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Repair Of Piston Pin And Pin Seat Hole In Diesel Generator Set Maintenance

Mar. 08, 2023

Today, let's talk about the repair of piston pin and pin seat hole in diesel generator set maintenance:


(1) Technical requirements.

① There should be a small amount of interference (generally 0.0025~0.04mm) at normal temperature, and a small amount of clearance when heating to 75~85 ℃, so that the piston pin can rotate in the pin seat hole. After cooling, the elliptical deformation of the piston skirt, namely the shortening of the long axis (perpendicular to the piston pin axis) and the elongation of the short axis (in the direction of the piston pin axis), should not exceed 0.04 mm. This is the key to the fitting of piston pin and pin seat hole. If the fit is too tight, the oil cannot enter, which will deteriorate the lubrication of the piston pin, aggravate the wear, and even cause the cylinder jamming. If the fit is too loose, the piston pin will hit the piston and connecting rod bushing during the reciprocating movement of the piston, and the wear will be aggravated. In serious cases, the piston pin will break or jump out, causing accidents.


② The contact area shall not be less than 75%. This is because the contact area is too small, the load per unit area increases, the wear is accelerated, the tightness is affected, and the service life of the machine decreases.

The matching of piston pin and pin seat hole is completed by honing or reaming the piston pin seat hole. When reaming the pin seat hole, the long-blade reamer shall be selected to enable the two pin seat holes to be reamed at the same time to ensure the concentricity of the two holes.


diesel generator set

(2) Reaming of piston pin seat hole.

① Select the reamer: select the dumpling knife according to the actual size of the pin seat hole, and clamp the dumpling knife on the vice to keep it perpendicular to the plane of the jaw.


② Adjust the reamer: the reamer is adjusted upward to reduce the size and downward to expand the size. Because the first cutter is to do experimental micro reaming first, the reaming amount of pin seat hole is very small, which is generally adjusted until the upper end of the blade exposes the pin seat hole. In the future, the adjustment amount of each knife should not be too large. Generally, it is better to turn the adjusting nut to 690 °. When the reaming amount is too small, the adjusting nut can be rotated again


③ Reaming: When reaming, hold the piston with both hands and press gently. The force of light pressure should be even, and the grip should be flat. Rotate the reaming clockwise. In order to make the pin seat hole reamed straight, each time the reamer is adjusted, it should be reamed from two directions of the pin seat hole. When it is tight to turn to a certain position, it can be slightly reversed, and then continue to rotate clockwise. Never turn hard when it cannot rotate, which will affect the surface of the blade and pin hole. Also, the piston should be reamed to the end. Take out the piston from the other end of the reamer. It cannot be reversed halfway. Because this will make the inner circle surface of the piston pin hole have the same number of steps as the number of movable reamer blades, so that in the working process, the fit clearance between the piston pin and the hole will rapidly increase. In order to improve the smoothness, the reaming amount of the reamer should be reduced as much as possible when it is close to reaming.


④ Trial fitting: During reaming, the piston pin shall be used for trial fitting at any time to prevent the piston pin seat hole from being reamed. When the reaming reaches about 1/3 of a pin seat hole with the force of the palm of the hand, the reaming shall be stopped. Then gently punch the piston pin into a pin seat hole with a wooden hammer or a copper punch and a hand hammer. After the contact condition is checked once or twice, continue to punch another seat hole. When pressing, the piston pin should be placed in the right position to prevent the pin from tilting and damaging the working surface of the pin seat hole. Finally, punch out the piston pin, check the contact surface, and properly repair it.


⑤ Scraping: scraping can not only increase the contact area between piston pin and pin seat hole, but also obtain appropriate fit tightness. When scraping, the blade should be at an angle of 30 °~430 °~40 ° with the axis of the pin seat hole, so as to avoid scratching the non-contact parts due to too large scraping area. The scraping shall be carried out from the inside to the outside, with the heavy scraping remaining light, and the large scraping remaining small. It is better to start scraping less or no scraping at the edges of both ends to prevent scraping into a horn shape. When the tightness and contact surface of the piston pin and the pin seat hole are close to appropriate, slightly scrape both ends. After scraping, make the tightness and contact surface meet the requirements.

Requirements for tightness: under normal temperature, it is appropriate for the gasoline engine to push the piston pin into 1/2~2/3 of a seat hole with the power of the palm of the hand. When the diesel engine requires the piston to be heated to 75~85 ℃ in water, apply engine oil on the piston pin and push it into the pin seat hole with slight force of the palm of your hand. Requirements for contact surface: more than 75% of the contact surface, and the marks on the working surface of the pin seat hole should be evenly distributed, with the same weight.


Founded in 1974, Jiangsu Starlight Electricity Equipments Co.,Ltd., a wholly-owned subsidiary of Jiangsu Starlight Power Group, is one of the earliest manufacturers of generating sets in China. Over the past 40 years, the company has won the recognition of users by relying on advanced testing equipment, modern production technology, professional manufacturing technology, perfect quality management system, strong R&D technology strength. For more details, please contact us with sales@dieselgeneratortech.com.

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