Measuring Piston - Mercury 25 EFI Service Manual

The measurement for cylinder taper should be taken at three depth locations: 15 mm (0.6 in.), 35 mm (1.4 in.), and 55 mm
(2.2 in.).
c
b
a
Cylinder Bore
Cylinder bore (standard)
Cylinder bore (service limit)
Out of round (service limit)
Taper (service limit)

Measuring Piston

Inspect piston wall for wear or damage. Replace piston if necessary.
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.
b
Piston
Diameter (standard)
Diameter (service limit)
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
Maximum clearance (service limit)
90-8M0105568 eng MARCH 2016
a -
b -
c -
3129
a
a - Piston diameter
b - Measure point 9 mm (0.35 in.)
22022
55 mm (2.2 in.)
35 mm (1.4 in.)
15 mm (0.6 in.)
0.020–0.055 mm (0.00079–0.00217 in.)
© 2016 Mercury Marine
Cylinder Block/Crankcase
61.00 mm (2.4016 in.)
61.06 mm (2.4039 in.)
0.06 mm (0.0023 in.)
0.08 mm (0.0032 in.)
60.96 mm (2.4000 in.)
60.90 mm (2.3976 in.)
0.150 mm (0.00591 in.)
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