3.9. A cranked shaft
Check up necks of a cranked shaft on a roughness. Any appreciable roughness specifies in necessity of repolishing or replacement of a cranked shaft.
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.
By 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, it will allow to reveal ovality and конусность at their presence.
Check up surfaces of contact of oil consolidation on each end of a cranked shaft on deterioration and other damages. If the neck from consolidation is worn strongly out, that, probably, replacement of a cranked shaft is required.
Deterioration шатунной necks is characterised by the knocks of metal tone arising at work of the engine 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 the knock of metal tone amplifying at increase of 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: 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 a dirt and alien particles, an engine or corrosion overload. The reason which has caused an exit of the bearing out of operation, it is necessary to eliminate before the engine will repeatedly gather.
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 engine oil can get to bearings and easily take root into its soft material. Larger particles, getting to the bearing, can scratch it or a neck of a cranked shaft. To prevent bearing failure for this reason, it is necessary to clear carefully all internal surfaces of the engine and to keep them clean at assemblage. It is recommended to observe 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 driving manner 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 cause 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. Steams and gases, being condensed in engine oil, form acid and a deposit. Acid together with engine oil gets to bearings and causes their corrosion.
Wrong selection of bearings at engine assemblage also becomes the reason of their exit out of operation. In the bearings established with a preliminary tightness, there is a backlash insufficient for maintenance of normal greasing of rubbing surfaces.
At installation of a cranked shaft it is necessary to consider the following.
Fig. 3.1–70. A cranked shaft: 1 – the aligning plug; 2 – a cranked shaft; 3 – bolts of fastening of covers of bearings; 4 – covers of bearings; 5 – a persistent half ring; 6 – the loose leaf of the radical bearing; 7 – the plug of the bearing used only with an automatic transmission; 8 - a persistent half ring; 9 - the loose leaf of the radical bearing with a lubricant flute; 10 – bolts
1. The aligning plug 1 (fig. 3.1–70) provides correct installation of covers of radical bearings.
Fig. 3.1–71. An arrangement and numbering of radical bearings of a cranked shaft
2. The radical bearing №1 is from outside a belt pulley, and the bearing №4 – from outside a flywheel (fig. 3.1–71).
3. At installation it is necessary to use new bolts 3 (fig. 3.1–70 see).
4. Persistent half rings 5 establish only on the radical bearing №4.
Lubricant flutes of persistent half rings should be directed outside.
Persistent half rings are used for adjustment of an axial backlash of a cranked shaft.
5. The loose leaf without a lubricant flute is established from outside bearing covers.
Fig. 3.1–72. Sequence of a tightening of bolts of fastening of covers of radical bearings
Блоты fastenings of covers of radical bearings tighten in the sequence shown in drawing 3.1–72, in four stages:
1st – tighten lateral bolts And by hand;
2nd – tighten bolts 1–8 moment 60 Н·м;
3rd – tighten bolts 1–8 on a corner 90 °;
4th – tighten lateral bolts And the moment 25 Н·м.
Measurement of axial and radial backlashes of a cranked shaft
Fig. 3.1–73. 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. 3.1–73).
Move a cranked shaft along an axis to one party against the stop and establish the indicator on 0. Move a cranked shaft along an axis to other party against the stop and fix value on the indicator. Rating value of an axial backlash of a cranked shaft of 0,07-0,23 mm, maximum permissible value – 0,25 mm.
For measurement of a radial backlash in bearings of a cranked shaft it is necessary to use calibrated plastic core Plastigage.
Turn away bolts and uncover also the loose leaf of the radical bearing. Clear the loose leaf, a cover 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 loose leaf and fix its bolts, having tightened the moment 30 Н·м. Thus a cranked shaft do not turn.
Turn away 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 value – 0,10 mm.