Mercury MerCruiser D2.8L D-Tronic Service Manual page 311

SERVICE MANUAL NUMBER 22
4. Measure piston outer diameter about 13 mm (1/2 in.) from bottom of skirt.
5. Proper clearance of piston ring in its piston ring groove is very important to provide
proper ring action and reduce wear.
Keep in mind that while the second (scraper) compression ring and the oil control ring are
typical in nature, the first (upper) compression ring is "trapezoidal" (tapered) in design. That
is, it has a 15 degree taper on both upper and lower surfaces.
Correspondingly, the first compression ring groove is tapered 15 degrees on top and
bottom.
Note also, that the upper ring's edge (parallel to cylinder liner) is not a straight cut. It is
rounded, or arced, in design.
IMPORTANT: Do NOT mistake these tapered or different design characteristics for
unusual wear patterns.
90-860074--1 FEBRUARY 2002
a - Outer Diameter Measurement Point - 13 mm (1/2 in.)
a
a - First Compression Ring - Trapezoidal (Tapered)
b - First Compression Ring Groove - (Tapered)
c - Outer Edge of Upper Compression Ring - (Arced)
a
b
ENGINE MECHANICAL
70229
c
70441
70440
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