Motorcycle genuine Pistons buy seven tips

First, the regular manufacturers of pistons generally used eutectic Al-Si alloy casting

Its aluminum piston hardness greater than 100HB (Brinell hardness), the tensile strength of 2450MPa or more. High-quality piston in the eutectic aluminum-silicon alloy composition of silicon content up to 13%, due to the thermal deformation of silicon is small, it has excellent thermal stability at high temperatures, but the high silicon content in the piston material, the piston processing Manufacturing process requires a relative increase.

Some unscrupulous companies in order to reduce production costs, the use of recycled waste aluminum alloy piston casting, this fake piston material minimal silicon content. If installed into the engine, because of its large thermal variability, as long as the engine temperature increases, the inevitable thermal expansion is too large, the piston skirt and cylinder wall friction caused by friction cylinder, the engine powerless and power down failure.

Simple pros and cons Identification method:

First, from the back of the piston (the top of the opposite) to observe the high silicon content of the back of the piston color is black, and the inside has a very clear manufacturer logo. The fake pistons silicon content is very low, the piston back color white (pure white aluminum);

Second, the regular factory production of high density piston, and fake pistons compared to its larger proportion. Therefore, the easiest way to identify the piston is to put the accessory piston and the regular manufacturer's piston (must be the same model, with the same displacement, the relevant size is the same) into the electronic scale, we will see.

Second, the formal requirements of the piston precision factory production is high

The top of the piston generally has group marks, usually groups A, B, C, and D, which are dimensional group marks of the skirt of the piston. In addition, the piston skirt also has a number of very fine groove, mainly used to store lubricating oil, to enhance the piston skirt lubrication. Defective pistons due to rough processing, it is impossible to go through such a sophisticated processing technology.

Quality goods piston skirt wall processing is very thin, the wall thickness. Support the caliper to measure the skirt skirt unilateral size, if the use of digital vernier caliper measurement, because of its high accuracy, the measurement results more accurate. If the difference between the wall thickness of 0.20mm or more, the piston temperature increases, due to varying wall thickness of the skirt, the thermal deformation is large and uneven, so that the piston skirt size does not reach its ideal circle, not only prone to leakage , But also produce abnormal percussive sound.

Third, the regular factory piston skirt cross section non-circular

The lower part of the piston ring groove (referring to the oil ring groove) to the bottom of the cylinder piston piston skirt, its role is when the piston reciprocating motion in the cylinder as a guide and bear the lateral pressure. Piston in the non-working state with its work in the force, under the heat is not the same. This is because the piston work will be subject to varying degrees of heat stress deformation.

Piston in working condition, due to stress and heat, along the direction of the piston pin piston deformation increases, while the deformation along the direction perpendicular to the piston pin is small. Therefore, in order to counteract and adapt to its thermal deformation, to ensure that the work of the piston shape is cylindrical, with the cylinder wall to adapt and have a suitable fit gap, in the non-working state, the piston from the axial direction, the size of the head Smaller, while skirt size slightly larger;

Piston cross-section (ie, cylindrical cross-section) to the long axis perpendicular to the piston pin axis direction should be oval. The length of the piston cross-section produced by the regular manufacturers varies from 0.15 to 0.25mm, and the relative position dimensions of the above vernier caliper or the digital caliper can be measured to compare advantages and disadvantages.

Fourth, the formal factory head size slightly smaller than the skirt size

Regular manufacturers generally will piston head size (above the first piston ring position) intentional car small 0.25 ~ 0.35mm (such as: CB125T motorcycle piston diameter of 44mm, while the piston head is 43.5mm), mainly to To prevent the combustion chamber temperature increases, the piston head thermal expansion is too large, resulting in pull cylinder or cylinder. Therefore, the available vernier caliper or digital caliper to measure the first piston ring above the piston head size, if there is no margin of 0.40 ~ 0.60mm, is unqualified.

Fifth, the regular manufacturer of thick piston head

The piston head is generally thicker in order to increase the strength and rigidity of the piston and to reduce the thermal resistance of heat flow from the top of the piston to the piston ring so that heat passes from the top of the piston through the piston ring and the cylinder wall to the heat sink or cooling Liquid, which can effectively prevent the top of the piston temperature is too high.

You may see some of the piston engine failure, the piston burning top (there is an irregular top of the hole melt) phenomenon. In the exclusion of spark plugs low value and engine overheating factors, the vast majority are due to the thickness of the top of the piston is caused by too thin.

General genuine piston top thickness of 3.0 ~ 4.0mm. Defective or fake piston top thickness of some less than 2.5mm. Simply place a ruler on the bottom of the piston and a vernier caliper (with depth caliper) measures the size of the piston from the top of the piston to the bottom of the piston minus the bottom of the piston from the bottom of the piston. This is the thickness of the top of the piston.

Use digital calipers to measure more accurately. If the measurement is not between 3.0 ~ 4.0mm, less than 2.5mm, absolutely can not be installed. In addition, the top part of the piston is generally sandblasted. The main purpose of sandblasting is to eliminate the casting stress on the top of the piston and prevent the piston from naturally deforming during use.

Sixth, the regular manufacturer of piston ring groove width size more accurate

Generally matched with the matching piston ring thickness size to ensure that the piston ring in the piston ring groove with the appropriate fit clearance, the gap is called the ring backlash; and the depth of the ring groove and the piston ring is the piston ring back Gap, if the backlash is too small, will make the piston ring sluggish in the piston ring groove, backlash is too large, it is easy to channeling oil. Therefore, the piston ring groove manufacturing brought great difficulty.

Quality piston is a regular manufacturer of precision CNC lathe system, the depth and width of the piston ring groove control are more accurate. As fake piston is a shoddy product, it is impossible to use precision CNC machine tools, but ordinary lathe car system, the depth and width of the piston ring groove can not be guaranteed.

To this end, the most convenient way to identify is that with the regular manufacturer of the same type of piston piston rings inserted into the groove, and then compare the measured with a feeler we will see.

Seven, pay attention to check the piston compression height

As each type of engine has a different compression ratio than the loaded heat load, the pistons with the same diameter differ in relevant dimensions. Among them, the piston compression height is an important part of the piston parts, it will affect the engine's compression ratio and ignition advance. Therefore, the replacement of the piston must be measured when the piston compression height.

Such as: Honda CHA125 forced air-cooled motorcycle (ie GY6 engine) on the piston diameter and Honda CH125 water-cooled motorcycle (Honda Shark water-cooled engine) the same piston diameter 52.4mm, but the piston pin hole to the size of the top of the piston is not Similarly, the former size is 20 ± 0.10 mm, while the latter size is 22.3 ± 0.05 mm. Again, the weight of the two pistons is also different, the former 77 ± 2 g, while the latter is 74 ± 2.5 g.

An unexpected failure can occur if the two pistons are mixed during maintenance. If the Honda CH125 water-cooled motorcycle fitted with Honda CHA125 forced air-cooled motorcycle piston, will make the engine compression ratio lower, causing lack of motivation, the maximum speed on the failure.

On the contrary, it will cause the valve to hit the piston top and other vicious failure, must not be negligent and cause disaster. Therefore, when replacing a piston, the old and new pistons must be worn together with the piston pin to compare their compression height.

Of course, in the comparison also pay attention to the two pistons in the first piston ring groove position is consistent. If the position difference is too large, the same will affect the engine compression ratio.