General Description of the Lotus Cortina Twin Cam

The engine is a four cylinder, twin overhead camshaft unit with a bore of 3.2506 in. (82.565 mm.) and a stroke of 2.867 in. (72.746 mm.). The capacity is 95.2 cu. in. (1,560 c.c.) and the compression ratio is 9.5 :1.

The cylinder bores are machined directly in the cast iron cylinder block, which is cast integral with the upper half of the crankcase, and are provided with full length water jacketing.

The cast iron crankshaft runs in five large diameter main bearings fitted with steel-backed copper/lead bearing liners. End-float and thrust are controlled by half-thrust washers located in the cylinder block on either side of the centre main bearing.

Seals pressed in the front cover and the rear oil seal carrier prevent oil leaks from the front and rear of the crankshaft. The front seal runs on the pulley hub whilst the rear seal runs on the crankshaft flange itself. A sintered bronze spigot or needle roller bearing is pressed into the end of the crankshaft to support the gearbox first motion shaft.

The connecting rods are ‘H’ section forgings having separate big end caps retained by two bolts and located by spring dowel pins. Big end bearing liners are, again, steel-backed copper! lead. The small ends have steel-backed bronze bushes.

Solid skirt aluminium alloy pistons with two compression and one oil control ring situated above the piston pin bore are used. The piston pins are fully floating and are retained in position by circlips installed in grooves at each end of the piston pin bore.

The cylinder head is an aluminium casting with fully machined hemispherical combustion chambers and separate ports for each valve. The valves, which have replaceable guides and valve seat inserts, are inclined to each other and the inlets are larger than the exhausts. The valves are operated by two overhead camshafts, one for inlet valves and one for exhaust, the valves being opened directly by the cams acting on piston-type tappets.

The camshafts are driven at half engine speed by a single row timing chain from a sprocket on the crankshaft via a sprocket on an auxiliary shaft and an idler sprocket on an adjustable tensioner. The camshafts each run in five bearings which have steel-backed white metal liners. A shoulder at the front of the camshaft locates it axially in the cylinder head and controls end-float.

The auxiliary shaft is a modification of the camshaft normally used in the push rod overhead valve unit and is retained to drive the oil pump, distributor and fuel pump. The auxiliary shaft runs in three steel-backed white metal bushes and is located by a sintered metal thrust plate bolted to the cylinder block front face. A skew gear, integral with the auxiliary shaft drives the distributor and oil pump, which are both mounted on the right-hand side of the engine. An eccentric, on the auxiliary shaft, operates the fuel lift pump also situated on the right-hand side of the engine towards the rear. The front journal of the auxiliary shaft has four slots machined in its periphery to regulate the supply of oil to the camshafts and tappet gear.

A cast iron flywheel is mounted on the crankshaft flange and ensures a smooth-running engine. The drive for the starter motor is provided by a steel ring gear shrunk onto the flywheel periphery.

The sump is a steel pressing and has a front well for the lubricating oil. The engine lubrication system is the force feed type incorporating a full flow oil filter. The oil pump, which is mounted externally on the engine, is of the eccentric bi-rotor type incorporating a non-adjustable plunger type relief valve.

An oil filler cap is located in the camshaft cover. Crankcase ventilation is by a closed system, crankcase fumes being discharged directly into the carburettor air intake cover.

A three point mounting for the engine and gearbox assembly is provided on sandwich type rubber insulators.


The cylinder block is cast iron and is cast integral with the upper half of the crankcase and is basically a 1,500 block bored out. This cylinder block can be identified by the number, 681F-6015-GA cast on the left-hand side of the block in place of the cast number prefix.

Internally the crankcase incorporates five main bearings with removable caps retained by bolts fitted without lockwashers. The intermediate and rear caps are identical, but their positions must not be interchanged. When dismantling these caps ensure that their positions are marked, this is normally done, in production, by a number 2 stamped on the front intermediate cap and 4 on the rear intermediate cap. The rear cap is not marked. All caps must be fitted with the cast arrows pointing forwards.

