Knocking and noise in the engine arise as a result of wear of its main parts and the appearance of increased gaps between mating parts. Engine knocks can be heard using a stethoscope, which requires some skill. Usually, when the liners wear out a lot, its antifriction layer melts, which is accompanied by a sharp drop in oil pressure. In this case, the engine must be stopped immediately, as further operation may lead to damage to parts. Increased oil consumption, excessive fuel consumption, and the appearance of smoke in the exhaust gases (at a normal oil level in the crankcase) usually appear when the piston rings are stuck or the cylinder rings are worn out. The occurrence of the ring can be eliminated without disassembling the engine, for which 20 g of a mixture of equal parts of denatured alcohol and kerosene should be poured into each cylinder of a hot engine overnight through the spark plug hole. In the morning, the engine should be started, run for 10-15 minutes, and then the oil should be changed.
Before diagnosing, the engine should be warmed up to the coolant temperature (90+-5) C. Listening with a stethoscope is carried out by touching the tip of the sound-sensitive rod in the interface area of the mechanism being tested. The operation of the piston-cylinder is listened to over the entire height of the cylinder at a low speed of rotation of the crankshaft with a transition to medium - knocking of a strong dull tone, increasing with increasing load, indicates a possible increase in the gap between the piston and the cylinder, bending of the connecting rod, piston pin, etc. . The piston ring mating - the groove is checked at the level of BDC of the piston stroke at an average rotation speed of the piston - a weak high-pitched knock indicates an increased gap between the rings and the piston grooves, or excessive wear or breakage of the rings. The connection between the piston pin and the bushing of the upper head of the connecting rod is checked at the TDC level at a low speed of rotation of the CV with a sharp transition to the average one. A strong, high-pitched knock, similar to frequent blows with a hammer on an anvil, indicates increased wear of the mating parts. The interface work between the crankshaft and the connecting rod bearing is monitored at low and medium rotational speeds (below BDC).
A dull mid-tone sound accompanies wear on the connecting rod bearings. The knock of the main bearings of the HF is heard in the same zones (slightly lower) with a sharp change in the rotation speed of the HF: a strong dull knock of a low tone indicates wear of the main bearings.
Compression check
Compression in the cylinders is determined by a compression gauge, which is a housing with a pressure gauge built into it. The pressure gauge is connected to one end of a tube, the other end of which has a spool with a rubber tip that fits tightly into the spark plug hole. By turning the engine crankshaft with the starter or crank, measure the maximum pressure in the cylinder and compare it with the standard ones. For gasoline engines, the nominal compression values are 0.75...1.5 (7 - 15 kgf/cm2). A drop in engine power occurs when piston rings are worn out or stuck in the grooves, pistons and cylinders are worn out, or the cylinder head is poorly tightened. These faults cause a drop in compression in the cylinder.
Consumption of compressed air supplied to the cylinders
To determine the leakage of compressed air from the space above the piston, the K-69M device is used. Air is supplied to the cylinders of a heated engine either through gearbox 1 of the device, or directly from the line through hose 4 to cylinder 7 through fitting 6, screwed into the hole for the spark plug or injector, to which hose 3 is connected using quick-release coupling 5. In the first case, check for leakage air or pressure drop due to leaks in each engine cylinder. To do this, use the gear handle 1 to adjust the device so that when the clutch valve 5 is completely closed, the pressure gauge needle is opposite the zero division, which corresponds to a pressure of 0.16 MPa, and with the valve fully open and air leaking into the atmosphere, it is against the 100% division. The relative leakage of the cylinder-piston group is checked by installing the piston of the cylinder being tested in two positions: at the beginning and end of the compression stroke. The piston is prevented from moving under the pressure of compressed air, including the gear in the car's gearbox. The compression stroke is determined by a whistle-signaling device inserted into the hole of the spark plug (injector). The condition of the piston rings and valves is assessed according to the readings of pressure gauge 2 when the piston is positioned at TDC, and the condition of the cylinder (cylinder wear in height) is assessed according to the readings of the pressure gauge when the piston is positioned at the beginning and end of the compression stroke and by the difference between these readings. The obtained data are compared with the values at which further operation of the engine is unacceptable. The maximum permissible air leakage values for engines with different cylinder diameters are indicated in the device instructions. To determine the location of the leak (malfunction), air under a pressure of 0.45-06 MPa is supplied from the line through hose 4 into the engine cylinders. The piston is installed at the end of the compression stroke at top dead center. The location of air breakthrough through the leak is determined by listening with a phonendoscope. Air leakage through the engine valves is detected visually by the vibration of the indicator fluffs inserted into the hole of the spark plug (injector) of one of the adjacent cylinders where the valves are open in this position. Air leakage through the piston rings can only be determined by listening when the piston is at ground level. in the area of minimal cylinder wear. A cylinder head gasket leak can be detected by bubbles in the radiator neck or at the connector plane. Total clearance in the upper head of the connecting rod and the connecting rod bearing Measuring the total clearance in the upper head of the connecting rod and the connecting rod bearing is another effective method for checking the condition of the crank mechanism.
