Description of Engine

DESCRIPTION OF ENGINE

The Gipsy Major Series 10, which is a development of previous Gipsy and Gipsy Major engines, is a conventional reciprocating engine. The design and construction follow well established aero-engine practice in general layout, materials, and in the shape of the individual components. Fig. 1 is a photo­ graph of a Gipsy Major 10 Mk.2 and the Frontispiece, at the beginning of this handbook, is a cutaway drawing of the same engine.

This chapter is, primarily, a description of the Gipsy Major 10 Mk. 2, Fig. I, but the majority of the information is equally applicable to all variants of the Gipsy Major 10 Mk. I, and to the variants of the basic Gipsy Major 10 Mk. 2. The differences between the Gipsy Major 10 Mk. 1 and the Gipsy Major 10 Mk. 2, and between the variants of each mark are described briefly in the introduction at the beginning of this handbook.

Contents
	Page		Page
Crankcase group	3	General	1
Camshaft	7	Miscellaneous	17
Camshaft bearings	5	Airscoop	17
Crankcase	3	Cooling baffles	18
Crankshaft	5	Cooling system	17
Front cover	6	Propeller hub	18
Main bearings	4	Rear cover and drives	7
Tappets and guides	7	Rear cover	7
Thrust bearing	6	Timing and accessory drive gears	11
Top cover	5	First timing gear	11
Cylinder group	13	Generator drive	13
Connecting-rods	17	Magneto drive	11
Cylinder barrels	13	Oil pump driving gear	12
Cylinder heads	13	Tachometer drive	12
Pistons, piston rings and gudgeon-pins	15	Vacuum pump and generator gear trains	12
Push rods	14
Valves and valve springs	14
Illustrations
	Fig		Fig
Gipsy Major 10 Mk. 2	1	Exploded drawing of intermediate gear assembly	17
Crankcase	2	Arrangement of magneto drives	18
Gipsy Major 10 Mk. 1 main bearing assembly	3	Generator drive assembly	19
Gipsy Major 10 Mk. 2 thin-wall main bearing	4	Cylinder barrel	20
Camshaft bearings	5	Cylinder head assembly	21
Top cover	6	Cylinder head assembly	22
Gipsy Major 10 Mk. 1 crankshaft with tapered front end	7	Valves and valve springs	23
Crankshaft with splined front end as fitted in Gipsy Major 10 Mk. 2 and in certain variants of the Gipsy Major 10 Mk. 1	8	Tappet, push rod and cover group	24
Thrust bearing assembly	9	Piston and connecting-rod	25
Retaining ring, oil seal, and oil seal housing	10	Section of piston rings	26
Camshaft	11	Artist's impression of cylinder cooling	27
Tappet and guide	12	Airscoop and baffles as fitted to early Gipsy Major 10 Mk. 1 engines (pre-mod. 1720)	28
Rear cover, external view	13	Airscoop and baffles	29
Rear cover, internal view	14	Gipsy Major 10 Mk. 2 propeller hub for metal propeller	30
Exploded drawing of rear cover assembly	15	Gipsy Major 10 Mk. 1 propeller hub for wooden propeller	31
Timing gear and accessory drives	16

Further information regarding the differences between the various engines is given in the Leading Particulars which follow the introduction, and the appropriate Operating Limitations are set out on page viii.

For the purposes of this chapter the engine components are divided into four groups : the crankcase; rear cover and drives; the cylinder group ; and miscellaneous.

The crankcase group includes the crankcase proper with the main and the camshaft bearings, the top cover, the crankshaft, the camshaft, and the tappets and guides.

The rear cover and drives group contains a description of the timing gear and of the accessory drives. Although some of the gears are actually mounted on the crankcase rear wall, they have been included in this part of the chapter to preserve continuity in the description of the gear trains.

There are four identical cylinder assemblies, each including a cylinder barrel and cylinder head, a piston and piston rings, and a gudgeon-pin and a connecting-rod. Each cylinder head carries a pair of valves and their rockers. For convenience the push rods and push-rod covers have been included in the cylinder group.

The cooling system of airscoop and baffles, and the propeller hub are described in the miscellaneous group which concludes this chapter.

CRANKCASE GROUP

The crankcase is divided in the horizontal plane on the crankshaft centre line. The term crankcase is generally used to indicate the lower and larger component (Fig. 2), the upper and smaller component being called the top cover (Fig. 6).

The crankcase is a light-alloy casting supporting the bearing and mounting loads, and containing the crankshaft, camshaft and tappets. The four cylinder assemblies are attached to its lower face, and the upper edge of the airscoop and cooling baffles are attached to its sides. The carburettor air-intake is also attached to the starboard side of the crankcase. The engine bearer arms, which are airframe components, are bolted to its side walls. The front scavenge filter is accommodated in the starboard wall and the fuel pumps arc mounted on the port wall.

The crankcase. which is stiffened by transverse webs, forms a rigid box-girder foundation for the engine. The intermediate webs and the crankcase rear wall are pierced so that oil can drain freely to either end of the crankcase, according to the attitude of the aircraft; holes in the port sides of these webs accommodate the intermediate camshaft bearings.

