There has always been such a rumor in the motorcycle circle, that is, the imported motorcycle engine is assembled at minus 40 degrees, when the engine is at room temperature, after heat expansion, the structure is very stable, and it is not easy to dismantle, so the overhauled engine is not as good as the original engine. And the domestic motorcycle factory can not reach such a level of assembly, so the domestic motorcycle is not as good as the imported motorcycle quality.

At first listen to feel that this statement is very reasonable, especially for those motorcycle white, do not understand any principle of motorcycle, feel that this statement is very cool, can say it will be considered to be the old driver of motorcycle, so he and another wave of motorcycle white to sell this statement. Slowly the rumor spread with such seriousness.

In fact, this rumor is not groundless, in mechanical assembly, there is low-temperature assembly, the term is called "cold assembly", the corresponding high-temperature assembly is called "red assembly", which is the common practice of the machinery manufacturing industry. Slightly more high-end engines are cold assembled.

Think about it, if you want to ensure the stability of the parts, the best way is to ensure that the minimum assembly gap between the parts is zero, and the assembly stability is achieved by using the elastic deformation of the material. The technical term is "interference fit". For example, a bearing and a bearing seat diameter is the same, is the bearing directly into the bearing seat? Of course, however, this assembly will produce a lot of tolerances, and even affect the service life of the bearing, can you let the bearing easily load the bearing seat, and let the bearing and the bearing seat match closely, at this time, there are two ways.

The first is to heat the bearing seat to expand, so that the aperture is increased and the bearing can be easily loaded into it. However, many bearing seats are inlaid with the crankcase, and the bearing seat is not the same material as the crankcase, one is steel, one is aluminum, and it is almost impossible to make the bearing seat have a great deformation.

The second is cold loading. Is to put the bearing into the liquid nitrogen bucket, through the principle of cold shrinkage, so that the diameter of the bearing can be reduced, easily loaded into the bearing seat, when the temperature returns to normal temperature, the bearing diameter will be restored to the original state, and the bearing seat to form an elastic extrusion, so as to achieve the purpose of interference fit. Cold loading will not destroy the stability of the material, and is used by more engine manufacturers.

It can be seen that the engine assembly has cold assembly and hot assembly, but it is not the worker in the workshop assembly at minus 40 degrees, in that case, the mechanical parts are at the same temperature, will have almost the same thermal expansion and contraction, which is not much different from the normal temperature assembly, let alone minus 40 degrees which assembly workers can bear?

So why do many users think that as long as the engine is overhauled, it will not work? Very simply, this is because the equipment conditions of many maintenance workers can not meet the requirements of factory manufacturing, so the assembly of the engine can not reach the original factory level, but not all maintenance stations can not reach, as long as the maintenance workers in the maintenance of the assembly of the engine, do clean parts, assembly as far as possible to do dust-free assembly, although the conditions are limited when cold installation is required. But it can also be done, for example, when installing engine bearings, we can put the engine bearings in the freezer of the refrigerator for half a day, and then blow the bearing seat with a hot air gun to about 100 degrees, in this case, the bearing into the bearing seat is relatively easy, and the assembly is tight, every time the engine overhaul, Assembly level and durability can basically reach the original factory level. So it's not that the engine failed after the overhaul, but that you may not have the right master!

Do not myth low temperature assembly or myth imported car quality stability. The low failure rate of imported cars is a variety of reasons, advanced manufacturing technology, reasonable product development, accessories material and processing reasons, and many domestic brands are currently insufficient technical reserves, but also too impetuous, eager to succeed, which leads to product quality and performance instability. Therefore, a rational and objective look at the investment of major manufacturers in research and development funds is the key data to identify the potential of the brand.

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