Armstrong Siddeley Panther IIA
Part 3: Induction, Ignition and Lubrication
Compiled by Kimble D. McCutcheon
Published 21 Dec 2024

 

Part 3: Induction, Ignition and Lubrication

Induction System

The Panther IIA was served by a single Claudel-Hobson A.V.T.70.H carburettor that was mounted at the lower end of an oil-jacketed elbow attached to the induction casing cover back. On leaving the elbow, the carburetted mixture passes to the fan chamber where the rotating fan slightly raised its pressure, and assured its even distribution to seven forked induction pipes. The induction pipes were mounted radially in gland housings equally spaced around the fan induction casing, and each served one front row and one rear row cylinder.

The carburettor used two separately-fed float chambers to supply two independent diffuser units controlled through separate choke tubes (venturis) and butterfly throttle valves that were mounted on a common spindle, which assured synchronization of the two diffuser units. Mixture control was effected by a common valve that admitted extra diffuser air to the upper end of each diffuser unit. A common accelerating pump was incorporated and through being interconnected with the throttle valves, delivered fuel to the bore of each choke tube each time the throttles were opened. The pump was fitted to supply the quantity of fuel lost by the inertia lag in the diffuser units that occurred when the throttle was opened. A common power jet was also passed fuel directly to the bore of each choke tube after the throttles were opened about 32° past the closed position. This jet was brought into action by the accelerating pump plunger, which was used for this purpose as a piston valve. The power jet was fitted to counteract the over compensation effected by the diffuser units. The carburettor body was in two main parts—the upper and the lower. The lower portion provided the pressure balance chamber, the two independent float chambers, and mountings for the choke tube lower ends. The lower portion also housed two delivery jets served by the accelerating pump and power jet, two floats, needle valves and seats; it was in this portion of the body that the accelerating pump and power jet were mounted. The upper portion of the carburettor carried the choke tubes, throttle valves, diffusers, and mixture control valve; it also provided the mounting for the carburettor to the induction elbow, and carried the link-work connecting the throttle spindle to the accelerating pump. The various carburettor components mentioned above are described in detail below.

Carburettor body lower portion details are shown in sketches I and IV of Figure 30. It featured two irregularly shaped side-by-side float chambers and cylindrical housings for the reception of the choke tube lower ends. The port (33) between the two choke tube sockets served a duct into the lower end of which a bifurcated pressure balance tube (40) was fitted so as to project into the pressure balance chamber beneath the choke tube sockets. It was through this pipe and duct that air reached the diffusers and the mixture control valve in the upper portion of the carburettor. The two bosses in the base of the pressure balance chamber, beneath the ends of the pressure balance tube, communicated through a duct with the power jet and delivery valve of the accelerating pump; the bosses received long delivery jets (39) that projected well into the choke tube bores. The accelerating pump barrel was received in the open-ended well at the side of one of the float chambers with which it communicated through two holes close to its upper end. A cylindrical housing (27) for the pump's small non-return delivery valve was mounted in a packing block (26), fitted beneath the barrel lower end. The valve discharged to a duct in the packing block that communicated with the duct in the carburettor body, which in turn served the delivery jets. A cover plate (29) sealed the lower face of the packing block. The power jet chamber was drilled horizontally close to the accelerating pump barrel housing with which it communicated via a short duct; the jet chamber open end may be seen in sketch IV of Figure 30, about one third of the way up the pump housing. The screwed plug in the base of each float chamber provided access to the base of a diffuser carried in the upper portion of the carburettor body.

Fig 31. Carburettor Ducts

The plunger type accelerating pump is shown in Figure 31. The brass pump barrel (18) was a push fit in the carburettor lower portion, and had a plug (21) soldered into the upper end to take a packing gland through which the plunger stem passed. The packing consisted of a cork cylinder and was compressed around the plunger by a washer retained to the plug by two setscrews. The barrel lower end communicated with the delivery valve housing in the packing block and cover. The delivery valve was a self contained unit consisting of a spring-loaded disc valve mounted in a cylindrical brass body that was screwed into the packing block.

The duralumin pump plunger (17) had a long stem above the plunger head, which was fitted with a phosphor-bronze piston ring around its upper end; the ring was pegged to prevent rotation. A large transfer duct was drilled from beneath the head to intersect a second duct through the base of the stem; this latter duct received a transfer valve similar to the delivery valve except that it was not spring-loaded. Fuel entered the pump barrel from the upper end through two holes (19) that registered with those in the wall separating the barrel housing from the float chamber. Fuel flowed through these holes to fill the space above the plunger. On the plunger upstroke, owing to the depression (suction) beneath the plunger, fuel was transferred to the barrel lower end through the transfer valve (22). A narrow slot (25) was formed in the wall of the barrel to register with the short duct leading to the power jet chamber. This slot was masked by the plunger until the throttles were opened 32° past the fully closed position; at throttle openings beyond this, the slot communicated with the fuel above the plunger. The plunger upper end stem was drilled for operation by a control lever carried on the carburettor body upper portion.

