It is not always easy to come to a conclusion about the advisability of a complete engine overhaul, since it is necessary to rely on a number of objective indicators.
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, apparently, is the timeliness of routine engine maintenance. With timely oil and filter changes, and with all other necessary maintenance work 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 of piston rings, valve guides and valve stem seals. It is necessary to ensure that leaks are not the cause of increased oil consumption, and only then draw a conclusion about the unsuitability of piston rings and valve guides. to determine the probable cause of the malfunction, measure the compression in the engine cylinders. Also carry out tests using a vacuum gauge and determine the nature of the readings of this device.
Check the oil pressure with a pressure gauge screwed in place of the oil pressure 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 or oil pump parts.
Loss of power, engine hesitation, detonation or metallic knocking, increased valve timing noise, and increased fuel consumption indicate the need for a major overhaul, especially if all of these signs of abnormal operation occur simultaneously. If performing all adjustments does not lead to improvement, then the only way to eliminate abnormal engine operation is a major overhaul. A major overhaul involves 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, and cylinders are bored or honed. After cylinder repair, 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 bearing journal caps of the camshafts, are also subject to replacement; if necessary, the crankshaft journals should be ground until normal clearances with the connecting rod and main 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 overhaul, repairs are also performed on components such as the starter, generator, and ignition distributor. As a result, the refurbished engine should have the qualities of a new unit and withstand significant mileage without failure.
During a major overhaul, important cooling system components such as hoses, drive belts, thermostat and coolant pump should be replaced. The radiator must be inspected for leaks and cleanliness of internal channels. If you purchased a remanufactured engine or an incomplete cylinder block, some suppliers do not provide a warranty on the operation of these units without a high-quality radiator flush. When overhauling the engine, it is also recommended to replace the oil pump.
Before beginning an engine overhaul, review the relevant procedures to get a feel for the scope of work and the requirements involved. If all rules and regulations are observed and all necessary tools and equipment are available, major repairs are not difficult to carry out, but they will require a significant investment of time. It will take approximately two weeks, especially if you need to contact a specialized workshop for repairs and restoration of 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 using 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 parts is checked in specialized workshops, where recommendations are also received for the replacement or restoration of certain parts.
It should be noted that the assembly of the units must be carried out with the utmost care in a clean room to avoid further failures of the repaired engine and ensure its reliable operation.