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3 - 20 ENGINE
This precaution will prevent cracked or broken piston ring
lands or piston rings.
The 6 cylinder connecting rods and pistons must be
removed through the top of the cylinder block while the 8
cylinder rods and pistons can be removed from either the top
or bottom. Thus, on the 6 cylinder engine it will be necessary
to remove the oil pan and cylinder head. Although it is not
necessary to remove the cylinder head in order to remove
the rod and piston assemblies on the 8 cylinder, it is advis-
able in order to facilitate proper checking of cylinder walls
and fitting of piston rings as well as removing cylinder ridge
and carbon deposits.
PISTON RINGS
The piston rings used in the 6 and 8 cylinder engines are
cast iron and are pinned to prevent rotation in the piston
grooves.
NOTE: The top compression ring for the 308 Cu. In. 6
cylinder engine is a chromium ring.
The rings are notched on the inner diameter at the gap slot.
FIGURE 21
Width of the notch is .125" total of which approxi-
mately .075" is at one end of the ring and .050" at the
other end. This offsetting of the notch enables a single pin
to anchor the 3 top piston rings without having the gaps
aligned on adjacent rings.
It will also be noted by reference to Figure 21 that the end
gap is equal to the back lash of the ring notch on pin.
Therefore, the ends of a ring are filled to obtain the desired
.005" to .009" gap on 8
cylinder and .006' to .014" on 6 cylinder, it is necessary to
file an equal amount from the notch in order maintain the
pin backlash at the same value. as the gap.
NOTE: To insure that the gap and backlash be main-
tained equal, ring filing to fit a bore size smaller than the
ring size should be avoided.
Service piston rings are available in .002 " , .005 " , .010",
.015 " , .020" and .030" over-size for the 6 cylinder engines,
and .003", .005", .010", .015", 020" and .030" over-size for
the 8 cylinder engine. Refer to your service parts manual for
the proper part number and size.
Make sure that successive rings are assembled to the
grooves with their gap on opposite sides of center line of
the ring retaining pin. In other words, if the top ring is
Installed with the short half of the notch on the right side of
the pin, the 2nd ring should be Installed with the short half
on the left side of the pin and the 3rd in the same relative
position as the first.
To avoid damaging piston rings or pistons , use
KMO-297-H Piston Ring Remover and Installer.
PISTON SIZE CODE
(8 Cylinder)
A code letter is stamped on the cylinder block along the
lower face of the valve chamber, Figure 22, to show the
original size of each cylinder.
FIGURE 22
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