The lower face of the crankcase is flat and has four apertures to accommodate the cylinder barrels. Steel studs are screwed into this face, four around each aperture, to secure the four cylinder assemblies to the crankcase. Along the port side are the eight light-alloy tappet guides, each held in place by a pair of studs and nuts.

At the front of the crankcase a face is machined concentric with the crankshaft centre line ; three studs which secure the thrust bearing housing and the front cover are screwed into this face, two further studs which secure these components being in a similar face machined on the front of the top cover.

1. Bearing Cap	4. Bearing, Crankcase Half
2. Bearing Locating Dowel	5. Oil Drilling
3. Bearing, Cap Half	6. Waisted Bearing Cap Stud

On both side walls of the crankcase are two rectangular faces each having four studs for the attachment of the engine bearer arms. A recess is bored in the centre of each rectangular face to receive a matching spigot on the bearer arms. An accurate spigot fit is necessary to ensure that the fixing studs are not loaded in shear. Other tapped bosses and studs are provided for attachment of the airscoop mountings, cooling baflles. and the carburettor air-intake, etc. Two faces on the port side of the crankcase adjacent to No. 3 cylinder position provide mountings for the fuel pumps. The facings are in the same plane as the camshaft on which are formed two eccentrics by which the pumps are actuated.

The crankcase rear wall projects downwards below the cylinder mounting face, and in conjunction with the rear cover provides the casing in which the timing gear, the magneto, oil pump, and tachometer drives are situated. A sump, which is also referred to as the settling tank, is attached to the bottom of the rear cover and the majority of the drain oil collects in this via a rectangular opening in the starboard side of the crankcase rear wall. The periphery of the rear wall is provided with studs for the attachment of the rear cover. When mod. 1721 (1876 for Gipsy Major 10 Mk. 1-1) is embodied, a reamed hole is provided in the rear cover mounting face just below the centre line on the port side, which aligns with a corresponding reamed hole in the cover. A fitting bolt is assembled in this position to afford improved location for the cover.

Each transverse web is drilled to form oil ducts through which oil is fed under pressure from a gallery in the top cover to the main bearings.

MAIN BEARINGS

Five split main bearings, which are numbered I to 5 from the front, and a thrust ball bearing, support the crankshaft. The ball bearing, which locates the crankshaft endwise, is attached to the front of the crankcase by its housing as described on page 6. The main bearings are carried in housings, the lower halves being machined out of bosses which are integral with the transverse webs and the rear wall of the crankcase. The foremost housing boss is extended forwards and joined to the front wall of the crankcase 'where it is machined to form the lower half of the housing for the thrust bearing housing, the upper half of this housing being in the top cover. Each bearing cap is secured by studs and nuts. The caps for No. 2, 3, 4, and 5 bearings are each secured by two studs. As the studs pass through the oil duct drilled in the crankcase webs they are waisted to permit the passage of oil to the bearings. The front bearing cap, which is longer than the others, is secured by four studs. Where mod. 1673 has been embodied, each bearing cap is located by two dowels.

In the Gipsy Major 10 Mk. I, and in a limited number of Gipsy Major 10 Mk. 2 engines converted from military Mk. 8 engines pre-mod. 1685, the main bearing housings are lined with flanged steel shells, each shell being coated with white-metal on the bearing surface. Rotation of the bearing shells in their housings is prevented by a dowel in the bearing cap, Fig. 3.

The lower half bearing shells contain oil holes and grooves ; the oil holes align with the oil ducts in the crankcase when the shells are in position and permit the oil to reach the crankshaft journals.

Gipsy Major 10 Mk. 2 engines, except as mentioned above, are fitted with thin-wall bearing linings in place of the flanged steel shells (Fig. 4). These linings consist of a strip steel backing lined with lead-bronze. A thin film of lead is deposited on the lead-bronze to eliminate ‘picking-up’ tendencies and to improve the bearing on the journal, and a film of indium which is infused into the bearing surface enhances the anti-friction properties and renders the bearing less susceptible to corrosion. The dowel in the bearing cap is replaced by a lip on each bearing shell, which engages in a rectangular wedge-shaped notch in the relevant bearing cap or crankcase web, to locate each bearing shell and to prevent it from turning.

The camshaft is carried lengthwise within the port side of the crankcase in five plain bearings. The front bearing consists of a blind light-alloy bush, which also serves as an end cover for the camshaft, and is secured to the front wall of the crankcase by an integral flange and three studs and nuts. The three intermediate bearings which ar.: carried in the transverse webs are of larger bore than the two end bearings so that the camshaft can be threaded through them for purposes of assembly and dismantling. Each intermediate bearing is identical and consists of a phosphor-bronze bush locked in position by a set-screw through the port wall of the crankcase. The rear bearing consists of a flanged alloy bush secured to the crankcase rear wall by two studs and nuts.

