4.4. Procedures of repair of petrol SOHC engines without their extraction from the car

Reduction of the piston of the first cylinder in the provision of the top dead point of a step of compression (VMT)

General information

The Top Dead Point (TDP) is called the highest point of a piston stroke in the cylinder. Strictly speaking, in 4-stroke engines in the course of rotation of a bent shaft this situation is reached by each of pistons twice: once at the end of a step of compression and the second - at the end of a final step. During the performing of settings of phases of gas distribution and installation of a corner of an advancing of ignition the provision of VMT of the end of a step of compression of the piston is in most cases used (usually the first cylinder).

Need for reduction of the piston (it) in the provision of VMT arises when holding many procedures, in particular such as removal/installation of camshafts, components of the GRM drive and distributor of ignition.

Some engines are designed in such a way that at a provorachivaniye of cranked or distributive shaft at the taken-off gas-distributing belt there can be an input of valves in contact with the bottoms of pistons that is fraught with risk of damage of the corresponding internal components, up to destruction of casting of a head of cylinders.

Do not allow change of provision of shaft after removal of a belt!

Order of implementation of the procedure


  1. Reduction of any of pistons in the provision of VMT is made by a provorachivaniye of a bent shaft of the engine. If to take a detached view of the engine of the GRM drive, the direction clockwise will be the normal direction of rotation of a bent shaft. Remember that the attempt of a provorachivaniye of a shaft counterclockwise can lead to violation of adjustments of phases of gas distribution. The first is the extreme cylinder from the GRM drive.
  2. Disconnect a negative wire of the accumulator. For the purpose of simplification of a provorachivaniye of the engine turn out all spark plugs.
  3. For the purpose of ensuring access to VMT tag on a camshaft cogwheel, remove the top cover of the GRM drive (see the Section Removal and installation of a cover of the GRM drive).
  4. Turn a bent shaft in the direction of an hour hand so that camshaft cams, managing directors of valves of the first cylinder were turned by the made narrower part up.
  5. It is possible to turn a bent shaft rotating a forward wheel by the established 5th transfer, or rotating a bent shaft for the central bolt of fastening of its pulley at the neutral provision of RKPP or AT and the cocked parking brake.

Do not turn the engine for a bolt of fastening of a cogwheel of the camshaft since at the same time it is possible to load a gear belt excessively.

  1. Combine a tag on a camshaft cogwheel with VMT tag on a cover of a gear belt. At the same time the tag on a pulley of a bent shaft (C14NZ engine) has to coincide with a tag on the lower cover of a gear belt. On X12SZ and C14SE engines the tag is on a cogwheel of a bent shaft. At the same time the piston of the first cylinder is in the provision of VMT.
Adjusting tags of VMT of the C14NZ engine
Adjusting tags of VMT of X12SZ and C14SE engines