Appendix B—Vertical Double-Acting Specifications
791 & 891 Bolt Torque Values
Specifications and Performance
1
Preliminary tightening—snug all head bolts in the sequence shown.
Final torqueing—torque all head bolts in the sequence shown to the
listed value.
2
Retorque to the listed value after 2–5 hours running time.
3
Dimensions for honing are included with new bushings (which must
be installed, then honed).
Specification ft•lb
Connecting rod bolt 40
Bearing carrier 40
Bearing cover 40
Crankcase inspection plate 9
Crosshead guide 65
Cylinder to head
1,2
65
Valve cover plate bolt 37
Valve holddown screw
2
40
Piston lock nut torque 150
Piston screw torque 8
Valve cap torque 25
Specification D791 D891 T791 T891
Bore of cylinder, inches (mm)
first stage
second stage
6 (152.4)
3.25 (82.5)
4.5 (113)
—
6 (152.4)
3.25 (82.5)
4.5 (113)
—
Stroke, inches (mm) 4.0 (101.6) 4.0 (101.6) 4.0 (101.6) 4.0 (101.6)
Piston displacement, cfm (m
3
/hr)
minimum @ 400 RPM
maximum @ 900 RPM
51.2 ( 87.0)
115.3 (196.0)
56.6 (96.2)
127.6 (216.8)
51.2 ( 87.0)
115.3 (196.0)
56.6 (96.2)
127.6 (216.8)
Maximum working pressure, psig (bar g)
first stage
second stage
350 (24.1)
600 (41.3)
465 (32.1)
—
350 (24.1)
600 (41.3)
465 (32.1)
—
Maximum brake horsepower, kW 45 (34) 45 (34) 45 (34) 45 (34)
Maximum rod load, lb (kg) 7,000 (3,175.2) 7,000 (3,175.2) 7,000 (3,175.2) 7,000 (3,175.2)
Maximum outlet temperature °F (°C) 350 (177) 350 (177) 350 (177) 350 (177)
Bare unit weight, lb (kg) 900 (408.2) 855 ( 3 87. 8 ) 1,060 (480.8) 1,015 (460.4)
791 & 891 Clearances and Dimensions
Specification Inches
Piston clearance (see Appendix E)
Clearance: connecting rod bearing to
crankshaft journal
0.0013
0.0033
Clearance: wrist pin to wrist pin
bushing (maximum)
3
0.001
Cylinder bore diameter (maximum)—
Single stage 891
4.515
Cylinder bore diameter (maximum)—
First stage 791
Second stage 791
6.018
3.260
Cylinder finish 16–32 RMS
Piston ring radial thickness (minimum)
Single stage 891
First stage 791
Second stage 791
0.082
0.155
0.082
Clearance: oil pump adapter shaft to
bushing (maximum)
3
0.0036
Crankshaft end play (cold)
0.002
0.003
Flywheel runout at O.D. (maximum) 0.020
Clearance: crosshead to crosshead
guide bore (maximum)
0.008
Crosshead guide bore finish
32 RMS
(limited
number of
small pits and
scratches are
acceptable)
23
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