Piston Diameter
1.
Measure the piston at a point 9 mm (0.35 in.) from the bottom, 90° to the piston pin. Replace the piston if out of
specification.
a - Piston diameter
b - Measure point 9 mm (0.35 in.)
Piston
Diameter (standard) 60.96 mm (2.400 in.)
Diameter (service limit) 60.90 mm (2.3976 in.)
2. Measure the piston to cylinder clearance. If out of specification examine the piston and cylinder bore further to determine
repair/replacement.
The minimum piston to cylinder wall clearance is defined by the formula: Minimum cylinder bore measurement – Maximum
piston diameter measurement = Piston to cylinder clearance.
Piston to Cylinder Wall Clearance
Minimum clearance 0.020–0.055 mm (0.0008–0.0022 in.)
Maximum clearance (service limit) 0.150 mm (0.0059 in.)
Piston Ring Side Clearance
Measure the piston ring side clearance. Replace the piston and rings if out of specification.
a - Top ring
b - Second ring
c - Oil ring
Piston Ring Side Clearance
Top "a" 0.03–0.08 mm (0.0012–0.0031 in.)
Top "a" (service limit) 0.10 mm (0.004 in.)
Second "b" 0.02–0.06 mm (0.0008–0.0024 in.)
Second "b" (service limit) 0.09 mm (0.0035 in.)
Oil "c" 0.03–0.13 mm (0.0012–0.0051 in.)
Oil "c" (service limit) 0.15 mm (0.0059 in.)
Piston Ring End Gap
Measure the piston ring end gap clearance. Replace the piston rings as a set if out of specification.
Cylinder Block/Crankcase
Page 4A-18 © 2018 Mercury Marine 90-8M0125265 eng NOVEMBER 2017
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