Contents: Knocking in the crankshaft main…↓ Knocking of connecting rod bearings ↓ Oil entering the coolant ↓ Coolant entering the oil ↓
The main faults of the crank mechanism include knocking of pistons and pins, knocking in the crankshaft bearings, loss of compression in the cylinders and engine power, leakage of coolant into the crankcase or, conversely, oil getting into the coolant. All these faults can be detected by monitoring the engine operation.
Knocks in the engine occur when parts of the crank mechanism wear out. They are listened to and the location of the knock is found using stethoscopes. The simplest stethoscope is a metal rod with an earpiece. By applying the tip of the rod to various points of the block or cylinder head, the cause of the knock is determined by the characteristic shades of sound and the place of its occurrence. There are also electronic stethoscopes consisting of a low-frequency transistor amplifier and a piezoelectric crystal sensor.
Determining engine faults by knocking sounds requires a lot of skill. In addition, to eliminate faults in the crank mechanism, it is necessary to remove the engine from the car and disassemble it completely or partially. Therefore, in the event of knocking or any other faults in the crank mechanism, it is recommended to contact a service station, where experienced specialists will determine and eliminate the fault.
Compression (pressure) in the engine cylinders is checked with a special device - a compression meter. It is a pressure gauge with a check valve. To measure compression, the compression meter tip is installed in place of the unscrewed spark plug and, turning the crankshaft with the starter, the maximum pressure in the cylinder is recorded on the pressure gauge.
Knocking in the crankshaft main bearings
Typically, it is a low-pitched metallic knock. It is heard in the lower part of the cylinder block and is detected when the throttle valve is opened sharply at idle. Excessive crankshaft clearance causes a sharper knock with uneven intervals, especially noticeable when the crankshaft speed increases and decreases smoothly.
Causes of knocking and ways to eliminate it:
- too early ignition. Check and adjust ignition timing;
- insufficient oil pressure. See chapter "Main faults of the lubrication system";
- increased clearance between the crankshaft journals and the main bearing shells. Contact a service station for inspection and, if necessary, for regrinding the journals and replacing the shells;
- increased clearance between the thrust half rings and the crankshaft. With the engine off, check the axial free play of the crankshaft by pressing and releasing the clutch pedal. In this case, the movement of the front end of the crankshaft should be no more than 0.35 mm. In case of a larger axial free play, contact a service station to replace the thrust half rings of the crankshaft.
Knocking of connecting rod bearings
Usually the knock of connecting rod bearings is sharper than the knock of main bearings. It is heard in the upper part of the cylinder block at idle speed of the engine when the throttle valve is opened sharply. The place of knocking is easy to determine by disconnecting the spark plugs one by one.
Causes of knocking and ways to eliminate it:
- insufficient oil pressure. See chapter "Main faults of the lubrication system";
- excessive clearance between the crankshaft journals and the bearings. Have the crankshaft journals ground and the bearings replaced at a service station.
Knocking of pistons and piston pins. The knocking of pistons is usually muffled, muffled, caused by the "beating" of the piston in the cylinder: It is best heard at low crankshaft speed under load. Knocking of the pins is distinct and sharp, increases with increasing crankshaft speed and disappears when the cylinder is switched off. It is heard in the upper part of the cylinder block.
[The article is taken from an online resource VAZbook.ru]
Causes of knocking and ways to eliminate it:
- increased clearance between pistons and cylinders. Repair the engine by boring and honing the cylinders and replacing the pistons;
- excessive clearance between piston rings and piston grooves. Replace rings or piston with rings;
- excessive clearance between the pin and the hole in the piston. Replace the piston and pin.
Low compression in cylinders (the engine does not develop full power). The compression gauge shows the compression value in the cylinder is less than 10 kgf/cm². Pour 20...25 cm³ of clean motor oil into the cylinder with low compression and measure the compression again. In this case, two cases can be observed.
a) The compression gauge gives a higher compression reading.
Causes of the malfunction and ways to eliminate it:
- broken or stuck piston rings in the piston grooves. Clean the rings and piston grooves from carbon deposits, replace damaged rings and pistons;
- excessive wear of cylinders and piston rings. Repair the engine by boring and honing the cylinders and replacing the pistons.
b) The compression gauge readings do not change. Set the piston to TDC of the compression stroke, brake the car with the parking brake, engage the highest gear and supply compressed air at a pressure of 2...3 kgf/cm² to the spark plug hole. An air leak will be observed.
Causes of the malfunction and ways to eliminate it:
- poor valve seating. Air leakage into the carburetor (the inlet valve is leaking) or into the muffler (leaky exhaust valve). For the cause and solution, see the chapter "Main faults of the valve timing mechanism";
- the cylinder head gasket is broken. Compressed air with a characteristic hissing sound passes into the adjacent cylinder. Remove the cylinder head and replace the gasket.
Oil entering the coolant
A decrease in the oil level in the engine is observed, an oil film appears in the expansion tank, the color of the coolant changes from gray to dark brown.
To check, remove the cylinder head, fill the cooling jacket of the cylinder block with water and supply compressed air to the vertical oil channel of the cylinder block (near the hole for bolt 5, see figure 22). If air bubbles are observed in the water filling the cooling jacket, then the cause of the malfunction is cavities or cracks in the bridges between the oil line and the cooling jacket of the cylinder block. In this case, the cylinder block must be replaced.
If the oil passages of the cylinder block are sealed, then oil may be getting into the coolant from the oil passages of the cylinder head. In this case, it is necessary to check the tightness of the cylinder head (see chapter "Main faults of the valve timing mechanism").
Coolant entering the oil
The liquid level in the expansion tank is constantly decreasing, and the oil level is increasing. The oil changes color from gray to milky white.
The causes of the malfunction are cavities, porosity or cracks in the walls of the cylinder block cooling jacket. To check this defect, it is necessary to disassemble the engine and check the tightness of the cylinder block cooling jacket in a bath with water, supplying compressed air to the jacket under a pressure of 2...3 kgf/cm².
If air leakage is not observed, it is necessary to check the tightness of the cylinder head (see chapter "Main faults of the valve timing mechanism").