The material offered to the attention of readers contains a wide range of information - from practical advice on purchasing the necessary spare parts to a detailed step-by-step description of the procedure for removing, checking the condition, repairing and installing internal engine components.
The procedure descriptions are written on the assumption that the engine has been completely removed from the vehicle and is mounted on a mounting stand or sturdy work bench. All information regarding engine repair procedures that can be performed in situ are provided in the 4-Cylinder Engines and V6 Engines sections of this Chapter.
It is not always easy to determine the moment when a major overhaul of the power unit is necessary. A whole host of different factors must be taken into account.
High mileage is not necessarily a sign that the engine needs a major overhaul. On the other hand, low mileage is also not a sufficient guarantee of the serviceability of the power unit. Perhaps the main factor determining the service life of the engine is the frequency and regularity of general and routine maintenance procedures. With normal care, the engine will reliably serve for many, many thousands of kilometers, while a careless attitude to the implementation of routine maintenance procedures coupled with a careless driving style can lead to the need for a major overhaul of the power unit after a very short period of time.
Excessive engine oil consumption can be considered a signal that it is necessary to check the condition of the piston rings, valve stem seals and/or valve guides. Naturally, first of all, you should make sure that the oil loss is not associated with the development of its external leaks. Contact a qualified specialist for help to determine the general condition of your car's engine based on the results of the compression pressure test in the cylinders (see Section Checking the compression pressure in the cylinders) and measurements of the vacuum depth at different initial parameters (see Section Engine condition diagnostics using a vacuum gauge).
Loss of developed power, disruption of rotation stability, excessive noise background of the valve mechanism, increased fuel consumption are usually quite characteristic signs of the need for a major overhaul of the engine, especially when all these factors appear simultaneously. If performing a full range of adjustments does not help in eliminating the problems, the only way out of the situation will be to carry out general mechanical work to restore the engine.
A major overhaul of the power unit means restoring all its operating parameters to the level typical of a new engine. During a major overhaul, piston rings are replaced and cylinder mirrors are restored (grooved and/or honed). If cylinders are grooved, pistons of the corresponding repair size are selected. Main and connecting rod bearings are usually replaced; if necessary, crankshaft journals can be grooved and restored. Valve maintenance is mandatory, as their condition at the time the engine needs a major overhaul is almost certainly poor. In parallel with the general overhaul of the power unit, auxiliary components such as the ignition distributor, starter, and generator are usually also refurbished. As a result of the overhaul, the engine parameters return to the values typical of a new unit, and the latter will be able to reliably serve for many, many thousands of kilometers.
Note: Critical cooling system components such as hoses, drive belts, thermostat and water pump MUST be replaced with new ones when performing a major engine overhaul. In addition, the condition of the radiator should be carefully checked (see Chapter Cooling and heating systems). If signs of leaks or obstruction are detected, the radiator should also be replaced. Many branded auto service workshops do not provide a guarantee for the operation of a rebuilt engine without professional cleaning and repair of the radiator. Do not forget to also check the condition of the oil pump (see the relevant Sections of this Chapter).
Before you start performing a major overhaul of the engine, carefully read the materials of this Section in order to theoretically prepare for the upcoming work. Note that a major overhaul of the engine does not require high professional training from the performer, but it takes a lot of time. You should plan to stop using the car for at least two weeks, especially if you need to seek help from a mechanical workshop to perform individual repair work. Do a little marketing by checking the availability of spare parts, tools and equipment. Prepare all the necessary materials in advance. Most of the work can be done using a regular set of locksmith tools, but some of the tests to determine the suitability of individual components for further use require the use of precision measuring equipment. In doubtful situations, seek help from specialists at the auto service workshop, who will always help you decide on the need to replace or repair any internal engine component.
Note: Before taking any parts to a car service center for refurbishment, perform a complete disassembly of the engine and all its internal components. Remember that the deciding factor in the advisability of an engine overhaul is the condition of its cylinder block. It is often cheaper and more reliable to replace a worn-out engine with a reconditioned one. Never start purchasing replacement components until you have thoroughly examined the condition of the block. Remember that time is the main cost factor in performing an engine overhaul, and therefore, there is no point in wasting it on installing worn-out or non-standard units and components.
In conclusion, we note that all efforts to perform restoration repairs of worn components will be wasted if the requirement for thoroughness and cleanliness during assembly of the unit is neglected.