The cylinder bores are machined directly into the cylinder block and, in production, are graded for size, the grade number, of each bore, being stamped on the push rod side of the cylinder block adjacent to the top face.


The cylinder head is an aluminium casting with fully machined hemispherical combustion chambers giving a compression ratio of 9.5 :1, and having separate ports for each valve.

The cylinder head is secured to the cylinder block by ten 1~6 in. (11.11 mm.) diameter bolts, 5.7 in. (144.78 mm.) long, with plain washers. The washers for the front left-hand bolts and the rear right-hand bolts have flats to provide clearance for the exhaust camshaft collar and the inlet camshaft rear bearing cap respectively. Three additional bolts, one each side of the front cover and one at the front of the cylinder head, in the centre, secure the front of the cylinder head to the timing case.

The tightness of the cylinder head bolts should be checked, with the engine cold, at the first 600 miles (1,000 km.) service. The tightness should also be checked 600 miles (1,000 km.) after replacing the cylinder head should it have been removed for any reason.

The cylinder head gasket is made of asbestos covered with copper on the top and tinplate underneath.

The valves are in two banks, the inlets on the right and the exhausts on the left, and operate in replaceable guides pressed into the cylinder head. These guides are located by circlips which are retained by the valve spring seats. The inlet and exhaust valve guides are not identical, the inlet guide being 1.520 in. (38.61 mm.) long and the exhaust 1.480 in. (37.59 mm.). The two guides may be readily identified by the fact that the inlet has a taper at the port end, which is 0.4 in. (10.16 mm.) long, whereas the exhaust guide is only slightly tapered, 0.2 in. (5.08 mm.) long. The valve guides may be removed and replaced, using a suitable remover and replacer tool. When replacing the valve guides heat the cylinder head to 1000 to 1500C. (212 to 3020F.). Valve guides are also available in 0.001 in. (0.03 mm.), 0.005 in. (0.13 mm.) and 0.006 in. (0.15 mm.) oversizes on the outside diameter, and it is advisable to check the size against the originals when replacing guides.

After fitting, ream the valve guide bore 0.3113 to 0.3123 in. (7.907 to 7.932 mm.) using a suitable reamer. The valve seats must then be recut, with the appropriate cutters, and the valves lapped in to ensure that the seal is concentric with the valve stem bore.

Recut the seats with the appropriate cutters fitted to pilot Tool No. 316-10 in handle Tool No. 316X. Where necessary the seats may be narrowed with top face and port cutters. If there is a hard glazed carbon deposit on the seat this may be removed with a glaze breaker. The valve seats should also be recut when they show signs of pitting or burning.

The valve seats have inserts which can be replaced when they become pocketed and can be obtained in 0.005 in. (0.127 mm.), 0.010 in. (0.254 mm.), 0.015 in. (0.381 mm.) oversizes.

Remove the inserts by machining two grooves 1800 apart and using a small chisel remove the remaining metal in the grooves, when the insert can be prised out of its location. Care must be taken during this operation to avoid damage to the sides and bottom of the recess. Machine the recess to the required dimension appropriate to the selected replacement insert (see table below). When fitting new inserts the cylinder head should be heated to a temperature of 2000C (3920F) maximum and immersing the valve seat inserts to a temperature not lower than —800C (—1120F). Press the insert into place, using a suitable replacer tool and allow the cylinder head to cool slowly and evenly in air.









Recess diameter


1.6245 in.—1.6235 in.

1.621 in.—1.620 in.

+0.005 in.

1.6295 in.—1.6285 in.

1.626 in.—1.625 in.

+0.010 in.

1.6345 in.—1.6335 in.

1.631 in.—1.630 in.

+0.015 in.

1.6395 in.—1.6385 in.

1.636 in.—1.635 in.









Recess diameter


1.4995 in.—1.4985 in

1.496 in.—1.495 in.

+0.005 in.

