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TM 5-4210-220-12
4-28. ENGINE - Continued
4-28.3 Air Compressor - Continued
(c) Check piston pins for wear. Piston pins that have a variation in diameter of more than 0.003 in.
must be replaced.
Rod Pin Diameter ........................................ 0.5620/0.5618 in. (14.275/14.270 mm)
(d) There are two styles of piston pin fit, both methods of checking are detailed below.
Interference fit piston and pin.
Check the fit of the piston pins in the piston and connected rod. Pin must have a light
interference fit in piston and slip fit rod. If any parts are worn, the complete piston and rod
assembly must be replaced.
Slip fit piston and pin (new models)
Check the fit of the piston pin and connecting rod. Pin should be a slip fit in the piston and rod.
Visually check for worn or damaged areas. Replace parts as required or replace with a complete
piston and rod assembly. The connecting rod and the rod bearing cap must be replaced as a
unit.
Piston Pin Hole ............................................ 0.5618/0.5615 in. (14.270/14.262 mm)
Connecting Rod Pin Hole ............................ 0.5624/0.5622 in. (14.285/14.280 mm)
Rod Pin Diameter ..........................................0.5620/0.5618 in. (14.275/14.27 mm)
(e) Check the fit of compression and oil rings in the piston ring grooves. Place rings in piston ring
grooves and measure side clearance. Place rings in the cylinder bores and measure gap.
Groove Clearance Compression Rings ...........0.0015/0.0045 in. (0.038/0.114 mm)
Oil Rings..........................................................0.0005/0.0045 in. (0.013/0.114 mm)
Piston Rings Compression ............................................................... 0.007/0.017 in
Gap in 2.7500 in. Bore .................................................................... (0.18/0.43 mm)
Oil Ring Gap in ................................................................................... 0.015/0.55 in
2 7500 in. Bore ............................................................................... (0.38/1.40 mm)
Clearance between ring and ring groove, or ring cap must be within limits. If clearance or gaps
are not within these limits, new rings must be installed.
NOTE
Whenever a complete compressor teardown is accomplished, new rings are recommended.
4-544
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