4.7.14. Check of a condition of radical and conrod bearings of a bent shaft
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. On an accompanying illustration examples of typical defects of inserts of bearings are given.
Typical examples of wear of bearings
|LACK OF LUBRICANT|
|CONICITY OF THE NECK|
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
In case of wear or damage of inserts of bearings, and also when it is not possible to achieve the correct size of a working gap, the situation can be corrected in the way described below, in the way of selection and installation of new inserts. 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.
If it is not possible to correct properly the size of working gaps by selection of inserts, the shaft should be replaced.
Usually selection of inserts is carried out by the experts making a pro-point of necks of a shaft. The standard size of new inserts is defined by depth of a pro-point of necks. The pro-point is usually carried out with a step of 0.25 mm. In certain cases radical and conrod necks are pierced on various depth. The pierced shaft usually as appropriate is marked. So, for example, marking of the 10-10 type usually means that both sets of necks are pierced on depth of 0.010 inches (0.25 mm) and it is necessary to select inserts of the corresponding size with belittling. Identification marking on the back of an insert is used by experts when determining dimensional group of bearings.