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Home >> Subaru >> 2021 >> Forester Base >> Repair and Diagnosis >> Engine Mechanical >> Mechanical >> Engine Mechanical System >> Cylinder Block >> Inspection >> Piston Ring

Piston Ring

  1. Make sure the piston ring is not broken or damaged.
  2. Using a cylindrical guide, insert the piston ring into the cylinder liner so that they are perpendicular to the cylinder wall, and check the piston ring gap using a thickness gauge. If it is not within the standard, replace the piston ring.
    NOTE:
    • Measurement should be performed at a temperature of 20°C (68°F).
    • Use piston ring with same size as piston when replacing piston ring.

    Piston ring gap: 

    Compression ring (top ring) 

    Standard 

    0.20 - 0.25 mm (0.0079 - 0.0098 in)

    Compression ring (second ring) 

    Standard 

    0.25 - 0.35 mm (0.0098 - 0.0138 in)

    Oil ring (upper rail and lower rail) 

    Standard 

    0.10 - 0.35 mm (0.0039 - 0.0138 in)

    G13224612Courtesy of SUBARU OF AMERICA, INC.
  3. Fit the compression ring straight into the piston ring groove, then check the clearance between compression ring and piston with a thickness gauge. If it is not within the standard, replace the compression ring.
    NOTE:
    • Measurement should be performed at a temperature of 20°C (68°F).
    • Before inspecting the clearance, clean the piston ring groove and compression ring.
    • Use compression ring with same size as piston when replacing compression ring.

    Clearance between compression ring and piston: 

    Top ring 

    Standard 

    0.040 - 0.080 mm (0.0016 - 0.0031 in)

    Second ring 

    Standard 

    0.030 - 0.070 mm (0.0012 - 0.0028 in)

    G08317252Courtesy of SUBARU OF AMERICA, INC.