A preliminary assessment of the condition of the crankshaft couplings can be obtained from the oil pressure in the main line and the nature of knocking in certain areas of the engine.
Oil pressure is checked using a KI-5472 GOSNITI device, which consists of a pressure gauge, a connecting hose with a nipple and a union nut, a damper to smooth out oil pulsations when measuring pressure, and replaceable fittings. To measure the pressure in the main line of a diesel engine, the device is connected to the oil filter housing by disconnecting the standard pressure gauge tube.
To check the pressure, do the following:
- connect to the oil filter housing KI-5472
- start and warm up the engine to normal thermal condition
- record the oil pressure in the line at the nominal and minimum stable crankshaft speed at idle
Knocks in the CV joints are listened to when the engine is not running using an electronic autostethoscope TU 14 MO.082.017, alternately creating a vacuum and pressure in the space above the piston using a compressor-vacuum unit KI-4912 GOSNITI or KI-13907 GOSNITI. Listen to knocks in interfaces piston bosses - piston pin, piston pin - upper head bushing connecting rod A, crankshaft journal - connecting rod mechanism.
If the oil pressure is below the permissible values, if there are knocks in the crankshaft joints, check the gaps in the indicated joints. If the oil pressure is low and there are no knocks, check the adjustment of the lubrication system drain valve. If this does not give positive results, check the oil supply by the pump and the condition of the pressure reducing valve of the lubrication system on the stand.
Determining the condition of the crankshaft by the gaps in its mates
A conclusion about the condition of the crankshaft can be made by the size of the gaps in its mates. The total clearance in the upper head of the connecting rod and the connecting rod bearing is measured with a KI-11140 GOSNITI device.
To measure gaps you need:
- set the cylinder being tested to TDC on the compression stroke and lock the crankshaft
- fix the device in the cylinder head instead by loosening the locking screw and lifting the guide with the indicator and the rod up
- lower the guide until the rod stops at the piston bottom (by tension) and secure it with a screw
- connect the distribution pipeline of the compressor-vacuum unit to the fitting of the pneumatic receiver
- turn on the installation and bring the pressure and vacuum in its receivers to 0.06-0.1 MPa and 0.06-0.07 MPa, respectively
- perform two or three cycles of supplying pressure and vacuum to the above-piston space by switching the distribution valve until stable indicator readings are obtained
- connect the compressed air receiver to the space above the piston with a tap and set the indicator to zero
- smoothly connect the rarefied air receiver to the space above the piston and use the indicator to first record the gap in the connection between the piston pin and the upper head of the connecting rod, then the total gap in the upper head of the connecting rod and the connecting rod bearing
The gaps in the crankshaft drive are measured 3 times and the average value is taken.
If the clearances of at least one connecting rod exceed the permissible values, the engine must be repaired.
Workplace No. 1 ____
TOPIC: Diagnosis of crankshaft and timing belt.
