• Tapatalk and Mobile iOS/ Android APPs no longer supported on aussiefrogs.com. Please delete on your device. Use the web interface instead.

Magazine Article. GS Flat Four engine rebuilld


Real cars have hydraulics
Source: "On The Road" magazine. Part 77
Article 1 of 2. Page 1

If your car has covered a high mileage and is using an excessive amount of petrol and oil, lacks power and is becoming increasingly noisy, it is probably due for a major engine overhaul. If the job is carried out carefully and diligently, it will certainly result in an increase in power, a reduction in fuel and oil consumption and a quieter-running engine which will be good for many more mites of trouble-free driving.
the cylinder head retaining nuts also retain the cylinder barrels in position on the studs.

The combustion clambers are hemispherical in shape which greatly aids efficient combustion and each cylinder head has its own overhead camshaft, driven by a toothed rubber belt from a duplex drive pulley on the front of the crankshaft, which operates the inlet and exhaust valves via rockers of conventional design.

The fuel pump is of the mechanical type and is operated by the right-hand camshaft (viewed from the driver's seat).

The ignition distributor is mounted on the rear left-hand side of the engine and is driven by a skew gear on the left- hand camshaft. The oil pump is externally mounted on the front of the engine and is driven at half engine speed by the drive-belt of the left-hand camshaft. An eccentric on the oil pump shaft drives the pump which pressurizes the hydraulic which, in turn, operates the braking and system suspension systems.

The power unit is air-cooled and air is forced through sheet steel ducting, which is bolted to the engine casing, by a cooling fan mounted directly on the front of the crankshaft. Engine cooling is also aided by an oil cooler which consists of an alloy matrix mounted above the right-hand cylinder bank in the air flow generated by the fan. A thermostatically controlled by-pass valve aids the rapid warming up of the oil by closing the inlet to the cooler matrix until the engine has had time to attain its normal operating temperature.

When to overhaul the engine Before diagnosing engine faults which indicate a major overhaul is necessary, it should be noted that the Citroen GS engine is characteristically smokey, especially on startup and tends to emit fumes from the exhaust system even when in good condition. This is due to the layout of the This is the first of two articles covering the work involved in removing, overhauling and replacing the air-cooled, flat- four design of engine that is fitted to certain Citroen GS and Ami Super models.

All the early models of the GS were fitted with a 1,015 cc engine, but consequently the capacity was increased for some models by altering the bore and the stroke of the power unit to 1,220 cc during 1972. The 1,015 cc engine was covered as an option in the Ami range until 1976 and was, until then, also available in the GS range in place of the larger engine. As the 1,015 cc engine is a relatively small engine, it usually is driven hard and therefore benefits from more frequent overhauls than the 1,220 engine fitted to later models, the latter being less highly-stressed.

Engine design The Citroen GS has a light-alloy crankcase which is manufactured in two halves, split in the vertical plane and joined on assembly by a number of bolts. The cylinders are individually cast, with finned barrels and fit on to long studs screwed into either side of the crankcase assembly.

The cylinder barrels are made of cast-iron while the cylinder heads, one for each pair of cylinders, are made of aluminium alloy. The cylinder heads are mounted on the same studs that are used to locate the cylinder barrels and



Real cars have hydraulics
Source: "On The Road" magazine. Part 77
Article 1 of 2. Page 2

Cylinders which allows oil to collect in the rocker boxes from whenceit is drawn into the combustion chambers and then emitted through the exhaust. Only when the amount of smoke produced by the engine becomes excessive can this be taken as an indication of severe wear, necessitating a comprehensive overhaul of the power unit. One sign to watch for particularly, however, is seepage of oil from the crankcase. When the bottom-end bearings am worm the excessive movement of the crankshaft can damage the crankshaft oil seals, causing considerable oil leakage.

When adequate performance can no longer be restored to the car by making routine adjustments to the carburation (see pages 170 to 175 and 187 to 191) ignition system (pages 97 to 102) and the valve clearances (pages 145 to 153) and if the lack of performance is accompanied by unusual noises from the engine it is time for a major overhaul.

The decision to undertake a DIY overhaul should be taken only after careful consideration. Although both time and money can be saved, the job requires care, some experience of similar work, a degree of mechanical skill and a fair amount of time. The job is best planned to cover two weekends so that you will have adequate time to remove and strip the engine, buy any new parts which are necessary, then re-build the unit and re-fit it to the car.

To carry out the work you will need a good basic tool kit plus a torque wrench, two stout pairs of axle stands and an engine hoist. The type of hoist which is hydraulically operated and mounted on wheels is the best one to have and these can be hired at quite reasonable rates from most tool hire shops. Whichever type of hoist you use, make quite certain that it can safely cope with the weight of the engine.

In addition, cars fitted with automatic transmission require a special tool, part number 3186-T, to retain the torque converter. This is available from your local dealer.