The power jet was a hollow, hex-headed plug screwed at the end further from the head, and fitted at that end with a disc drilled with a calibrated orifice. A washer fitted behind a flange at the back of the head sealed the jet chamber outer end when the plug was screwed home. Fuel entered the plug through a hole in the side opposite the duct leading to the accelerating pump barrel slot. Fuel left the plug through the calibrated orifice in the disc at its inner end, and passed through the jet chamber inner end to a duct serving the delivery jets; this same duct was also served by the accelerating pump. Sketch IV of Figure 30 shows the power jet and duct arrangement. The power jet was employed to add to enrich the mixture delivered to the engine the proportion of fuel lost by diffuser unit over-compensation.

The delivery jets served the dual purpose of dividing the fuel passed from the power jet or accelerating pump equally between the two carburettor sides, and of delivering it to the air stream through the throats of the choke tubes. Each jet consisted of a length of tubing soldered at the lower end into a screwed plug, and having a small plug with a central calibrated orifice soldered into the upper end. The screwed base plugs were received in the bosses in the pressure balance chamber beneath the choke tube sockets.

Fuel was supplied to each float chamber through a union screwed into a boss formed below the recess at the back of each chamber. The seating (31) for a bottom-fed needle valve was screwed into the upper end of each boss. Each seating consisted of a brass plug screwed at the lower end, and formed above the seating proper as a tubular guide for the  needle valve body. A ring of holes drilled around the guide base portion permitted fuel, after passing the valve, to enter the float chamber. The stainless steel valve (32) was of the shape shown in Figure 31. Four deep grooves in the body were provided for lightening purposes and to minimize the friction between its sides and the guide. The valve was operated by the forked end of a lever fitted to a cork float of the shape shown in sketch I of Figure 30; the lever was pivoted at its center upon a screw entering the float chamber from the side.

The carburetter upper body portion (Sketches I, III and V of Figure 30) comprised two large cylindrical passages that ran completely through the casting to form the main gas passages, and receive the choke tubes and throttle valves; these passages were jacketed at the upper ends with warm scavenge oil. When the two carburettor body portions were assembled, the facing around the lower ends of the main gas passages sealed the upper end of the pressure balance chamber; the facing around and across the remainder of the casting base sealed the two float chambers from atmosphere and from one another. The screwed socket to the rear of each main gas passage received a diffuser unit which, when the two portions of the carburettor body were assembled, projected into the fuel in one of the float chambers.

A duct (14) was taken from the socket for each diffuser unit to a separate port, close to the inner end of a conical chamber for the mixture control valve, which may be seen at the back of the casting between the two main gas passages; through these ducts diffuser air reached each diffuser unit, and from each duct a leak hole (34) was taken to act as a vent for its respective float chamber. Each diffuser socket was continued above the screwed portion and provided a cylindrical junction chamber for three ducts. The first duct (6) was taken horizontally from the junction chamber base to the nearer gas passage where it registered with the end of a short tube taken through the choke tube bore; through this duct the emulsified fuel and air left the diffuser unit. The second duct (9) was taken to one of two ports near the mixture control valve chamber outer end; through this duct air was admitted, via the mixture control valve, to decrease the depression above the end of the diffuser unit. The third duct was a short one, drilled vertically from the upper end of the junction chamber to intersect yet another duct (7), which was taken to the nearer main gas passage just level with the throttle valve lower lip. It was through these last two ducts that fuel for slow running reached the main gas passage; an adjustable setscrew was fitted so as to partly obstruct the intersection of the two ducts and thus regulate the amount of fuel supplied.

Each diffuser unit consisted of three main components: the diffuser housing, the diffuser tube, and the main jet and slow running tube. The tubular diffuser housing (35) was screwed at the upper end into the socket in the carburettor upper portion where it was permanently locked by a grub screw; after being fitted, the air duct (14) was drilled to break through its upper end. The lower end of the housing was internally threaded to take the main jet, which forced the diffuser tube upper end against an internal shoulder in the housing upper end, above the air duct mouth (14). The open-ended diffuser tube (38) was shouldered externally for its concentric location in the diffuser housing bore. Six rings of three equally-spaced holes were drilled in the diffuser tube sides.