TOP COVER (Fig. 6)

As stated on page 3, the crankcase is divided in the horizontal plane on the crankshaft centre line and the upper component is called the top cover. In effect this component is a lid closing the open top of the crankcase, and is secured by twenty-seven bolts and nuts and eight studs. The rear cover is fastened to the rear of the top cover by eight set-bolts. Two lifting eyes are screwed into the upper surface of the cover for use when slinging the engine. The front end is machined to accommodate the upper half of the thrust bearing housing, and is provided with two studs in the front face, which, in conjunction with the three studs mentioned on page 3, secure this housing and the front cover to the crankcase/top cover assembly. At the rear it is flanged to mate with the upper portion of the rear cover. The top cover is a magnesium alloy casting stiffened by internal webs and contains the main oil gallery. This oil gallery consists of a duct cored in the casting along the starboard side with branch ducts drilled into it from the top cover/crankcase joint face. These align with corresponding ducts drilled in the crank­ case and feed oil from the gallery to the main bearings. To enable the oil ducts to be cleaned efficiently, later engines are provided with detachable blanking plugs.

CRANKSHAFT (Figs. 7 and 8)

The crankshaft extends forward to form an integral propeller shaft, and is provided with either a one-in-ten taper and a round-ended feather key, or with a No. I S.B.A.C. spline to suit the propeller hub; the first being standard for the Gipsy Major 10 Mk. 1 and the second for the Gipsy Major 10 Mk. 2 - the splined crankshaft is, however, fitted to certain variants of the 10 Mk. I which can be identified by the suffix A after the mark number.

The splined crankshaft is of larger diameter, and therefore stronger, than the tapered type.

FIG8

The crankshaft is machined from a nickel­ chromium steel forging and has four cranks or throws with cranks No. I and 4 at I80 degrees to No. 2 and 3. The journals and the crankpins are hollow, both for lightness and to act as oilways, their open ends being closed by discs and sealing washers secured in pairs by axial bolts. Holes drilled in the crankwebs connect the bore of each crankpin to its adjacent journal. Oil enters the crankshaft at journals No. 2 and 4 which are drilled radially and passes through the drilled passages in the crankwebs to the crankpins to lubricate the big-end bearings via a hole drilled radially in each crankpin. Female splines in the rearmost journal engage male splines on the integral shaft of the first timing gear, which is secured by a retaining bolt and dished end cap at the front of the journal, in a similar manner to the sealing arrangements of the hollow journals and crankpins. The starter dog, which transmits the torque from the starter to the crankshaft, is bolted to a flange on the rear face of the timing gear.

THRUST BEARING (Figs. 9 and 10)

The thrust bearing is a single-row, deep groove type of ball bearing capable of dealing with thrust in either direction. The inner race of the bearing is of the divided type. In addition to locating the crankshaft endwise it transmits the propeller thrust through the crankcase and the engine mountings. It is carried in a bronze housing located in the forward end of the crankcase and the top cover. The complete ball bearing is permitted a small amount of end-float in its housing, the requisite amount being obtained by the use of shims between the front cover and the bearing housing flange. The actual number of shims fitted on initial assembly is stamped on the crankcase adjacent to the front cover. A thrust bearing washer with oil flow and return slots is situated between the ball bearing and the front cover. The crankshaft cone which is situated immediately forward of the thrust bearing is fitted with two oil sealing rings to prevent the escape of oil at the front of the engine. On engines with mod. 1840 embodied the front cover and the cone are redesigned, and oil leakage from the crankcase is prevented by a single Weston oil seal housed in the crankcase front cover.

FIG9 FIG10

The thrust bearing fitted to the Gipsy Major 10 Mk. I is different from that described above. The inner race is not divided and there is no separate housing; the outer race being housed directly in the crankcase and top cover. Unlike the Gipsy Major 10 Mk. 2 thrust bearing, the outer race of the 10 Mk. 1 bearing is permitted no end-float, being positively nipped between the front cover and the rear of the counterbore in the crankcase and top cover. On the 10 Mk. 2, the inner race of the thrust bearing is clamped against a flange on the crankshaft indirectly by means of the nut which secures the propeller hub but on the I O Mk. I the inner race is clamped directly by its own individual nut on a thread cut on the crankshaft just behind the tapered portion. To reduce the stress con­ centration in this region, the latest tapered crank­ shafts have a sleeve shrunk on to locate the thrust bearing and to carry the thrust-bearing-nut thread ; thus obviating the need to cut a thread in the actual crankshaft;

FRONT COVER

The crankcase front cover is in effect a retaining plate for the thrust bearing and on engines with mod. 1840 embodied the cover also forms a housing for the oil seal. The cover is secured both to the crankcase and the top cover by studs which pass through the flange of the thrust bearing housing.

