TM 5-3810-300-24-&P-3
1.6 Piston and Piston Rings
Fig. 20 - Comparison of Fire Rings
If any bind occurs between the piston and the liner,
examine the piston and liner for burrs. Remove burrs
with a fine hone (a flat one is preferable) and recheck the
clearance.
Fitting Piston Rings
Each piston is fitted with a fire ring, two compression
rings and two oil control rings (Fig. 19).
The top (fire) ring and the upper compression ring
Fig. 19 - Piston Ring Location (Non-
(second groove) are pre-stressed. Both are identified by
Turbocharged Engine)
an oval mark on the top side. In addition, the fire ring
has a black oxide or copper colored finish on the top
A new cylinder liner has an inside diameter of 4.2495" to
side.
4.2511 " The piston-to-liner clearance, with new parts,
will vary with the particular piston diameter (refer to
NOTE: The current piston crowns (18.7:1
Section 1.0). A maximum clearance of .012 " is
compression ratio) have a tapered fire ring
allowable with used parts.
groove.
With the cylinder liner installed in the cylinder block, hold
the piston skirt upside down in the liner and check the
clearance in four places 90 apart (Fig. 18).
Use feeler gage set J 5438 to check the clearance. The
spring scale, attached to the proper feeler gage, is used
to measure the force in pounds required to withdraw the
feeler gage.
Select a feeler gage with a thickness that will require a
pull of six pounds (26.7 N) to remove. The clearance will
be .001 "greater than the thickness of the feeler gage
used, i.e., a .004" feeler gage will indicate a clearance of
.005 " when it is withdrawn with a pull of six pounds (26.7
N). The feeler gage must be perfectly flat and free of
Fig. 21 - Measuring Piston Ring Gap
nicks and bends.
Page 94
