How to distinguish the motorcycle pistons ? part4

6. The piston ring groove width dimension produced by regular manufacturers is more accurate

     Generally, it matches the thickness of the matching piston ring to ensure that the piston ring has an appropriate fit clearance in the piston ring groove. If the backlash is too small, the piston ring will be sluggish in the piston ring groove, and if the backlash is too large, oil will easily escape. Therefore, it is very difficult to manufacture the piston ring groove.

     High-quality pistons are made by regular manufacturers with precision CNC machine tools, and the depth and width of the piston ring grooves are controlled more precisely. Since the fake and inferior pistons are shoddy products, it is impossible to use precision numerical control machine tools, but they are turned on ordinary lathes, and the depth and width of the piston ring grooves cannot be guaranteed.

     For this reason, the easiest way to identify it is to insert a piston ring of the same model as the piston produced by a regular manufacturer into the piston ring groove, and then use a feeler gauge for comparison and measurement to see the outcome.

7. Pay attention to check the compression height of the piston

     Due to the different compression ratios and heat loads of various engines, even pistons with the same diameter have differences in relative dimensions. Among them, the compression height of the piston is an important dimension in the piston parts, which will affect the compression ratio and ignition advance angle of the engine. Therefore, be sure to measure the compression height of the piston when replacing the piston.

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

     If the two kinds of pistons are mixed during maintenance, unexpected failures will occur. If the Honda CH125 water-cooled motorcycle is equipped with the piston of the Honda CHA125 forced air-cooled motorcycle, the compression ratio of the engine will be reduced, causing insufficient power and failure to increase the maximum speed.

     On the contrary, it will cause vicious failures such as the valve colliding with the piston top, and must not be negligent and lead to catastrophe. Therefore, when replacing the piston, the new and old pistons must be put together with a piston pin to compare their compression heights.

     Of course, when comparing, it is also necessary to pay attention to whether the positions of the two pistons are consistent between the first piston ring grooves. If the position difference is too large, it will also affect the compression ratio of the engine.