4.2.15. Survey of radical bearings and bearings of the lower head of a rod

Even in case of installation of new radical bearings and bearings of the lower head of a rod at overhaul of the engine, old bearings have to be kept for a careful research as their state can give valuable information on the general condition of the engine. Inserts of bearings break into various groups depending on their thickness, insert belonging to a certain group is defined by means of the color code applied on an insert - also inserts can have marking on a back surface. Keep in mind that the table given below is fair only before the second repair of thickness of inserts - for the third and fourth repair only insert thickness is specified.

B202/B234 engines till 1993 of the issue.




Nominal red blue
1st repair yellow green
2nd repair white brown

B204 and B234 engines since 1994 of the issue.



The thinnest



yellow (the size applied
only for spare parts)

1st repair


Typical damages of bearings

A — Istsarapyvaniye dirt particles; particles of dirt eat in bearing material
B — Insufficient greasing; attrition of a covering
With — the Wrong installation; shining (zapolirovanny sections)

D — Conicity of necks of bearings; the covering is wiped from all surface
E — Real wear (on radius)
F — Exhaustion of material of the bearing; sinks and pockets on the surface of bearings

Damage of bearings usually results from a lack of lubricant, availability of dirt or foreign particles of the bearing, an overload of the engine or excessive corrosion. The reason of emergence of malfunction of the bearing has to be surely corrected (if it is possible) before starting assembly of the engine, in order to avoid repetition of a problem.

At survey of inserts of bearings take from the block of cylinders / case of a cover of radical bearings, rods and covers of bearings of the lower heads of rods. Spread out them on a pure surface in the same order in what they were installed in the engine. It will help you to compare a condition of bearings to a condition of the corresponding necks of the crankshaft. At survey do not touch surfaces of inserts of bearings with fingers as inserts are extremely gentle and can be easily damaged.

Dirt and other foreign particles can get to the engine in various ways. They can remain there at assembly of the engine or through system of ventilation of a case. Dirt and particles can get to oil and then to bearings. Often there is a metal shaving which appeared when machining the engine or at usual wear of the engine. Later after restoration of the engine in its components there is an abrasive, in particular, if details were not carefully cleaned by one of the recommended methods. Irrespective of a way of hit, foreign particles most often are got or taken root into the soft surface of bearings and are easily identified. Large particles do not take root into bearings, and leave deep scratches on the surface of bearings and necks or are erose. The only and best way of avoidance of such damages of bearings is careful cleaning of all details and contents them in absolutely pure places during the procedure of capital repairs and assembly of the engine. Besides, it is recommended frequent and regular holding a procedure of change of motive oil and an oil filter.

Insufficient lubricant (or the greasing termination) can be result of several interconnected reasons. The excessive overheat (which dilutes oil), an overload (as a result of which oil filters through the surfaces of bearings) and oil leak (because of excessive gaps in bearings, wear of the oil pump or high turns of the engine) - all these reasons can lead to the termination or a lack of greasing. Also blocking of oil channels which usually results from discrepancy of oil openings of inserts of bearings can be the reason of the termination of greasing of bearings - as a result of a lack of greasing bearings fail. At insufficient greasing material of the bearing is usually wiped and forced out from a steel holder of the bearing. Temperature can sometimes increase to a point when steel holders accept blue color because of an overheat.

The driving manner exerts impact on duration of service life of bearings. Frequent and full opening of the gate, driving at small speeds leads to extremely high loads of bearings accompanied with replacement of an oil film. Such loadings lead to bending of bearings and emergence of thin cracks in their surface (exhaustion of material). As a result material of bearings weakens in various points and escapes from a steel holder of the bearing.

Frequent driving on short distances lead to formation of corrosion of bearings. Insufficient warming up of the engine leads to formation of condensate and the gases causing corrosion. These products accumulate in motive oil, forming a deposit and acids. At hit of oil in bearings acid causes bearing material corrosion.

Also the wrong installation leads them to emergence of malfunction of bearings at assembly of the engine. Too hard installation of bearings leads to formation of an insufficient radial gap and therefore to oil starvation of bearings during the operation of the engine. The dirt and foreign particles which got under a back wall of an insert of the bearing leads to formation of bald spots on bearings and as a result leads to destruction of bearings.

During assembly do not touch a bearing insert surface with hands; there is a risk of damage of very gentle surfaces of inserts or hit on a surface of inserts of particles of dirt or other deposits.

As it was mentioned in the beginning of this section, inserts of bearings have to be replaced at capital repairs of the engine. Not observance of this recommendation is false economy. For the choice of inserts of the bearing see the Section Installation to the place of the crankshaft and measurement of a radial gap of radical bearings.