The main jet (36) was a brass plug screwed into the diffuser housing lower end, and had four calibrated holes drilled through it. A blind hole was drilled in the center of the plug upper face to take a length of tubing, the upper end of which was steadied in the short duct in the upper end of the diffuser socket junction chamber. This tube was known as the slow running tube, and had a plug with a central calibrated aperture soldered about two-thirds of the way up its bore; this aperture formed the slow running jet. Fuel from the diffuser housing entered the slow running tube through four holes near its lower end and, emulsifying air from the housing entered through two holes above the jet plug.

The diffuser operated on the standard Claudel-Hobson principle. It was assumed that the mixture control valve was closed. When the engine was stationary, fuel flooded the diffuser housing, diffuser tube and slow running tube, covering all but the uppermost ring of holes in the diffuser tube. An air space existed above the fuel in the diffuser housing and was in communication with the pressure balance chamber via the ducts (14) and (33). When the engine was running with the throttles in the slow running position, a slight depression was applied to the diffuser tube bore and a considerable depression to the slow running tube bore. The depression applied to the diffuser tube was relieved only by air drawn through the ring of air holes near the upper end of the tube, while that applied to the slow running tube was relieved only by fuel drawn from the slow running jet and air from the holes above the jet. When the throttle was opened beyond the slow running position, the depression applied to the diffuser tube bore increased considerably and could no longer be relieved solely by air drawn through the exposed air holes; fuel was then drawn from the diffuser tube. At small throttle openings, the main jet was able to supply fuel at the same rate at which it was drawn off, with the result that the fuel level in the diffuser tube was unaltered, and the depression acting on the fuel surface remained constant.

After the throttle was opened beyond a certain point, the depression applied to the diffuser tube was such that, under the existing conditions, the main jet was unable to replace the fuel at the same rate as that at which it was being withdrawn from the diffuser tube. As a result of this, the fuel level in the diffuser tube and housing commences to fall and the second ring of holes in the diffuser tube was eventually exposed. As soon as this occurs, air from the upper end of the diffuser housing rushes through these holes, as well as through the top row of holes, with the result that the actual depression applied to the surface of the fuel in the diffuser tube was decreased, and the rate of fuel withdrawal diminished. If the jet, which was now operating under a slightly increased head, was still unable to cope with the demand made upon it, the fuel level continued to fall until sufficient air holes in the diffuser tube were uncovered to produce the desired result, after which the fuel level remained constant until the throttle setting was next altered. The purpose of thus diminishing the depression available for the withdrawal of fuel from the diffuser tube was to counteract the tendency of the mixture to become over rich as the throttle was opened. Actually, over compensation was effected by the diffuser, and it has been found necessary to add the power jet so as to strengthen the mixture delivered to the engine.

The mixture control valve was an adjustable cock by which an air stream was admitted to the space above each diffuser unit, decreasing the depression acting thereon when it was desired to weaken the mixture at altitude. The valve had a conical head formed with an operating spindle at the larger or outer end. Two ports machined near the valve outer end were located at opposite ends of a diameter and communicated with a central duct bored from the valve inner end. The valve was retained under spring pressure in a conical sleeve fitted in the recess at the rear of the main gas passages. Two ports drilled near the sleeve outer end tracked with the ports in the valve and registered with the ends of the ducts leading to the chambers above the diffuser units. The sleeve inner end was short of the two diffuser air ducts (14), and being open permitted the valve bore to receive air from the pressure balance chamber via the duct (33). A conical cover, retained to the carburettor body by three setscrews, retained the sleeve in its housing, and provides the anchorage for a coil spring by which the valve was seated in the sleeve. The valve stem end projected through the cover and had a lever pinned to it by which the valve was operated. The lever bore a lug that, by traveling between two lugs on the cover, limited the valve travel between the fully open and closed positions. A setscrew prevented the sleeve from turning in its housing.

The choke tubes were of the section shown in Figure 30. Each tube was retained in its socket by a setscrew carried in the carburettor body upper portion. A short length of tube was pressed radially into the side of each choke tube so as to project into the throat, and was so positioned that the outer end registered with the discharge duct from the nearer diffuser.

The butterfly-type throttle valves were mounted upon a common spindle. Sketch V of Figure 30 shows that a duct was formed across the center of each valve at right angles to the spindle. When the valves were set for slow running and the engine was " ticking over," the lower end of each duct was located opposite the mouth of the slow running fuel duct in its respective gas passage. Under these conditions, some of the fuel issuing from the ducts in the carburettor body passed to the ducts in the throttle valves and then issued from the upper ends and from holes (3) at the valve upper face centers. Therefore, the slow running fuel was discharged from three points into the air stream past the partly closed throttle valves. Two holes (47) were drilled as shown the under surface of the duct across each valve; these holes admitted air to break down the depression existing in the ducts, which would otherwise take charge of all fuel issuing from the ducts in the body. Each valve was retained on the spindle by a small plate let into a recess in the valve upper face so as to engage a notch in the spindle; two screws retained the plate to the valve. The spindle was supported in three bushes carried in the carburettor upper portion; the port end terminated flush with the side of the carburettor body, while the starboard end projected to take two control levers.

