Selection of Piston Pin and Repair of Bushing

1. Selection of piston pin

When the engine is overhauled, replace the new piston pin together with the piston.

Under normal circumstances, there are corresponding color marks on the piston pin seat hole, the end face of the piston pin, and the small end of the connecting rod. Different colors indicate different matching tolerance zones. When matching, the piston and piston pin are matched according to the color. The quality requirements of the piston pin are: surface roughness ≤ Ra0.20μm, no rust spots, cylindricity tolerance not greater than 0.025m, should choose the same factory, the same grade, the same group of piston pins, in order to make the weight and size consistent.

2. Repair of connecting rod bushing

1) Selection of connecting rod bushing/sleeves

There should be a certain amount of interference between the outer diameter of the connecting rod bushing and the small end hole of the connecting rod to ensure that the bushing does not go out of the outer circle during operation. The matching between the connecting rod bushing, the small end of the connecting rod and the piston pin should meet the specified standard value.The matching requirements between the piston pin and the connecting rod bushing are: there should be a certain matching clearance at room temperature, and the contact surface should reach more than 75%.

2) Repair of bushings

The correct fit between the piston pin and the bushing is achieved by trial fitting and repairing and scraping of the bushing.

Trial match:
In the trial match, when the pin can be pushed into 1/3-2/5 of the sleeve with the palm of your hand, press the pin into the sleeve or use a hammer to drive the copper gun into the sleeve, and clamp it on the vise , Pull the connecting rod back and forth, and after grinding, take out the piston pin, check the contact marks and repair it.

Scraping:
Trim according to contact marks and tightness. The essentials are: the trimming surface of the knife and the bushing is at an angle of 30°~40°, so that the trimming area is not too large, and the uncontacted parts are also scraped off. When repairing scraping, it should be carried out according to the principle of from the inside to the outside, scraping heavy and leaving light, scraping large and leaving small. At the beginning, the edges of both ends should be scraped less or not scraped to prevent scraping into a bell mouth, until the tightness and contact surface are close to the right , and then trim the ends slightly. When the scraping is enough to push the pin into the bushing with the force of the palm, the tightness is appropriate, and the contact surface should reach more than 75%.

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