4.26. Check of a state and selection of inserts of radical and conrod bearings of a bent shaft

Fatigue deformation

Pockets and cavities are specified

Wrong landing

Sites, zapolirovanny to gloss, are specified

Dirt hit

A — Are specified scratches
B — Are specified the foreign particles introduced in a surface

Lack of lubricant

The local wipe of a blanket is specified

Excessive wear

Operation of a blanket on all area is specified

Conicity of a neck

Radial wear of a local order is specified

Check of a state

In spite of the fact that bearings of a bent shaft in the course of capital repairs of the engine are subject to replacement without fail, old inserts should be kept for the purpose of attentive studying of their state which results can give a lot of useful information about the general condition of the engine. Examples of typical defects of inserts of bearings see above.

Exit of bearings out of operation can occur owing to a lack of lubricant, hit of particles of dirt, overloads of the engine and development of corrosion. Regardless of the nature of defects, the cause of damage of inserts has to be removed in the course of performance of capital repairs of the engine in order to avoid a recurrence.

For survey take inserts of bearings from the beds in the engine block / the lower heads of rods and radical / conrod covers and spread out them as installation on a pure working surface. Organization of placement of inserts will allow to tie the nature of the revealed defects to a condition of the corresponding necks of a shaft.

Dirt and foreign particles get to the engine in various ways. They can be left in the block in the course of assembly of the unit, or get via filters or system of ventilation of a case. All particles getting to motive oil, finally, sooner or later, appear in bearings. Often the metal sawdust which is formed in the course of normal operation of internal components of the engine takes root into soft material of inserts. The probability of presence at bearings of traces of an abrasive is high, in particular, when due attention was not paid to cleaning of the block after completion of recovery repair of the engine. Regardless of a way which foreign particles get to the engine as a result they with high degree of probability are introduced in a soft surface of inserts of bearings of a bent shaft and easily come to light at visual survey of the last. Large particles usually are not late in inserts, but leave on their surface and the surface of necks of a shaft noticeable traces in the form of scratches, cavities and zadir. The best guarantee from such troubles is the responsible attitude to cleaning of components after completion of capital repairs of the engine and care of respect for purity at assembly. Frequent regular change of motive oil also allows to prolong service life of bearings significantly.

Oil starvation can be a consequence of several various, but often interconnected phenomena. So, the overheat of the engine leads to fluidifying of engine oil and its replacement from working gaps of bearings. The lack of lubricant of bearings can speak the excessive size of working gaps, and also usual leaks (internal or external). Continuous excess of turns of the engine is often found reason of replacement of oil from gaps of bearings. The violation of passability of maslotok (which is usually connected with the wrong combination of openings at installation of components) also leads to reduction of supply of lubricant to bearings. Typical result of oil starvation is the full or local wipe / выщербливание a blanket of inserts from a metal substrate. At the same time working temperature can rise to such level that the substrate as a result of an overheat gets a bluish shade.

The driving manner also peculiar to the owner of the car has significant effect on service life of bearings. The movement with a small speed on an overgear leads to the considerable overloads of bearings which are followed by replacement of an oil film from their working gaps. Such overloads lead to increase in plasticity of inserts and emergence of cracks in a blanket (fatigue deformation). At the same time surface material begins to crumble and separate from a steel substrate. Operation of the car in a city cycle (frequent trips on short distances) leads to development of corrosion of bearings because the insufficient warming up of the engine involves loss of condensate and release of chemically aggressive gases. These products accumulate in motive oil, forming slags and acids. At hit of such oil in bearings aggressive substances promote development of corrosion of inserts.

The wrong installation of inserts in the course of assembly of the engine can also be the reason of their bystry destruction. Too hard landing does not provide the required size of a working gap of bearings that leads to their oil starvation. Under inserts (in the course of their installation) foreign particles formation of eminences from which blanket is quickly wiped is result of hit.

Selection of inserts

Radical bearings



Standard diameters of radical necks of a bent shaft and beds of the corresponding bearings can have insignificant dispersion for the purpose of which compensation inserts of radical bearings of several standard dimensional groups are issued (on thickness) — number of group is beaten out on cheeks of cranks and on the bottom of the block of cylinders.

A — Numbers of standard dimensional groups of radical necks of a bent shaft are beaten out on cheeks of the corresponding cranks
B — Numbers of standard dimensional groups of beds of radical bearings are beaten out on the bottom of the block of cylinders

Calculation of number of dimensional group of an insert is carried out by addition to number of group of a neck of number of group of a bed. So, for example, if the neck has the dimensional 1 group, and a bed of the corresponding bearing — "2", it is necessary to choose an insert of the dimensional 3 group. For definition of dimensional group of inserts the color code is used.

  Marking of a bed of the bearing
"0" "1" or "I" "2" or "II"

Marking of a neck of a bent shaft


0 (Black)

1 (Brown)

2 (Green)

"1" or "I"

1 (Brown)

2 (Green)

3 (Yellow)

"2" or "II"

2 (Green)

3 (Yellow)

4 (Blue)

If the bent shaft was exposed to a pro-point, it has to be completed with inserts corresponding repair (with belittling) the sizes. Usually selection of inserts is carried out by the experts making a pro-point of necks of a shaft. Regardless of a technique of determination of the required size of inserts working gaps of bearings have to be then are checked with use of the measuring Plastigage set (see Installation of a bent shaft and check of working gaps of radical bearings).

If it is not possible to correct properly the size of working gaps by selection of inserts, the shaft should be replaced.

Conrod bearings

The selection of connecting rods is made on the basis of determination of size of working gaps in the corresponding bearings (see Spetsifikatsiiya Ustanovk of conrod and piston assemblies and check of size of working gaps in conrod bearings of a bent shaft).

All bearings

Remember that the final parameter defining correctness of selection of inserts is the result of measurement of working gaps in bearings. Safely ask any questions representatives of the company HUNDRED companies Infiniti.