Engine overhaul, in fact, after a serious illness in life, although it seems to have healed, the indicators of the body are normal, but the body bones are not as good as before. The same is true for the overhauled engine, and even if the professional repair shop, even if the 4S shop drags the engine to the manufacturer to repair, it is impossible to restore the performance and stability of the original factory.
Therefore, used cars that have overhauled the engine, it is best not to touch, even if it is cheap, it is necessary to stay away. Because no matter how sophisticated the repair process, there are several problems.
1, the problem of low temperature assembly
In the assembly of the engine, cold mounting, that is, low temperature assembly, is often used, that is, the use of the interference of the parts to achieve the role of fastening parts. For a simple example, if you want to tighten the screws and nuts, cool the screws, assemble them on the nut through the principle of thermal expansion and contraction, and wait until the temperature returns to normal, you can achieve a very tight effect, which is why many engines are still very precise for more than ten years. However, the repair shop does not have the conditions for low-temperature assembly, and can only use hot mounting, that is, the nut is heated and expanded, and then the screw is inserted into the nut, but this will cause the parts to deform, or the strength will be reduced, laying hidden dangers for future failures.
2, the problem of process card
When the engine is assembled in the original factory, the tightness of each part is standard, such as a few turns of the screw, how much torque is how many cows and meters, within a certain tolerance range are OK, for example, which screw is installed first, which screw is installed later, what is the way of fixing, will affect the sealing performance of the engine cylinder, in some repair shops, in any case, it is impossible to achieve the same assembly level as the original factory, even if the engineer of the engine assembly gives you a restoration, it is difficult to restore it.
3, the problem of parts
In the engine overhaul, but also involved in a problem, that is, the problem of parts, in the engine maintenance, usually used are sub-factory parts or OEM parts, rarely used to the original parts, even if the original parts, different batches of products, there are also differences, these differences will be gradually reflected in the use of the engine process
Therefore, the overhauled engine, it is almost impossible to restore the effect of the original factory, and it is very good to achieve 80% of the original factory state.