-
7/29/2019 ctb41
1/4
January 31, 1997No. 41
THE
NEWSLETTER
PAGE 1 OF 4
PISTON TO ROD REASSEMBLY PROCEDURE
Ariel is responding to field inquiries for an Ariel approved
procedure that can be used in the field.
This procedure for the reassembly and torquing of piston rod
assemblies should be used withboth new and used components. The
goal is to provide information for consistent assembly
techniques that minimize piston rod assembly failures.
Ariel provides the following procedure to assist in field
compressor repairs, but realizes you mayhave additional questions
concerning specific repairs. You are encouraged to contact
Ariel'sField Service group if you have questions or require
additional information concerning this
procedure.
1. Clean all piston rod assembly parts thoroughly. Be sure
piston is internally clean and dry.
NOTE: Any reassembly of used parts requires the recleaning and
re-lubricating of threads andseating surfaces.
2. Inspect collar (or collar area on rod, when collar is
integral and not separable), piston and
piston nut for nicks, burrs or scratches. Dress surfaces with a
fine grit stone as required. Fitcollar and nut into piston to
verify the outside diameter fits, turn freely by hand in the
piston.
3. Inspect piston rod threads and collar shoulder. Threads are
to be clean and free of burrs.
Install collar and nut onto piston rod to verify inside diameter
fits, rotate freely. Run pistonnut down by hand until piston
threads protrude to verify freedom of thread engagement.Remove nut
and collar.
4. Install piston rings in cylinder bore without piston to
measure end gaps. Ariel recommendsreplacing piston rings when end
gap is increased three times its original amount. If pistonhas wear
band, install and place piston in cylinder bore and measure piston
to cylinder
clearance at bottom of piston. Replace the wear band before it
has worn enough to allow thepiston to touch the cylinder bore. Wear
band clearance can be measured before piston rodassembly is removed
from cylinder. See "Clearances" data in Section 1 of the
Operator's
Manual - "Design Specifications & Data" for tolerances.
5. Clamp piston rod into an appropriate rod holding fixture,
using PVC liners to protect rodfinish. Verify that holding
fixture's PVC liners are clean and oil free. Clamp the piston rods
as
close to the collar shoulder as possible without hitting
piston.
NOTE: 1. Ariel's D-0961 clamping device (see Figure 1) is
available for 1.125"through 2" (29 mm through 51 mm) diameter
piston rods. Tighten D-0961's four 7/8" x 14 TPI capscrews to 344
lb-ft (466 Nm).
NOTE: 2. For 2.5" (64 mm) diameter piston rod, use a clamping
device that produces 60tons (140 kN) of clamping force (see Figure
2).
-
7/29/2019 ctb41
2/4
January 31, 1997
No. 41
THE
NEWSLETTER
PAGE 2 OF 4
Nominal Piston Rod Diameter Clamping Force Required
Inches mm Tons kN
1.125 29 8.67 19.3
1.5 38 20.4 45.4
2 51 35 78
2.5 64 60 140
6. Apply a thin coating of "Never-Seez" (anti-seize and
lubricating compound, Mil Spec A-907)to piston rod shoulder and rod
collar locating band, and collar face in contact with the
piston,then slide collar onto rod.
NOTE: "Never-Seez" is manufactured by Bostick, Boston Street,
Middleton, MA, 01949 USA,Telephone: 508-777-0100
7. Apply a thin coating of "Never-Seez" to piston rod threads at
the piston end, then slidepiston onto rod and collar.
NOTE: One end of the piston is machined .002" (0.05 mm)
undersize across a 3/4" (19 mm)wide band for manufacturing
purposes. If piston is symetrical and can be installed in
either
direction, assemble with the undersize band toward the head
end.
8. Apply a thin coating of "Never-Seez" to the piston nut
threads and piston mating face. Installnut and hand tighten to make
up the piston rod assembly.
9. Tighten the piston nut to the recommended torque shown in
table below (Operator's Manual
Section 1 - Design Specifications & Data). It may be
necessary to use a torque multiplier toachieve the desired
torque.
Required Piston Nut Tightening Torque
Nominal Piston Rod
Diameter
Piston Nut Size Torque Value
Inches mm Inch x TPI LB-FT Nm
1.125 29 7/8 x 12 222 301
1.5 38 1-1/4 x 12 695 942
2 51 1-5/8 x 12 1590 2156
2.5 64 2 x 12 (see note 2) 3970 5383
-
7/29/2019 ctb41
3/4
January 31, 1997
No. 41
THE
NEWSLETTER
PAGE 3 OF 4
NOTE: 1. When torque multipliers are used on larger fasteners,
divide the desired fastener
torque by the actual mechanical advantage (which accounts for
frictional loss thru themultiplier), rather than design mechanical
advantage, to determine torque wrench setting.
Example: An X4 torque multiplier, model TD-1000 has a design
mechanical advantage of 4.0,but an actual mechanical advantage of
3.6. Therefore a 1590 lb-ft (2156 Nm) required torque
needs 442 lb-ft (599 Nm) applied torque to the X4
multiplier.
NOTE: 2. Ariel uses a hydraulic torque wrench on 2"x 12 TPI
piston nuts, used on 2.5" nominal
diameter piston rods. The 3970 lb-ft (5383 Nm) value is based on
Ariel rod stretch test results.Torque values for other rod sizes
are calculated.
10. After torquing, the piston rod should not protrude more than
.010" (0.25 mm) past the piston
face.
11. Apply a thin coating of "Never-Seez" to two new Allen set
screws. Two new Allen wrenchesare also required per nut at each
tightening and are discarded after their one time
destructive use. Install the set screws and tighten so that the
Allen wrench is permanentlydeformed by tightening past its yield
point (twisted through a 15 degree arc).
12. Prick-punch the piston nuts, within 1/16" (1.5 mm) of set
screw threads, to lock the set
screws in place. Prick-punch marks should deform nut screw
threads to lock the set screw inplace.
13. Weigh the piston rod assembly with the piston rings and wear
band included. Stamp the
weight on the piston's head end. Flatten any raised lips to
avoid clearance measurementerrors. Record this weight for future
reference.
PISTON NUT TORQUING SPANNER
Nominal Rod
Diameter
Nominal Piston
Nut Size
ArielPart Number
Inches mm Inch x TPI
1.125 29 7/8" x 12 A-0279
1.5 38 1-1/4" x 12 A-0424
2 51 1-5/8" x 12 B-1410
2.5 64 2'' x 12 B-1503
-
7/29/2019 ctb41
4/4
January 31, 1997
No. 41
THE
NEWSLETTER
PAGE 4 OF 4
Figure 1: Piston and Rod Torquing Fixture - 1.125 thru 2" (29
thru 51 mm) Rod Size
Figure 2: Piston and Rod Clamping Requirements - 2.5" (64 mm)
Rod Size
TorqueMultiplier
TorqueWrench
Piston Nut Torquing
Adapter P/N B-1503 (NotPart of Standard Tool Box)
Piston
Collar60 Tons (140 kN)of Clamping Force
Piston Rod
Nut w/ (2)Set Screws1/8" (3 mm) Thick
PVC Liner To ProtectPiston Rod Finish
Fixture Part Number D-0961
Collar
Piston NutSpanner
TorqueWrench
PistonRod
Piston
Allen Wrenches (2)
Torque Multiplier
Nut w/ (2) Set Screws
3/4" (19 mm) Wide
Undersize Band
