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The Faults and Solutions of Diesel Generator Set Piston

Feb. 28, 2020


Piston is the main moving part of diesel engine, which is one of the important components of the combustion chamber of diesel engine. The piston, cylinder head and cylinder sleeve constitute the combustion chamber of diesel engine, which bears the gas force and transmits it to the crankshaft through piston pin and side bar, so as to make the crankshaft rotate and output power. At the same time, in the process of compression, it also bears the thrust of the side bar.


During the use of diesel generator set piston, what faults maybe occur? And How to deal with them?

In the process of using diesel generator set, the position of piston easy to wear is ring groove, followed by skirt and pin seat hole.

1.Wear of piston ring groove

The piston ring moves in the ring groove, so that the piston ring groove is subject to the maximum wear in the height direction, so that it becomes a ladder or trapezoid. The main reason of wear is the unit pressure of piston ring on the groove wall and the influence of high temperature. The wear rate of ring groove depends on the roughness of piston ring plane and the structure of piston to a great extent.


Solutions: When the wear of the piston ring groove is widened and the side clearance of the piston ring is greater than the specified allowable value, the piston ring groove can be turned on the lathe according to the enlarged piston ring.

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2.Wear of piston pin seat hole

The wear of piston pin seat hole is generally smaller than that of piston ring groove. The wear rate depends on the roughness of piston pin hole and the fit between piston pin and pin hole. Due to the action of gas pressure and inertia force, the wear of piston pin seat hole is not round, and the biggest wear occurs in the direction perpendicular to the piston crown.


Solutions: When the wear of the piston pin seat hole exceeds the specified value, the pin hole shall be reamed to the repair size with a reamer, and an enlarged piston pin shall be equipped.


The selection and matching of piston pin shall be based on the inner diameter of the worn pin hole, and the enlarged piston pin (generally 0.025-0.05mm larger than the inner diameter of the pin hole) which is similar to the inner diameter shall be selected. If you still feel loose when selecting the largest piston pin, you should re select the piston.  The selected piston pin is new, and its conicity and out of roundness shall not exceed 0.005mm. For multi cylinder diesel engines, the quality difference of piston pin of each cylinder shall not exceed 10g. The interference between piston pin and pin seat hole shall be 0.025-0.04mm under normal temperature (15-25 degrees).


3.Wear of piston skirt

When the piston is in normal operation, its skirt is perpendicular to the piston pin seat hole, due to the effect of side pressure, the cylinder wall is directly rubbed, and the surface of the cylinder has regular wispy wear marks. When the piston is working, its head seldom contacts the cylinder wall because of the piston ring, because of the strong heat on the top, the metal is also thick and easy to expand. Although the skirt is in contact with the cylinder wall, its unit pressure is not large, and the lubrication condition is good, so the wear is also small. Because of the side pressure produced when the piston and connecting rod run at high speed, the piston will form radial wear.


Therefore, the measurement of piston availability depends on the increased clearance between the piston and the cylinder wall. The increase of clearance will aggravate the wear of piston and cylinder wall. The rotating speed is unstable, the power decreases, the oil consumption increases, and the exhaust gas emits blue smoke.

Solutions: When the wear of the piston skirt, the out of roundness and taper of the piston skirt are greater than the specified value, they should be replaced.


Generally, the piston can be inspected by observation and judgment after being damaged. When the exhaust pipe of diesel engine emits blue smoke and the power drops, most of the faults occur in the ring groove or piston ring; when the engine is idling, the air leakage in the crankcase can be heard. It is difficult to repair the piston. When the piston is seriously worn, burnt or broken, it should be replaced with a new piston of the same model.


If the piston of diesel generator set fails, it will hinder the normal operation of the unit. Therefore, if you find the piston fault of the unit, you must repair it in time.


Starlight Power is a manufacturer of power generating set in Jiangsu China, founded in 1974. We are not only provide technical problem solutions, but also supply high quality diesel generator set (20kw-3000kw), if you have purchase plan, do not hesitate to contact us by email sales@dieselgeneratortech.com, we will guide you to select the most suitable genset.

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