CAMSHAFT (Fig. 11)

The camshaft is a one­ piece hollow shaft with five bearing journals, four inlet cams, four exhaust cams, and two fuel pump cams ; it is carried in five plain bearings situated in the lower port side of the crank­ case as described on page 5. Axial movement of the camshaft rearwards is pre­ vented by an integral flange bearing against the front race of the rear bearing. Forward movement is presented by the front face of the camshaft timing gear rotating against the rear face or the bearing. The camshaft timing gear is located on the rear end of the camshaft by a Woodruff key and is secured by a tab-washer and nut. Four alternative keyways are provided in the timing gear these are so spaced that different angles between each keyway and the nearest full gear tooth may be selected for fine adjustment of the valve timing.

FIG11

TAPPETS AND GUIDES

FIG12

Four pairs or steel tappets act as cam followers to transmit the motion of the cams to the valves via push rods and rockers. The upper end of each hollow cylindrical tappet body is machined with a rectangular foot curved on the cam following face, the lower end being fitted with a replaceable hardened steel cup to provide a working surface for a hardened steel ball fitted in the upper end of the push rod. The aluminium alloy guides are flanged, each being secured to the crankcase by two studs and nuts. with a moulded joint ring interposed to prevent leakage of oil from the crankcase. For the same reason, the barrel of each guide is turned with two oil retaining grooves towards its upper end. A slot in each guide engages the rectangular foot of the tappet and prevents it from rotating.

REAR COVER AND DRIVES

REAR COVER (Figs. 13, 14 and 15)

The magnesium alloy rear cover bolted on the back of the crankcase and top cover encloses the timing gear and the drives and provides mounting faces for all the accessories. It is machined with mounting faces for the magnetos, the oil pump, the oil sump, the starter, the tachometer drive, the engine breather unions, and the generator, and vacuum pump. The magnetos are secured by set-bolts to two horizontal inverted platforms on either side of the rear cover. The two magneto drives project to port and starboard from a narrow section of the cover situated below and slightly to port of the centre of the two platforms. Displacement to port is necessitated by the impulse starter coupling. which is situated between the starboard magneto and its drive.

The oil pump mounting face is situated below the magneto drives, and t h, sump for drain oil is bolted to an opening at the lowest point of the rear cover.

The mounting for the starter is situated in the centre of the cover in line with the crankshaft.

The tachometer drive components are assembled directly into the rear cover with the drive connection situated to port of the starter. The engine breather and oil tank vent connections consist of an elbow and a union adapter respectively, both being secured by studs to the upper starboard side of the rear cover.

The generator is located directly above the starter on the rear face of the cover. The vacuum pump mounting is on the port side of the narrow section of the cover between the starter and generator. A blanking plate with a union adapter is fitted to the unused accessory mounting face on the starboard side ; oil is supplied through this adapter to lubricate the vacuum pump and generator drive oilways in the rear cover walls.

FIG13

1. Generator mounting face	7. Port Simms coupling—driving half
2. Crankcase breather union	8. Suction filler mounting face
3. Oil tank vent pipe union	9. Engine-speed ( 1 to 1) tachometer drive as fitted to Gipsy Major 10 Mk. I (except Mk. 1-7), and 10 Mk. 2-1.
4. Starter mounting face	10. Vacuum pump mounting face
5. Starboard magneto mounting arm	11. Early type of generator coupling
6. Oil pumps unit

FIG14

1. Generator-drive driven gear—early type	6. Settling tank mounting face
2. Generator-drive idler gear	7. Magneto driven spiral gear
3. Generator driving gear	8. Magneto drive static spindle—support bush
4. E.S.I. intermediate gear	9. Generator and vacuum pump intermediate gear
5. Oil pumps gear	10. Air compressor mounting face

FIG15

1. Oil seal bolt	16. Blanking cover, for generator mounting face
2. Generator idler gear	17. Starter adapter	30. Magneto driving gear bolt
3. Generator pinion	18. Starter adapter shim	31. Vacuum pump drive housing
4. Key	19. Slotted nut	32. Washer
5. Thrust washer mounting face	20. Distance piece	33. Thrust washer
6. Tab washer	21. Tachometer drive	34. Blanking cover for vacuum pump
7. Nut	22. Oil pump	35. Bevel pinion nut
8. Thrust washer	23. Key	36. Lock washer
9. Circlip	24. Driving shaft	37. Magneto driven gear
10. Breather shield	25. Oil baffle	38. Vacuum pump bevel pinion
11. Breather connection	26. Bearing housing	39. Shim
12. Vent shield	27. Ball hearing	40. Shim
13. Vent connection	28. Oil retainer	41. Driving shaft
14. Blanking cover, for redundant compressor mounting		42. Driving shaft housing
15. Generator drive coupling	29. Magneto coupling flange	43. Driving gear assembly

TIMING AND ACCESSORY DRIVE GEARS (Fig. 16)

THE FIRST TIMING GEAR, which is secured to the rear end of the crankshaft, is the first driving gear for the whole drives group. This gear, together with the starter dog and its method of attachment to the crankshaft are described on page 6. The camshaft timing gear is d1iven off this gear through an intermediate gear, as illustrated in Fig. 16.

