Analysis of the Causes of Piston ring breakage in the ring groove

The causes of piston ring breakage are usually as follows.

The opening clearance of the piston ring is too small. When replacing the piston ring, if the ring is mistakenly inserted at the upper part of the cylinder where the wear is the greatest for the opening clearance inspection, or if it is not filed at all according to the specified opening clearance value, when the piston ring descends to the lower part of the cylinder liner where the wear is the least (or due to thermal expansion), the opening clearance disappears and it swells up, causing the ring to tightly press against the inner wall of the cylinder liner and move, resulting in breakage.

(2) The edge clearance between the piston ring and the ring groove is too large. When the side clearance increases, the piston ring vibrates in the groove, which is not only unfavorable for air tightness but also may cause the inner sea to not break due to vibration. The main reason for the unnecessary complaint of edge clearance is that when the inner diameter of the cylinder is unequal after the cylinder liner wears out, the piston ring, in addition to bearing the reciprocating motion of the piston, also performs opening and closing movements within the ring groove itself, thereby intensifying the wear of the upper and lower planes between the ring and the ring groove. Practical experience has shown that the wear of the first two ring grooves on the piston is much faster than that of the other ring grooves.

(3) There is severe carbon deposition in the ring groove. Carbon deposits can cause the ring grooves to be uneven, subjating the piston rings to alternating bending during operation and thus making them prone to breakage.

(4) Carbon deposits form a circle of flanges on the upper part of the cylinder wall or steps are formed due to wear. In this case, when the piston reached the top dead center position, the first five steps were confused by the impact and broke.

Two additional reasons are as follows.

(1) Carbon deposit bonding. The piston rings are stuck in the ring grooves by carbon deposits. During movement, the piston rings are impacted and thus break, which is also a common cause.

(2) The connecting rod is twisted. After replacing the piston rings in a single-cylinder diesel engine, sometimes several rings break as soon as the engine starts running. This is mainly due to the distortion that Lian Xuan has developed. When the piston moves upward, the twisted connection causes the piston rings to be subjected to a torsional force and break completely. After discovering this phenomenon, the rod should be inspected and corrected.

Based on experience and some analysis, I believe the main reasons for the breakage of piston rings are as follows.

Piston rings are divided into gas rings and oil rings. The ones that break are mostly the first gas ring. Although this first gas ring has been chrome-plated, its degree of wear is still more severe than that of other rings because the working environment it is in is harsher than others. This is one of the reasons why the first gas ring is prone to breakage.

(2) If the opening clearance, edge clearance or back clearance of the piston ring is too small, it is prone to breakage due to jamming when the ring expands due to heat.

(3) If the fuel supply time is too early, the diesel engine will strike, the engine temperature will rise, and the carbon deposits will increase, causing the piston rings to wear and break prematurely.

(4) When the connecting rod is bent or twisted, or when the copper sleeve at the small end of the connecting rod is not properly assembled or milled off, the piston connecting rod assembly may experience uneven force distribution during movement, causing the piston rings to wear unevenly or even break.

(5) If the machine temperature is too high, the piston rings may get stuck or stick to the cylinder, which can easily cause the piston rings to break during operation.

(6) Piston rings are generally made by casting gray cast iron and alloys, and casting defects can also easily cause piston ring breakage.

From the current actual situation, the common reasons for the easy breakage of piston rings are as follows.

(1) The quality of the piston rings is too poor.

(2) The opening clearance of the piston ring is too small.

(3) After the old cylinder is replaced with a new ring, the first air ring strikes the cylinder liner shoulder.

(4) The opening of the piston ring expanded too much during assembly.

(5) There is severe carbon deposit in the cylinder.

The following are two examples of piston ring breakage.

(1) A S195 diesel engine overheated due to lack of water during operation. The operator immediately stopped the machine and shut it off. After the engine temperature dropped and sufficient cooling water was added, they were ready to start it. However, at this point, the crankshaft could no longer be turned, and the first piston ring had broken during disassembly and inspection. This is because when the engine is overheated and the engine is turned off too abruptly, the piston rings stick to the cylinder. The correct approach should be to let the engine idle for a while and wait until the engine temperature drops somewhat before turning it off. Immediately turn the crankshaft after turning off the engine until the machine temperature drops further.

(2) A S195 diesel engine was difficult to start due to excessive wear of the piston rings. After replacing the new rings, it started smoothly. However, after working for a period of time, the engine automatically shut down and the piston rings were pulled apart. It was finally found that the cause was that the opening gap of the piston ring was too small, and it got stuck after expanding due to heat.