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PISTON ACTIVE SEAL AREA REPAIR
PISTON REPAIR PROCEDURE
Pistons with scratches or scoring in the active seal areas, denoted as d10 and d11 in
the illustration, may be repaired by polishing as long as the damage is less than .1mm
(.004 inch) deep. Damage more than .1mm (.004 inch) deep requires piston
replacement. Note that scratches in area d12 are not as critical, but the diameter of
area d12 is. After repairing a piston in areas d10, d11, or d12, measure the diameters
with a micrometer and contact the NPK Service Department to confirm that the piston is
still within usable specifications. Areas d8 and d9 are not critical. Light buffing to
smooth out scratches is all that is required.
MODEL
d8
in mm
d9
in mm
d10
in mm
d11
in mm
GH06
1.14 29 1.18 30 4.17 106 4.17 106
GH07
1.18 30 1.22 31 4.17 106 4.17 106
GH1
1.61 41 1.73 44 5.20 132 4.65 118
GH2/GHS2
1.61 41 2.05 52 5.20 132 4.65 118
GH3
2.17 55 2.56 65 5.51 140 5.08 129
GH4
2.2 56 2.8 71 7.32
186
5.98
152
GH6
2.56 65 3.31 84 7.80 198 6.38 162
