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Home >> Subaru >> 2019 >> WRX STI Limited >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 13 (Engine Mechanical System (Except For STI)) >> Cylinder Block >> Inspection >> Piston Ring

Piston Ring

WARNING: This page is about a different variant/trim than selected.
  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 

    0.40 - 0.50 mm (0.0157 - 0.0197 in)

    Oil ring (upper rail and lower rail)

    Standard 

    0.10 - 0.35 mm (0.0039 - 0.0138 in)

    G09480624Courtesy 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 

    0.045 - 0.085 mm (0.0018 - 0.0033 in)

    G08317252Courtesy of SUBARU OF AMERICA, INC.