1.5045 in.—1.5035 in


+0.010 in.

1.5095 in.—1.5085 in.

1.506 in.—1.505 in.

+0.015 in.

1.5145 in.—1.5135 in.

1.511 in.—1.510 in.

The tappet bores are sleeved, these being available in 0.001 in. (0.025 mm.) and 0.015 in. (0.38 mm.) oversize. Should it be necessary to fit new sleeves, the cylinder head must be machined to obtain an interference fit of 0.0035 in. (0.089 mm.) to 0.0045 in. (0.114 mm.) between the head and the new tappet sleeve. Heat the cylinder head to 1500C (3020F) before fitting the sleeves. When cool machine the sleeve bore to the dimensions shown. After machining, recut the scallops to give clearance to the cams.


The free flow multi-branch exhaust manifold is fabricated from welded steel tubes and has a separate pipe for each cylinder. These pipes are paired together, Nos. 1 and 4 forming one pair and Nos. 2 and 3, which pass inside of Nos. I and 4, the other, the pipes of each pair being joined to form a common outlet. The outlet pipes from each pair then enter the exhaust system. The exhaust manifold assembly is secured to the cylinder head by flanges welded to the pipe ends and retained with brass nuts.


The timing case is made in two pieces, a back plate on the cylinder block and a front cover which also incorporates the water pump and the oil level dipstick tube. Four timing marks are also incorporated on the front cover which, when a timing mark on the rear flange of the crankshaft pulley is aligned with one of them gives 300 B.T.D.C., 200 B.T.D.C., 100 B.T.D.C. and T.D.C. respectively.

The back plate is located on the cylinder block front face by a single bolt situated immediately below the water pump and is retained by the front cover, the front cover bolts passing through the back plate into the cylinder block. Where the back plate is not directly attached to the cylinder block, the back plate and front cover are secured together with nuts and bolts having fine threads. All bolts screwing into the cylinder block have coarse threads. As the bolts have different lengths and threads it is important that they are correctly located, as shown.

        (1) Bolt ¼ in. - 20 U.N.C.x 2 ¼ in. long
        (2) Bolt ¼ in.
— 28 U.N.F. x 2 ¼ in. long and nut
        (3) Bolt 5/16 in - 18 U.N.C.x 2 ¼ in. long
        (4) Bolt 5/16
in. - 18 U.N.C.x 1 in. long
        (5) Bolt ¼ in.- 20 U.N.C.x ¾ in. long
        (6) Bolt 5/16 in. - 18 U.N.C.x 1 ¼ in. long
        (7) Bolt 5/16 in. - 24 U.N.F. x l ¾ in. long and nut

The back plate gasket is made of brown waxed paper and must be fitted without sealer as this may clog the timing chain oil feed. Before assembling the back plate to the cylinder block, check that it is flat. Ensure that the back plate lies flat on the cylinder block front face and is not cocked up by the main oil gallery plug.

The front cover is fitted without a gasket, an oil-tight joint being made by using ESEE-M4G-1008A jointing compound. A gasket on top of the front cover and back plate seals the joint between the cylinder head and the timing case. Three bolts are on each side of the front cover and one at the front of the cylinder head in the centre under the camshaft cover, secure the timing case to the cylinder head.

To prevent oil leaks from around the crankshaft pulley boss an oil seal is pressed in the front cover.

The oil seal can be removed, after first removing the front cover, by supporting the cover around the seal and driving the seal out from the rear with remover Tool No. P.6161 fitted to a 550 handle. Invert the tool and drive a new seal into the housing, again from the rear, and supporting the cover around the seal. The use of Tool No. P.6161 ensures that the seal protrudes 3/64 in. (1.19 mm.) inside the cover.

When fitting the cover it is important that the oil seal is aligned concentrically with the crankshaft and pulley boss. To facilitate this a centraliser Tool No. P.6150 is inserted into the seal while fitting the cover.

