It is not always easy to come to the conclusion about the feasibility of a complete overhaul of the engine, since it is necessary to be based on a number of objective indicators.
High mileage is not a sufficient indicator of the need for a major overhaul, on the other hand, low mileage does not exclude the need for a major overhaul. The most important indicator, apparently, is the timeliness of routine maintenance of the engine. With timely oil and filter changes, as well as when all other necessary maintenance work is performed, the engine will serve 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 guides and seals. Make sure that leaks do not cause increased oil consumption, and only then conclude that the piston rings and valve guides are unsuitable. to determine the probable cause of the malfunction, measure the compression in the engine cylinders. Also test with a vacuum gauge and determine the nature of the readings of this device.
Check the oil pressure with a pressure gauge screwed in instead of the oil pressure 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 or parts of the oil pump.
Loss of power, engine dips, knocking or metal knocking, increased noise from the gas distribution mechanism, increased fuel consumption indicate the need for major repairs, especially if all of these signs of abnormal operation appear at the same time. If the performance of all adjustments does not lead to improvement, then the only means of eliminating abnormal operation of the engine is a major overhaul. 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, cylinders are bored or honed. After the repair of the cylinders, which is carried out in a specialized workshop, it will be necessary to install pistons of repair sizes. The connecting rod and main bearings of the crankshaft, as well as the covers of the bearing journals of the camshafts, must also be replaced; if necessary, the crankshaft journals should be ground to restore normal clearances with the connecting rod and main bearings. As a rule, valves are also subject to repair, since their condition at the time of repair, as a rule, is not entirely satisfactory.
During the overhaul of the engine, repairs are also carried out on such units as the starter, generator and ignition distributor. As a result, the repaired engine must have the qualities of a new unit and withstand a significant mileage without failure.
During a major overhaul, important parts of the cooling system such as hoses, drive belts, thermostat and coolant pump should be replaced. The radiator should be examined for tightness and cleanliness of the internal channels. If you purchased a remanufactured engine, or an incomplete cylinder block, then some suppliers do not guarantee the operation of these units without high-quality flushing of the radiator. When overhauling the engine, it is also recommended to replace the oil pump.
Before starting an engine overhaul, review the relevant procedures to get an idea of the scope and requirements of the work ahead. Subject to all norms and rules, with all the necessary tools and fixtures, overhaul is easy to perform, 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 and 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 more 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.
It should be noted that the assembly of the units should be carried out with the utmost care in a clean room to avoid further failures of the overhauled engine and ensure its reliable operation.