Ural diesel vehicles are equipped with a KamAZ-740 engine of the third configuration.
Therefore, engine repair and maintenance are described in the articles on the repair of the diesel engine of the «KamAZ» vehicle KamAZ engine
Engine malfunctions during operation are determined by:
- power loss;
- increased fuel and oil consumption;
- reduced oil pressure;
- nature of knocks and operating noise.
Engine power loss affects the dynamic qualities of the vehicle: poor acceleration, climbing hills in a lower gear, reduced maximum speed.
Engine power loss can also be characterised by a decrease in compression value in one or more cylinders.
A decrease in compression value in the engine cylinders indicates wear of the piston rings and leaky valves.
Compression is measured using a compression tester on a warm engine at a coolant temperature of at least 80 °C and at a minimum idle speed (600 rpm).
To determine the compression pressure value, install the compression tester in the cylinder head bore instead of the injector and clamp it with the injector mounting bracket.
Place a hose made of petrol-resistant rubber onto the fitting of the checked section of the injection pump and lower its end into a container to collect the fuel that will come from the pump section during the compression check.
Then start the engine and record the pressure shown by the device's pressure gauge at the minimum crankshaft speed of the engine.
Measure the compression in the remaining cylinders in the same way.
For a serviceable engine, the compression value should be at least 30 kgf/cm², and the pressure difference between cylinders should not exceed 2 kgf/cm².
The reference fuel consumption, specified in the technical characteristics of the vehicle, is determined by measuring fuel consumption when a loaded vehicle moves at a speed of 40 km/h in top gear in two opposite directions on a flat horizontal asphalted section of a highway 1 km long.
When the other units of the vehicle are in good condition, an increased reference fuel consumption is a consequence of the unsatisfactory technical condition of the engine.
Longitudinal and transverse section of the engine
Transverse section of the engine
Increased oil consumption (in the absence of leaks) indicates wear of the cylinder-piston group, coking of the hole in the grooves for the oil scraper rings, burning of the rings.
Reduced oil pressure (with the lubrication system working properly) is a consequence of significant wear of the crankshaft and camshaft bearings.
The causes of a sudden and sharp drop in oil pressure in the main oil line can be clogging and jamming in the open position of the oil pump valve, the lubrication system, as well as emergency wear, damage to the bearing shells of one or more bearings.
Valve jamming and emergency wear of the bearing shells can be a consequence of operating the engine with dirty oil.
To detect the oil and determine the nature of the knocks and noise, use a stethoscope.
The tone of the knock, as well as the place where it is best heard, can determine the cause and location of the malfunction.
Strong knocks of a high (metallic) tone, intensifying with an increase in crankshaft speed, are characteristic of the piston hitting the valve when the spring breaks or the valve jams in its guide.
Knocks heard in the upper part of the cylinder block, subsiding with an increase in crankshaft speed and increasing when it decreases, can be caused by scoring of the working surface of the cylinder liners or pistons.
When clearances increase in the connections of the piston with the piston pin or the piston pin with the connecting rod small end, as well as in the main and connecting rod bearings, knocks may appear, easily audible under load, with a sharp change in fuel supply.
When the clearance between the piston and the cylinder liner increases, a dull knock is heard after a cold start, subsiding or disappearing completely after the engine warms up.
A high-pitched sound in the valve area usually indicates increased clearances between the rocker arm tip and the valve stem end.