Cylinder liner cloverleafing
Despite the close control of the cylinder surface temperature, acids are still formed which must be neutralised by the cylinder lubricating oil, this requires that the correct quantity and Total base number(TBN) grade of oil is injected into cylinder. Immediately the oil enters the cylinder it will start neutralising the acid, becoming less alkalinity may be depleted before it has completely covered the liner surface, further contact with acids may leads to the oil itself becoming acidic, this will leads to phenomenon known as cloverleafing in which high corrosive wear occurs on the liner between the oil injection points severe cloverleafing can result in gas blow by past the piston rings and ultimate failure of the liners, Source: reed's motor engineering knowledge, 78