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

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 remove rings from pistons — try not to damage walls of the last incidentally.
  2. 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!

  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.

  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.

  1. 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), pistons are subject to replacement.

  1. Define a landing gap of pistons in the cylinders for what measure diameters of the last (see Check of a condition of the block of the engine) and subtract from them diameters of the corresponding pistons. Measurement of diameter of the piston is performed on a persistent surface at an angle 90 ° to an axis of a piston finger and on the set removal from a skirt cut.

On the engines considered in the present manual selective landing of pistons is provided in cylinders. At the same time cylinders and pistons are as appropriate marked.

A — Location of marking of dimensional groups of cylinders
B — At installation of conrod assemblies pistons have to are developed by forward tags on the bottoms on the engine forward


  1. If the landing gap of the piston in the cylinder exceeds admissible value (see Specifications), the block should be given to a pro-point with a selection of new pistons of repair diameter.
  2. 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.

  1. Mark pistons on compliance to the cylinders — numbers of cylinders are fabrichno applied on rods and covers of conrod bearings.

  1. Remove a lock ring of fixing of the piston on a rod.

  1. Warm up pistons in an oil bathtub up to the temperature of 60 — 70 °C, then squeeze out piston fingers of the top heads of rods.

Alternatively pistons can be removed at the room temperature with application of a special press.

  1. Check rods for existence of signs of deformations. Compare results of measurements to requirements of Specifications, in case of need make replacement.

    A — Check of a rod on a bend
    B — Check of a rod on twisting


  1. For the purpose of definition of landing gaps measure diameter of a piston finger and openings under its landing in the top head of a rod and in the piston.

    A — Measurement of diameter of a piston finger and an opening under its landing in the top head of a rod
    B — Measurement of diameter of an opening in the piston under landing of a piston finger


  1. Compare results of the corresponding calculations to requirements of Specifications, replace excessively worn-out components — when squeezing from a rod of the top plug use a suitable mandrel, when landing track correctness of combination of oil openings.
  1. At assembly the new lock ring is established on the piston by the party equipped with a facet (if the facet in general is provided) from the piston. Having put a ring warm up the piston in an oil bathtub, put on a rod (track correctness of orientation of components on tags) and press a finger (the rod has to appear precisely in the middle).
  1. Put the second lock ring (also new) and check freedom of rotation of the piston on a finger.
  1. At installation of piston assemblies track that pistons were deployed by forward tags on the bottoms on the engine forward. Do not forget that number marking on covers of conrod bearings and the lower heads of rods has to settle down on the one hand assemblies.
  1. Evenly tighten bolts of covers of bearings with the required effort and check the size of an axial side play of rods on pins of a bent shaft. Compare results of measurements to the required effort, in case of need replace the corresponding rods and/or a bent shaft.