Goal of the work: Acquisition of skills and abilities in diagnosing crankshaft and timing gear parts
Students from the group ______ who have passed the appropriate level are allowed to perform laboratory work.
theoretical training course and safety briefing (certified by personal signature)
| № | Last name, initials of the student | Student signature confirming completion of safety training |
Workplace equipment:
stands with engines ZIL-130, ZMZ-53, KamaAZ-740, compression gauge K-181, a device for measuring relative leaks in the cylinders of the K-69M engine, gas meter GKF-6, vacuum gauge, wrenches.
Operating procedure:
1. Determination of compression in engine cylinders
One of the indicators characterizing the technical condition of the parts of the cylinder-piston group is the pressure P tc at the end of the compression stroke, which is determined on a preheated engine with the spark plugs turned out and the throttle and air valves fully open. When measuring, turn the crankshaft with a starter (150-180 rpm) or manually, using a handle, approximately 10-12 revolutions. The P ts value is determined with a compression meter, the tip of which is tightly inserted into the holes for the spark plugs or injectors. The compression pressure value for each
the cylinder is determined 2-3 times. In this case, the difference in readings across the cylinders should not exceed 1 kgf/cm 2
Draw up a report on item 1. Indicate the nominal and maximum compression values of the engine being tested.
2.Determination of relative cylinder leakage.
To assess the technical condition of the cylinder-piston group and valve mechanism, the most common method is based on measuring the relative leakage in the gaps (the size of which depends on the degree of wear of the joints) of air supplied under pressure into the engine cylinders through the holes for spark plugs or injectors.
Relative air leakage through the gaps is measured with a model K-69M device, designed for automobile engines with a cylinder diameter of 50-130 mm.
To make the measurement more accurate, before diagnosing it is necessary to warm up the engine to a normal thermal state (75...80°C), then loosen the spark plugs and restart the engine for 10...15 s. Unscrew the spark plugs, and on a diesel engine, disconnect the fuel pipes, fastening nuts and remove the injectors. Remove the cover from the distributor-distributor and the current carrier, and for diesel engines K-69M
Assemble the index from the accessory kit.
Connect the K-69M device to the engine. All parts of the device are attached to the bottom of the panel. On the top side of the panel there is a measuring pressure gauge, outlet and inlet fittings, an air pressure reducer and a screw for periodic adjustment of the device. A connecting hose is attached to the outlet fitting using a union nut to supply compressed air to the engine cylinder. The device kit includes accessories used in diagnosing the cylinder-piston group and engine valves.
If compressed air is supplied into the cylinder cavity through the hole of the spark plug through a cross section of a constant size and under a certain pressure, then the condition of the cylinder can be judged by the amount of air passing through the leaks in the cylinder. Compressed air is supplied to the cylinder from the main line (from a cylinder) at a pressure of 0.16 MPa, which is maintained by the gearbox and recorded by a pressure gauge. Then air through
the nozzle enters the engine cylinder. Thus, the device divides the air flow into two parts: one part of the flow is before the calibrated hole, the other part is after the calibrated hole. Before the calibrated hole, the pressure is maintained constant, and after the calibrated hole, the pressure value changes depending on the tightness of the cylinders.
The higher the tightness in the space above the piston, the greater the pressure measured by the pressure gauge. In a worn engine, the pressure behind the calibrated hole is less, since the air flow into the crankcase will increase. For the new engine, the pressure behind the calibrated hole will be close to the pressure of 0.3---0.6 MPa in front of the calibrated hole. For ease of use of the device, its scale is calibrated not in absolute values of air leakage, but in percentage of the maximum, i.e., such a leakage that is possible when air is freely escaping from the device into the atmosphere. The actual condition of the cylinder-piston group or valves is assessed using tables or the shaded part of the scale, where the permissible amount of air leakage is indicated as a percentage.
