Piston Ring

WARNING: This page is about a different car, the 2012 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

If the piston ring is broken, damaged or worn, or if its tension is insufficient, or when the piston is replaced, replace the piston ring with a new part of the same size as piston.
NOTE:
- The top ring and second ring have the mark to determine the direction for installing. When attaching the ring to the piston, face these marks towards the top side.
- Oil ring consists of the upper rail, expander and lower rail. When attaching the oil ring to the piston, pay attention to the direction of each rail.
Fig 1: Piston Ring Upper Rail, Expander And Lower Rail
Courtesy of SUBARU OF AMERICA, INC.

Using the piston, insert the piston ring and oil ring into the cylinder so that they are perpendicular to the cylinder wall, and measure the piston ring gap with a thickness gauge.

PISTON RING GAP SPECIFICATIONS CHART

		Standard mm (in)
Piston ring gap	Top ring	0.20 - 0.25 (0.0079 - 0.0098)
	Second ring	0.37 - 0.52 (0.015 - 0.020)
	Oil ring rail	0.20 - 0.50 (0.0079 - 0.0197)

Fig 2: Measuring Piston Ring Gap With Thickness Gauge

Courtesy of SUBARU OF AMERICA, INC.

Fit the piston ring straight into the piston ring groove, then measure the clearance between piston ring and piston ring groove with a thickness gauge.

NOTE: Before measuring the clearance, clean the piston ring groove and piston ring.

PISTON RING GROOVE SPECIFICATIONS CHART

		Standard mm (in)
Clearance between piston ring and piston ring groove	Top ring	0.040 - 0.080 (0.0016 - 0.0031)
Clearance between piston ring and piston ring groove	Second ring	0.030 - 0.070 (0.0012 - 0.0028)

Fig 3: Measuring Clearance Between Piston Ring And Piston Ring Groove

Courtesy of SUBARU OF AMERICA, INC.