DIY work possible on GS engines

Because of the limited access to the engine while it is in the car, the unit must be removed before the work can be carried out as it is not even possible to remove the cylinder heads while the engine is in position in the car. With the engine out of the car, all oil seals are renewable by the DIY mechanic and it is also possible to renew the cylinders and pistons. The cylinder heads can be overhauled without any problems but if the big-end bearings are at fault the only solution is to buy a factory re-conditioned crankshaft with con-rods and big-end bearings already fitted.

Removing the engine-preliminary steps

Before starting work, make sure that you have all the necessary special tools and equipment. The engine is removed from the front of the car after removing the front bodywork panel and disconnecting the power unit from the transmission.

If desired, it is possible to remove the engine and the transmission as a single unit without disconnecting them and details of how to do this are given below.

The first job is to prepare the car for its change in weight when the engine is lifted away. Slacken the front road wheel nuts and then raise the car and support it on axle stands placed underneath the car behind the front wheel arches.

Slacken the pressure regulator bleed screw (fig. 2), move the height control lever to the high position and then allow the rear suspension to settle fully (see pages 1866 to 1872).

Using a suitable jack, raise the rear end of the car and support it on a second pair of axle stands. Check that there is no pressure remaining in the front suspension system by operating the hydraulic front suspension cylinders to see if they move up and down freely. If they do not, release the remaining pressure by operating the manual control lever of each height corrector assembly. Remove both of the front road wheels from the car and the work of removing the engine can begin. From this stage patience will be vital.

Removing the front panel
Start by disconnecting both of the battery leads as a safety precaution. Mark the relative positions of the hinges on the bonnet by using a wax pencil or paint of a suitable colour so that the bonnet can be positioned correctly on re-assembly.

With an assistant steadying the bonnet, undo the retaining nuts and lift away the panel.

The next stage is to remove the front grille which is held



Real cars have hydraulics
Source: "On The Road" magazine. Part 77
Article 1 of 2. Page 3

in place by two bolts. Using a suitable spanner slacken the two bolts and pull the grille forwards to disengage the slotted mounting brackets (fig 3), .then lift it upwards to disengage the lower mounting pegs from their grommets and, finally lift the grille away from the car completely.

Detach the electrical connections from the headlights and the sidelights by pulling them off carefully and, to avoid confusion on re-assembly, label each connection clearly. The sidelights are held in place by spring clips which can be prised free with a screwdriver (fig 4); the light units themselves can then be lifted away.

To remove the head- lamps, unclip each of the three headlamp adjusters from their plastic housings on the back of the headlamp assemblies (fig 5) and then lift the headlamps out of their mountings in the front panel and store them in a safe place where they will not be damaged.

Pull off the electrical collections to the horn which are of the spade terminal type then unbolt the horn bracket and lift it away from its mounting (fig. 7). Unclip the wiring harness from the cowling and then disconnect the alternator wiring, labelling each connection clearly as you do so. Push the bonnet locking lever to the right and then detach the control cable from the bonnet lock (fig. 8) then unclip the cable from the wings and tie it clear of the engine bay.

To gain access to the engine and leave it free to be removed, the ducting between the front grille and the engine cooling fan has to be taken off the car. The ducting is held in place by three bolts on either side and eight bolts along the bottom. Using a spanner of the correct size, undo and remove all 14 of the retaining bolts and lift the cowling out of the engine bay while feeding wires through (fig. 10).

The lower front panel, which also incorporates the central portion of the front bumper, is attached to the car body by a slumber of screws. Start by unbolting the two end sections of the bumper and lifting them away from their respective mountings (fig. 11 ) Working from the top of the panel, remove the two screws, one on each. side, which mount the front panel to the inner wings.

Then working from underneath the car, remove the two screws on each side which further secure the front panel to the inner wings.

The height-control unit guard plate must be removed next and this is done by unscrewing and taking out the three screws which hold it in place and lifting the guard away from its mounting on the right-hand inner wing panel.

Still working from underneath the car. remove the six screws which attach the panel to the underbody then lift the lift the panel away from the car lay it aside in a safe place (fig. 12) so that it does not become an obstacle.

Disconnecting the electrics

You may find it helpful when it comes to re-assembly to label each electrical lead as it is removed by wrapping a piece of clearly marked masking tape around it. Pull each plug lead off and detach the high-tension (HT) lead from the coil by pulling it out of its mounting. Using a suitable screwdriver, prise open the clips which secure the distributor cap to the distributor body and then remove the cap (fig. 14). Using a spanner of the correct sized undo the nut which holds the power feed cable for the starter motor to its terminal on the motor housing (fig. 15), remove the nut and washer, then lift the cable off the terminal and, after suitably labelling the cable, tuck it out of the way.



Real cars have hydraulics
Source: "On The Road" magazine. Part 77
Article 1 of 2. Page 4

These leads have spade or bullet type connectors and
should be removed at this stage the low-tension (LT) connections from the main harness to the ignition coil and from the ignition coil to the distributor, the oil pressure sender connection and, finally, the lead to the oil thermal switch (fig. 16) Having done this, tuck the wires away.

Disconnecting the ancillary components.

If you have not already done so, remove the spare wheel and then unbolt and remove the spare wheel carrier bracket (fig. 17), having first undone the hydraulic pipe bracket.

