4.7.12. Check of a condition of components of conrod and piston group

All engines


  1. Previously conrod and piston assemblies have to be carefully cleared. Rings need to be removed from pistons.

Piston rings are subject to replacement without fail.

  1. By means of special adaptation, or several probes of lezviyny type remove rings from pistons, - try not to damage walls of the last incidentally.

Removal of piston rings by means of the probe of lezviyny type (it is better to use at the same time two-three probes)

Remember that rings are made of fragile metal and can break at strong unclamping, - be not wounded!

  1. Scratch out traces of coal deposits from the bottoms of pistons. After removal of the main layer of deposits smooth out a surface manually a wire brush or a piece of a fine-grained emery paper.

Do not use for cleaning made of soft material and pistons easily subject to an erosion wire nozzles to the electric drill at all! After cleaning the marking applied on the bottoms of pistons has to differ clearly.

  1. By means of special adaptation clean flutes under installation of rings on pistons. It is alternatively possible to use a fragment of an old piston ring for this purpose, however be careful, - do not scratch a bottom and walls of a flute and do not cut fingers.

Clearing of flutes under installation of piston rings by means of the special tool

  1. Having removed the main deposits, wash out conrod assemblies by solvent and carefully dry them, whenever possible with use of compressed air. Check passability of maslovozvratny openings in back walls of flutes under installation of piston rings, and also oil openings in the lower heads of rods.

When using compressed air do not forget to put on goggles!

  1. If walls of pistons and a mirror of cylinders are not damaged and excessively are not worn-out, and the block of the engine was not pierced and not replaced, need for replacement of pistons also disappears. Normal wear of pistons is shown in the form of vertical traces of development on a persistent surface and a small weak point of landing of the top compression ring in the flute. Do not forget that replacement of piston rings is made without fail, regardless of their state.
  2. Attentively examine each of pistons on existence of cracks in a skirt, around ledges under installation of piston fingers and around an arrangement of rings.
  3. Check persistent surfaces of a skirt of the piston for existence of scratches, the bottom - on existence of through openings and progar on edge. Presence of scratches on a skirt can be regarded as a sign of long overheats of the engine, or too early ignition of air-fuel mix, - check serviceability of functioning of the cooling system. Progara at the edges of the bottom are the certificate of a detonation. Anyway, the cause of the revealed violation has to be removed in order to avoid a recurrence. Also leak of the soaked-up air, the wrong configuration of air-fuel mix, violation of installation of a corner of an advancing of ignition, the wrong functioning of systems of ignition and EGR can act as the possible reasons of education listed defects.
  4. Pointed corrosion of pistons in the form of cavities speaks about hit in combustion chambers and/or a case of the engine of cooling liquid. Besides, take care that the cause of internal leaks was removed.
  5. Estimate the size of a side gap of landing of piston rings in the flutes for what enclose a new ring outside in the flute on the piston and the probe of lezviyny type measure the remaining gap Repeat measurement in two-three points on flute perimeter. You watch to mixing compression rings, - top differs from the second. If the size of a gap exceeds admissible value (see Specifications in the Head Dvigateli), pistons are subject to replacement.

Check of a gap of landing of a piston ring in a flute

  1. Determine the size of a landing gap of pistons in the cylinders for what measure diameters of the last (see the Section Cleaning and check of a condition of the block of cylinders) and subtract from them diameters of the corresponding pistons. Measurement of diameter of the piston is performed on a persistent surface of a skirt at an angle the 90th hail. to an axis of a piston finger and on the set removal from the bottom. If the landing gap of the piston in the cylinder exceeds admissible value (see Specifications in the Head Dvigateli), the block should be given to a pro-point with a selection of new pistons and piston rings of repair diameter.

Diameter of the piston is measured in the plane, a perpendicular axis of a piston finger …

  1. Estimate correctness of landing of pistons on rods, having tried to rotate components in opposite directions. Existence of a little noticeable side play speaks about excessive wear of a joint. For correction of a situation it is necessary to deliver conrod and piston assemblies in a workshop of car service where necessary recovery repair and replacement of fingers will be made.

Petrol engines

On all petrol engines piston fingers are put in the top heads of rods with a tightness and have floating landing in lugs of pistons in view of what implementation of the procedure of removal of pistons from rods (in case of such need) has also to be entrusted to specialists of car service. In parallel, rods can be checked for existence of signs of a bend, twisting and other deformations with use of the special diagnostic equipment.

Needlessly it is not necessary to remove pistons from rods.

Diesel engines


  1. On diesel engines fingers have floating landing as well in rods and are fixed on pistons by means of lock rings. In case of need, having hooked the suitable screw-driver, remove lock rings and manually squeeze out a finger of assembly. Mark the removed finger by means of an adhesive tape on accessory to the conrod and piston assembly and remove to the reliable place. Lock rings at assembly are subject to replacement without fail.

Removal of a lock ring of a piston finger

  1. Survey the top head of a rod and a piston finger on existence of signs of wear, and zadir of other mechanical damages. Measure by a micrometer diameter of a finger, compare result of measurement to requirements of Specifications in the Head Dvigateli, in case of need make replacement. If the finger or a rod is worn-out, both details are subject to replacement.
  2. Rods (in the absence of mechanical damages) do not need replacement, - visually estimate their existence of signs of obvious deformations, in the presence of suspicions on bend/twisting, ask for the help specialists of car service, or make replacement of defective components.
  3. Having estimated a condition of all components, prepare replaceable details. Replaceable pistons come to the market of spare parts complete with fingers and lock rings.

Lock rings can be got separately.

  1. Make assembly of pistons with rods so that the ledge on a rod from the bearing appeared from a flywheel, the arrow on the bottom of the piston has to specify in the direction of a GRM belt of the engine

The rod is established on the engine by a ledge (A) towards a flywheel / a driving disk, the arrow which is beaten out on the bottom of the piston has to specify in an opposite direction (towards the GRM drive)

  1. Slightly oil piston fingers pure motive, and fix by them pistons on the top heads of rods. Make sure of freedom of turning of the piston concerning a rod on a finger axis. Establish new lock rings (locks up) and make sure of reliability of their landing in reception flutes.

All engines


  1. Check rods for existence of cracks and other mechanical damages. Temporarily uncover the lower heads, take inserts of old bearings, wipe beds in covers and heads and check them for existence of agnails, zadir and roughnesses. Having finished check, enclose inserts into place, establish covers on the lower heads of rods, and by hand tighten fixing bolts.

If the engine is under repair for the purpose of elimination of knock of fingers, replace conrod assemblies.