6.6. A cranked shaft
Check up necks of a cranked shaft on a roughness. Any appreciable roughness specifies in necessity of repolishing of a cranked shaft or its replacement.
If the cranked shaft was перешлифован, check up absence of agnails round apertures for greasing. The found out agnails remove надфилем or шабером and carefully clear apertures and channels of a shaving.
Using a micrometer, measure diameter radical and шатунных necks of a cranked shaft and compare results to specifications. Necks measure in several points both on diameter, and on length that will allow to reveal ovality and конусность if they are.
Check up contact surfaces on each end of a cranked shaft on deterioration and other damages. If the neck is worn strongly out from an epiploon, that, probably, replacement of a cranked shaft is required.
Deterioration шатунной necks is characterised by knocks of metal tone at engine work, especially under loading, at small frequency of rotation, and reduction of pressure of oil.
Deterioration of radical necks of a cranked shaft is characterised by strong vibration of the engine and knocks of the metal tone, amplifying at increase in frequency of rotation of the engine, and also reduction of pressure of oil.
Even if radical and шатунный bearings are subject to replacement at engine major repairs, they are necessary for examining carefully as on their defects it is possible to judge a technical condition of the engine.
The bearing can fail because of a lack of greasing, hit of pollution, alien particles, an engine or corrosion overload. The reason of failure of the bearing should be eliminated before the engine will repeatedly collect.
For survey of bearings remove and spread out them in the same order in what they have been established on the engine. It will allow to define a corresponding neck of a cranked shaft and will facilitate search of malfunctions.
Alien particles can get to the engine various ways. Metal particles appear in engine oil as a result of normal deterioration of the engine. Small particles together with oil can get to bearings and easily take root into their soft material. Larger particles, getting to the bearing, can scratch the bearing or a neck of a cranked shaft. To prevent bearing failure for this reason, carefully clear all internal surfaces of the engine and keep them clean at engine assemblage. It is recommended to observe also demanded periodicity of replacement of oil with the filter.
Insufficient greasing of necks of a cranked shaft can be caused many reasons: an oil heat, an engine overload, oil leak and so forth
The manner of driving of the car also influences durability of bearings. At completely open throttle заслонке on low frequency of rotation of a cranked shaft of the engine loading on bearings raises and there is an expression from a zone of contact of an oil film. High loadings lead to occurrence of cracks in a working part of the bearing that in turn can lead to a separation of an antifrictional layer from a steel basis.
Movement on short distances leads to corrosion of bearings because the engine does not leave on the stabilised working temperature at which water steams and corrosion gases leave. Being condensed in engine oil, they form acid and a deposit. Acid together with engine oil gets to bearings and causes corrosion.
Wrong selection of bearings at engine assemblage also becomes the reason of failure of bearings. In the bearings established with a preliminary tightness, there is insufficient for maintenance of normal greasing a backlash.
At installation of a cranked shaft it is necessary to consider the following.
Fig. 3.4–38. A cranked shaft: 1 – the aligning plug; 2 – an asterisk; 3 – a persistent ring; 4 – a cranked shaft; 5 – a cover of bearings; 6 – a bolt; 7 – a persistent half ring; 8 – the loose leaf of the radical bearing; 9 – the plug; 10 – an adjusting pin; 11 – a persistent half ring;
12 – the loose leaf of the radical bearing
Persistent half rings 7 and 11 (fig. 3.4–38) are established only on the fourth radical bearing and used for adjustment of an axial backlash of a cranked shaft.
Lubricant flutes of persistent half rings should be directed outside.
Loose leaves 8 and 12 without a lubricant flute are established from outside covers of bearings.
At installation it is necessary to use new bolts of fastening of covers of bearings.
Fig. 3.4–39. Sequence of an inhaling of bolts of fastening of covers of radical bearings
Bolts of fastening of covers of radical bearings tighten in the sequence shown in drawing 3.4–39, in three stages:
1st – the moment 30 Н·м;
2nd – the moment 50 Н·м;
3rd – tighten on a corner 90 °.
Measurement of axial and radial backlashes of a cranked shaft
Fig. 3.3–50. Installation of an arm with the indicator of hour type for measurement of an axial backlash of a cranked shaft
Establish on the block of cylinders of the engine an arm with the indicator of hour type so that the measuring tip of the indicator rested against a counterbalance of a cranked shaft (fig. 3.3–50 see).
Move a cranked shaft along an axis to one party against the stop and establish an arrow of the indicator of hour type on 0. Take away a cranked shaft along an axis in other party against the stop and fix the value shown by the indicator. Rating value of an axial backlash of a cranked shaft of 0,090-0,251 mm, maximum permissible – 0,30 mm.
For measurement of a radial backlash in bearings of a cranked shaft it is necessary to use calibrated plastic core Plastigage.
Unscrew bolts and uncover the radical bearing and the radical loose leaf. Clear the radical loose leaf, a cover of the bearing and a neck of a cranked shaft.
Cut off a slice of the plastic calibrated core which length is equal to width of the bearing, and lay it along an axis of a cranked shaft on a neck of the radical bearing.
Establish a cover of the radical bearing with the radical loose leaf and fix its bolts, having tightened their moment
30 Н·м. Thus a cranked shaft do not turn.
Unscrew bolts and again uncover the radical bearing. Compare width of the deformed plastic core to the measuring scale put on packing of a plastic core. On a scale define a radial backlash. Rating value of a radial backlash of a cranked shaft of 0,018-0,045 mm, maximum permissible – 0,10 mm.