The carburettor control gear comprised separate control levers for the mixture control valve and throttle spindle, and an adjustable linkwork that interconnected the throttle spindle with the accelerating pump plunger. The mixture control lever was a plain arm pinned to the mixture control valve spindle at one end, and having a ball-ended pin at the other for attachment to a link from a control shaft on the induction elbow. The throttle control lever was also a plain arm; it was pinned at one end to the throttle spindle and carried a peg at the other for connection to a second link to a control shaft on the induction elbow. Interconnection between the throttle spindle and the accelerating pump plunger was effected as follows: A short lever was pinned to the throttle spindle on the inside of the throttle control lever, and was connected through a curved link to one arm of a lever carried on the side of the main gas passage. The second arm of the curved lever was on the further side of the pivot pin and received the head of a pin from which a link was taken to the upper end of the accelerating pump plunger spindle. The head of the latter pin was eccentric to the pin stem, and could be set and locked by a cotter screw in any desired position with respect to the lever. This eccentric-headed pin enabled power jet opening timing adjustment with respect to  throttle opening. The jet was brought into operation as soon as the top of the pump plunger, in its down stroke, uncovered the slot in the pump barrel side. As the eccentric pin head was turned, the plunger was raised or lowered in the barrel without any accompanying throttle spindle movement. The small lever pinned to the throttle spindle for pump linkwork actuation bore a lug that, when the throttles were set for slow running, bore on an adjustable setscrew in a second lug on the side of the main gas passage.

An air intake scoop was attached to the flange around the mouth of the pressure balance chamber to receive air warmed by its passage past the heads of cylinders 1F and 4R; the end of the scoop was shaped to clear the induction pipes of the cylinders concerned. The union in the scoop base was for connection to a pipe by which overflow fuel was drained clear of the engine. A wide mesh wire screen was fitted between the air scoop joint flanges and pressure balance chamber.

The induction elbow was a junction piece by which the mixture issuing from each carburettor main gas passage was conducted to a common gas passage before being delivered to the engine. In effect, the elbow was an inverted Y-piece, the upper end being formed as an elbow so that when it was attached to the intake facing on the induction casing cover, the branch axes were vertical. A flange around the elbow upper end provided for its attachment to the induction casing cover, and a studded facing was formed around the bifurcated lower end for the carburettor attachment. An oil jacket extended from around the facing at the elbow lower end to a point just below the flange at the upper end, numerous baffle webs being cast between the jacket and elbow proper. The front and rear jacket ends were formed by cover plates; the rear plate was provided with four bushed brackets in which the main carburettor control shafts were mounted. A steady bracket for the carburettor fuel pipe was fitted to the rear cover plate. Figure 32 shows the induction elbow fitted to the carburettor. The uppermost union on the elbow back was the main outlet union from the jacket; the lower inlet union was on the jacket starboard side. The union high up on the jacket port side communicated with the oil space, and fed a pipe taken to the gas distributor spindle housing. The remaining union communicated via a boss across the oil space with the common gas passage, and from it was taken a pipe to the oil and fuel pump fuel drain. The lug low down on the elbow front  received the end of a steady bracket taken to the induction casing cover.

Two hollow control shafts were carried horizontally, one above the other, in brackets integral with the induction elbow rear cover plate. A lever was pinned at the port and near the upper shaft starboard end, the former lever being connected to the throttle control rod in the aeroplane and the latter, by an adjustable link, to the control lever on the carburettor throttle spindle. A lever was pinned at the port end and center of the lower shaft, the former being connected to the mixture control rod in the aeroplane and the latter, through an adjustable ball socket ended link, to the lever on the mixture control valve. In addition to the levers mentioned above, the two shafts were fitted a short distance outside the port supporting bracket, with an interconnecting linkwork that ensured the mixture control valve could be opened only by an amount depending on the throttle opening, and was closed automatically as the throttle was closed.

The linkwork consists of a long forked lever, pinned to the throttle control shaft, and having pin jointed to the outer end a long link made from flat strip. The link lower end was machined with a long axial slot, which received a pin through the knuckle end of a short lever pinned to the mixture control shaft; Figure 32 illustrates this construction. A sleeve pinned to the mixture control shaft outside each supporting bracket located that shaft axially in the bracket, while the starboard control lever, and a sleeve pinned to the shaft outside the port bracket, perform the same function for the throttle control shaft.

