If the crankshaft has been ground, check for burrs around the oil holes. Remove any burrs found with a needle file or scraper and carefully clean the holes and channels from chips.
Using a micrometer, measure the diameter of the crankshaft main and connecting rod journals and compare the results with the technical data. Necks are measured at several points both in diameter and length, this will reveal ovality and taper, if any.
Check the oil seal contact surfaces at each end of the crankshaft for wear or other damage. If the seal journal is badly worn, the crankshaft may need to be replaced.
Wear of the connecting rod journal is characterized by metallic knocks that occur when the engine is running under load, at low speeds, and a decrease in oil pressure.
Wear of the crankshaft journals is characterized by strong engine vibration and a metallic sound that increases with increasing engine speed, as well as a decrease in oil pressure.
Even if the main and connecting rod bearings are to be replaced during the overhaul of the engine, they must be carefully examined: their defects can be used to judge the technical condition of the engine.
The bearing can fail due to lack of lubrication, dirt and foreign particles, motor overload or corrosion. The cause of the bearing failure must be corrected before the engine is reassembled.
To inspect the bearings, remove and arrange them in the same order in which they were installed on the engine. This will identify the appropriate crankshaft journal and facilitate troubleshooting.
Foreign particles can enter the engine in various ways. Metal particles appear in engine oil as a result of normal engine wear. Small particles along with engine oil can get into the bearings and easily penetrate into its soft material. Larger particles entering the bearing can scratch it or the crankshaft journal. To prevent bearing failure from this cause, all internal surfaces of the motor must be thoroughly cleaned and kept clean during reassembly. It is recommended to observe the required interval for changing the oil with filter.
Insufficient lubrication of the crankshaft journals can be caused by many reasons: high oil temperature, engine overload, oil leakage, etc.
Driving style also has an impact on bearing life. When the throttle is fully open at a low engine speed, the load on the bearings increases and the oil film is squeezed out of the contact zone. High loads lead to the appearance of cracks in the working part of the bearing, which in turn can cause the anti-friction layer to separate from the steel base.
Short distance driving results in corrosion of the bearings as a result of the motor not reaching a stabilized operating temperature that removes water vapor and corrosive gases. Vapors and gases, condensing in engine oil, form acid and sediment. The acid, along with the engine oil, gets into the bearings and causes them to corrode.
Incorrect selection of bearings during engine assembly also causes their failure. In bearings installed with preload, there remains a gap that is insufficient to ensure normal lubrication of rubbing surfaces.
When installing the crankshaft, consider the following.
Pic. 3.1–70. Crankshaft: 1 - centering sleeve; 2 - crankshaft; 3 – bolts of fastening of covers of bearings; 4 - bearing caps; 5 - persistent half ring; 6 - insert of the main bearing; 7 – the bearing plug used only with an automatic transmission; 8 - persistent half ring; 9 - main bearing shell with an oil groove; 10 - bolts
1. Centering sleeve 1 (pic. 3.1–70) ensures proper installation of the main bearing caps.
Pic. 3.1–71. Location and numbering of crankshaft main bearings
2. Main bearing #1 is on the pulley side and bearing #4 is on the flywheel side (pic. 3.1–71).
3. When installing, you must use new bolts 3 (see fig. 3.1–70).
4. Thrust half rings 5 are installed only on the main bearing No. 4.
The lubrication grooves of the thrust half rings must be directed outward.
Thrust half rings are used to adjust the axial clearance of the crankshaft.
5. A bushing without an oil groove is installed on the side of the bearing cover.
Pic. 3.1–72. The sequence of tightening the bolts of the main bearing caps
The main bearing cap bolts are tightened in the sequence shown in Figure 3.1–72 in four stages:
- 1st - tighten the side bolts A by hand;
- 2nd - tighten bolts 1–8 to 60 Nm;
- 3rd - tighten bolts 1–8 at an angle of 90°;
- 4th - tighten the side bolts A torque 25 Nm.
Measurement of axial and radial clearances of the crankshaft
Pic. 3.1–73. Installation of a bracket with a dial indicator for measuring the axial clearance of the crankshaft
Install the bracket with the dial indicator on the engine block so that the measuring tip of the indicator rests against the counterweight of the crankshaft (pic. 3.1–73).
Move the crankshaft along the axis to one side until it stops and set the indicator to 0. Move the crankshaft along the axis to the other side until it stops and fix the value on the indicator. The nominal value of the axial clearance of the crankshaft is 0.07–0.23 mm, the maximum allowable value is 0.25 mm.
To measure the radial clearance in the crankshaft bearings, a calibrated Plastigage plastic rod must be used.
Turn away bolts and remove a cover and loose leaf of the radical bearing. Clean the bearing, cover and crankshaft journal.
Cut off a piece of plastic calibrated rod, the length of which is equal to the width of the bearing, and lay it along the axis of the crankshaft on the main bearing journal.
Install the main bearing cap with bushing and bolt it to 30 Nm. Do not turn the crankshaft while doing this.
Turn away bolts and again remove a cover of the radical bearing. Compare the width of the deformed plastic rod with the measuring scale printed on the packaging of the plastic rod. On the scale, determine the radial clearance. The nominal value of the radial clearance of the crankshaft is 0.018–0.045 mm, the maximum allowable value is 0.10 mm.
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