Engine Piston Ring


1. Description

The piston ring is designed to prevent pressure from leaking out of the gap between the piston and the cylinder. There are three piston rings that function to keep the combustion chamber airtight as the top two compression rings serve to disperse the heat from the pistons to the cylinder. Also they act to scrape off excess oil on the cylinder wall in order to create the minimum film of oil necessary while preventing excess oil from entering the combustion chamber.

2. Marks of ring

The name of the manufacturer and the oversize mark

are inscribed on the piston ring.


Pay attention to the following when assembling:

The surface with the mark should face up.

Do not confuse the order of the compression rings.

When the No. 1 compression ring does not have the mark, it may be located on the side of the ring. In the case that there are no marks in both locations, consult the Repair Manual to judge the difference in shape.

In order to reduce pressure leakage as much as possible, assemble the piston ring end gap at the separated position as in the illustration. Check the ring end gap when using a new piston ring.

3. Ring end gap

The ring end gap must be from 0.2 – 0.5 mm when at room temperature. If the piston ring end gap is too large, pressurized gasses will leak out through the gap. If the ring end gap is too small, the two ends of the piston ring will touch each other due to heat expansion and cause the ring to expand. This may result in scoring of the cylinder wall or the piston ring itself may break.


When measuring the ring end gap, insert the piston ring in the piston cylinder at the place with the least amount of wear.

The position for measuring the ring end gap differs according to the engine models.

4. Ring pumping effect and ring flutter

(1) Ring pumping effect

The piston ring moves up and down inside the piston ring groove while the engine is running. This acts to pump oil on the ring, helping to improve lubrication. If the gap between a piston ring and piston ring groove is too large, the pumping effect will also be large, resulting in an increase in oil consumption.

(2) Ring flutter

When the piston ring vibrates up and down or side to side in the piston ring groove, ring performance decreases. When this condition continues, the piston ring or piston ring groove will experience abnormal wear and may eventually result in seizing.

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