Mercedes W123 Own Work Man 1976-1986 (eBook)

ENGINE

The Mercedes passenger car, Type W123, is powered by a water-cooled in-line engine, which has 4 or 6 cylinders depending on the displacement.

The engine number - arrow - in the MERCEDES engines is engraved on the cylinder block at the front left side under the inlet manifold. It consists of a 6-digit identity number and a 10-digit serial number. Within the identity number the first 3 digits refer to the basic construction of the engine. This means the arrangement of, for example, the camshaft and valves, as well as the construction of the engine block which is the same in all engines in which the first 3 digits correspond with one another. Generally this number is used for the identification of the engine. In the illustration, for example, the engine 102 is represented, besides this the 4 cylinder engines 115 and the 6 cylinder engines 110 as well as 123 are built into the MERCEDES model W123.

The second 3 digit number, in this case 980, indicates that the engine, and in particular the cylinder head is tuned for an injection system.

Often in references to the engine number, the engine end-number is only given, which means the last 6 digits of the serial-number.

The various engines are discussed in separate sections. Chapters which apply to all engines are covered in the section on Engine 102, which is discussed first. Then those few aspects of engines 115 and 123 which differ from Engine 102 are covered.

Engine 102

The identification number 102, which indicates an in-line engine with 4 cylinders, which is fitted either with a carburetor or a fuel injection system. This engine was built into the models 200 and 230 E since July 1980.

The power unit is fitted into the engine compartment longitudinally and can only be lifted out with a suitable crane.

The cylinder bores are embedded in the grey cast iron engine block. In the case of extreme wear or ridging of the cylinder walls, the cylinders can be ground out by a specialist workshop. Subsequently, however, oversized pistons must be installed. The crankshaft is found in the bottom part of the cylinder block, and is supported by 5 crankshaft main bearings. The crankshaft is connected to the connecting rod by means of bearings, which connect to the pistons. The bottom part of the engine is formed by the oil sump in which the engine oil, which is needed for lubrication and assists cooling, collects. The cylinder head is bolted onto the top of the engine block. It is made of aluminium because it has better heat conducting properties and a low specific weight compared to cast iron.

The cylinder head is a cross flow head. This means that the fresh fuel-air mixture flows into one side of the cylinder head and the burned gases flow out of the opposite side. Due to the cross flow arrangement rapid gas-exchange is ensured. The camsahft is found in the top of the cylinder head. It is driven by a timing chain from the crankshaft. A hydraulic timing chain tensioner ensures that the chain always has the correct tension. The camshaft drives the valves by means of rocker arms. The rocker arms rest on adjusting bolts, with which the valve clearance is adjusted during maintenance.

The oil pump takes care of the lubrication of the engine, and is located in the front of the oil sump and is driven by the auxiliary shaft. The auxiliary shaft is situated on the left side of the engine block and is driven by the crankshaft timing chain. The oil is distributed to the bearings of the crankshaft and the camshaft as well as the cylinder bores, by means of bores and pipes.

The water pump is attached to the front of the engine block. The pump is driven by a fanbelt which also drives the alternator. An additional fanbelt drives the power steering pump. It is important that the cooling system is filled with a mixture of antifreeze to give corrosion protection.

The fuel is supplied to the engine through a single Stromberg Flachstrom carburetor which is practically maintenance-free.

The ignition spark is produced by a transistorised ignition system which keeps the ignition point almost constant. The distributor is attached to the left side of the engine block and is gear driven by the auxiliary shaft. In the same way the mechanical fuel pump is driven by a cam on the oil pump shaft, under the distributor.

Technical Data

Engine removal and refitting

The engine complete with gearbox is removed from above. It is recommended to read the chapter on gearbox removal. For the removal of the engine, a crane or engine hoist is needed. Under no circumstances may the engine be lowered by means of a trolley jack, as the jack would cause serious damage to the engine.