The heater control box which regulates the flow of air to the Interior of the car is located on the rear right-hand side of the engine bay (when viewed from the driver's seat) and is held in place by three self-tapping screws and washers. Disconnect the control cable from the solderless nipple connector and lift It clear of the work area.

Now, using an 8 mm open-ended spanner, undo and remove the three bolts that mount the heater control box and lift the box away, detaching the air feed hoses as you do so by pulling them off . Stlll working at the rear of the engine, slacken the clip which secures the fuel pipe to the inlet of the fuel pump and pull the pipe away. Plug the end of the pipe to prevent any petrol from leaking out of it and to avoid the possibility of dirt entering the fuel system.

The next stage is to disconnect the choke and accelerator cables from the carburettor The choke Inner cable is attached to an operating lever by a screw-operated clamp and a similar clamp holds the outer cable to a bracket on the main body of the carburettor Slacken both clamping bolts then lift the cable away and tuck it out of the way on the side of the engine bay (fig. 18).

Detach the throttle cable by after removing the spring clip from the pivot pin of the throttle operating lever and then lifting the cable away The cable can be completely removed from the engine bay after unclipping the other end of the cable from the accelerator pedal Take care, however, not to lose the return spring.

Disconnecting the hydraulic system

Detach the fluid Inlet pipe from the hydraulic fluid reservoir, having first slackened the screw of the retaining clip which secures it to the inner wheel arch housing Next, from the pressure regulator remove the pipe which is retained by two clips, one on the fuel pump flange and one on the pressure regulator itself (fig. 19) Blank off the ends of the pipes with a suitable plug after the pipes have been removed in order to prevent fluid from leaking out.

The following two paragraphs apply only to cars fitted with semi-automatic transmission If you are working on a car fitted with a manual gearbox ignore them.

On cars with semi-automatic transmission, the pressure regulator must be removed completely. Disconnect the two leads which supply power to the electro-magnetic valve then remove the steel pipe which feeds into the two-way union having first removed the bolt that attaches the pipe to the cross-member.

Undo the two bolts which mount the pressure regulator unit to the body of the car then lift the unit out of the engine bay. Do not remove the electro-valve or disconnect it from the torque converter control system. Pull away the flexible duct which directs air to the torque converter oil cooler.

Remove the six screws which retain the upper section



  • gs_engine_rebuild_page_4_picces.jpg
    80.6 KB · Views: 4,377


Real cars have hydraulics
Source: "On The Road" magazine. Part 77
Article 1 of 2. Page 5

the left-hand cooling duct (when viewed from the driver's seat), detach the two rubber sealing rings then maneuver the duct clear of the engine bay.

Remove the induction pipe as well and plug the openings in the cylinder heads and the carburettor heater box left by the removal of the pipe. Using a suitable spanner, undo and remove the starter motor mounting bolts then withdraw the starter motor from the front of the engine bay.

Next, by working through the starter motor housing aperture, the three bolts which retain the torque converter drive plate (can be withdrawn. A special tool, part number 3186-1, available from Citroen dealers, is needed to hold the torque converter in position while the engine is being lifted out of the car.

Detach the heating duct covers located beneath the exhaust pipes on either side of the engine by unbolting them and lifting them away. Working underneath the car, loosen the retaining bolts which hold the central exhaust pipe to the gearbox then slacken the clamps which hold each of the two exhaust downpipes to their respective manifolds and disengage them.

Suitable lifting tackle should now be attached to the engine, taking care that it is not positioned in such a way that it might damage any of the components when the weight of the engine is taken by the sling. A purpose-built sling for these engines is available under part numbers 251 I-T and if you can obtain one it will make the job much easier.

Now is a good time to check all round the engine bay, collect any loose parts and move any disconnected components that may hamper the easy removal of the power unit. You should then check that none of the disconnected pipes are leaking and make absolutely sure at this stage that only the engine mounts and the transmission are preventing the engine from being withdrawn from its compartment.

Removing the engine

Securely attach the sling to the engine then take the weight of the engine on the hoist, making absolutely certain that it is safe and well supported.

Working from underneath the car, undo and remove the two front engine mounting retaining bolts. Raise the engine on the hoist until it comes into contact with the upper suspension cross-member.

Insert a support under the transaxle unit-a jack or a piece of wood will be adequate-to prevent the unit from dropping down when it is detached from the engine, making sure that the support does not trap the clutch cable.

Using a suitable spanner, undo and then remove the four bolts which attach the transmission unit to the power unit casing. Have an assistant raise the engine on the hoist while you pull it forward to disengage the gearbox input shaft from its matching splines in the clutch centre plate. When the engine is completely free of the transmission unit, withdraw it from the car taking care that the distributor does not foul on the left-hand inner wing panel (fig. 20).

While the engine is suspended, remove the sump plug and drain the engine oil into a suitable container. If you are not using a trolley hoist the engine can be manhandled by two people from a fixed hoist and lowered to the ground with the sling still attached. Move the unit to a suitable working area having first cleaned it thoroughly with a proprietary degreasing such as Gunk or Jizer; both are available from accessory shops and motor factors.