The oil level dipstick tube is pressed into the front cover and its upper end must be 4.90 in. (124.5 mm.) vertically above the front cover bottom face if the correct oil level is to be attained.


The crankshaft rear oil seal is pressed into the aluminium carrier, bolted to the cylinder block rear face, and runs on the periphery of the flywheel mounting flange. After removing the carrier, the oil seal can be easily replaced. Support the carrier, close to the seal, and drive the seal out, using a remover/replacer Tool No. P.6165 fitted to a 550 handle. Reverse the carrier, the remover/replacer tool and fit a new seal.

When fitting the carrier the seal must be aligned concentrically with the crankshaft if oil leaks are to be avoided. Locate a centraliser Tool No. CP.6173 in the seal and over the crankshaft while tightening the seal carrier retaining bolts.


The pressed steel sump has a front well, incorporating a longitudinal baffle, for the lubricating oil and is bolted to the base of the cylinder block. A drain plug is located in the right-hand side. The gaskets are made of cork with aluminium foil lamination.

When fitting the sump apply sealer ESEE-M4G-1008A to the front cover and rear oil seal carrier to cylinder block joints, and also to the ends of the grooves in the front cover and rear oil seal carrier. Then fit new sump gasket, followed by the cork packing strips. Refit the sump and tighten the bolts.


The camshafts and valves are enclosed by an aluminium cover, which also covers the camshaft sprockets and chain. This cover is retained by eight self-locking nuts and flat washers which screw onto four of the camshaft bearing cap studs. The camshaft cover gasket is made of cork. Jointing compound is not normally used, although it can be applied to the cover to hold the gasket in place.

The oil filler cap is situated on the camshaft cover at the rear of the left-hand side.



The valves, which have 450 seats, are inclined at 270 to the vertical, the inlet valve head being larger than the exhaust. Their respective diameters are 1 17/32 in. (38.89 mm.) and 1 5/16 in. (33.34 mm.).

The valves are fitted with double valve springs, the inner spring has right-hand coils and the outer left-hand. The springs sit on a pressed steel seat located around the valve guide and retained by the valve guide circlips. The springs are attached to the valve stems by spring retainers with tapered split collets. The valve springs may be fitted either way round.


The valves are operated by two identical overhead camshafts, one for inlet valves and one for exhaust valves, the valves being opened directly by the cams acting on piston type tappets. The tappets are located in the cylinder head immediately above the valves. All the tappet bores in the cylinder head have sleeves. The valve clearances are adjusted by shims located underneath the tappets and resting in the valve spring retainer on top of the valve stem. The shims are available in a number of sizes from 0.065 in. (1.651 mm.) to 0.120 in. (3.048 mm.) in increments of 0.001 in. (0.025 mm.). The shim’s thickness is etched around the periphery although originally it was etched on one side. When fitting this type the etched side must be adjacent to the valve stem. Any roughness caused by the etching should be removed before fitting the shim by rubbing on fine emery cloth.

The two camshafts, which are identical, give a lift of 0.35 in. (8.89 mm.) and the timing shown. The camshafts each run in five bearings with steel-backed white metal liners, four of them ¾ in. (19.05 mm.) wide and the rear one ½ in. (12.7 mm.).

The camshaft bearing caps are located by studs screwed into the cylinder head and retained by self-locking nuts and flat washers. These caps must always be kept in their respective positions and are numbered to facilitate this. The numbers are also stamped on the cylinder head adjacent to the bearing caps.

Adjusting Valve Clearances

The valve clearances should be, inlet 0.005 to 0.007 in. (0.13 to 0.18 mm.) and exhaust 0.006 to 0.008 in. (0.15 to 0.20 mm.) Later exhaust valves with Part No. B26E020 rolled on the stem have a clearance of 0.009 in. (0.23 mm.) to 0.011 in. (0.28 mm.).

In order to check the clearance of a valve, turn the camshaft until the toe of the cam is at 1800 to the tappet being checked. Then select a feeler blade or blades that can just be inserted between the tappet and the heel of the cam to measure the clearance. Note the clearance and repeat the procedure for the other valves.

