2. High mileage does not always indicate the need for a major overhaul and, conversely, low mileage does not guarantee that no overhaul is needed. Probably the most important factor is the frequency of engine maintenance. An engine that has had frequent and regular oil and filter changes and all other maintenance procedures performed should provide long and reliable service. Conversely, an engine that has been neglected in its maintenance routine may require a major overhaul very quickly.
3. Very high oil consumption is an indication of problems with the piston rings, valve stem seals and/or valve guides. However, before deciding to replace the rings and valve stem seals, check whether the excessive oil consumption is not the result of simple leaks. To determine the real cause, perform a compression test as described in part A of this chapter.
4. Check the oil pressure with a sensor installed in place of the oil pressure switch and compare the obtained pressure value with the technical conditions. If the pressure is low, most likely the main and connecting rod bearings and/or the oil pump gears are worn.
5. Loss of power, rough running, knocking or metallic noises in the engine, increased noise in the valve train and high fuel consumption may also indicate a need for a major overhaul, especially if these symptoms occur simultaneously. If a full service does not correct the situation, the only solution is an engine overhaul.
6. Engine overhaul includes restoration of all internal parts to the technical characteristics of a new engine. During overhaul, the cylinder liners are replaced (where they are installed), pistons and piston rings. As a rule, new main and connecting rod bearings are installed; if necessary, the crankshaft can be replaced to restore the journal size. The valves are also serviced, as they are not in the best condition at the time of repair. If the engine is disassembled, other parts such as the distributor, starter and alternator can also be disassembled and repaired. The end result of the repair should be a "like new" engine that will serve without problems for many kilometers.
Note: During a major overhaul, critical cooling system components such as hoses, thermostat, and water pump should be replaced. It would be a good idea to add the oil pump to this list as well. The radiator should be thoroughly checked to ensure that it is not leaking or clogged.
7. Before you begin rebuilding an engine, read the entire procedure to familiarise yourself with the requirements and scope of the job. Rebuilding an engine is not a difficult job if you follow all the instructions carefully, have the necessary tools and equipment, and meet all the specifications. However, the rebuild is a very labour-intensive operation. Plan on it taking at least two weeks, especially if rebuilding work is required. Check the availability of engine parts and make sure you have or can borrow all the necessary tools and equipment. Most work can be done using general-purpose hand tools, but you will need some precision measuring equipment to check the parts. You may often need expert advice on rebuilding or replacing parts.
Note: In order to make the right decision about the necessary work to restore the parts (especially the cylinder block/crankcase or crankshaft), completely disassemble the engine and check all the parts. The condition of these parts is the determining factor when deciding whether to assemble the engine from "native" parts or buy reconditioned units. Therefore, do not purchase or install parts until you have thoroughly checked them. The basic rule is that time determines the cost of repairs, so you should not install worn or non-standard parts.
8. As a final note, we remind you that a long life with minimal care for a reconditioned engine is ensured by careful assembly in a clean environment.