Mercedes S-Class W-140
1991-1999 of release
Repair and car operation
+ Mercedes-Benz Cars of a class S (W-140)
+ Operation manual
+ Routine maintenance
Compression check in engine cylinders
Engine check by means of the vacuum gage
Belt of a streaming drive of auxiliary units
+ 6-cylinder petrol engines (M104.944 and M104.990/994)
+ 8-cylinder petrol engines (M119.970/981 and M119.971/981)
+ 12-cylinder petrol engines (M120.980/982)
+ 6-cylinder diesel engines (OM603.971)
+ 6-cylinder diesel engines (OM606.961)
+ Systems of cooling, heating
+ Power supply system and release
+ engine Electric equipment
+ gear shifting Box
+ Avtomaticheckaya transmission
+ Brake system
+ Suspension bracket and steering
+ Onboard electric equipment
Compression check in engine cylindersThe compression provides guidance on an engine condition. 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 the 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.
The engine should be heated-up to working temperature, the storage battery - is completely charged. You also will need the help of the assistant.
Take a safety lock of the fuel pump from the assembly block, (address to Head Onboard electric equipment). Start the engine and wait, while it will decay. If the engine is not got, scroll a starter about 10 seconds.
For receiving access to spark plugs uncover a maslozalivny mouth and remove a plastic cover of the engine. Establish a cover into place.
Disconnect ignition system, having disconnected the socket from the ignition coil. Turn out all spark plugs (see. Section Check and replacement of spark plugs, check of a condition of high-voltage wires (petrol models) Heads Routine maintenance).
Establish компрессометр in an opening of a candle of the first cylinder. It is desirable to use kompressometry which tip is rolled in a candle opening.
Ask the assistant to hold a pedal of an accelerator completely pressed and to include a starter. After several cycles the compression in the cylinder will reach the maximum value and will not change any more. Write down the received result.
The most admissible difference of pressure in separate cylinders can make 3.0 bar (for diesel engines 5.0 a bar).
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. Low value after the first cycle, not increasing after the following, signals that or valves are not tight, or laying of a head of the block (the crack in a head can be the reason also) is punched. To decrease in a compression can lead deposit existence on plates of valves.
It is necessary to mean that because of 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, should be approximately identical to all cylinders.
If pressure is in any cylinder at level minimum admissible and even below, for clarification of the reason execute the following actions. Pour in in the cylinder through an opening for a candle a teaspoon of impellent oil and repeat compression measurement.
If oil addition temporarily improved a compression, the reason of its decrease, most likely, is wear of the piston, rings or the cylinder. If the increase in a compression did not occur, it is possible to assume that the reason - in a 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 chambers of combustion or in a case of the engine will confirm this assumption.
If the compression in one of cylinders approximately for 20 % is lower, than in the others, besides turns of idling are unstable, the reason, probably, excessive wear of a cam of a cam-shaft.
After completion of check establish to the place of a spark plug (address to Head Routine maintenance), 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.
Values of pressure of a compression for various engines are given in Specifications.
Check on leaksDuring this check are defined speed of an exit from cylinders of the compressed air pumped in them and directly a place of leaks. This check is alternative to compression check. Moreover, from many points of view it is much more effective as visually to reveal a source of leak simpler, 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.