3.2.2.11. Radical and conrod bearings
Types of wear of radical and conrod bearings
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A. Scratches because of hit of the dirt introduced in covering material |
D. Conicity of necks, a bearing covering wipe from all surface on bearing length E. Formation of a fillet on an edge of the bearing F. Fatigue wear, formation of craters or pockets |
Check of a state
In spite of the fact that radical and conrod bearings at capital repairs of the engine are subject to obligatory replacement, the bearings which were in operation should be stored in the place of their installation for careful check as wear tracks on these details allow to restore the general condition of the engine. Inserts of bearings are subdivided into dimensional groups on thickness, belonging to each dimensional group is specified by the color marking applied on an insert.
Insufficient lubricant, presence of dirt and foreign particles, overload of the engine and corrosion are causes of destruction of bearings of a bent shaft. Irrespective of the reason which caused destruction of bearings it should be eliminated before final assembly of the engine to avoid repeated damages of these details.
When checking a condition of bearings they should be got from the block of cylinders, covers of radical bearings of a bent shaft, conrod covers and rods. Lay out inserts on a pure surface in the same order in which they were established on the engine. It will allow to establish the corresponding support of a bent shaft in which the bearing underwent the increased wear. When checking the prikasaniye by fingers is not allowed to a working surface of inserts not to apply on them additional damages.
Dirt and foreign particles get to the engine for various reasons - in the course of assembly, via filters or system of ventilation of a case. Pollution can also get to oil, and from it – to bearings. Often at pollution there are metal particles from machining of details of the engine, or owing to wear at normal operation of the engine. Sometimes at pollution there are remains of abrasive materials after carrying out pritirochny and grinding works, especially at insufficient washing and a clearing of the engine after their termination. Irrespective of the origin reason foreign pollution usually take root into soft alloy of the bearing and are easily distinguishable. Large particles will not be able to take root into the bearing and lead to emergence of scratches and zadir on surfaces as bearing and necks of the crankshaft. The best way of the prevention of such wear is careful washing of details and maintenance of faultless purity at assembly of the engine. For the prevention of premature wear it is also recommended to a thicket to change oil and filters.
Insufficient lubricant of the engine ("oil starvation") can be caused by a number of the interconnected reasons. An engine overheat (causes oil fluidifying), overloads concern to them (cause expression of oil from the surface of bearings) and pressure decrease because of leak (emission) of oil (because of the raised gaps in bearings, wear of the oil pump, big frequency of rotation of a bent shaft). Also blocking of oil channels, usually owing to a nesovmeshchennost of lubricant openings in crankshaft bearings with openings in the block of cylinders and in rods is the reason of the accelerated wear of bearings of a bent shaft that causes insufficient lubricant and an exit from bearings out of operation. When insufficient lubricant is a cause of destruction, there is a wipe or expression of material of a covering of the bearing from a steel basis. Temperature increases up to such level that from an overheat there is a vykrashivaniye of a steel basis of the bearing which gets a bluish shade.
Durability of bearings of a bent shaft also significantly depends on skills of driving. Bearings experience the raised strain at the movement with completely open butterfly valve, or with a small speed on an overgear (in the heavy modes of the engine). At the raised loadings there is an expression of an oil film. Bearings experience flexural deformations at which microcracks (fatigue wear) are formed. As a rule there is a bearing covering separation from a steel basis in the form of small particles.
Trips on small distances can be the reason of corrosion wear of bearings as because of insufficient warming up the condensed moisture and gases causing corrosion do not manage to be removed. These components collect in oil, causing formation of acids and insoluble rainfall. In process of intake of oil to bearings there is a corrosion under the influence of acids, causing destruction of bearings and their exit out of operation.
The wrong installation of bearings at assembly also results in their premature wear. If the gap in bearings is less than norm, then their lubricant is complicated that results in wear as well as owing to "oil to starvation". The dirt or small particles which got under a bearing insert lead to a local raising of an insert and to the increased wear in this part.
At assembly do not touch with fingers insert surfaces, otherwise it is possible to scratch a surface or to bring on a dirt particle insert.
As it was already noted, at capital repairs of the engine inserts of radical and conrod bearings are subject to obligatory replacement. The neglect this rule and economy on repair is led to extremely undesirable consequences.