Induction Pipes

The cylinders were fed from the induction casing through seven branched induction pipes. The inner end of each pipe was received in a packing gland in the induction casing. The longer branch attached to the inlet flange of a front-row cylinder and the shorter branch to an adjacent rear-row cylinder. Ring nuts, locked with circlips, retained the pipe ends to the cylinders.

Priming System

All cylinders had priming provision except 1F and 1R. Fuel from a hand pump was taken to a T-union connecting the upper ends of two mild steel tubes bent into a ring and clipped to the front of the flange around the crankcase back; the ring lower ends were joined by a junction union. A small T-shaped piece was brazed into the priming ring thus formed opposite each induction pipe, and was provided with a union for the attachment of a branch pipe. The branch pipes were taken up the backs of the induction pipes and, where the latter divide, had T-pieces brazed to their ends, from which the ends of further pipe lengths were taken along each induction branch. These pipes were clipped to the induction branches and at their outer ends secured by nipples and union nuts to elbows screwed into priming bosses on the inlet ports of respective cylinders. These elbows retained atomizing plugs in the priming boss bores. Fuel on escaping from the helical grooves around the plugs ends broke up into a fine spray and was delivered directly into the port.

Ignition System

The ignition system was based on two B.T.H. type S.C. 14-1A magnetos mounted on the induction casing back in the position shown in Figure 33. The port magneto served the exhaust plugs and the starboard magneto served the inlet plugs. Fixed timing was employed, the contact breaker casings being locked to the magneto bodies in the fully advanced position. Each magneto was driven at 1.75 times crankshaft speed from a layshaft in the induction casing drive housing through the serrated rim of a disc keyed to its spindle. Standard metal-braided high-tension cables with A.G.S. terminal fittings connected the magnetos and sparking plugs. The numerals shown in Figure 34 on the terminal fittings were engraved on the actual fittings concerned. All insulating sleeves for cables serving front-row cylinders were colored black while rear-row cables were colored red.

Cables exiting the magnetos passed in pairs through slotted holes around the induction casing rim either directly or after passing through one or more aluminium bonding clips carried on the induction casing cover back. Figure 34 indicates the actual run of each cable between the magneto and the induction casing flange. The cables passing through each hole were separated by an aluminium wedge, which was retained in the hole by a setscrew fitted in a lug in the induction casing rim front. After passing through the hole, each pair of cables was routed to the induction pipe branch of its respective cylinder, was steadied thereon in one clip on the shorter branches and two on the longer; the cable pair was further steadied by other clips on the cylinder head and valve rocker bracket tops. The sparking plug terminal end of each cable was attached to the sparking plug by an A.G.S. terminal adaptor. No bonding wires were employed on the engine.

Lubrication System

Five oil circuits comprised the engine lubrication system

The Induction Casing Low-Pressure Circuit

The five circuits were served by four pumps of which three were mounted as a unit beneath the front cover and one on the auxiliary drive unit side. The group of three pumps consisted of the feed pump, the auxiliary scavenge pump, and the main scavenge pump. The fourth pump was known as the auxiliary oil pump.

The feed pump served main feed circuit, receiving oil through an external pipe from the aeroplane storage tank and delivering it to a filter integral with the pump unit. From the filter, oil passed, via an oil space above the pump and filter chamber tops, to the spindle bores on which the pump pinions were mounted. Oil supplied to the driving pinion spindle passed to the crankshaft via a duct in the intermediate bearing housing in which the upper end of the spindle was steadied. Oil supplied to the driven pinion spindle passes from the spindle lower end to an external pipe serving the auxiliary feed circuit and a pressure gauge. A spring-loaded relief valve was fitted between the lower end of the driven pinion spindle and the inlet side of the main scavenge pump; when the feed pressure exceeded 50 psi, the valve lifted and by-passed oil to the main scavenge pump.

The auxiliary scavenge pump operated the auxiliary scavenge circuit, receiving oil draining to the front cover bottom and returning it directly to the tank. Oil reached the pump inlet side through ducts in the pump attachment facing on the front cover and in the feed pump casing.

The main scavenge pump operated the main scavenge circuit. Oil draining from the intermediate bearing housing walls, crankcase and induction casing collected in a sump bolted to the crankcase between cylinders 4R and 5R. The oil passed through a screen incorporated in the sump before being conducted via an external pipe to the main scavenge pump inlet side. Oil leaving the pump was delivered to the union on the carburettor jacket port side, passed through the jacket and was transferred to the jacket lower end around the induction elbow. Two oil outlet unions were provided at the induction elbow jacket upper end; most oil returned to the pump through the larger of these, and from the smaller it passed to the low-pressure circuit.

