Crankshaft - Mercury 40 Service Manual

CLEANING PISTON RING GROOVES
IMPORTANT: The piston rings are half – keystone
rings – (tapered on the top side) – follow cleaning
and inspection carefully! Chromed ring is in-
stalled on top.
CAUTION
Care must be taken not to scratch the side sur-
faces of ring groove. Scratching the side sur-
faces of the ring groove will cause damage to the
ring groove.
Use a bristle brush and carbon remover solution
to remove carbon from side surfaces.
A tool can be made for cleaning the inner diameter
of the tapered ring grooves. The tool can be made
from a broken tapered piston ring with the side ta-
per removed to enable inside edge of the ring to
reach the inside diameter of the groove. Carefully
scrape the carbon from inner diameter of ring
grooves. Care must be taken not to damage the
grooves by scratching the surfaces of the
grooves.
MEASURING PISTON SKIRT
Measure piston skirt at right angle (90 ) to piston pin
centerline, 0.50 in. (12.7 mm) up from bottom edge
of skirt.
90-852572R1 JANUARY 1998
Enlarged View of
Piston Ring Grooves
PISTON PISTON SKIRT
SIZE DIAMETER
Standard 2.950 in.
Piston (74.93 mm)
.015 2.965 in.
Oversize (75.31 mm)
.030 2.980 in.
Oversize (75.69 mm)

Crankshaft

Inspect crankshaft to drive shaft splines for wear.
(Replace crankshaft, if necessary.)
Check crankshaft for straightness. (Replace as
necessary.)
Inspect crankshaft oil seal surfaces. Sealing sur-
faces must not be grooved, pitted or scratched.
(Replace as necessary.)
Check all crankshaft bearing surfaces for rust, wa-
ter marks, chatter marks, uneven wear and/or
overheating. (Refer to "Connecting Rods".)
If necessary, clean crankshaft surfaces with cro-
cus cloth as shown.
.50 in.
(12.7 mm)
CYL. BORE
FINISH HONE
2.988 in.
(75.895 mm)
3.003 in.
(76.276 mm)
3.018 in.
(76.657 mm)
POWERHEAD - 4-25