Hose off the degreasing carefully and then dry the unit thoroughly.



  • gs_engine_rebuild_page5_piccies1.jpg
    80.1 KB · Views: 3,269


Real cars have hydraulics
Source: "On The Road" magazine. Part 77
Article 1 of 2. Page 6

Removing the engine and gearbox as a single unit

If you have decided to carry out work on the transmission at the same time as overhauling the engine, the two units can be removed as a combined unit by carefully following the instructions given below.

Carry out the preparatory work already described up to and including the removal of the heater control box and the disconnection of the choke and accelerator cables from the carburettor. In addition, remove the leads from the reversing light switch and from the starter inhibitor switch if the car is fitted with semi-automatic transmission.

Disconnect the inner ends of the drive-shafts as described on pages 1754 to 1760. Slacken the clutch cable adjustment right off then remove the cable from the clutch operating arm. Unscrew and remove the handbrake adjuster nuts and lock nuts from the calipers. Locate the gear change linkage on the rear top of the transmission casing then remove the linkage retaining clip from the pivot pin. Slide the pivot pin out of its housing then disengage the gearchange lever from the linkage mechanism completely. Remove the spring clip which holds the speedometer cable to its drive housing on the transmission casing then pull away the cable.

Working from underneath the vehicle, slacken the three clamps which hold the Y-shaped exhaust collector box in position then carefully remove the collector box. On cars fitted with semi-automatic transmission, the flexible pipes to the torque converter oil cooler must be disconnected and, on early models, the fluid bleed screw must also be removed.

Disconnect the intake pipe from the high-pressure pump by slackening the retaining clip and pulling it away and then remove the pipe retaining bracket from the right-hand wheel arch. This is held by a captive nut and a bolt.

On all models, the main hydraulic supply pipe which carries the fluid to the two-way union must be disconnected and this can be done by unscrewing the pipe and lifting it away. Undo and remove the fluid supply pipe from the left-hand front brake caliper. Similarly, disconnect the return pipe from the pressure regulator assembly but leave the regulator unit itself in position.

Working from underneath the car, disconnect the front engine mounting as described above, having just taken the weight of the engine/gearbox unit on the hoist. Also, remove the gearbox-to-body mounting by undoing the retaining bolt and lifting the unit away.

Working from inside the car, remove the gear lever retaining collar by unscrewing it, then lift the rubber dust cover and drive out the retaining pin using a small diameter drift or a suitable pin punch. The lever can now be lifted away from the gearbox. There is no need to detach the gearbox from the engine at this stage as the two units can be removed from the vehicle together.

Finally, with the aid of an assistant to guide the unit, remove the engine and the gearbox from the car. Make sure that the hoist can cope with the weight of the engine and gearbox together, especially if the car is fitted with the heavier semi-automatic gearbox.

The second part of this article describes in detail how to strip and re-assemble the power unit and includes all the relevant data on permissible wear tolerances of the components together with full instructions to ensure that your overhaul is completely successful and accomplished as quickly as possible and with the minimum financial outlay.



  • gs_rebiuld_page6_piccies.jpg
    104.8 KB · Views: 3,166


Real cars have hydraulics
Source: "On The Road" magazine. Part 78
Article 2 of 2. Page 1

Overhauling a flat-4 engine Part 2

Although it is unconventional in design when compared to most modern power units, dismantling and overhauling a Citroen flat-four engine is a job well within the scope of the DIY mechanic. Provided the job is carried out slowly and carefully, you will not only save considerable sums in garage bills, you will also signifigantly improve the overall performance, power and economy of your engine.

The first part of this article deals with the removal of the unit from the car; this part deals with the engine overhaul itself. Make sure that you have plenty of time to finish the job without having to rush. Note, also, that the correct tools are essential if the work is to be carried out property and in reasonable time. In addition to a comprehensive set of metric spanners (and preferably sockets as well) you will need a torque wrench and a special Citroen tool for removing the valves, part number 1652-T. You will also need paraffin (kerosene) for cleaning purposes, a tube of jointing compound and adhesive such as Loctite. Remember that as well as any new parts that will be required, you will have to replace all the gaskets on re-assembly and all the oil seals.

Dismantling the engine-preliminary steps

If it has not already been removed, the first step is to take off the starter motor.
Unlike the majority of starter motors, the two mounting bolts on this unit are fitted it right argles to the longitudinal axis of the starter motor and are, therefore undone by working from the side of the unit which is furthest away from the engine. There is no need to remove the air ducting at this stage of the overhaul. Undo the two bolts which hold the starter motor in place and then lift the motor out of its housing (fig. 2).

The next component to be removed is the alternator.
In order to obtain enough clearance to lift the alternator out of the engine bay, first slacken the four bolts which hold the fan shroud in place and pull the shroud forward as far as possible.

Slacken the pivot, undo and remove the adjuster arm bolt then push the alternator in towards the engine to slacken the drive-belt tension and slip the drive-belt off the alternator pulley. Undo and remove the pivot bolt then lift the alternator away from its mounting (fig. 3).

