Cause | Method of elimination |
The engine does not start | |
| No fuel in carburetor: | |
| - fuel lines are clogged | – flush and blow out the fuel tank and fuel lines |
| - the fuel pump is faulty | – check the operation of the pump and replace damaged parts |
| The ignition system is faulty | (See. subsection 9.6.1) |
| The carburetor air damper remains closed during the first flashes in the cylinders | Fix the leak in the carburetor starter |
Engine runs rough or stalls at idle | |
| Engine idle speed adjustment is out of adjustment | Adjust idle speed |
| The carburetor idle speed economizer control system is faulty: | |
| – air suction through hoses connecting the economizer to the intake manifold | – check the hoses and their connections, replace damaged hoses |
| – the pneumatic valve control unit is faulty | – replace the control unit |
| – the pneumatic valve is faulty | – replace the pneumatic valve |
| – the microswitch is damaged or its installation is incorrect | - check the microswitch, adjust its setting |
| Air leakage through a damaged drainage tube | Replace the drain tube |
| Air leakage through gaskets in the connections of the intake manifold to the carburetor or to the cylinder head | Tighten the mounting nuts or replace the gaskets |
| Air leak through a damaged hose connecting the intake manifold to the brake booster | Replace the damaged hose |
| The clearances between the levers and the camshaft cams are damaged | Adjust the gaps |
| The carburetor is faulty: | |
| - the jets or channels of the carburetor are clogged | – blow out the jets and channels with compressed air |
| - water in the carburetor | - remove water from the carburetor, drain sediment from the fuel tank |
| – the tightness of the diaphragm of the starting device is broken | - replace the diaphragm |
| The ignition system is faulty | (See. subsection 9.6.1) |
With a smooth increase in engine speed to 1600 min⁻¹ the engine operates cyclically (the speed fluctuates from 1600 to 1200 min⁻¹) | |
| The carburetor microswitch is damaged or its installation is broken | Adjust the microswitch setting or replace it |
The engine does not develop full power and does not have sufficient throttle response | |
| Incomplete opening of the carburetor throttle valves | Adjust the throttle actuators |
| The air filter is dirty | Replace the filter element |
| The ignition system is faulty | (See. subsection 9.6.1) |
| The fuel pump is faulty | Check the pump operation and replace damaged parts |
| The carburetor is faulty: | |
| – the accelerator pump is faulty | – check the pump performance, replace damaged parts |
| - the main jets are clogged | – blow out the jets with compressed air |
| – the air damper is not fully open | – adjust the damper drive |
| – the fuel level in the float chamber does not correspond to the norm | – adjust the float setting |
| The clearances between the levers and the camshaft cams are damaged | Adjust the gaps |
| Insufficient compression - below 1 MPa (10 kgf/cm²): | |
| – the cylinder head gasket is broken | - replace the gasket |
| - burnt pistons, broken or stuck piston rings | – clean the rings and piston grooves from carbon deposits, replace damaged rings and pistons |
| - poor valve seat fit | – replace damaged valves, polish seats |
| - excessive wear of cylinders and piston rings | – replace pistons, bore and hone cylinders |
| Too early ignition | Adjust the ignition timing |
| Insufficient oil pressure | (Cm. below) |
| The flywheel mounting bolts are loose | Tighten the bolts to the recommended torque |
| Increased clearance between journals and main bearing shells | Grind the journals and replace the bearings |
Knocking of crankshaft main bearings | |
| Usually a dull, metallic knock. It is detected when the throttle valve is opened sharply at idle. Its frequency increases with increasing crankshaft speed. Excessive axial clearance of the crankshaft causes a sharper knock with uneven intervals, especially noticeable with a smooth increase and decrease in crankshaft speed. | |
| Too early ignition | Adjust the ignition timing |
| Insufficient oil pressure | (Cm. below) |
| The flywheel mounting bolts are loose | Tighten the bolts to the recommended torque |
| Increased clearance between journals and main bearing shells | Grind the journals and replace the bearings |
| Increased clearance between thrust half rings and crankshaft | Replace the thrust half rings with new ones of increased thickness |
Knocking of connecting rod bearings | |
| Usually the knock of connecting rod bearings is sharper than the knock of main bearings. It can be heard 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. | |
| Insufficient oil pressure | (Cm. below) |
| Excessive clearance between the crankshaft journals and the bearings | Replace the bearings and grind the journals |
Knocking of pistons | |
| This knock is usually muffled and quiet: it is caused by the piston "beating" in the cylinder. It is best heard at low crankshaft speeds and under load. | |
| Increased clearance between pistons and cylinders | Replace pistons, bore and hone cylinders |
| Excessive clearance between piston rings and piston grooves | Replace rings or pistons with rings |