The feed pump delivery side served the auxiliary feed circuit via the bore of the driven pinion spindle and the union at the pump casing base. From the union a pipe was taken to a junction piece on the crankcase between cylinders 1F and 4R. One branch of this junction piece served the oil union on the crankcase lifting eye, a second served the oil sprayer that lubricated the bearing for the auxiliary drive shaft driving wheel, while a third served a pipe taken to an oil pressure gauge. Oil supplied to the crankshaft lifting eye was delivered to the crankcase through a calibrated jet, was broken up by the rotating parts and assisted in cylinder and piston lubrication, which otherwise tended to run dry on engine startup. Oil delivered to the bearing housing for the auxiliary drive shaft driving wheel filled that housing and the pocket to its rear, eventually escaping to the space between the rear diaphragm and induction casing, whence it drained to the sump serving the main scavenge pump.

The induction casing low-pressure circuit received oil from the smaller outlet union on the induction casing elbow, and had the amount of oil in the circuit maintained constant by the auxiliary oil pump, which delivered excess oil to the crankcase. A pipe was taken from the smaller outlet union on the induction elbow jacket to a union that fed the gas distributor spindle upper bearing. Oil leaking past this bearing lubricated various auxiliary drive components and eventually drained to a sump in the drive housing base on the intermediate casing cover. This sump contained a screen through which oil was withdrawn by the auxiliary oil pump and delivered to a union on the starboard side of the 1R cylinder socket. This union delivered directly to the space between the rear diaphragm and the induction casing, after which the oil drained to the sump serving the main scavenge pump. The auxiliary oil pump purpose was solely that of preventing the sump in the drive housing from becoming over-filled. Before starting the engine, the sump was filled by hand to a level predetermined by a cock in the side of the sump.

Crankshaft, Reduction Gear, Cam Drum and Connecting Rod Lubrication

Oil supplied to the main oil pump driving pinion spindle passed to a duct in the intermediate bearing housing in which the spindle upper end was steadied. The upper end of this duct broke into the bearing housing proper and registered with a transfer hole in the intermediate bearing itself. Oil passing through this hole filled the groove around the bearing inside, lubricated the bearing and passed, via a number of transfer holes in the reduction gear annulus sleeve, annulus hub and crankshaft, to the crankshaft bore.

On entering the crankshaft bore flowed fore-and-aft. Oil flowing forward left the shaft through a hole in a plug fitted in the shaft end and through two small holes at the center of a tube fitted diametrically through the shaft. Oil passing through the plug filled the bore of the airscrew shaft and, leaking backwards, lubricated the bush between that shaft and the crankshaft front end.

Oil escaping from the tube ends and from the bush rear end passed to an annular space between the airscrew shaft rear end and the crankshaft. Some of this oil passed through transfer holes in the airscrew shaft end, and some passed rearwards through the airscrew shaft rear bearing. Oil passing through the transfer holes in the airscrew shaft traveled via other transfer holes in the sun wheel rear bearing inner race to the sun wheel bore, and was then transferred to the two sun wheel bearings and to the airscrew shaft front bearing. Some oil supplied to the sun wheel bore passed through transfer holes between the wheel teeth and assisted in gear tooth lubrication.

Oil supplied to the airscrew shaft rear bearing, after passing through the bearing, filled a conical baffle riveted to the inside of the annulus and, on leaving the baffle, passed to an oil retaining lip around the airscrew shaft back. Ducts beneath this lip conducted oil to the planet pinion spindles bores and then to the pinion bores themselves. Oil supplied to the planet pinions bores lubricated the roller bearings housed therein, and finally escaped from the pinions ends and through transfer holes taken between the teeth. Oil escaping from the pinion rear ends was flung into the annulus back and on leaving the annulus further lubricated the gear teeth.

Oil escaping from the intermediate bearing rear end was deflected into an oil retaining lip around the cam bearer front end. From this lip, ducts routed the oil to planet pinion spindle bores from where it was transferred to the planet pinions bushes. More oil was supplied to the oil retaining lip than could be used by the planet pinion spindles, and consequently overflowed and was atomized by the rotating drum. The gear teeth, cam surfaces, tappets and cam drum bearings were lubricated by this atomized oil.

Oil flowing rearwards down the crankshaft bore passed via the plug in the crankweb front, and the ducts in the center web, to the two crankpin bore plugs. In each crankpin, four holes were drilled into the bore of the plug housed therein, and through these holes the big end bearing of each master rod received its oil supply. Oil exuding from the master rod ends was atomized and, in conjunction with that sprayed from the lifting eye, lubricated the auxiliary rod knuckle pin ends, all gudgeon pin ends, the cylinder walls, the main bearings, the idler wheel bearings, and the fan intermediate gear bearings.

