TM 5-3895-346-14
PISTON AND PISTON RINGS
ENGINE OVERHAUL
Figure 7. Reaming Piston Pin Bushings
Use feeler gage set J 5438-01 to check the clearance.
The spring scale, attached to the proper feeler gage, is
used to measure the force in pounds required to with-
draw the feeler gage.
Figure 8. Measuring Piston-to-liner Clearance
Select a feeler gage with a thickness that will require a pull of 6 pounds to remove. The clearance will be 0.001
inch greater than the thickness of the feeler gage used, i.e., a 0.004 inch feeler gage will indicate a clearance of
0.005 inch when it is withdrawn with a pull of 6 pounds. The feeler gage must be perfectly flat and free of nicks
and bends.
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, three compression rings, and two oil control rings (Fig. 1).
The current top compression (fire) ring can be identified by the bright chrome on the bottom side and oxide
(rust color) on the top. The former ring had a plain metal color on both sides.
A two-piece oil control ring is used in both oil ring grooves in the pistons for non-turbocharged (naturally
aspirated) engines. A one-piece oil control ring is used in the upper ring groove and a two-piece ring in the
lower ring groove in the pistons for turbocharged engines. Brazil-built engines use non-slotted upper oil control
rings and low tension expanders.
All new piston rings must be installed whenever a piston is removed, regardless of whether a new or used
piston or cylinder liner is installed.
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