Should the clearances require adjusting, remove the appropriate camshaft by unscrewing the bearing cap nuts evenly and lift the camshaft out.

NOTE — If this operation is being done on the engine it will be necessary to remove the camshaft sprocket first. To facilitate replacement it is advisable to set the valve timing marks and to slacken the timing chain tensioner before removing the sprocket.

Remove the tappets by lifting them out with a valve grinding sucker and remove the shims, keeping them in their correct order. The correct clearance may be obtained by fitting a different size shim between the valve stem and tappet. A thinner shim will be required to increase the valve clearance and a thicker one to reduce the clearance. The shim’s thickness is etched around the periphery or on the side, but if this has worn off or if the shim appears to be worn, measure the thickness accurately with a micrometer. Select a shim to give the correct size from the following formula:

Shim thickness required = A - C.C.

Where A. is the actual valve clearance

C.C. is the correct valve clearance

Fit the shims into the recess in the valve spring retainer, where applicable, with the etched number on the underside. Do not use more than one shim for each valve. Any roughness caused by the etching should be removed before fitting the shim by rubbing on fine emery cloth. Fit the tappets and the camshaft. Ensure that the camshaft bearing caps are fitted in their correct positions and that the nuts are tightened gradually and evenly, starting with the centre pair and working outwards, to a torque of 9 lb. ft. (1.2 kg.m.). Refit the sprockets and timing chain (see "Valve Timing") commencing with the exhaust and then reset the ignition timing.


The auxiliary shaft runs in three steel-backed white metal bushes located in the right-hand side of the cylinder block. The front journal of the auxiliary shaft has four flats machined in its periphery to regulate the oil supply to the camshafts.

The auxiliary shaft front and rear bushes are both approximately ¾ in. (19.05 mm.) wide, the front one having an additional oil hole for the camshaft oil feed, and the centre bush approximately 5/8 in. (15.88 mm.) wide.

The bushes available in service are pre-sized and require no machining after fitting. When one bush requires replacement it is advisable to replace all three bushes as auxiliary shaft alignment may be affected if only one bush is changed.

Remove the auxiliary shaft bearing bushes, using camshaft bearing remover Tool No. P.6031 with adaptor set P.6031-3. Locate the remover and guide detail "-3a" adjacent to the collar and with the spigot in the bearing. If the centre bush is being removed use the centraliser detail "-3d". Remove the bush by screwing down the wing nut.

Replace the auxiliary shaft bushes in a similar manner (using Tool No. P.6031 with adaptor set P.6031-3).

These bushes must be assembled with the split upwards and the oil holes in line with the corresponding holes in the cylinder block. A line scribed on the remover and guide detail "-3a" can be used as a guide to facilitate this.

The auxiliary shaft is retained by a sintered iron thrust plate bolted to the cylinder block front face and located in a groove behind the auxiliary shaft flange.


The camshafts and auxiliary shaft are driven at half engine speed by a single row timing chain from a sprocket on the crankshaft. Chain tension is controlled by an adjustable tensioner located between the auxiliary shaft and the inlet camshaft.

The chain tensioner consists of an idler sprocket mounted on a lever pivoted in the cylinder head and a spring-loaded adjustable plunger, acting on the lever against chain tension, located in the right-hand side of the front cover.

When correctly adjusted there should be ½ in. (12.7 mm.) free movement in the chain between the two camshaft sprockets. This can be checked with the camshaft cover removed. To adjust the chain tension slacken the adjuster locknut and screw the adjuster in or out until the correct free movement has been obtained. Then tighten the locknut. Alternatively, the chain tension may be adjusted dynamically. To adjust, screw the adjuster in or out (as for static adjustment) to achieve the minimum noise level. A tight chain will whine and a slack chain will rattle.

