Mercury 150 EFI Service Manual page 362

Piston with two half keystone (half tapered) rings
MEASURING PISTON ROUNDNESS
Piston has a barrel profile shape and is not a true diameter.
1. Using a micrometer, measure dimension "A" at location shown. Dimension "A" should
be as indicated in chart following.
Standard Piston
0.015 in. Oversize Piston
2. Using a micrometer, measure dimension "B" at location shown. Dimension "B" should
be within 0.008 in. of dimension "A."
Cylinder Heads and Exhaust Divider Plate
1. Inspect internal surface of cylinder heads for possible damage (as a result of piston or
foreign material striking cylinder heads).
IMPORTANT: Cylinder head warpage should not exceed 0.004 in. (0.1 mm) over the
ENTIRE length of the cylinder head. If measured warpage, as determined on a surface
block, exceeds 0.004 in. (0.1 mm) or a discontinuity of up to 0.004 in. (0.1 mm) exists
in a narrow portion of the cylinder head's surface length, then the cylinder head should
be replaced.
2. Replace cylinder head(s) as necessary.
3. Thoroughly clean gasket surfaces of exhaust divider plate.
4. Inspect exhaust divider plate for deep grooves, cracks or distortion that could cause
leakage. Replace parts as necessary.
90-883728 JULY 2001
150/175/200 Piston
a
a - Dimension A at right angle (90 ) to Piston Pin
b - Dimension B (inline with Piston Pin)
Enlarged View of
Piston Ring Grooves
3.494 in.
3.509 in.
1/2 in.
(12.7mm)
b
POWERHEAD
Dimension "A"
.001 in. (88.747 mm .025
mm)
.001 in. (89.128 mm .025
mm)
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