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301-350-400 V 8 ENGINE VI CODES Y-P-Z
6A5-2 1
PISTON PIN
Fit
Piston pins normally do not become loose enough to
cause a knock or tapping until after very high mileage and
in such cases the piston and rod can be reamed and oversize
pins installed.
The piston pin fit in the piston is .0003" to .0005" loose
with pin and bosses clean and dry.
Piston and pin must be at room temperature when
checking fit and pin must be able to
fafl
fiom piston by its
own weight.
CYLINDER BORES
Inspect
IMPORTANT: (301 engine only) final bore operations
are done in production using a deck plate which
simulates the cylinder head in its installed position. For
this reason, bore measurements may vary from area to
area when gaged with the head removed. Accurate
measurements and/or piston fit data can be obtained by
gaging bores only at right angles from the crankshaft or
piston pin centerline.
Inspect cylinder bores for wear or excessive taper, with
an accurate cylinder gage 5-8087 or comparable, at top,
middle and bottom of bore. (Fig. 6A5-45). Measure cylinder
bore at right angles to the centerline of the piston pin.
Variation in measure from top to bottom of cylinder indicates
the taper in the cylinder. If the top of the cylinder bore is
larger than the bottom by .003", the cylinder should be
rebored and a new piston fit. Cylinder bores can be measured
by setting the cylinder gage dial at zero in the cylinder at the
point of desired measurement. Lock dial indicator at zero
before removing from cylinder, and measure across the gage
contact points with outside micrometer, with the gage at the
same zero setting when removed from the cylinder (Fig. 6A5-
46).
Fine vertical scratches made by ring ends will not by
themselves cause excessive oil consumption, therefore,
honing to remove them is unnecessary.
HONING OR BORING
If a piston other than standard size is to be installed, the
cylinder should be bored, rather than honed, to effect a true
bore.
When honing to eliminate taper in the cylinder full
strokes of the hone in the cylinder should be made in addition
to checking measurement at top, middle and bottom of bore
repeatedly.
NOTE: Surface finish should not exceed 7 to 15 micro.
When boring, always be sure the crankshaft is out of the
way of the boring cutter when boring each cylinder.
Crankshaft bearings and other internal parts must be covered
or taped to protect them during boring or honing operation.
When taking the final cut with a boring bar, leave .001" on
the diameter for finish honing to give the required piston to
cylinder clearance specifications. (Honing or boring
Fig. 6A5-45 Measuring Cylinder Bore - Typical
Fig. 6 A 5 - 4 6 Measuring Cylinder Bore Gage
operation must be done carefully so that specified clearance
between pistons, rings, and cylinder bores is maintained).
IMPORTANT: (301 engine only) boring of the block
should not be attempted without the use of a deck plate
to simulate the cylinder head in its installed position.
By measuring the piston to be installed at the sizing
points (Fig. 6A5-47) and adding the mean of the clearance
specification, the finish hone cylinder measurement can be
determined. It is important that both the block and piston
be measured at normal room temperature.
After final honing and before the piston is checked for
fit each cylinder bore must be thoroughly cleaned. Use soapy
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