Measured with the piston position at c. m. t (the end of the compression stroke, determined using a special signaling device installed in a threaded fitting). Air leakage through leaks is determined
indicator or by ear If. Table 1
O 
relative air leak measured at the end of the compression stroke is greater than the permissible value (Table 1), then it is necessary to determine
its value when the piston is in position. m.t. (beginning of the compression stroke). If the difference in the values of the relative air leakage when the piston is positioned at TDC. and n.m.t. more than the permissible values, then the cylinder-piston group needs to be repaired
Draw up a report on clause 2. Indicate the nominal and limit values of the relative leakage of the cylinders of the engine being tested.
3. Checking the amount of gases breaking into the engine crankcase.
To measure the amount of gases escaping into the crankcase ^
1
engine uses a gas flow meter or meter 6
brand GKF-6 (used to measure gas consumption in everyday life) or a rotameter. Before measurement, the engine crankcase is sealed. Gas breakthrough is measured at maximum power mode at maximum engine crankshaft speed. This mode is created for 30 seconds when driving in lower (second or third) gear with the throttle fully open and the car braking with the foot brake.
Draw up a report on clause 3. Indicate the nominal and limit values of the amount of gases breaking into the crankcase of the engine being tested.
Security check questions:
1. Reasons for decreased compression in engine cylinders.
2. Explain the technology for checking compression in engine cylinders.
3. Explain the technology for determining the relative leakage of cylinders using the K-69M device
4. Explain the technology for checking the amount of gases escaping into the engine crankcase
Teacher's mark: ___________________
LAB REPORT No. ___
performed by students gr. M- ____« ___» __________ 20___
| № | Last name, initials of the student | Student's signature |
6. Methods, means and technology for diagnosing crankshafts and engine timing belts
KShM. The crank mechanism includes a cylinder-piston group (cylinder liners, pistons and piston rings), a crankshaft with connecting rod and main bearings, connecting rods with bushings, piston pins and a flywheel.The main indicator of the condition of the cylinder-piston group is the crankcase oil consumption for waste. In order to determine oil waste with sufficient accuracy, several control shifts are required with precise measurements of the amount of added oil and fuel, which is extremely labor-intensive. In this case, it is impossible to take into account oil leaks through the tightness of the crankshaft oil seals and crankcase connectors. In addition, oil loss changes insignificantly over a long period of engine operation and only with significant wear of parts of the cylinder-piston group, in particular piston rings, does it begin to increase sharply. This nature of the change in oil loss depending on the operating time makes it difficult to predict its residual life.
The wear rate of engine joints can be judged by the concentration of wear products in the crankcase oil, determined using a spectrographic setup. In this case, to assess the degree of wear of the main parts, along with regular spectral analysis of oil samples taken at certain intervals of engine operation, it is necessary to know their chemical composition and the ratio of wear rates of joints. The advisability of disassembling the engine for repair or troubleshooting is judged by a sharp increase in the concentration of the main elements in the working oil.
The most widely used method for assessing the condition of the cylinder-piston group is to determine the amount of gases breaking into the crankcase. When measuring the amount of gases using a conventional device, such as a rotameter, due to the high resistance to the exit of gases from the crankcase and the presence of excess pressure in the crankcase, some of the gases escape into the atmosphere through the crankshaft seals and other leaks, bypassing the device.
To avoid this, during measurements it is necessary to suck gases from the crankcase, ensuring that they pass only through the measuring device.
Crankcase oil waste and the amount of gases breaking into the crankcase when the engine is running on all cylinders are integral (total) assessment indicators of the technical condition of the piston group cylinder.
To assess the condition of each cylinder individually, they are turned off one by one. Then calculate the difference between the gas flow rate obtained by decompressing the cylinder under test and the average gas flow rate obtained by decompressing each of the remaining cylinders. If all cylinders are in the same condition, the indicated difference will be insignificant. If it turns out to be large, then this indicates an emergency condition of this cylinder.
