3.9. Bent shaft

Check necks of a bent shaft for a roughness. Any noticeable roughness indicates the need regrindings or replacements of a bent shaft.
If the bent shaft was перешлифован, check lack of agnails around openings for lubricant. Remove the found agnails with a file or a shaber and carefully clear openings and channels of shaving.
Measure by a micrometer diameter of radical and conrod necks of a bent shaft and compare results to specifications. Measure necks in several points both on diameter, and on length, it will allow to reveal ovality and conicity at their existence.       
Check the surfaces of contact of oil consolidation on each end of a bent shaft for wear and other damages. If the neck from consolidation is strongly worn-out, then, perhaps, replacement of a bent shaft will be required.
Wear of a conrod neck is characterized by the knocks of metal tone arising during the operation of the engine under loading with a small frequency of rotation, and reduction of pressure of oil.
Wear of radical necks of a bent shaft is characterized by strong vibration of the engine and the knock of metal tone amplifying at increase in frequency of rotation of the engine and also reduction of pressure of oil.
Even if radical and conrod bearings are subject to replacement at capital repairs of the engine, they need to be examined carefully: on their defects it is possible to judge technical condition of the engine.
The bearing can fail because of a lack of lubricant, hit of dirt and foreign debris, an overload of the engine or corrosion. The reason which caused a bearing exit out of operation should be eliminated before the engine repeatedly gathers.
For survey of bearings remove and spread out them in the same order in what they were established on the engine. It will allow to define the corresponding neck of a bent shaft and will facilitate search of malfunctions.
Foreign debris can get to the engine in various ways. Metal particles appear in engine oil as a result of normal wear of the engine. Small particles together with engine oil can get to bearings and it is easy to take root into its soft material. Larger particles, getting to the bearing, can scratch it or a neck of a bent shaft. To prevent failure of the bearing for this reason, it is necessary to clear carefully all internal surfaces of the engine and to keep them clean at assembly. It is recommended to observe the required frequency of replacement of oil with the filter.
Insufficient lubricant of necks of a bent shaft can be caused by many reasons: high temperature of oil, engine overload, oil leak and so forth.
The driving manner also exerts impact on durability of bearings. At completely open butterfly valve at a low frequency of rotation of a bent shaft of the engine load of bearings raises and there is an expression from a zone of contact of an oil film. High loadings lead to emergence of cracks in a working part of the bearing that in turn can cause a separation of an antifrictional layer from a steel basis.
The movement on short distances leads to corrosion of bearings as a result the engine does not come to the stabilized working temperature at which water vapor and corrosion gases are removed. Vapors and gases, being condensed in engine oil, form acid and a deposit. Acid together with engine oil gets to bearings and causes their corrosion.
The wrong selection of bearings at assembly of the engine also becomes the reason of their exit out of operation. In the bearings installed with a preliminary tightness there is a gap insufficient for providing normal lubricant of the rubbing surfaces.
At installation of a bent shaft it is necessary to consider the following.

Fig. 3.1-70. Bent shaft: 1 – the aligning plug; 2 – bent shaft; 3 – bolts of fastening of covers of bearings; 4 – covers of bearings; 5 – persistent half ring; 6 – insert of the radical bearing; 7 – the bearing plug used only with the automatic transmission; 8 - persistent half ring; 9 - an insert of the radical bearing with a lubricant flute; 10 – bolts



1. The aligning plug 1 (fig. 3.1-70) provides the correct installation of covers of radical bearings.

Fig. 3.1-71. Arrangement and numbering of radical bearings of a bent shaft



2. The radical bearing No. 1 is from a belt pulley, and the bearing No. 4 – from a flywheel (fig. 3.1-71).
3. At installation it is necessary to use new bolts 3 (see fig. 3.1-70).
4. Persistent half rings 5 establish only on the radical bearing No. 4.
Lubricant flutes of persistent half rings have to be directed outside.
Persistent half rings are used for adjustment of an axial gap of a bent shaft.
5. The insert without lubricant flute is established from a bearing cover.

Fig. 3.1-72. Sequence of tightening of bolts of fastening of covers of radical bearings



Blota fastenings of covers of radical bearings tighten in the sequence shown in the figure 3.1-72 in four stages:
The 1st – tighten side bolts And by hand;
The 2nd – tighten bolts 1–8 moment of 60 N · m;
The 3rd – tighten bolts 1–8 on a corner 90 °;
The 4th – tighten side bolts And the moment of 25 N · m.

Measurement of axial and radial gaps of a bent shaft

Fig. 3.1-73. Installation of an arm with the indicator of hour type for measurement of an axial gap of a bent 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 bent shaft (fig. 3.1-73).
Move a bent shaft along an axis to one party against the stop and install the indicator on 0. Move a bent shaft along an axis to other party against the stop and record value on the indicator. Nominal rate of an axial gap of a bent shaft of 0,07-0,23 mm, maximum permissible value – 0,25 mm.
For measurement of a radial gap in bearings of a bent shaft it is necessary to use the calibrated plastic core of Plastigage.
Turn off bolts and remove a cover and an insert of the radical bearing. Clear an insert, a cover and a neck of a bent shaft.
Cut off a piece of the plastic calibrated core which length is equal to bearing width, and lay it along an axis of a bent shaft on a neck of the radical bearing.
Establish a cover of the radical bearing with an insert and fix it by bolts, having tightened the moment 30 N · m. At the same time do not turn a bent shaft.
Turn off 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. Determine a radial gap by a scale. Nominal rate of a radial gap of a bent shaft of 0,018-0,045 mm, maximum permissible value – 0,10 mm.