The distributor cap will have already been taken off as described on page 2134. Using paint and a small brush, mark both the distributor body and the distributor mounting flange so that the distributor can be set in approximately the correct position on re-assembly. Using a suitable spanner, slacken the retaining nuts and lift away the distributor (fig. 4). Remove all four spark plugs.

There are two makes of carburettor fitted to the GS engine, either Solex or Weber, but the removal procedure is the same in both cases. Undo the retaining clip screw and pull away the fuel pipe having first removed the push-fit vacuum-operated ignition advance/retard pipe then plug the end of the pipe with a 7 mm diameter bolt.

Undo the eight nuts which hold the inlet manifold flanges to the cylinder heads, then lift the manifold away with the carburettor still attached (fig. 5) and remove the



  • rebuild_gs_motor_part2_page1_piccies.jpg
    72.7 KB · Views: 3,289


Real cars have hydraulics
Source: "On The Road" magazine. Part 78
Article 2 of 2. Page 2

old gaskets from the manifold mounting flanges. These can be discarded. The mechanical fuel pump is mounted on the right-hand side of the engine and driven by an eccentric on the right- hand camshaft. Remove the two mounting nuts and spring washers then pull the pump off its mounting studs and lift it away. The fuel pump is insulated from the heat of the engine by a spacer which should also be removed.

Removing the inlet and exhaust manifold pipes
The inlet and exhaust manifold pipes are mounted on studs screwed into flanges on the cylinder heads. To remove the pipes, undo and remove the nuts along with their washers and then pull the manifold pipes away from the cylinder heads and store the complete assembly.

Moving to the front of the engine, remove the starting handle dog by undoing it with a suitable spanner. It is generally quite tight and it may be necessary to remove the flywheel (see below) and insert a bar between two mounting bolts to prevent the crankshaft from turning while the starter dog is being slackened. the starter dog secures the cooling fan to the front of the crankshaft and, after it has been removed, the fan can be taken off its mounting (fig. 6) and the alternator drive-belt removed.

Removing the clutch and flywheel

Slacken the cover bolts in small progressive steps until the pressure of the clutch operating springs has been completely released then lift away the bolts, the clutch cover plate arid the centre plate located beneath it.

Some assistance will be required when removing the flywheel as the retaining bolts are tightly torqued on manufacture and may prove difficult to remove.
Have an assistant hold the flywheel with a screwdriver blade engaged with the teeth of the starter ring gear while he steadies the engine throughout the operation of removing the flywheel. Using a socket of the correct size and a stout tommy bar, undo and remove the six flywheel retaining bolts then lift the flywheel away from its mounting range on the crankshaft (fig. 7).

Removing the camshaft drive-belts
The two belts which drive the camshafts are driven from a duplex pulley mounted on the front of the crankshaft which comes apart in two sections once the starter dog and the engine cooling fan have been removed. Slacken the nut locking the tensioned jockey wheel in position and move the wheel downwards by hand to relieve the tension on the camshaft belts. Label each belt, then slide them off the



  • gs_rebuild_parts_page2_piccies1.jpg
    61.8 KB · Views: 3,380
  • gs_rebuild_part2_page2_picces2.jpg
    90.6 KB · Views: 2,923


Real cars have hydraulics
Source: "On The Road" magazine. Part 78
Article 2 of 2. Page 3

camshaft pinion along with the front half of the crankshaft drive pinion. Remove the rear drive pinion from the crankshaft together with its protection plate then carefully remove the Woodruff key from the crankshaft, tapping it gently with a hammer and screwdriver if it is a tight fit.
Undo the nuts which hold the drive-belt tensioned jockey wheels to their shaft and remove them (fig. 9).

The next components to be removed are the camshaft pinions themselves. Before the retaining nuts can be unscrewed, the pinion must be locked in position; do this by inserting a suitable bar through one of the holes in the front of the pinion and wedging it against a suitably robust section of the cylinder head casting (fig. 10). Undo and remove the retaining nuts and then lift the pinion off the camshaft. Remove the other pinion in the same way.

Removing the external oil feed pipes

The valve gear in each cylinder head is supplied with oil by externally mounted pipes running from the oil switch mounting. To remove the pipes, undo the union nuts with a suitable spanner then lift them away (fig. 1 1), wiping up any oil that spills on to the engine as you do so. Next remove the oil pressure switch and the oil thermal switch from the engine. Both components are screwed into the main crank- case castings. Disconnect the oil feed pipes from the oil cooler by slackening the retaining clips and pulling the pipes away from the unions, then unbolt and remove the oil cooler matrix. Finally unscrew and remove the oil filter canister, which is of the disposable type.

Removing the cylinder heads

Start by removing the oil cooler matrix which is mounted on the crankcase above the cylinder heads and is retained in place by four bolts.
Slacken the eight cylinder head nuts working in a diagonal sequence, loosening each nut a small amount at a time to prevent distortion of the casting. When all the nuts have been removed, slide the cylinder head off its eight studs and lift it away (fig. 13). You may need to break the joint by gently tapping the cylinder head in question on a substantial part of the casting with a soft-faced hammer.