FIG16

THE MAGNETO DRIVE (Figs. 16, 17 and 18) is taken from an intermediate gear between the first timing gear and the camshaft timing gear. A hollow shaft, integral with the intermediate gear, is fitted internally with two plain bearings which rotate on a stationary spindle secured to the rear of the crankcase. The other end of the spindle is supported in a bushed hole in the rear cover. The magneto driving gear is bolted to a flange at the rear end of the hollow shaft. At the front of the shaft, between the intermediate gear and the crankcase, is a ball thrust bearing which takes the end thrust from the spiral gear.

FIG17

The final magneto drive is provided by the magneto driven gear which is mounted below. and at right angles to, the driving gear. The driven gear is situated in the centre of a hollow integral cross-shaft which is keyed to a second hollow shaft, the latter being supported across the narrow section of the engine rear cover by two ball bearings. Two Simms couplings, one at either end of the cross-shaft, transmit the drive to the magnetos, positive radial location being ensured by keyways in the coupling hub engaging the key already mentioned. The assembly is secured by a through­ bolt, which also clamps the inner races of the ball bearings between the driven gear shaft and the back of the couplings. The hub of each coupling rotates in an oil retaining plate which is machined internally with a helical groove, for the purpose of returning escaping oil to the inside of the rear cover.

FIG18

1. Oil hole from No. 5 main	5. Driven spiral gear
2. Intermediate gear [hearing	6. Driving spiral gear
3. Thrust bearing	7. Static spindle
4. Simms vernier half coupling	8. Oil retaining plate

THE QUARTER ENGINE-SPEED TACHOMETER DRIVE is taken from the timing intermediate gear, which is of sufficient width to mesh with both the camshaft gear and the tachometer driving gear. The latter gear is secured to the tachometer driving shaft, which runs in two plain bearings in the rear cover at the rear end. A second driving gear is integral with this shaft. The remainder of the gears are contained in a drive housing which is secured to the outside of the rear cover and is enclosed by a small cover having an adapter for the flexible drive. In the drive housing are two plain bearings, the lower supporting a shaf1 with an integral driven pinion on the rear end. A driven gear, which meshes with the second driving gear already described, is pinned to the front end. The pinion drives the larger gear of the compound intermediate gear which rotates in the upper plain bearing. The pinion of the compound intermediate gear drives the final driven gear with its integral shaft, which is provided with a square hole to accommodate the tachometer cable end fining. The final driven shaft rotates in a bearing in the tachometer drive cover situated in line with the driven pinion, Fig. 38 at the end of this chapter.

The alternative tachometer (E.S.I.) drives, which may be found on the Gipsy Major 10 Mk. I, and engine-speed tachometer drive fitted to the 10 Mk. 2 pre-mod. 1634 and the 10 Mk. 2-1 are illustrated in Fig. 32 to 37 on pages 19 and 20 at the end of this chapter.

THE OIL PUMP DRIVING GEAR is attached directly to the oil pump shaft and meshes with the camshaft timing gear. The shaft is adequately supported inside the pump anti no additional bearings are required.

The VACUUM PUMP AND GENERATOR GEAR TRAIN is driven from a common gear, known as the vacuum pump and generator intermediate gear: which meshes with the first tinting gear on the crankshaft. The gear is secured by a Woodruff key and nut, to the forward end of the integral shaft of the vacuum pump driving bevel gear, which is supported by plain hearings in a circular Hanged housing bolted inside the rear cover. The vacuum pump drive is then transmitted to the port side of the rear cover via a driven bevel gear. This gear also has an integral shaft which is supported by a flanged housing secured to the vacuum pump mounting face. in a similar manner to the driving bevel gear. The end of the driven bevel gear shaft is slotted to engage with the tongue on the vacuum pump drive coupling.

THE GENERATOR DRIVE

(Fig. 19) consists of three gears in addition to the common drive gear already described. The first driving gear is bolted to the rear face of the latter, and in turn drives the final driven gear via an idler gear. The idler gear is supported by an integral shaft which rotates in plain bearings in the rear cover. The idler gear shaft is hollow to allow the passage of oil from the bearings to the face of the gear teeth, leakage of oil from either end being prevented by an oil seal shaft. This consists of an oil sealing disc machined with an integral stem. The disc blanks off the forward end of the idler shaft, the stem which passes through the shaft being fitted with an oil sealing washer and nut to seal the rear end of the shaft. The oil seal washer has a sufficiently large diameter to retain the idler shaft in its bearings.

FIG19

The final driven gear shaft is located in the bearings in the rear cover by a thrust washer and circlip at its rear end. Female serrations within the forward end of the final gear shaft transmit the torque through corresponding serrations on a quill shaft, and a splined coupling at its rearmost end, to the generator. To obviate wear on the generator armature splines, the coupling is clamped to the generator armature by a tapered sleeve and a nut; thus wear is confined to the quill shaft and the relatively inexpensive coupling instead of occurring on the generator armature.