A comparative assessment of the technical condition of the cylinders can be given by the compression in them (compression end pressure). However, it is not the density of the gas distribution valves that must be taken into account. The difference in compression values between new and worn engines increases with decreasing crankshaft speed. Therefore, it is recommended to determine compression at the starting speed of the crankshaft. In order to give a correct comparative assessment of the condition of the cylinders by compression, the equality and constancy of the crankshaft rotation speed and the temperature of the cylinder walls must be observed when checking each of them separately. Due to the fact that the crankshaft rotation speed depends on the technical condition of the starting device, and the temperature of the cylinder walls depends on the engine test conditions (preheating it, ambient temperature), compliance with the noted conditions is not always possible. Consequently, compression is an approximate indicator of the technical condition of the cylinder-piston group. One of the signs of weak compression is difficulty starting the engine (especially in cold weather), due to the excessively low temperature of the compressed air, which does not ensure self-ignition of diesel fuel.
The condition of the crankshaft bearings can be judged by the clearances in them. The ellipse and taper of the shaft journals do not need to be checked before disassembling the engine for repairs, since these indicators are a consequence of bearing wear.
Over the years, many researchers have been searching for in-place methods for assessing the technical condition of crankshaft bearings using diagnostic parameters. The most well-known methods are those based on determining the following indicators: oil pressure in the main oil line, the amount of oil flowing through the bearings per unit time, noises and knocks arising from impacts in the interfaces during engine operation, knocks arising from the collision of parts as a result of artificial movement of the piston and connecting rod by the amount of gaps in the joints.
Listening to the engine while it is running has become widespread. As the clearances in the bearings increase, characteristic knocking noises appear, audible in certain areas and under corresponding engine operating conditions. However, these knocks are clearly audible when the gaps exceed the permissible values. In this case, the quantitative assessment of the gaps depends on the hearing qualities and experience of the operator.
Timing belt The main indicators of the technical condition of the gas distribution mechanism are the tightness of the valves to the head seats, the gaps between the valve stems and the rocker arms, the valve timing, the degree of wear of the cams, camshaft bearings and timing gears, the condition of the gasket and cylinder head, as well as the elasticity of the valve springs.
The presence of leaks in the mating of the valve plates and head seats can be determined by the characteristic hissing or whistling of air in the inlet and outlet channels of the head or pipelines if you turn the crankshaft by hand with the rocker arms and air cleaner removed.
A method has been developed that makes it possible to quantify valve leaks based on the air flow passing through each valve individually when supplied to the combustion chamber of an idle engine.
The location of the valve plates relative to the bottom of the head (valve recess) can be determined in two ways. In the first method, the distance between the plane of the bottom of the head and the plane of the end of the valve plate is measured directly with the head removed. In the second method, the specified distance is determined indirectly - by the distance between the plane of the end of the valve stem and the machined plane of the head on the side of the valve mechanism, measured on the engine with the valve box cover removed. The first method is usually used when repairing an engine, and the second when diagnosing components and assemblies during operation.
The degree of wear of the camshaft cams is assessed by the height of the cams, which can be determined directly on the engine by the amount of movement of the valves, taking into account the gaps between their rods and the rocker arms.
The elasticity of valve springs without removing them from the engine can be determined by the force of pressing the valves to the head sockets.
Unsatisfactory operation of the gas distribution mechanism, accompanied by a decrease in engine power and efficiency, is possible due to a violation of the valve timing. If the phases are disrupted due to incorrect connection of the distribution gears (not according to the marks), the beginning of the opening and the end of the closing of the valves are shifted by the same angle relative to c. m.t. pistons of all cylinders. If the cause of the phase shift is wear of the parts of the gas distribution mechanism, then due to uneven wear of components and parts, mainly the camshaft cams, the angles of the beginning of the opening and the end of closing of the valves may differ slightly from each other. Therefore, to reduce the labor intensity of the valve timing of multi-cylinder engines, it is recommended to check the opening angle of the intake valve of the first and last cylinders and evaluate them by the arithmetic average value obtained from the measurements.