Repeat the removal procedure for the other cylinder head.
There are oil return tubes fitted between the cylinder heads and the crankcase which can now be pulled away.

Removing the cylinder barrels and the pistons

When both of the cylinder heads have been removed, mark each of the cylinder barrels clearly if you are intending to re-use them so that they can be replaced in their original positions. Slide the cylinder barrels off the studs, supporting the pistons as they come out of the barrels (fig. 14).

If you are simply planning to fit new piston rings and overhaul the cylinder heads, no further dismantling is necesarry. If, however, there is excessive cylinder wear or bearing rattle, the pistons should be removed and replaced with a new set along with new cylinder barrels.
To remove each piston, use circuit pliers to prise out the two wire circling which retain the gudgeon pin (fig. 15).

When the circling have been removed, push out the gudgeon pins using a suitable mandrel. You may find that the pins are too stiff to remove by hand pressure alone. If this is the case, do not resort to hammering them out as it is quite likely that you will damage the con-rods. Tight gudgeon pins can be removed by the use of a gudgeon pin extractor which is a relatively inexpensive tool available from most good accessory shops or tool suppliers. Keep each gudgeon pin with the piston from which it is removed.

Parting the crankcase halves

Undo the five bolts which mount the oil pump shaft housing and then gently lever the entire assembly out of the crankcase
using a suitable screwdriver (fig. 16).

The crankcase of the Citroen GS is manufactured in two halves which are split through the vertical axis and clamped together by a number of nuts and bolts. In order to remove the crankshaft and con-rod assembly, the two halves of the crankcase have to be separated.

Position the crankcase assembly so that the left-hand crankcase half (when viewed from the driver's seat with the engine in the car) is facing downwards and support the unit firmly. Undo the nuts and bolts around the unit, then lift the right-hand crankcase half away from the remainder of the unit. You may find the two halves difficult to separate and, if this is the case, tap the edges of the joint firmly with a soft-faced hammer to break the seal.

Dismantling the crankcase components

Lift the crankshaft and con-rod assembly out of the left- hand crankcase half and lay it aside for inspection (fig. 18).
Remove all of the main bearing shells by gently easing tiler out of their housing with the careful use of a screwdriver if necessary. On re-assembly, fit new main bearing shells.
The oil strainer is retained by two bolts and the pipe is a shrink fit in the crankshaft casing. To remove the strainer, first undo and remove the two retaining bolts and then try and pull the pipe out of its locating hole in the casting. If the pipe will not come free, gently apply heat by pouring hot



  • rebuild_gs_part2_page3_piccies1.jpg
    64.3 KB · Views: 3,210


Real cars have hydraulics
Source: "On The Road" magazine. Part 78
Article 2 of 2. Page 4

water over the area where the pipe joins the casting; this will expand the metal of the casting sufficiently to allow the pipe to be withdrawn (fig. 19).

Overhauling the cylinder heads

The first stage in overhauling the cylinder heads is the removal of the rocker shafts. Start by slackening the lock nut on each rocker, then back off the rocker. adjuster screw until there is no pressure being exerted on the camshaft by any of the rockers. Next, remove the blanking plugs at each end of the rocker shaft together with their spacers, copper sealing washers and "O" ring seals. Make a careful note of the order in which these components are fitted to the shaft to avoid confusion when you come to re-fit them. Use a suitable stud extractor to remove the rocker cover mounting stud from the cylinder head casting and then, using a 3 mm Allen key, undo and remove the shaft retaining grubscrew which is located in the central camshaft bearing housing.

Now withdraw the rocker shaft from the cylinder head, making sure that you collect all of the rockers and springs.

There are cups fitted under the adjuster screws so be sure that you collect all of these. Take care not to mix up any of the components; mark the shafts "left" and "right" and keep them, along with all their respective components, in separate boxes. Remember, also, to mark clearly which shafts are inlet and which shafts are exhaust.

To remove the camshafts, undo and remove the two bearing retaining bolts then drive the camshaft complete with the rear bearing assembly out of the cylinder head, using a soft-faced hammer. The rear camshaft bearing is integral with the camshaft and, therefore, cannot be removed. There is an oil seal at the front of the cylinder head which can be prised out carefully with a

Due to the angle of the valves within the cylinder head, it is not possible to remove the valves using a conventional valve spring compressor. To compress the springs you will need a piece of steel rod, 16 mm (1l/16in) in diameter, which is the same length as the rocker shaft or, alternatively, an old rocker shaft and a Citroen spring compressor lever, part number 1652-1. Fit the dummy shaft in place and place a block of wood under the valve to be removed to prevent the valve opening when the spring is compressed.
Insert the lever and compress the valve spring fully.

Remove the valve retaining split collets, release the spring and withdraw it along with the retaining cup and thrust washer. Remove the rubber oil seal from the valve stem then lift the valve out of the cylinder head. Repeat the process for the seven remaining valves, pushing each through a marked piece of cardboard to ensure they can be re-assembled in the correct order.

