Mercedes M-Class W163

since 1997 release

Repair and operation of the car

Check of compression pressure in cylinders

PERFORMANCE ORDER

Implementation of the procedure of check of compression pressure will require the help of the assistant. The compression gives an idea of a condition of the engine. Results of check show whether as it should be valves and pistons (piston rings), or they are worn-out. Whether Besides, results of check allow to make the decision to replace the engine whether complete repair is required to it or to replace sealing laying of a head of cylinders enough. For check it is required компрессометр which for petrol engines is offered in specialized shops for reasonable price. For diesel engines it is necessary компрессометр with a limit of measurements approximately to 40 bars. Warm up the engine up to the normal working temperature (about 80 °C), make sure of completeness of a charge of the rechargeable battery.

Petrol models

PERFORMANCE ORDER

Kill the engine and, according to a complete set, uncover the power unit, assembly of the air cleaner and, - at the corresponding complete set, - the rezonatorny camera with a connecting sleeve (see the Head of the Power supply system and production of the fulfilled gases). Turn out spark plugs and turn the engine a starter. Fill a nozzle of a kompressometr in a candle opening of the first cylinder. Squeeze out the accelerator pedal and, turning the engine a starter, consider indications of the measuring instrument (the help of the assistant will be required), - write down result of measurement. Working in a similar manner, serially measure compression pressure in the remained engine cylinders. Kill the engine, disconnect компрессометр, screw spark plugs and establish into place all components which were removed for the purpose of ensuring access.

Diesel models

Kill the engine and uncover an airdistributing sleeve of a path of system of pressurization and an overlay of a cover of a head of cylinders.

Check of compression pressure on the diesel models equipped with the series 612 engine

1 — the Cover of an airdistributing sleeve of a path of system of pressurization 2 — the Overlay of a cover of a head of cylinders 3 — Kompressometr	4 — the Connecting hose 5 — the Carving nozzle R9 — the Glow plug

Check of compression pressure on the diesel models equipped with the series 628 engine

M612

PERFORMANCE ORDER

Turn out glow plugs. By means of a carving nozzle with a flexible connecting hose connect компрессометр to a candle opening of the first cylinder. Further act as it should be, similar described above for petrol engines.

M628

Check of compression pressure on the diesel models equipped with the series 628 engine

All models

PERFORMANCE ORDER

Compare results of measurement by requirements of Specifications. The most admissible difference of pressure in separate cylinders can make 1.5 bars (for diesel engines of 3.0 bars). The compression grows in the serviceable engine very quickly. The low value shown after the first cycle, increasing with the subsequent cycles indicates wear of piston rings. The low value after the first cycle which is not increasing after the following signals about that, something valves are untight, or laying of a head of the block is punched (also the crack in a head can be the cause). Can lead existence of a deposit on plates to decrease in a compression of valves. It must be kept in mind that because of the different speed of rotation of a starter on different models the results received as a result of measurements can differ. The results received at measurement of a compression have to be approximately identical to all cylinders. If pressure is in any cylinder at the level of minimum admissible and even below, then for clarification of the reason perform the following operations. Pour in the cylinder through an opening for a candle in a teaspoon of motive oil and repeat measurement of a compression. If oil addition temporarily improved a compression, most likely, wear of the piston, rings or the cylinder is the reason of its decrease. If increase in a compression did not happen, then it is possible to assume that the reason - in leakage of valves or the punched laying of a head of the block. Low compression in two next cylinders almost for certain — a consequence of breakdown of laying of a head. Availability of cooling liquid in combustion chambers or in a case of the engine will confirm this assumption. If the compression in one of cylinders is about 20% lower, than in the others, besides turns of idling are unstable, then the reason, perhaps, excessive wear of a cam of a cam-shaft. After completion of check establish to the place of a spark plug (address the Head the Current leaving and service), put on them tips of high-voltage wires, attach the socket to the ignition coil. Establish into place a plastic cover of the engine and a safety lock of the fuel pump.

Check of cylinders on leaks

PERFORMANCE ORDER

During this check are defined exit speed from cylinders of the compressed air pumped in them and directly the place of leaks. This check is an alternative to check of a compression. Moreover, from many points of view it is much more effective as visually it is simpler to reveal a leak source, than to comprehend results of measurement of a compression. The equipment necessary for check on leaks, does not belong to public therefore performance of this check should be entrusted specialists of the service center.