CYLINDER GROUP

CYLINDER BARRELS (Fig. 20)

The four cylinder barrels are machined from carbon steel forgings and are identical. The external surface is closely finned over the greater part of the cylinder, to provide rapid heat dissipation. Four semi-circular grooves are cut along the length of the cylinder fins to accommodate the holding-down studs. A spigot which enters the aperture in the crankcase facing is formed at the upper end : a machined collar on the cylinder limits the depth of entry into the aperture. The spigot diameter is stepped up immediately adjacent to the collar. and is ground to size so as to locate the cylinder within the crankcase aperture. The joint between the collar and the facing is made with a moulded synthetic rubber ring. The inwardly projecting length of the spigot forms an oil dam which prevents oil from flooding the cylinder. Each barrel is securely clamped between its cylinder head and the crankcase by four high-tensile steel studs, the head being located by a spigot on the barrel. A copper-asbestos washer is employed between the barrel and the head to ensure a gas-tight joint.

FIG20

CYLINDER HEADS (Figs. 21 and 22)

The cylinder heads are also finned externally for cooling purposes and are machined from aluminium alloy castings. Two valve seat inserts of high thermal expansion steel arc shrunk into the valve pockets formed on the longitudinal centre line, with the inlet valve insert behind the exhaust. The exhaust insert is screwed into position and the inlet insert is retained by peening. Conical valve seats are machined on the inserts at an included angle of 120 degrees. The valve pockets terminate in faced flanges on the starboard side of the engine. the inlet flange being vertical and the exhaust flange facing downwards at an angle of 45 degrees. Both flanges are fitted with studs for securing the manifolds and copper-asbestos gaskets are used to ensure gas-tight joints. A horizontal platform cast on the head across the two ports is bored to receive the phosphor-bronze valve guides and holes are drilled in the platform for attachment of the rocker bracket. Brass sparking plug adapters are screwed and shrunk into the sides of the combustion chamber, and locked by dowels. Immediately below each starboard sparking plug adapter, a 4 B.A. stud is fitted between the fins for the attachment of a thermo-couple.

FIG21 FIG22

VALVES AND VALVE SPRINGS (Fig. 23)

One inlet and one exhaust valve is fitted to each cylinder head, the exhaust valve being sodium cooled and of larger section than the inlet valve. Normally, the Gipsy Major 10 Mk. I exhaust valves are not sodium cooled and, therefore, these engines are limited to fuels containing not more than 4 cc. of T.E.L. per Imperial gallon.

Two concentric valve springs are used to close each valve, the inner ends of the springs bearing on a steel collar which is fitted over the valve guides, the outer ends being located by a flanged collar secured to the end of the valve stem with a pair of conical split collets. Grooves which engage corresponding grooves in the valve stem are formed in the bore of the collets.

The two valve rockers, together with the push rods, transmit the motion of the cams to the valves. The rockers are forged steel levers pivoted in the centre and supported in pairs on a single bracket secured to the cylinder head by three bolts, which pass through the rocker platform and are secured by plain nuts. A rocker pivot spindle is clamped to the lower end of the bracket and the two rockers are supported on phosphor-bronze bearings, one at each end of the spindle. Each rocker is held by a thrust spring and cup-washer, the assembly being retained by a cotter pin at each end of the spindle. One end of each rocker is fitted with an adjustable, ball-ended hardened steel set-screw, which locates in the cup-end of the push rod. A small, domed steel pad, which contacts the end of the valve stem, is peened to the other end of the rocker arm, both the pad and the end of the valve stem being hardened to reduce wear. A separate hardened thimble is fitted on the valve stem of the Gipsy Major 10 Mk. 1 valves.

FIG23

A pressed-steel casing and a cover enclose the whole valve operating gear, the casing being secured to the cylinder head by the rocker bracket bolts. The cover is secured to the casing by one central captive screw. Leakage of oil at the cover joint and from the screw aperture is prevented by a synthetic rubber ring and an oil seal washer respectively. Protruding from the bottom of the cover and welded to it. is a vertical vent pipe to which is attached a small collar for indicating the oil level required to lubricate the valve operating components.

PUSH RODS (Fig. 24)

The push rods are light alloy tubes with case-hardened steal tips pressed into the ends. The upper tip is spherical to engage the cup in the end of the tappet, the lower tip being cupped to receive the ball-end of the rocker adjusting screw. The push rods are enclosed in separate covers each consisting of three aluminium tubes. The outer ends of the upper and lower tubes are belled, the upper to locate in a recess in the tappet guide, and the lower in a ferrule welded to the rocker casing. Synthetic rubber rings are used to prevent the escape of oil at these points. The cover assembly is completed by a centre tube, housing a helical coil spring, into which the inner ends of the upper and lower tubes are inserted to butt against the spring. To remove a push rod it is only necessary to telescope the cover tube against the tension of the spring and the push rod is exposed.

FIG24

PISTONS, PISTON RINGS AND GUDGEON-PINS (fig. 25)

The four slipper type, flat crowned pistons are machined from aluminium alloy forgings. The gudgeon-pin is supported by two substantial webs which transmit the thrust directly from the crown of the piston to the gudgeon-pin. The latter is made of high-tensile steel and located endwise in the gudgeon-pin bore by a thrust washer and circlip at each end.

