and ground, with hardened bearing surfaces. Counterweights may be
removable. Passages for pressure lubrication shall be rifle drilled into
the crankshaft. The crankshaft shall be free of sharp corners with drilled
holes or changes in section finished with generous radii and highly
polished. Main bearings shall be steel backed babbit type or
anti-friction, roller type. Crankshaft shall be counterweighted and
balanced.
2.3.6.3
Connecting Rod
Connecting rod shall be of heat treated forged steel, drilled for pressure
lubrication, and removable without removing crankshaft. The crankpin
bearings shall be the steel backed babbit type. The crosshead pin bearings
shall be bronze. Crosshead pin shall be full floating.
2.3.6.4
Crossheads
Crossheads shall be box type, cast iron or steel with babbitted wearing
surfaces or shoes which are adjustable and replaceable unless means of
adjustment are provided in the crosshead guides.
2.3.6.5
Distance Pieces
Distance pieces shall be extra long, single compartment, and of sufficient
length to prevent oil carryover. No part of the piston rod shall
alternately enter the crankcase (crosshead housing) and the air compression
cylinder stuffing box. The rod shall be fitted with an oil slinger or
wiper to prevent oil loss from the crankcase, preferably of a split design
for easy access to the piston rod packing. Access openings of adequate
size shall be provided to permit removal of the assembled packing case.
2.3.6.6
Pistons and Piston Rods
a.
Pistons shall be lightweight castings of anodized aluminum alloy
or cast iron. Cast iron pistons shall be chromium plated or
otherwise treated for corrosion resistance. Pistons shall be
fitted with not less than two fluorocarbon compression rings in
individual ring grooves. Wear bands of fluorocarbon material, if
required, shall be of one-piece construction. Pistons which are
removable from the rod shall be attached to the rod by a shoulder
and lock nut design. The nuts on the end of the rod must be
positively locked in place. The rod shall be positively locked to
the crosshead to prevent rotation.
b.
Piston rods: Piston rods shall be of SAE 4140 alloy steel as a
minimum with rolled or ground threads. Rods shall be surface
hardened to 50 Rockwell C hardness in the packing or other wear
areas and nondestructively tested for cracks by the magnetic
particle or liquid penetrant methods. Rod finish in the packing
area shall be 0.25 to 0.51 micrometers 10 to 20 microinches,
except that for carbon packing the finish shall be 0.15 to 0.20
micrometers 6 to 8 microinches. Piston rods shall be hard chrome
plated.
2.3.6.7
Piston Rod Packing
The piston rod shall be sealed against air leakage by floating,
self-adjusting seal rings. The packing box shall be water cooled. Packing
box and packing gland clearances shall be adequate to prevent scoring of
SECTION 15214N
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