Pistons of automobile engines have drain-back-slots (through the piston skirt wall) in most cases, so that the oil in the oil ring groove can be sent back to the sump. Some oil sometimes flows from the large end of the connecting rod into the oil ring groove through these drain back slots. In other words, the drain back slots cause contradictory effects. We have, therefore, mounted covers on the piston inner wall to prevent this reverse flow. Excess oil is sometimes sucked up into the combustion chamber under the engine braking condition. This amount of oil was reduced with the use of these covers.
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