FIG25

Three piston rings of rectangular section, two of which are compression rings and the third a scraper ring, are situated in grooves between the gudgeon-pin and the crown, the scraper ring being nearest the gudgeon-pin. A recess in which oil collects is formed between the stepped-down portion of the scraper ring, which must face the gudgeon-pin, and a similar step in the ring groove (fig. 26). The oil then drains to the inside of the piston through two rows of holes drilled radially in the stepped portion of the piston and the ring groove. To assist bedding down, the working face of the compression rings is machined with a slight taper, and to assist assembly an engraved letter C indicates the face that must be nearest the piston crown.

FIG26

The connecting-rods are machined from aluminium alloy forgings, the shank of each being a substantial ‘I’ section. The big-end of the rod is split in the plane of the crankpin centre line, the cap being held to the rod by four bolts and nuts locked with split pins. A split, steel-backed, white-metal lined bearing is fitted in each big-end and is prevented from rotating by a dowel in the connecting-rod half of the bearing, while end float is prevented by flanges round the edges of the bearing shells. With each crankshaft revolution two oil holes drilled in each cap half bearing shell and the bearing caps, align with a radial hole in the crankpins and allow the escape of pressure oil into the crankcase to provide splash lubrication for the cylinder walls and the camshaft. The small-end of the connecting-rod which is unbushed, is provided with a drilled hole to lubricate the gudgeon-pins. This oil hole is drilled on the centre axis of the connecting-rod, but on later type rods, introduced by mod. 1607, this single hole is replaced by two slightly smaller holes drilled at 45 degrees to the centre axis.

MISCELLANEOUS

COOLING SYSTEM (Fig. 27)

An airscoop and an arrangement of baffles, is employed to direct air around the finned cylinder barrels and heads and so utilize for cooling purposes the air entering the engine cowling during flight. The airscoop is fitted along the port side of the cylinders and air enters through the open front end which is aligned with an opening in the engine no cowl. A back plate closes the rear end of the air­ scoop and causes a pressure to be built up therein. The air flows across the engine through the gaps between the cylinders to the region of low pressure on the starboard side of the engine, inter-cylinder baffles across the starboard side of the gaps preventing the immediate escape of air until it has flowed completely round each cylinder. It then escapes between the baffles and leaves the engine cowling through suitably placed exits at the rear.

FIG27

AIRSCOOP (Figs. 28 and 29)

The airscoop, which is made in two parts, is secured to stud m the crankcase at its upper location, and to supporting plates on the cylinder heads at its lower location. It is divided horizontally to facilitate easy removal of the lower portion, which is secured both to the cylinder head support plates and to the upper portion by wing nuts. This provides a quickly detachable panel for access to the cylinder heads and sparking plugs.

FIG28

1. Inter-cylinder baffles	5. Airscoop—front half
2. Baffle support brackets	6. Airscoop rear half
3. Draw wires	7. Back plate
4. Airscoop lower support plates	8. Airscoop upper support plate

FIG29

Early Gipsy Major 10 Mk. I engines (pre-mod. 1720) had a different type of airscoop. As shown in Fig. 28, this airscoop is made in two pieces and s cured to the cylinder-head and crankcase support plates by long draw-wires. These draw-wires pass through hinges rolled on the edges of the airscoop and the support plates and are secured by locking pins attached to brackets riveted to the assembly. The airscoop backplate is secured to the crankcase and to the fixed portion of the air­ scoop. It contains apertures for the ignition harness, either screened or unscreened, the redundant aperture being blanked off by a small metal disc and rubber grommet.

COOLING BAFFLES

The three cylinder baffles are made from a single sheet of aluminium and are so con­ structed that they are joined along the top edge by which they are bolted to the side of the crankcase immediately above the cylinders. The bottom edges of the baffles are anchored to the cylinder heads by brackets.

FIG30

PROPELLER HUB (Fig. 30)

The propeller hub is machined internally with splines to mate with those on the crankshaft, and to transmit torque from the crank­ shaft to the propeller, the hub being located concentrically with the crankshaft by the front and rear propeller cones. The rear cone is situated immediately in front of the crankshaft thrust bearing : a sawcut through one point in the cone permits it to close in and grip the crankshaft when the hub nut is tightened, but. due to the natural spring in the cone, also facilitates its removal. The front cone, which forms part of the propeller hub assembly, is located on the plain portion of the crankshaft forward of the splines and is formed in two halves for assembly to the flange on the rear end of the propeller hub securing nut. The hub withdrawal nut, which is located on the waisted part of the hub nut, is screwed into the hub in front of the cone. As the hub nut is unscrewed, the front cone bears against the withdrawal nut and draws the hub forward off the propeller shaft. Eight bolts are disposed around the hub rear flange and the front plate to secure the propeller. The bolts are inserted through the rear flange of the propeller hub, the heads being secured by a single locking plate attached to the rear face by eight set­ screws. The nuts are locked by an octagonal locking plate which engages with the vernier pattern plate used to lock the propeller hub nut. Four cheese-head set-screws inserted through both plates secure the locking arrangement to the front plate. The set-screws screw into tapped holes in the front plate and are drilled to receive locking wire. When used with r metal Fairey Reed propeller, the front of 1 ,e propeller hub nut has a cylindrical projection to carry the propeller spinner.