Excessive chain movement may also result in the chain knocking against the damper pad, located down the left-hand side of the front cover. When replacing the retaining screws, ensure that they are thoroughly clean and apply a thin line of EM-4G-52 plastic sealer to the screw threads to prevent any possibility of oil leaks or loosening in service.

The inlet camshaft and the auxiliary shaft sprocket are not interchangeable. The exhaust camshaft sprocket, although similar, has the timing mark in a different position and must only be used on the exhaust camshaft if the correct timing is to be readily obtained. To identify it from the other sprockets it is marked "EX".

The camshaft sprockets, which are located by dowels, are retained by centre bolts and large flanged washers. The bolts are locked by spring washers and should be tightened to 25 to 30 lb. ft. (3.46 to 4.15 kg.m.). The auxiliary shaft sprocket is also located by a dowel but is retained by two bolts locked with a locking plate. An adaptor positioned between the sprocket and the auxiliary shaft gives correct timing chain alignment and is retained by the dowel.

Valve Timing

Maximum performance can only be obtained if the valve timing is correctly set. To facilitate this, timing marks are incorporated on the camshaft sprockets and the crankshaft pulley.

The timing is correct when the timing mark on the pulley is in line with the T.D.C. timing mark on the front cover and the timing marks on the inlet and exhaust camshaft sprockets are inwards and level with the camshaft cover mounting face.


The cast iron dynamically balanced crankshaft runs in five main bearings having steel-backed copper/lead liners with a lead/indium overlay.

The crankshaft main bearing journals may be ground 0.010 in. (0.25 mm.) or 0.020 in. (0.51 mm.), undersize. When grinding crankshafts undersize it is important to maintain the correct fillet radii at all times. The centre main bearing journal has a double radius of 0.070 in. (1.78 mm.) and 0.080 in. (2.03 mm.) and the rear main bearing has a double fillet radius, the inner radius of which must be maintained at 0.100 to 0.110 in. (2.54 to 2.79 mm.) when regrinding. The remaining main journal fillet radii are 0.110 to 0.096 in. (2.79 to 2.44 mm.). The crankpin journal fillet radii are 0.080 to 0.094 in. (2.03 to 2.39 mm.). Grind the bearing journals with the crankshaft and grinding wheel revolving in an anti-clockwise direction as viewed from the front of the shaft. Ensure that the fillet radii are smooth and free from visual chatter marks. The main bearing journal length between the thrust faces can be increased by up to 0.020 in. (0.51 mm.) providing an equal amount is machined from each face and the corresponding oversize thrust washers fitted. When grinding the rear main journal, ensure that the width of the machining wheel is 1.30 to 1.33 in. (33.02 to 33.78 mm.), that it has a fillet radii of 0.100 to 0.110 in. (2.54 to 2.79 mm.), and that the wheel is positioned 0.074 in. (1.879 mm.) from the rearface. The crankpin length must not exceed 0.010 in. (0.25 mm.) oversize.

Main bearing journal ovality should not exceed 0.0004 in. (0.010 mm.) T.I.R. and taper 0.0005 in. (0.013 mm.). The centre main bearing run-out relative to the front and rear journals should not exceed 0.002 in. (0.05 mm.) T.I.R. The thrust faces should be smooth and square to the bearing journal within 0.0005 in. (0.013 mm.) T.I.R. After grinding, the journals should be polished with a fine lapping paper and the crankshaft revolving clockwise to produce a good surface finish.

Crankshaft end-float is controlled between 0.003 in. (0.076 mm.) 0.008 in. (0.203 mm.) by half thrust washers located in the cylinder block at the centre main bearing. Standard size washers and 0.0025 in. (0.064 mm.), 0.005 in. (0.127 mm.), 0.0075 in. (0.191 mm.) and 0.010 in. (0.254 mm.) oversize washers are available.

A sprocket is located, by a woodruff key, on the front end of the crankshaft, adjacent to the front main bearing journal to drive the auxiliary shaft and camshafts. This sprocket can be removed by using a puller Tool No. P.6116, and replaced with Tool No. P.6032. When replacing the sprocket ensure that the key is pressed squarely into the keyway and that the sprocket is fitted with the boss to the rear.

