High mileage is not a sufficient indicator of the need for overhaul, on the other hand, low mileage does not exclude overhaul. 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 maintenance can cause a sharp decrease in the resource. Increased oil consumption indicates worn piston rings 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 amount of work to be done, measure the compression in the cylinders, or check the tightness of the combustion chamber, for which it is recommended to contact an experienced specialist.
Oil pressure can be checked by unscrewing the gauge (arrow) and screwing in its place the adapter of the pressure gauge (4-cylinder engines).
In 6-cylinder engines, the sensor (arrow) located at the front of the engine, on the oil cooler adapter.
If increased noise or knocks are heard during engine operation, then the probable cause of them may be wear on the connecting rod or main bearings.
Unscrew the standard sensor and measure the oil pressure with a pressure gauge, compare the value obtained with that indicated in the manual. If the pressure is low, the cause may be wear on the thrust bearings or the oil pump.
power loss, "failures" in the operation of the engine, increased noise from the gas distribution mechanism, increased fuel consumption indicate the need for a major overhaul, especially if all these factors appear simultaneously. If all adjustments fail to improve, repair is the most appropriate remedy. A major overhaul consists of restoring engine parts to the condition specified in the technical data for a new engine. During the overhaul, the piston rings are replaced, and the cylinder walls are bored to the repair size (or honed).
After the repair of the cylinders, the installation of new pistons will be required. The connecting rod and main bearings must also be replaced; if necessary, the crankshaft should be ground to restore clearances with the connecting rod and main bearings. As a rule, the valve mechanism does not change, since its condition at the time of repair is usually quite satisfactory. During the overhaul of the engine, the repair of such units as the carburetor, ignition distributor, starter and generator is also carried out. As a result, the engine should have the qualities of an almost new unit and serve without fail for a long time.
Before starting an engine overhaul, review the relevant procedures to get an idea of the scope and requirements of the work ahead. Major repairs are simple, but time consuming. Approximately it will take at least two weeks, especially if for repair and restoration of parts (grinding, boring) will have to go to a specialized workshop. 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 parts is checked in specialized workshops, in which they receive recommendations for replacing or restoring parts.
Attention! You should contact the car service workshops only after completely disassembling the engine and checking all the parts, especially the cylinder block, 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 only after a thorough check of its technical condition. Make it a rule that the true cost of repair is time, then you won't have to pay for 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.