If cases of twisting of camshafts occur, mainly due to bearings seizing after engine repair. This malfunction can be detected by measuring the angles at which the intake valves of the first and last cylinders begin to open. Under normal shaft conditions, these angles will be of the same order. When designing and fine-tuning engines, the valve timing is calculated and adjusted taking into account the thermal gaps between the valves and rocker arms, which are also established by calculation. In fact, the opening of the valves begins after the thermal gap has been completely selected. It follows that the valve timing must be checked at nominal valve clearances.
To make an approximate assessment of the valve clearances without removing the cover, use a conventional stethoscope, the tip of which is applied to the valve box. If the gaps in the valve mechanism area are excessively large, clear metallic knocks are heard at low crankshaft speeds. This method is subjective. If knocking noises are detected, it is necessary to stop the engine, open the valve box and check the clearances by direct measurements.
The total wear of the timing mechanism parts (timing gears, bearings and camshaft cams) can be determined by the phase shift towards the retardation. An approximate assessment of the condition of the timing gears and camshaft bearings can be made by noise and knocking using a stethoscope.
Check the crank mechanism of the starting engine for knocks, the value of the total gap in the crankshaft elements and the size
created vacuum.
Knocks are checked when the engine is not running, for which the piston is installed in the top half. on the compression stroke and fix it in this position. A special adapter screwed into the hole of the spark plug or filler valve is used to connect the tip of the KI-13907 compressor-vacuum unit to the space above the piston. With the installation tap closed, the compressor is turned on and a pressure of 0.2...0.25 MPa and a vacuum of 0.06...0.07 MPa are created in the receiver. Adjust the pressure to 0.2 MPa, apply the tip of the stethoscope to the cylinder block in the area of the piston pin, open the valve, and alternately creating a vacuum and compression in the space above the piston, listen for knocks in the upper head of the connecting rod. Continuing to maintain the specified pressure and vacuum in the receivers, and applying the tip of the stethoscope to the crankcase and cylinder, listen for knocking in the bearings. Significant knocking indicates the need to check the gaps in these joints.
When checking the gaps, unscrew the spark plug from the head. ignition and install instead the KI-11140 device with a dial indicator (Fig. 5.5.), and the indicator leg should be recessed by 1.5. .2 mm.
By opening the distribution valve, a vacuum is created in the chamber. The zero value of the indicator scale is combined with a large arrow. After this, pressure is created in the chamber. Move the tap to the neutral position and calculate the difference in the indicator readings. The result obtained will show the amount of the total gap in the crank-connecting rod mechanism interfaces. If this gap exceeds the permissible value of 1 mm, then the engine must be disassembled to directly measure the gaps in each bearing assembly.
To measure the vacuum value, disconnect the tip of the compressor-vacuum unit. Screw in the filler valve, if it has been turned out. The KI-5315 vacuum analyzer is inserted into the spark plug hole (Fig. 6.5.). By turning the crankshaft with the starter, measure the vacuum value. If it is less than 0.03 MPa, then the starting engine must be disassembled to examine the parts of the cylinder-piston group and determine the scope of repair work.
Power System Maintenance
Clean the carburetor. To do this, unscrew the fuel supply fitting from the carburetor body, clean it of dirt and blow through the mesh with a counter flow of gasoline or kerosene. If it is heavily soiled, remove it from the fitting and blow through with compressed air. If the starting engine operates intermittently, then remove the idle screw and the nozzle screw. They are washed in gasoline and blown with compressed air. Blow air through the idle channels and the main jet hole.
For a floatless carburetor K-06 (11.1107), remove the diaphragm cover, then the gasket and diaphragm, and rinse all parts and the body in gasoline.
Reassemble the carburetor in reverse order. In this case, the diaphragm must be installed so that its large metal disk is inside the chamber (fuel cavity).
After installing the carburetor on the engine, check and adjust the automatic throttle control rods. To do this, open the damper completely (until the stop stops in the housing boss), and without changing the position of its levers and the regulator levers, attach the rod to the damper lever, changing the length of the rod if necessary.
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