Crankshaft Rear Gear Wheel Lubrication

Some oil draining down the rear diaphragm front collected in two oil troughs at the front ends of two drain pipes passed through the diaphragm and bolted to it. These pipes were located above the crankshaft housing bearing and on each side of it. One pipe drains on to the wheel smaller portion, the other on to the wheel larger portion.

Some oil draining down the rear diaphragm front face was collected in a small trough riveted to the diaphragm opposite the pump hollow spindle end on that received unfiltered oil draining from the front cover and returned it directly to the tank. The main scavenge pump received oil draining from the filter in the sump beneath the crankcase, and delivered it to the aeroplane tank via jackets around the carburettor and induction elbow. The pressure relief valve delivered to the main scavenge pump intake side. The pump casing consisted of three aluminium castings mounted one above the other and separated from each other by two steel sealing plates.

The upper pump casing provided the pressure pump chamber and the filter chamber upper end. This casing was open at the lower end and closed at the upper. A long standard accommodating the pump driving spindle upper portion being formed upon the  pump chamber roof. Oil entered the pump chamber through a union in one side of the casing, and was delivered to the filter chamber through a port in the opposite side of the chamber (see sketch II of Fig. 37). After passing through the filter, the oil was delivered to a space above the pump chamber roof, where it passes to the driving spindle standard bores and the driven pinion spindle (see sketches I and IX of Figure 37). Oil supplied to the standard passed to the driving spindle bore and then to a duct in the front cover. Oil supplied to the driven pinion spindle passed to the relief valve and to an external pipe serving the auxiliary drive shaft bearing housing, driving gear and the crankcase oil sprayer. Sketch II of Figure 37 shows the transfer valve, which was fitted in a duct between the pump chamber inlet and delivery side. However, as previously stated, this valve was no longer used and may be regarded as a blanking plug. A pump unit attachment flange for the whole front cover was provided around the driving spindle standard, and was formed with a port through which oil draining from the front cover passed to a duct taken through the casing to feed the auxiliary pump casing inlet side.

The center pump casing provided the auxiliary scavenge pump chamber and the filter chamber center portion. The casing was open at both ends, but the pump chamber was separated from the feed pump chamber above it and the main scavenge pump chamber below it by two steel sealing plates of the same shapes as the casing joint flanges. In addition to sealing the pump chamber ends, these plates formed joints between the filter chamber center, upper and lower portions that ran continuously through them as shown in sketch IX of Figure 37. Oil from the casing feed pump duct entered the pump chamber inlet side as shown in sketches VIII and III of Figure 37, and was returned to tank through the union in the casing side.

The lower pump casing provided the main scavenge pump chamber and the filter chamber lower end. The pump chamber was open at the upper end and closed at the lower, while the filter chamber portion was open at each end. Scavenge oil from the crankcase entered the pump chamber through the union above the relief valve on one side of the body and left through the larger of the two unions on the opposite side. The smaller of the two unions on the delivery side of the casing received oil from the feed pump through the driven pinion spindle via a duct beneath the floor of the pump chamber.

The duct beneath the pump chamber floor also communicated with the pump intake side through the relief valve, a spring-loaded plunger housed in a steel sleeve fitted between one end of the duct and a chamber in communication with the pump intake side; the outer and blind end of the sleeve can be seen in sketches IV, V and IX of Figure 37 below and to the rear of the pump inlet union. When the feed pump delivery side pressure exceeded 50 psi, the plunger was forced along the sleeve bore against the spring pressure and uncovered a hole through which the oil passed to the scavenge pump inlet side. The pressure at which the transfer hole was exposed variable by the interposition of various shims between the spring and the blind sleeve end.

Both the driving and driven pinions of all pumps were of magnesium alloy and of the same transverse section. The feed pump pinions were both of the same depth but were shallower than the two scavenge pump pinions, which were all of similar depth. The driving pinions of all pumps were keyed to the driving spindle, while the driven pinions were freely mounted on a second spindle. Pinion end float in the pump chambers was adjustable by the interposition of steel shims shaped like the figure 8 between the pinions and chamber ends.

The long driving spindle was drilled from its upper end for about four-fifths of its length. A bevel gear, through which the pump was driven, was keyed to a parallel portion near the spindle upper end, and rested against a shoulder; it was not otherwise located. Four holes were drilled near the spindle upper end for transferring filtered feed oil to its bore (see sketches VIII and IX of Fig. 37), and three recesses were machined in the spindle sides for the keys by which the pinions were driven. The spindle was supported in three bushes housed one in the end of the standard on the feed pump casing, one in the feed pump chamber roof, and one in the main scavenge pump chamber base. The flange around the uppermost bush received all the bevel gear thrust; the plug sealing the housing for the bottom bush providing an anchorage for the filter cap lock plate.