A cast iron pulley for driving the water pump, fan and generator is also located by the same key as the sprocket and is retained by a centre bolt fitted with a spring and a flat washer.

Oil leaks around the crankshaft pulley boss are prevented by an oil seal pressed into the front cover. To further assist sealing, the crankshaft is fitted with an oil slinger which reduces the quantity of oil around the seal.

The clutch pilot spigot bearing is located in a bore machined in the centre of the crankshaft flange. The spigot bearing can be removed with adaptor Tool No. CP.7600-7 fitted to remover Tool No. CP.7600A or B and replaced with Tool No. P.7137.


The connecting rods are H section steel forgings with detachable big end caps. The caps are located by two hollow dowel pins pressed into the connecting rod and retained by two bolts fitted without lockwashers. The connecting rod can be identified by the number forged on the web. An oil squirt hole machined in the connecting rod feeds oil from the crankpin to the non-thrust side of the cylinder bore.

The steel-backed big end bearing liners have copper/lead bearing surfaces with a lead/indium overlay. The upper liner which locates in the connecting rod incorporates an oil hole, the lower liner being plain.

The connecting rod small end bearing is a steel-backed lead/bronze bush, which is not available in service, the connecting rod being serviced with the bush already fitted.

When dismantling an engine examine the piston markings to check the connecting rods for straightness. A heavy marking on the piston skirt above the pin on one side together with a correspondingly heavy marking below the pin on the other side indicates a bent connecting rod which should be replaced. The connecting rod small and big ends should be parallel and square to the longitudinal centre line within 0.0005 in. per inch (cm.) length.

When assembling a connecting rod to the piston ensure that it is fitted the correct way round. The marking "125E FRONT" is embossed on the web to facilitate this.

Connecting Rod Numbering

Connecting rods are numbered when installed in the engine during manufacture, to facilitate correct reassembly should they be dismantled.

The number is etched on the side of the big end so that a cap replaced with the numbers together must be in its original position. Never reassemble a bearing cap to another connecting rod.

It is advisable when removing connecting rods from an engine to check that the connecting rods have been numbered correctly. Where the connecting rods are unmarked they should be suitably stamped unless the connecting rods are being scrapped.


The aluminium alloy pistons are of the solid skirt type and have recesses machined in the crown to give clearance for the inclined valves. Each piston has three rings, two compression and one oil control ring, situated above the piston pin bore. The top compression rings are cargraph plated (red) to provide initial lubrication and the two lower rings are copper plated for identification purposes.

The lower compression ring is stepped externally on the bottom face and the upper ring is chrome plated and tapered. Both rings are marked "TOP" and must be fitted this way round. The ‘micro-land oil control rings may be fitted either way round. This type of oil control ring can be identified by the narrow ring lands.

The piston pin is offset in the piston 0.04 in. (1.016 mm.) towards the thrust side of the engine, to minimise piston slap and uneven loading of the skirt thrust face during the power stroke. Therefore, it is important that the piston is fitted the correct way round and to facilitate this the piston crown is marked "FRONT" and must face forwards when the piston is fitted to the engine.

The tubular steel piston pins are fully floating and are retained in position by circlips installed in grooves at each end of the piston pin bore.

On assembling the piston, pin and connecting rods the assemblies are weighed. The maximum variation of weight between the piston and connecting rod assemblies fitted in an engine is 6 grams. When changing pistons or connecting rods in service, it is good practice to check the weights of the piston, pin and connecting rod assemblies and, it necessary, select parts to ensure that the weight variation between the respective assemblies does not exceed 6 grams. Oversize pistons and rings are available in 0.015 in. (0.38 mm.) sizes.

