4A-28 - POWERHEAD 90-824052R3 JUNE 2002
MEASURING PISTON ROUNDNESS
Piston has a barrel profile shape and is not a true
diameter.
Standard 135 and 150 (carbureted) Models -
122 cu. in. (1999cc)
1. Using a micrometer, measure dimension “A” at
location shown. Dimension “A” should be as indi-
cated in chart following.
Piston
Dimension “A”
Standard Piston 3.115 in. ± .002 in.
.015 in. Oversize Piston 3.130 in. ± .002 in.
.030 in. Oversize Piston 3.145 in. ± .002 in.
2. Using a micrometer, measure dimension “B” at
location shown. Dimension “B” should be within
.008 in. of dimension “A”.
29/32
in.
(23mm)
a
b
a - Dimension “A” at Right Angle (90°) to Piston Pin
b - Dimension “B” (in line with Piston Pin)
Standard 175, XR6, Magnum III, 150 EFI, 200 EFI
Models and High Performance Pro Max/Super
Magnum 150, 200, 225 Models - 153 cu. in.
(2508 cc)
1. Using a micrometer, measure dimension “A” at
location shown. Dimension “A” should be as
indicated in chart following.
Piston
Dimension “A”
Standard Piston 3.494 in. ± 0.001 in.
.015 in. Oversize Piston 3.509 in. ± 0.001 in.
2. Using a micrometer, measure dimension “B” at
location shown. Dimension “B” should be within
0.008 in. of dimension “A.”
1/2 in.
(12.7mm)
a
b
a - Dimension “A” at RIGHT Angle (90°) to Piston Pin
b - Dimension “B” (in line with Piston Pin)
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. (0.1mm) over the ENTIRE length
of the cylinder head. If measured warpage, as
determined on a surface block, exceeds 0.004 in.
(0.1mm) 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
may be re-surfaced up to 0.010 in. (0.25mm).
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.
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