Knocking of intake and exhaust valves | |
| Operating with increased valve clearances causes a characteristic knocking sound, usually at regular intervals; its frequency is lower than any other knocking sound in the engine, since the valves are driven by the camshaft, the rotation frequency of which is half the rotation frequency of the crankshaft. | |
| Increased clearances between the levers and camshaft cams | Adjust the gaps |
| Valve spring failure | Replace the spring |
| Excessive clearance between valve stem and guide | Replace worn parts |
| Camshaft cam wear | Replace the camshaft and valve levers |
| Loosening the lock nut of the camshaft adjusting bolt | Adjust the clearance between the lever and the camshaft cam, tighten the lock nut |
Insufficient oil pressure at idle with a warm engine | |
| Foreign particles entering the oil pump pressure relief valve | Clean the valve from foreign particles and burrs, wash the oil pump |
| The oil pump gears are worn out | Repair the oil pump |
| Excessive clearance between the bearings and the main journals of the crankshaft | Grind the journals and replace the bearings |
| Oil pressure relief valve sticking | Replace the valve |
| Use of motor oil of the wrong brand and quality | Replace the oil with another one recommended in subsection 3.6 |
Excessive oil pressure on a warm engine | |
| Oil pressure relief valve sticking | Replace the valve |
Increased oil consumption | |
| Oil leaking through engine seals | Tighten the fasteners or replace the gaskets and seals |
| Wear of piston rings and pistons or engine cylinders | Rebore the cylinders and replace the pistons and rings |
| Broken piston rings | Replace the rings |
| Coking of the slots in the oil scraper rings or in the piston grooves | Clean the slots and grooves from carbon deposits |
| Worn or damaged valve stem seals | Replace the valve stem seals |
| Increased wear of valve stems or guide bushings | Replace valves, repair cylinder head |
Increased fuel consumption | |
| The air damper is not fully open | Adjust the damper drive |
| Increased vehicle drag | Check and adjust tire pressure, brake system, wheel alignment |
| Incorrect ignition timing | Adjust the ignition timing |
| The vacuum regulator of the ignition distributor is faulty | Replace the vacuum regulator or distributor |
| High fuel level in carburetor: | |
| – the needle valve or its gasket is not sealed properly | – check for foreign particles between the needle and the valve seat, replace the valve or gasket if necessary |
| - sticking or friction preventing normal movement of the float, float leakage | – check and replace the float if necessary |
| The carburetor air jets are clogged | Clean the jets |
| The carburetor idle economizer valve does not close the outlet at forced idle: | |
| – the pneumatic valve control unit is faulty | - replace the block |
| – the pneumatic valve is faulty | – replace the pneumatic valve |
| – the microswitch is faulty or its installation is incorrect | – adjust the microswitch setting or replace it |
| – idle economizer is faulty | – replace damaged economizer parts |
Engine overheating | |
| Weak tension of the pump and generator drive belt | Adjust the belt tension |
| Insufficient amount of fluid in the cooling system | Add coolant to the cooling system |
| Incorrect ignition timing | Adjust the ignition timing |
| The outer surface of the radiator is heavily contaminated | Clean the outer surface of the radiator with a jet of water |
| Thermostat is faulty | Replace Thermostat |
| Faulty radiator plug valve (opening pressure less than 0.05 MPa (0.5 kgf/cm²) | Replace the plug |
| Coolant pump is faulty | Check the pump operation, replace it or repair it |
Rapid drop in fluid level in expansion tank | |
| The radiator is damaged | Repair the radiator or replace it |
| Damage to hoses or gaskets in pipeline connections | Replace damaged hoses or gaskets |
| Leaking liquid from the heater tap | Replace the faucet |
| The hose clamps are loose | Tighten the clamps |
| Leaking fluid through the coolant pump seal | Replace the seal |
| The radiator cap or gasket is damaged | Replace the plug |
| The cylinder head gasket is damaged | Replace the gasket |
| Fluid leakage through microcracks in the block or cylinder head | Check the tightness of the block and cylinder head; if cracks are found, replace damaged parts |
| Leakage of fluid through microcracks in the housing or cover of the coolant pump, expansion tank or inlet pipe | Check for leaks; if cracks are found, replace damaged parts; minor leaks can be eliminated by adding a sealant of the NIISS-1 type to the coolant |
Excessive camshaft drive chain noise* | |
| From the general engine noise, the noise of the camshaft drive chain stands out when gaps appear between the engagement elements and is clearly audible at low crankshaft rotation speeds. | |
| The chain has become loose due to wear | Tighten the chain |
| Chain tensioner shoe or guide shoe failure | Replace the tensioner shoe or guide |
| Chain tensioner plunger rod sticking | Eliminate the jam |
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