type 52 JFF 2 - 2U 2046. These carburettors are of the twin choke type with exposed jets.

GOVERNOR
In each inlet manifold a longitudinal shaft controlled by the engine governor carries a butterfly opposite each carburettor butterfly, thus completely overriding the driver. The governor is of the centrifugal type driven from the timing gears and incorporated in the drive to the water pump. The inlet manifolds have drain holes to deal with excess wet fuel.

AIR CLEANERS
Carburettor air is drawn from the engine compartment, having first passed through two centrifugal pre-cleaners via flexible trunks and thence via a breeches pipe through three oil bath type cleaners which are mounted immediately above the carburettors.

The pre-cleaners are of the vertical tube type with tangential intakes at the sides and the outlet at the top. The oil bath cleaners are of the orthodox pattern with annular gauze elements.

Air cleaners from above engine bay.	Air cleaners being cleaned and reassembled.

PETROL PUMPS
Four Solex mechanical type petrol pumps each incorporating a bowl type filter are mounted at the nearside rear of the engine. An electric pump is provided for priming. A manual priming pump is mounted on the fighting compartment bulkhead and supplies fuel direct to the inlet manifold.

EXHAUST
The exhaust manifolds which are mounted on the outside of each bank are of cast iron and each deals with three cylinders. The rear manifold on each side is spigotted into the leading one. A sheet metal outer cover runs the full length of the engine on each side to provide an air duct for manifold cooling. Two silencers are vertically mounted on the tail plate. Hinged flaps are fitted to their outlets which are normally secured in the open position but are closed for submersion.

FUEL TANKS
There are four petrol tanks, two at each side of the engine compartment. The top tank in each side is of wedge shape and the lower is rectangular. The total capacity of the tanks is approximately 125 gallons.

The tanks on each side are coupled, the upper wedge shaped tanks feeding the lower by gravity. The filler caps are accessible on each side by the removal of a circular B.P. screwed cover. An asbestos screen is fitted to the engine side of each rectangular tank.

COOLING
Water - radiators, centrifugal pump and four fans.

Trainees receiving instruction on the Tigers motor.

IGNITION
The cylinder head of each bank carries a 6 cylinder Bosch magneto, driven by a spur pinion and idler from the camshaft timing wheel. These magnetos have an automatic advance and retard device which enables the rotating magnets to flick over in a retarded position below normal engine tick over revs. This produces a fat spark no matter how slowly the engine is turning over. The ignition leads pass through a short screened hose direct from magneto to cylinder head cover of each bank, thus reducing the minimum the amount of screening required. Totally enclosed 14mm. Bosch sparking plugs are fitted, one per cylinder.

STARTERS
Two starters are fitted - one electric and one inertia. The Bosch 24V axial motor is mounted on the starboard side of the engine at the forward end and immediately above it a Bosch hand operated inertia starter, also of the axial type. The hand crank for the inertia starter, is carried in suitable clips on the tail plate, the orifice being covered by a B.P. sealing plate when it is not in use.

ACCUMULATORS
The accumulator consists of two 12V 150amp/hrs batteries stowed on the hull floor astride the propeller shaft immediately ahead of the engine bulkhead.

They are normally connected in parallel but a series/parallel switch permits a change over to 24V for starting.

RADIATORS
There are two film type radiators mounted transversely at the rear of the engine compartment - one on the nearside and one on the offside.

The radiators are coupled and a common filler cap is provided in the near-side unit. A pressure relief valve is mounted on the offside radiator and a balance pipe maintains equal pressure in the two radiators.

Relief valves are fitted in the water inlet and outlets to the engine to avoid air locks when external hot water circuit is in use. The capacity of the water system is approximately 16 gallons.

Cooling fans.	Radiators.

FANS
A twin fan assembly is mounted transversely at each side of the rear of the engine compartment. The fans are of radial flow type and are mounted in aluminum housing bolted to the radiators. A two speed drive is taken off the timing gears and a short universally jointed shaft carries this drive to the fan drive housing which is mounted on the rear plate of the engine compartment. In this housing the drive is split and taken on each side transversely to each fan assembly through universally jointed shafts. An oil pump is mounted on the housing and supplies oil from the fan drive casing to each fan assembly. The level of oil in the housing is checked by means of a dipstick accessible when the engine hatch is open and is replenished through a filling orifice in the fixed portion of the engine compartment cover.

LUBRICATION
The engine sump is dry and a pressure fed lubrication system is used. The pressure pump draws oil from a cannister mounted on the offside of the engine and directs it into a gallery in the crankcase casting, from which it is led off to the cylinder heads and timing gears. The crankshaft receives oil under pressure through a muff which is piped to the pressure gallery. The connection from the oil container to the pressure pump is via oil-ways in the crankcase casting. The scavenge pumps, which are set at opposite ends of the engine, have a common output into the heat exchanger from whence it is returned to the oil cannister. The oil capacity is 28 litres (6.1 gals).

WATER PUMP
Water returning from the nearside radiator enters the engine cooling system at an oil/water heat exchanger, mounted at the rear nearside of the engine from which a pipe leads to the water pump. The output from the pump is directed into the cylinder block water jacket from whence it is circulated through the cylinder heads. The outlets from the cylinder heads are coupled and from them the water enters the top of the offside radiator, from the bottom of which it is directed to the top of the nearside radiator.