The process of decarbonizing cylinder heads and grinding in valves is covered in detail on pages 490 to 495. One point to take into consideration is that the cylinder heads on these engines are made of Aluminium Alloy and extreme care must be taken when cleaning them not to score the surfaces.
While the engine is dismantled, it is a good idea to renew the valve springs as they are not particularly expensive.

Inspecting the crankshaft

The crankshaft assembly on the Citroen GS engine cannot be serviced by a DIY mechanic so if it is no longer in usable condition, it will have to be exchanged for a factory- assembled unit.

First examine the main bearing journals for signs of scoring and general wear. The condition of the surfaces of the main bearing shells will give a good indication of the



  • rebuilding_gs_motor_part2_page4_piccies.jpg
    102.2 KB · Views: 6,070


Real cars have hydraulics
Source: "On The Road" magazine. Part 78
Article 2 of 2. Page 5

state of the crank. Check the big-end bearing wear by grasping each con-rod firmly and attempting to move it up and down on the big-end journal. If any play is detected, the crankshaft must be exchanged for a new one. To check the condition of the small-end bearings, insert the relevant gudgeon pin into the eye of the con-rod and check for any free play. These should be replaced by a specialist.

The one servicing job that can be done on the crankshaft assembly by the DIY mechanic is the replacement of the rear crankshaft bearing if it is excessively worn. Remove the crankshaft oil seal, discard it and then withdraw the damaged bearing by pulling it off the end of the shaft. Soak the new bush in engine oil for one hour so that it becomes thoroughly impregnated. Push the new bush on to the crankshaft leaving a clearance of 5 mm (3/16in) for the new oil seal at the end of the shaft. Lightly grease the new oil seal and push it into position with the flat face outwards.

Inspecting the pistons and cylinder barrels
It is not possible to have the cylinders of the GS engine re-bored so, if one or more of the cylinders or pistons is faulty, the barrels and pistons will have to be replaced as a complete new set purchased from your Citroen dealer.

Carefully examine the pistons for signs of excessive wear or cracks, particularly on the thrust faces. Examine the wails of the bores for signs of wear ridges or scoring, then feel around the top of the cylinders for any "steps" caused by excessive wear. If the barrels and pistons are not badly worn they can be used again, but it is a good idea to fit new piston rings as this will generally improve the compression of the engine and reduce the oil consumption. Full details of how to clean out the piston ring grooves and fit piston rings are given on pages 1593 to 1598.

Reassembling the engine
When re-building an engine meticulous cleanliness is essential if the unit is to give long and reliable service when completed. All components that are being re-used should be cleaned thoroughly in petrol or paraffin (kerosene) then blown through with compressed air. Particular attention must be given to oil galleries. Once the various components have been examined and replaced where necessary, re-assembly can begin. Keep a pressure oil can filled with the correct grade of engine oil close at hand and lubricate all moving components generously before re-fitting them.

Starting with the left-hand crankcase half, fit the oil strainer pipe into its hole in the casting, having previously applied a bonding adhesive such as Loctite Bearing Fit, which is available from most motor accessory shops, to both the outside of the pipe and the hole. Re-fit the two strainer retaining nuts and tighten them to l .4 kg/m (l0lb/ft) with the torque wrench.
Before re-fitting the crankshaft, check the big-end bearing end-float between the big-end bearing eyes of each con-rod and each of the crankshaft webs. Measure the clearance with feeler gauges (fig. 20); it should be between 0.08 mm (0.003in) and 0.13 mm (0.004in). If the clearance on any big-end exceeds these figures, the crankshaft will have to be replaced by a new assembly.

Clean the bearing housings thoroughly in both halves of the crankcase there fit the replacement main bearing shells in position, making sure that they are correctly seated. Oil the shells and the crankshaft journals liberally then carefully place the crankshaft assembly in the left-hand crankcase.

Joining the crankcase halves
Before joining the two halves of the crankcase, check the joint edges to make sure that they are clean and free from any scores or burrs that could affect the oil sealing properties of the assembled unit. Coat the mating faces of both crankcase halves with jointing compound, allow a few minutes for the compound to partially harden, then fit the right-hand crankcase casting to the left-hand casting.

Fit the clamping bolts and tighten the shorter ones to 1.5 kg/m (111b/ft) and the longer bolts to 4 kg/m (281b/ft). Now fit new front and rear crankshaft oil seals having oiled them lightly before drifting them carefully into place. Always fit new seals as it is false economy to re-fit old ones even if they appear to be capable of further service. Rotate the crank- shaft by hand to check that it moves freely in the bearings, taking care not to damage the con-rods as you do this.

Re-assembling and re-fitting the oil pump
Liberally oil the inner and outer pinions of the pump and fit them together into the main housing. Then fit the oil pump cover plate to the main housing so that the cavities on the plate face inwards and the small hole is in line with the large cavity in the upper section of the main housing.

