High mileage is not a sufficient indicator of the need for major repairs, on the other hand, low mileage does not exclude the need for major repairs. The most important indicator seems to be the timeliness of routine engine maintenance. With a timely change of oil and air filter, as well as when performing all other necessary maintenance work, the engine serves reliably for many thousands of kilometers. On the contrary, insufficient or untimely maintenance can cause a sharp reduction in engine life.
Increased oil consumption indicates wear on the piston rings, valve stem seals and (or) valve guides. Make sure that leaks do not cause increased oil consumption, and only then conclude that the piston rings and guide bushings are unsuitable. To determine the likely cause of the malfunction, measure the compression in the engine cylinders.
Check the oil pressure with a pressure gauge screwed into place of the emergency oil pressure contact sensor and compare the test result with the standard value. If the oil pressure is low, then the cause may be worn main and connecting rod bearings and (or) oil pump parts.
power loss, "failures" in engine operation, detonation or metal knocks, increased noise from the gas distribution mechanism, increased fuel consumption indicate the need for major repairs, especially if all these signs of abnormal operation appear at the same time. If all adjustments do not result in an improvement, then the only remedy is to repair with the replacement or restoration of parts.
An overhaul consists in restoring engine parts to the condition specified in the technical data for a new engine. During a major overhaul, pistons and piston rings are replaced. The connecting rod and main bearings are also subject to replacement, and if necessary, the crankshaft is resurfaced until the standard clearances in the main and connecting rod journals with the main and connecting rod bearings are restored. As a rule, valves are also subject to repair, since their condition at the time of repair is usually not entirely satisfactory. During the overhaul of the engine, the repair of such units as the ignition distributor, starter and generator is also carried out. As a result, the overhauled engine should have the qualities of an almost new unit and withstand significant mileage without failure.
Attention! During a major overhaul, important parts of the cooling system such as hoses, thermostat and coolant pump should be replaced. The radiator must be carefully examined for tightness and cleanliness of the internal channels. When overhauling the engine, the oil pump should also be replaced.
Before starting an engine overhaul, review the relevant procedures to get an idea of the scope and requirements of the work ahead. If all the rules and regulations are observed, if all the necessary tools and fixtures are available, and if all the technical requirements are met, it is not difficult to overhaul, but it will take a significant amount of time. Approximately it will take at least two weeks, especially if you have to go to a specialized workshop to repair or restore parts. Check the availability of spare parts and take care of purchasing the necessary special tools and equipment in advance. Almost all work can be done with a standard set of tools, although precise measuring instruments will be needed to check and determine the suitability of certain parts. Often, the condition of the parts is checked in specialized workshops, which also receive recommendations for the replacement or restoration of certain parts.
Attention! You should contact the car service workshops only after completely disassembling the engine and checking the condition of all parts, especially the cylinder block and crankshaft, in order to decide which maintenance and repair operations will be performed in the workshops. Since the condition of the cylinder block is the determining factor in making a decision on its further repair or on the purchase of a new repair cylinder block, it is necessary to buy spare parts or perform machining operations on related parts only after a thorough check of its technical condition. Make it a rule not to make hasty, unreasonable decisions - otherwise, repairs can be more expensive due to the installation of worn or repair parts.
In conclusion, we note that the assembly of any units should be carried out with all care in a clean room in order to avoid further failures of the repaired engine and ensure its reliable operation.