Piston Selection

During engine manufacture the cylinder bores and pistons are graded. The piston grade number is stamped on the piston crown and, in production, each cylinder bore grade number is stamped on the push rod side of the cylinder block, adjacent to the top face, during engine assembly. These grade numbers ensure that when the piston is fitted there is a clearance of 0.0030 to 0.0036 in. (0.076 to 0.091 mm.) between the piston and the cylinder bore.

When selecting standard size pistons, measure each cylinder bore at a point 1 9/16 in. (39.69 mm.) from the cylinder block top face, across the axis of the crankshaft, and refer to the table in the Specification, Servicing and Repair Data section, to determine the grade of piston required. Select a piston with a grade number corresponding to that found for the cylinder bore.


The cast iron flywheel is located concentrically on the crankshaft flange and retained by six bolts fitted without lockwashers.

The flywheel ring gear is shrunk onto the flywheel and locates in a retention groove. The ring gear can be removed by cutting between two adjacent teeth with a hack saw and splitting the gear with a chisel. In no circumstances should pressure be applied in an attempt to dismantle the ring gear for repositioning on the flywheel.

When replacing the ring gear it must be heated evenly to a temperature not exceeding 6000F (3160C) or the ring gear wear-resistant properties will be destroyed. If the ring gear is heated by a naked flame place the ring gear on a bed of fire bricks and then play the flame in a circular motion onto the bricks about ¼ to ½ in. (6.35 to 12.7 mm.) from the inside of the gear until it reaches the required temperature. The correct temperature can be detected by using a special type of temperature sensitive crayon, or alternatively by polishing a section of the ring gear and heating until it turns blue. Fit the ring gear with the chamfers on the leading faces of the gear teeth relative to the direction of rotation. Allow the ring gear to cool naturally in air, DO NOT QUENCH.

The flywheel and ring gear assembly are dynamically balanced to close limits. The clutch is located on the flywheel by three dowels and is retained by six bolts with spring washers.


The oil pump and filter assembly is bolted to the right-hand side of the cylinder block and can be removed with the engine in place. The oil pump, which is driven by a skew gear on the engine auxiliary shaft, is of the eccentric bi-rotor type and has the full flow element type filter bolted to a mounting flange integral with the oil pump body.

Oil enters the pump through a tube pressed into the cylinder block sump face. A spring-loaded filter gauze located on the end of this tube provides primary filtration. The gauze can be removed by bending back the retaining lug and sliding the gauze out sideways. A pressure relief valve oil return pipe is also pressed into the cylinder block sump face parallel to the inlet tube.


The full flow type oil filter is bolted to a mounting flange integral with the oil pump body.

To remove the filter unscrew the securing bolt and withdraw the filter body and element. Remove the sealing ring from the groove in the filter body mounting flange, then locate the new ring (supplied with the replacement element) in the groove at four diametrically opposite points. Do not fit the ring at one point and then work it round the groove as the rubber may stretch, thus leaving a surplus which may cause an oil leak. Thoroughly clean the filter body and insert the new element. Locate a new washer (again supplied with the replacement element) on the securing bolt and refit the filter assembly to the oil pump body.


The ventilation system is of the closed type relying on blow-by for displacement of the gases.

Engine fumes leave the crankcase through a ventilation tube located vertically on top of the fuel lift pump mounting pad. This tube connects the crankcase with a chamber integral with the cylinder head. A drilling in the top of this chamber provides a connection with the inside of the camshaft cover. The fumes are discharged directly into the carburettor air intake cover by a tube incorporating a flame trap.


The engine and gearbox assembly has a three-point mounting on bonded rubber insulators. The two front insulators consist of a rubber block bonded between the engine mounting bracket and a mounting plate, incorporating a weld nut on the inner face. A single bolt is thus used to secure the insulator to the mounting bracket on the front crossmember.

The single rear insulator is secured to a pad on the gearbox extension housing and consists of rubber blocks bonded between steel channel section plates. A retainer is located beneath and in front of the insulator when fitted to the crossmember, which is located by a spacer at each end and is bolted to the car underbody.

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