The driven pinion spindle was tubular and was a free fit in the pump pinions. The spindle was supported in two open-ended bushes housed one in the feed pump roof chamber and one in the main scavenge pump chamber base of the. A shoulder around the spindle between the pinions of the two scavenge pumps effects its end location in the pump.

Oil delivered to the feed pump filter chamber passed to the interior of a filter capsule pack, and then to the bore of a vertical tube upon which the capsules were mounted. The tube upper end was received in a socket in the filter chamber upper end and was in communication with the delivery oil space above the feed pump chamber; the tube lower end was steadied in, and normally sealed in, a socket integral with a cap screwed into the filter chamber lower end. A coil spring fitted above the tube upper end caused a shoulder around the tube to press the filter pack capsules up to a boss on the cap that sealed the filter chamber. If the filter capsules was blocked, the pack and mounting tube were forced upwards against spring pressure and unfiltered oil passed directly to the tube bore lower end, through ports in the socket that supported it. Each filter capsule consisted of two large brass gauze washers soldered together around their outer edges, and at their inner edges to shoulders at the upper and lower ends of a short brass sleeve. A number of holes were drilled in the sleeve walls, and oil, having passed through the gauze washers, passed in turn through these holes to a helical groove around the mounting tube. Oil delivered to the groove around the mounting tube passed via a number of transfer holes to the tube bore , and was delivered to the oil space above the feed pump chamber. A strip of steel, bent to a spiral, was fitted between the gauze ends of each capsule to prevent their collapse.

The crankcase oil sump was an open-ended aluminium casting bolted to the facing around the crankcase drainage port between cylinders 4F and 5R. Oil flowing through the opening at the sump upper end passed to the interior of a gauze-covered cage, held up into a recess beneath the opening by a cap screwed into the sump lower end. After passing through the gauze, the oil entered the sump main body from which it was withdrawn through a pipe studded to a facing low down at the front.

A crankcase breather (Fig. 38)incorporating a non-return air valve was fitted to an adaptor plug screwed into the crankcase on each side of cylinder 1R so as to vent from the space between the rear diaphragm and induction casing. The two-piece breather casing, shaped as shown in Figure 38, was secured to the mounting plug by a stud taken through the front compartment of both portions. The two casing portions were separated by a perforated brass plate. A gravity-loaded disc valve and a set of baffle plates were mounted over the stud in the lower casing front compartment while the two rear compartments were filled with aluminium shavings. The breather casing front compartment upper portion was also filled with aluminium shavings, while the rear compartment, which was open-ended, was empty. When crankcase pressure built up, air enters the breather through holes in the adaptor plug, lifting the disc valve that seated on the plug, and passed upwards and around the baffle plates, which trapped most of the suspended oil. The air was further cleansed by its passage through the aluminium shavings housed in the breather upper and lower portion, and eventually passed to atmosphere from the open ended compartment at the breather rear. Oil trapped by the baffle and in the aluminium shavings drained to the breather base and collected around the projecting adaptor plug end. On a depression occurring in the crankcase, the breather air valve was drawn onto its seating and the oil withdrawn to the bore of the plug through a transfer hole beneath the valve seating.

Exhaust Collector Ring

The exhaust collector ring was in two portions, each of which served seven cylinders and delivered in a downward direction to the engine rear. The port ring section served cylinders 1R, 5F, 2R, 6F, 3R, 7F and 4R. The starboard section served the remaining cylinders. The main portion of each ring consisted of a streamline cross section trunk pipe of bent to a radius a little greater than that of the cylinder exhaust valve port circle. Articulated branch pipes were taken from each trunk to the cylinders concerned, and a tailpipe was welded into it near the center, so as to point downwards and to the rear when the ring was positioned on the engine. Of the seven branch pipes, two were taken from domed caps welded to the trunk ends, and the remainder from stubs welded into the trunk at intermediate points. Ball joints were provided between each of the trunk end caps and intermediate stubs, and the seven branch pipes, the outer ends of which had split sockets to embrace the stubs on the cylinder exhaust flanges. The sockets were drawn up around the stubs by cotter screws that also engage grooves around the stubs. Each collector ring portion was secured by hose clips to two steel brackets, each of which was clipped beneath two of the nuts by which the induction casing flange was secured to the engine mounting in the airframe. Each trunk was steadied at the center by an adjustable stay taken to studs that secured the two ignition clips to the bracket and head of cylinder 3R for the port trunk and cylinder 6R for the starboard trunk.

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