TM 10-4320-318-14
6-8. MAINTENANCE OF PISTON - (Cont)
(1) Inspect piston and piston rings for cracks, chips, and burrs.
(2) Replace defective components. (Piston rings must be replaced as a set.)
(3) Clean ring grooves in piston. Inspect for cracked and worn lands.
NOTE
If any of the clearances do not meet specifications, piston is defective.
Piston diameter = 2.8724 in. (72.96 mm)
Ring groove width (1 compression ring) = 0.0835-0.0827 in. (2.12 - 2.10 mm)
Ring groove width (11 compression ring) = 0.0819 - 0.0812 in. (2.08 - 2.06 mm)
Ring groove width (scrapper ring) = 0.1592-0.1584 in. (4.04 -4.02 mm)
(4) Insert ring into cylinder. Use piston to push ring down to a point approximately 1 in. (25.4 mm) from top
of cylinder. Measure and record ring end gap. Remove ring.
(5) Repeat step (4) until all rings have been checked.
NOTE
If ring gaps do not meet specifications, piston rings are defective.
I compression ring = 0.008-0.031 in. (0.20-0.80 mm).
II compression rings = 0.0010-0.059 in. (0.25-1.5 mm).
Scraper ring = 0.008-0.059 in. (0.20-1.5 mm).
(6) Inspect wrist pin bushing for burrs, worn spots, and discoloration. If defective wrist pin bushing, replace
the piston.
c.
INSTALL.
(1) Install piston rings (5) onto piston (3).
(2) Insert one circlip (1) into groove in wrist pin bore (6) with opening at 12 or 6 o’clock position.
(3) Install piston (3) onto connecting rod (4). Make sure that the opening of combustion chamber on top of
piston is on flywheel side of crankcase.
(4) Insert wrist pin (2) into wrist pin bore (6). Wrist pin (2) must contact circlip (1).
(5) Install second circlip (1) with opening at 12 or 6 o’clock position.
6-21
