The ring bank is broken at transition arc mostly in main thrust surface of piston:

1. Bad combustion of engine cause excess coke in ring groove and adhesion of piston ring, the opening of ring is vibrated vertically, and bumps the ring bank and results in the breakage of the ring bank.

2. Unreasonable joint interval between piston ring and ring groove makes the ring flutter during the working and results in breakage of piston ring bank.

3. Inferior piston materials, its strength is not qualified for design needs, the ring bank is easily broken, an obvious casting error is existed in the broken parts, but there is no high-temperature color difference on the piston surface.

4. Abnormal combustion gives rise to over high temperature of engine. The strength of the ring bank is decreased; the bank is easily broken at main thrust surface under larger force.

5. When the engine is too hot under overload run, the strength of the ring bank is decreased. The impact force between piston ring and ring groove becomes stronger, and results in the breakage of piston ring bank.

6. The wearing of cylinder sleeve over the steps, the steps may bump the first ring and results in the breakage of ring bank.