This chapter describes the most common and important engine maintenance and repair procedures, with the exception of those requiring special skills and tools, such as engine overhaul procedures, which should be entrusted to a car service specialist. Below are the M60/1, M60/2 and M73 petrol engines and the M57 and M67 diesel engines. Work on engines M51, M52 and M62 is carried out in the same way.
Six types of engines are installed on the cars in question: 6-cylinder turbodiesel M51 (SOHC), 6-cylinder diesel M57 (DOHC), M52 6-cylinder petrol engine (DOHC), 8-cylinder V-shaped petrol (M60, M62) and diesel (M67) engines (DOHC), as well as a 12-cylinder V-shaped gasoline engine M73 (SOHC). The abbreviations SOHC and DOHC indicate the presence of one or two camshafts per cylinder bank, respectively (and therefore 2 or 4 valves per cylinder), located at the top of the engine. The power unit is installed along the car and removed from the engine compartment upwards with a crane.
Its head and cylinder block of the M52 engine are cast aluminum alloy. Unlike traditionally used cast iron, aluminum alloy has a higher thermal conductivity and less weight. This contributes to better cooling and lower fuel consumption.
The cylinder block of the M51 turbodiesel engine is cast iron, the cylinder head is made of light alloy. With increased wear and the presence of scoring on the walls of the cylinder walls, they can be honed with the subsequent replacement of old pistons with oversized pistons.
M51 engine
1 - Camshaft
2 - Hydraulic pusher
3 - Valve
4 - Turbocharger
5 - Thermostat
6 - Water pump
7 - Oil pump
8 - Viscous clutch
9 - Drive belt
10 - Drive belt tensioner
11 - Timing chain
12 - Vacuum pump
13 — the Inlet pipeline
The cylinder head of all engines has a so-called transverse scavenging. This means that the fuel mixture enters the cylinders from one side, and the exhaust gases (OG) come out with another. This scheme promotes faster gas exchange.
The timing drive is carried out from the crankshaft through the chain; multi-ribbed belts are used to drive auxiliary units. M52 engines are equipped with a timing system (VANOS) by offsetting the intake camshaft relative to its sprocket. Timing timing is controlled by the engine control unit (ECM, DME) depending on the number of revolutions of the crankshaft by opening and closing a special oil valve.
M52 engine
1 - Ignition coils
2 - Camshafts
3 — Hydraulic pusher
4 - Oil pump
5 - Drive belt
6 - Water pump
7 - Thermostat
8 - Oil filter
9 - Timing chain
10 — the Inlet pipeline
The valves are driven by the camshafts via hydraulic tappets. There is no need to adjust valve clearances during maintenance. On SOHC engines, the intake and exhaust valves are driven by a single shaft, while on DOHC engines, a separate camshaft is used to drive the intake and exhaust valves.
But the piston has 2 compression rings and one oil scraper ring. The crankshaft is located in the main bearings.
The oil supply to the lubrication system is carried out by an oil pump, which in a 6-cylinder gasoline engine is located in the front in the crankcase and is driven from the crankshaft. On the M51 diesel engine, the oil pump is located in the timing chain cover and is driven via a gear train. Oil is sucked in from the oil pan and fed through holes and pipelines to the bearings of the crankshaft and camshaft, as well as to the working surfaces of the cylinders.
The coolant pump is located at the front of the cylinder block. A cooling fan is driven from the pump shaft through a viscous coupling when the appropriate temperature is reached. The water pump is driven through a multi-ribbed belt, which simultaneously drives the generator. The cooling system is filled with a mixture of antifreeze, corrosion protection and water with a low lime content.
The preparation of the air-fuel mixture is controlled by the injection system, which, together with the ignition system and some other systems, is part of the engine management system. This ensures a stable low content of harmful substances in the exhaust gases. The ignition system has no moving parts, which eliminates their wear. In a diesel engine, the distribution of fuel over the cylinders is controlled by an electronic control unit (ECM, DDE).
Gasoline engines are designed to run on AI-95 gasoline, however, due to the presence of detonation control, other types of fuel can also be used. If AI-98 gasoline is used, then under normal operating conditions, fuel consumption is reduced and engine power is increased. When AI-91 gasoline is used, engine power decreases and fuel consumption increases.
Preparatory operations
Before carrying out any engine maintenance procedures, clean the engine compartment and the external surfaces of the power unit using a special solvent. This treatment will prevent dirt from getting inside the engine.
If necessary, depending on the nature of the work ahead, the hood can be removed in order to provide freedom of access to the components to be serviced (see chapter Body). To prevent accidental damage to the paintwork, cover the fenders of the car with special covers or old blankets.
Excessive consumption of engine oil can be considered a signal to check the condition of the piston rings, valve stem seals and / or valve guides. Naturally, first of all, you should make sure that oil losses are not associated with the development of its external leaks. Check cylinder compression (see Section Compression pressure test), to determine the general condition of the engine.
Loss of power, rev stability, excessive valve train noise, and increased fuel consumption are usually fairly common signs that an engine needs an engine overhaul, especially when all of these factors occur at the same time. If performing a full range of adjustments does not resolve the issue, the only recourse is to perform a general mechanical rebuild on the engine.
The overhaul of the power unit involves the restoration of all its operating parameters to the level characteristic of the new engine. During the overhaul, it is mandatory to replace the piston rings and restore the cylinder mirrors (turning and/or honing). Usually, the main and connecting rod bearings of the crankshaft are replaced, if necessary, turning and restoring its necks can be made. It is mandatory to service the valves, the condition of which at the time of the need for an overhaul of the engine almost certainly leaves much to be desired. In parallel with the general repair of the power unit, reconditioning of the starter and generator is also usually carried out.
Critical cooling system components such as hoses, drive belts and thermostat must be replaced with new ones during engine overhauls. In addition, you should carefully check the condition of the radiator (see chapters Vehicle settings and routine maintenance and Engine cooling, heating, ventilation and air conditioning systems). If there are signs of leaks or obstruction, the radiator should be replaced. Don't forget to check the condition of the oil pump as well.
Overhaul of the engine does not require high professional training from the performer, but it takes a lot of time. You should plan to stop using the car for at least two weeks, especially if you need help from a mechanic shop to carry out some restoration work.
Most of the work can be done with the usual set of hand tools, however some of the checks to determine the suitability of individual components for further use require the use of precision measuring equipment. In doubtful situations, seek help from service station specialists.
Do not forget that the decisive factor in the question of the advisability of overhauling the engine is the condition of its cylinder block. It is often cheaper and more reliable to replace a worn engine with a remanufactured one.
In conclusion, it can be seen that all efforts to carry out the refurbishment of worn components will be wasted if careless attention is paid to the requirement of cleanliness during assembly of the unit.