Carefully lay the pump operating rod in its correct position and fit a temporary guide stud to one of the lower holes in the oil pump housing.
Take the oil pump shaft and fit a new "O" ring seal to it, oil the shaft and the hydraulic pump drive eccentric assembly and then fit a shim on the back of the pump drive pinion to prevent damage to the "O" ring. Fit the drive pinion over the shaft and guide stud then engage the hydraulic pump connecting rod on its eccentric and remove the guiding stud. Fit the five mounting bolts and new tighten them to 1.7 kg/m (121b/ft). Remove the shim from the back of the pinion then check the pump turns freely.



  • gs_rebiuld_part2_page5_piiccies.jpg
    61.9 KB · Views: 2,938


Real cars have hydraulics
Re-fitting the pistons and cylinder barrels
Clean the carbon deposits away from the tops of the pistons if you are re-using the original components, then fit the gudgeon pins into one of the gudgeon pin bosses and then, using a piston ring clamp, insert the piston into the cylinder barrel so that the figure "9" stamped on the piston crown is facing the right way up.

Carefully slide the cylinder barrel over the studs and, when it is correctly positioned, push the gudgeon pin fully home and re-fit the circuits.

Push the barrel fully home and then repeat the process for the remaining three pistons and cylinder barrels.

Re-fitting the cylinder heads
Re-assemble the cylinder heads by reversing the dismantling procedure. The notches in the camshaft bearing housing must be lined up with the groove machined in the cylinder head. The torque figure for the crankshaft securing nuts is 1.7 kg/m (121b/ft). When re-fitting the rocker shaft retaining grub screws, use Loctite Screw Fix to secure them.

Rotate the crankshaft so that the pistons on the side of the engine being worked on are at the mid-stroke position then, using a new head gasket, fit the cylinder head over its mounting studs and push it into contact with the cylinder barrels, guiding the oil return tubes into their respective opinions as you do so.

Fit the eight securing nuts with their washers and tighten diagonally opposite nuts, starting with the central four nuts, to a final torque figure of 1.8 kg/m (l31b/ft) for the 12 mm nuts and a figure of 2.5 kg/m (17lb/ft) for the 13 mm nuts.

Re-fitting the camshaft
drive components Fit both camshaft drive pinions to their respective cam- shafts, making sure that the locating pin on the mounting flange is fully engaged in both cases, then fit the retaining nuts and tighten them to 8.2 kg/m (591b/ft), preventing the pinions from rotating using the method described above.

Re-assemble the belt drive wheels to the front of the crankshaft, attaching the belts as you do so. Rotate the crankshaft until the mark on the top of the front drive wheel is vertical and position the left-hand camshaft wheel so that the mark is also at the top ; now accurately position the right-hand camshaft pinion so that the mark is at the bottom. Turn the oil pump drive pinion until the mark is also at the bottom and then fit both of the drive belts so that the two white Darks on each belt are in line with the mark on the crankshaft wheel and the marks on the camshaft.

To check that the belts are correctly fitted, count the number of teeth between the camshaft pinion and the crankshaft pinion on both camshaft belts. There should be 32 teeth (33 on the 1,220 cc engines) on the left-hand belt between the marks and 42 (43 on 1,220 cc engines) on the right-hand belt. When you are sure that the belts are correctly positioned, tighten the pensioner wheel retaining nuts to 1.8 kg/m (13lb/ft).

Adjust each of the tappets in turn with each valve rocker on the lowest point of its respective camshaft lobe. The specified clearance is 0.2 mm (0.008in) when the engine is cold. The remainder of the re-assembly technique is largely a matter of reversing the dismantling procedure.

The fly-wheel bolts should be tightened to 6.9 kg/m (50lb/ft). When the engine is completely re-assembled, install it in the car by reversing the dismantling procedures described on pages 2132 to 2137.

Refer to pages 97 to 102 and make the base settings to the points and ignition timing. Fill the engine with the correct grade of engine oil and prime the high-pressure pump by filling it with LHM fluid, having first removed the suction pipe from the hydraulic fluid reservoir. Slacken the pressure regulator bleed screw then carefully start the engine.

Immediately the engine is running, re-connect the suction pipe to the hydraulic fluid reservoir and tighten the pressure regulator bleed screw. Run the engine, carefully, until it is warm then switch off and check for oil and hydraulic fluid leaks and road-test the car.

Running-in the new engineThe newly re-built engine should not be driven hard during the first 1,000 km (620 miles) and the running-in should be progressive without straining the engine in any gear.
After the engine has covered 1,000 km (620 miles) change the engine oil, lit a new oil filter, re-tighten the cylinder bolts to the correct torque (see above) and re-set the ignition timing and each of the valve clearances.
A carefully re-built engine that has been rim-in properly will give many thousands of mites of satisfactory service.



  • rebuild_gs_part2_page6_picces1.jpg
    34.5 KB · Views: 2,893
  • gs_rebuild_part2_page6_piccies2.jpg
    28 KB · Views: 2,818

Ken W

1000+ Posts
Seeing the Kens are working on 3 GS engines at present, I found this article interesting but I lost a little faith when he started talking about fitting new head gaskets.

Cheers, Ken