When used with a wooden propeller, a spinner attachment stud is screwed into the propeller hub nut.

Fig. 31 shows a section through the propeller hub fitted to the Gipsy Major 10 Mk. 1, with the tapered crankshaft.

FIG31

1. Spinner	4. Key	7. Locking ring
2. Hub bolts	5. Timing pointer	8. Crankshaft
3. Hub	6. Oil Return grooves	9. Hub retaining nut

FIG32

A. SPIRAL GEAR.	D. OIL PUMP DRIVING GEAR.	G. FIRST TIMING GEAR.
B. MAGNETO DRIVING GEAR	E. CAMSHAFT TIMING GEAR.	17. E.S.I. D RIVING GEAR.
C. MAGNETO DRIVEN GEAR.	F. INTERMEDIATE GEAR.	34. E.S.I. D RIVING SHAFT.

FIG33

8. OUTER BUSH.	14. PLAIN NUT.	33. COVER.
10. JOINT WASHER.	20. PLAIN NUT FOR STUD.	34. DRIVING SHAFT.
11. INNER BUSH.	21. SPRING WASHER.	35. HOUSING.
12. DRIVING GEAR.	27. KEY.
13. LOCK WASHER.	32. STUD FOR COVER

FIG34

8. OUTER BUSH.	20. PLAIN NUT FOR SCREW AND STUD.	26. HOUSING.
10. JOINT WASHER.	21. SPRING WASHER.	27. KEY.
11. INNER BUSH.	22. COVER.	31. COUNTERSUNK SCREW.
12. D RIVING GEAR.	23. AUXILIARY GEAR.	32. STUD FOR COVER.
13. LO CK WASHER.	24. DRIVING SHAFT
14. PLAIN NUT.	25. SHORT BUSH.

FIG35

1. CAP FOR HOUSING.	8. OUTER BUSH.	15. BEARING.
2. DRIVING SHAFT.	9. DRIVEN GEAR.	16. BLANKING CAP *
3. WASHER.	10. JOINT WASHER.	17. SPACING WASHER *
4. ADJUSTING WASHER.	11. INNER BUSH.	18. BEARING.
5. PLUG.	12. DRIVING GEAR.	19. SHORT BUSH.
6. TAB WASHER.	13. LOCK WASHER.	27. KEY.
7. CASING.	14. PLAIN NUT.

* Only fitted if single E.S.I. Drive is required.

FIG36

B. MAGNETO DRIVING GEAR.	J. GENERATOR DRIVE IDLER GEAR.
C. MAGNETO DRIVEN GEAR.	K. GENERATOR DRIVE.
D. OIL PUMP DRIVING GEAR.	L. VACUUM PUMP DRIVE.
E. CAMSHAFT TIMING GEAR.	M. VACUUM PUMP DRIVING BEVEL.
F. INTERMEDIATE GEAR.	28. E.S.I. D RIVEN SHAFT.
G. FIRST TIMING GEAR.	40. E.S.I. DRIVEN SHAFT.
H. VACUUM PUMP AND GENERATOR INTERMEDIATE GEAR.	49. E.S.I. D RIVING SHAFT.
I. GENERATOR DRIVING GEAR.

FIG37

25. BUSH FOR AUXILIARY GEAR.	39. COVER (SINGLE DRIVE).
27. KEY.	40. D RIVEN SHAFT.
26. DRIVEN GEAR.	41. BUSH.
29. LOCK WASHER.	49. ORIVING SHAFT.
30. PLAIN NUT.	62. COVER (DUAL DRIVE).
63. AUXILIARY GEAR : THIS PART IS IDENTICAL WITH ITEM 23 ON PAGE 19.

FIG38

27. KEY.	45. FERRULE.	55. PILLAR FOR OILJET UNION.
28. DRIVEN GEAR.	46. ADAPTER.	56. PLAIN NUT.
29. LOCK WASHER.	49. DRIVING SHAFT.	57. SPRING WASHER.
30. PLAIN NUT.	50. HOUSING.	58. STUD FOR COVER.
41. BUSH.	51. INTERMEDIATE GEAR.	59. PLAIN NUT.
42. DRIVEN GEAR.	52. DRIVEN SHAFT.	60. SPRING WASHER.
43. DRIVING PINION.	53. COVER.	61. BOLT FOR HOUSING.
44. DOWEL.	54. WASHER FOR OILJET UNION.

Note — Where, in fig. 32 to 38, the same reference number appears on more than one illustration, the component is identical in each instance, and where the part is also illustrated in the Gipsy Major 1 and 10 Spare Parts List, the reference number used on these illustrations is the same as that used in the Spare Parts List.