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Aviation History
1939
1939 - 1651.PDF
548 ffigsas MAY 25, 1939 only with the camshaft pinion, but also with an idler gear which in turn drives the oil pump and one magneto. The other magneto is driven by the camshaft pinion. The camshaft is equipped with four large-diameter bearings. It is machined from carbon case-hardening steel to B.S. Specification S.14. Each bearing surface is scrolled and runs in bushes housed in the crankcase. A fifth bearing is situated in the rear wall of the crankcase. This bearing—a plain bronze one—has an ex ternal annular groove which registers with a small pocket or well in the crank case; oil accumulates in the groove and ensures lubrication of the bearing. The camshaft pinion is keyed on to the end of the shaft, which, incidentally, is hollow and equipped with a keyed plug fitted into the end to supply the drive for the petrol pump. Of simple design, the vertically mounted, case-hardened tappets bear on the cams. The slipper-type tappets are . housed in detachable Dural guides which fit into the raised bosses cast integral with the crankcase. The push-rods are encased in tubes, the lower ends of which fit into special oil-resisting rubber-lined recesses while the other ends are located by sliding a section of rubber tubing over each tappet guide. The rubber is retained by means of belled-out ridges on the push-rod tubes. Accessory Details The short shaft driving each spigot-. type magneto is carried in two journal bearings together with a plain scrolled Dural bearing housed in a bolted-up cas ing. Provision is made for a tachometer drive and generator. Following normal Cirrus practice, the timing cover can be removed without disturbing the gears. Attached to the cover is the special triple reciprocating oil pump unit, together with the com bined Amal petrol pump and filters. The oil pump is of an unusual design and incorporates an eccentrically mounted Dural rotor. Inside three chambers drilled transversely across the axis of the rotor are three pistons which are located on a squared shaft which forms the axis of the rotor. The pistons are free to slide across the axial shaft and bear against the walls of the cylinders formed in the rotor. Owing to the eccentric motion of the rotor the pistons travel up and down their respective bores which register with ports cut in the walls of the rotor casing. The pump delivers oil at the rate of The four-throw crankshaft is fitted with a deep groove journal thrust race at its forward end. one gallon every 22 seconds. The two outside pumps are for scavenging the oil, which is delivered back to the oil tank through two simple barrel-type gauge fil ters. The delivery pump is equipped with a special filter having a series of hollow gauze discs tapering towards their cir cumference. These discs are mounted on a tube with holes drilled to coincide with each disc; oil flows through this tube and out via the discs. A simple pressure release valve is incorporated. Incidentally, one scavenging pump is attached to a small oil gallery which passes through the intermediate walls cf the crankcase to the forward end of the engine, its object being primarily to cope with excess oil accumulating during the course of a dive. All three filters can be withdrawn in situ from beneath. When specified, a special B.T.-H. inertia starter is bolted to the timing case ; one bolt, however, passes through to the crankcase wall in order to cope with the thrust of the starter when it is engaged. The starter, incidentally, was originally developed by the Cirrus Engine Department at Brough. The two Simms magnetos, mounted one on each side of the crankcase, incorporate automatic advance and retard mechanism. Petrol is supplied to the Type A.i 48G Claudel-Hobson carburetter, by means of an Amal twin pump with twin filters which is mounted on the timing case cover and driven by a keyed tongue en gaging with the camshaft. The carburetter, which has an inde pendent altitude control, is equipped with a special Amal flame trap, the shape of which enables use to be made of the warm air inside the engine cowling. The down-draught carburetter is attached to a single light alloy induction manifold Installation details—with dimensions in centimetres—of the Cirrus Major 150. casting which is secured by two accessible bolts to each inlet port and is provided with a suction elbow for vacuum controls. By simply loosening the steady attached to the flame trap, withdrawing the eight manifold bolts and disconnecting the petrol pipe and two control connections, the whole induction system can be withdrawn as a unit. All Cirrus Major engines are supplied complete with the induction system al ready described, together with twin magnetos, eight sparking plugs, airscrew boss and spinner, resilient bearer feet, cylinder cooling chute and baffles, ex haust stubs and a tool-kit for running adjustments. The finish of the engine is olive green with stove-enamelled cylin der fins. Other external parts are either cadmium plated or stove enamelled. The B.T.-H. inertia starter, together with the B.T.-H. C. 3,000 60-watt 12-14-volt generator, are fitted when specified. Maintenance instructions advise that after the engine has been run in service for fifty hours the oil should be changed, petrol and oil filters, jets and sparking plugs should be cleaned, and the magneto and valve clearances be checked. The engine should be given a top overhaul after 300 hours, and at 600 hours it will be due for a complete overhaul. It is obvious that great care and attention has been paid to accessibility, and the absence of extraneous fittings makes the engine one of the cleanest designs we have seen. It is obvious that the ground engineer's task has been con siderably simplified by careful design. CONTRIBUTORS TO THE CONSTRUC TION OF THE CIRRUS. Accles and Pollock, Ltd., tubing; Amal, Ltd., fuel pumps, flame trap elements; Albion Drop Forgings Co., Ltd., gear stampings; Birmingham Aluminium Casting Co., Ltd.. aluminium and Elektron castings; W. T. Clarke and Co., Ltd., spinner; Dermatine Co., Ltd., oil-resisting joints; E. M. V. Engineering Co., Ltd., machined gears; Fletcher Bros., steel pressings; Glacier Metal Co., Ltd., con-rod and main bearings; Hall and Hall, Ltd., joints; High-Duty Alloys, Ltd., connecting- rod stampings; Hughes Johnson Stampings. Ltd., stampings; H. M. Hobson, Ltd., carburettors; Hofi- mann Manufacturing Co., Ltd.', ball bearings. Richard Klinger, Ltd., joints; K.L.G. Sparking Plugs, Ltd., plugs; Laystall Eng. Co., Ltd., crank shafts; Light Production Co., Ltd., pistons; Wm. Mills, Ltd., aluminium castings; Motor Com ponents, Ltd., valves; Manganese Bronze and Brass Co., extruded bronze; Phosphor Bronze Co., Ltd., valve guides and bronze castings; J. Richards and Sons, Ltd., induction pipes and cowling. J. Stone and Co., Ltd., valve-guide castings; Specialloid, Ltd., pistons; Sterling Metals, Ltd., Elektron castings; Smith's Stamping Works, Ltd., stampings; Geo. Salter and Co., Ltd., all springs; Simms Motor Units, Ltd., magnetos and couplings; Joseph Sankey and Sons., Ltd., steel pressings; Geo. Turton Platts and Co., Ltd., cylinder billets; Weyburn Eng. Co., Ltd., camshafts and tappets; Wellworthv Piston Rings, Ltd., piston rings; Chas. Weston and Co., Ltd., oil seals; James Walkerand Co., Ltd., joints; Henry Wiggin and Co., Ltd., Monel metal; Northern Rubber Co., Ltd., rubber mouldings.
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