As several connections also have to be undone working from below the car, four trestles as well as a trolley jack are needed. Before the engine assembly is lifted, the mudguards should be protected by blankets. The bonnet does not need to be removed.

The engine can also be removed without the gearbox. The gearbox must then be supported by a jack and an intermediate layer of wood; connecting bolts must be loosened and the gearbox separated from the engine with a lever.

Caution:

In vehicles with air-conditioning the cooling gas must be released and the system emptied (workshop-job). Only the removal of the 4-cylinder engine will be described, but the procedure is identical for 6-cylinder engines

Removal

• Open the bonnet into the vertical position. Open the bonnet. Pull the locking lever -1- out of the notch on the left bonnet hinge -2-, lower the bonnet a little to do this so that the locking lever can be loosened. Pull the locking lever out of the notch on the right hinge, and open the bonnet to the vertical position.

Caution

The left locking lever must rest in the top notch of the bonnet hinge.

• Disconnect the earth cable from the battery.

• Disconnect the positive cable, from the battery -arrows- and retainer at the fire wall -a-. Open the cable strap of the fire wall and lay the positive cable over the engine.

• Drain the coolant, see page 79.

• Remove the radiator, see page 74.

• Remove the air filter, see page 98.

• In vehicles with hydraulic level control: remove the Allenhead bolts -arrows- and put aside the pump with pressure pipes. Undo the retaining cap.

Caution

Do not undo the two inner Allenhead bolts which tighten the lid. These bolts have a continuous thread, visible between the lid and the housing.

• With an appropriate syringe, suck the hydraulic oil out of the reservoir of the power steering unit or disconnect the pipes from the steering gear and drain the fluid into a suitable container.

• Remove the axial throttle control shaft. To do this unclip the regulating rods, pull out the safety clip -arrow-, push the shaft to the back and remove.

• Disconnect the coolant pipes at the front coolant flange, at the testing socket and below at the automatic choke. First loosen the hose clamps and push right back.

• Disconnect the bleed tube from the thermostat and waterpump housing.

• Disconnect heating tube from the back of the cylinder head.

• Mark the fuel feed pipe and the fuel pressure pipe with tape and disconnect.

• Pull the grey vacuum lead from the inlet manifold.

• Disconnect the vacuum lead for the brake servo from the inlet manifold and put to one side. Do not lose the washer.

• Mark the following electrical leads, loosen the cable straps and disconnect the leads from their holders: middle cable of distributor cap, green control lead at distributor, earth cable of the testing socket, all the plugs of the testing socket and carburetor, plugs and transmitters for the air mixture gauge, blue plug on the cold starting valve, black plug on the auxiliary air sliding valve, plug connections on the side airfilter attachments and in front on the inlet manifold. For this press together the serrated surfaces.

• Disconnect the holders for the cable straps in the front of the inlet manifold.

• Disconnect the plug of the alternator. To do this lift out the spring retainer with a small scewdriver and push it aside. Pull out the plug and pull the cables out of the supports.

• Disconnect the electric leads on the starter. If the engine is being removed without the gearbox, remove the starter (except engine 115 and injection engine 102), see page 227.

• Disconnect the cables for the TDC-transmitter at the test socket. To do this remove the two bolts of the socket from the support and pull the grey lead with plug from underneath.

• Put the vehicle on blocks, see page 244.

• For vehicles with an engine mounting damper -45-: unbolt the damper at the frame cross-member -48-, by removing the nut -40-. Other illustrated, parts: 41 - washer, 30 mm diameter, 42 - rubber stopper, 43a - engine support, 49 - damper bearing, 50 - bolt M6x45 mm, 51 -spring washer.

• Remove the steering damper.

• Remove the front engine mounting, see page 17.

• Unbolt the exhaust system at the exhaust manifold flange.

• Remove the lower bolt of the starter and undo the support of the speedometer cable.

• Disconnect the chassis earth strap.

Caution:

If the engine is removed with the gearbox, the following jobs are to...