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 is probably the timeliness of routine engine maintenance. With timely oil and air filter changes, as well as with all other necessary maintenance work, the engine serves reliably for many thousands of kilometers. Conversely, insufficient or untimely maintenance can cause a sharp reduction in engine life.
Increased oil consumption indicates wear on the piston rings, oil-removing caps, and / or valve guide bushings. Make sure that leaks are not the cause of increased oil consumption, and only then make a conclusion about the unsuitability of the piston rings and guide bushings. To determine the probable 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, the cause may be wear of the main and connecting rod bearings and (or) oil pump parts.
Loss of power, engine "dips", detonation or metallic knocks, increased noise from the valve timing mechanism, increased fuel consumption indicate the need for a major overhaul, especially if all these signs of abnormal operation appear simultaneously. If performing all adjustments does not lead to improvement, then the only remedy is repair with replacement or restoration of parts.
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Major repairs involve restoring engine parts to the condition specified in the technical data for a new engine. During a major repair, pistons and piston rings are replaced. Connecting rod and main bearings are also subject to replacement, and if necessary, the crankshaft is reground 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 a major engine repair, such units as the ignition distributor, starter and generator are also repaired. As a result, the repaired engine should have the qualities of an almost new unit and withstand a significant mileage without failures.
Attention! During a major overhaul, important cooling system components such as hoses, thermostat, and coolant pump should be replaced. The radiator should be thoroughly inspected for leaks and cleanliness of internal channels. During a major overhaul of the engine, the oil pump should also be replaced.
Before starting a major engine overhaul, read the description of the relevant procedures to get an idea of the upcoming scope of work and the requirements for them. If all the rules and regulations are observed, if all the necessary tools and devices are available, and if all the technical requirements are met, a major overhaul is not difficult to perform, but it will require a significant investment of time. It will take approximately two weeks, especially if you have to contact 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 performed using 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 parts is checked in specialized workshops, where they also receive recommendations for replacing or restoring certain parts.
Attention! You should contact a car service workshop only after completely disassembling the engine and checking the condition of all parts, especially the cylinder block and crankshaft, in order to decide what maintenance and repair operations will be performed in the workshops. Since the condition of the cylinder block is a determining factor in deciding on its further repair or on purchasing a new repair cylinder block, you should buy spare parts or perform machining operations on related parts only after thoroughly checking its technical condition. Make it a rule that you should not make hasty, unfounded decisions - otherwise, the repair may cost more due to the installation of worn or repair parts.
In conclusion, we note that the assembly of any units should be carried out with the utmost care in a clean room in order to avoid further failures of the repaired engine and ensure its reliable operation.