F
OR
M
ODELS
: JGI, JGM, JGN, JGP
AND
JGQ
S
ECTION
5 - M
AINTENANCE
PAGE 5-29
to the nut
3.
After the piston nut has been removed, the piston and collar will slip off the end
of the rod.
Piston and Rod Reassembly
1.
Clean all piston and rod assembly parts thoroughly. Be sure piston is internally
clean and dry.
2.
Inspect each part for nicks, burrs or scratches and dress surfaces with a fine grit
stone as required.
3.
Inspect the piston rod threads and collar shoulder. Threads should be clean and
free of burrs. Fit collar and nut into piston to verify the outside diameter fits, and
turn freely by hand in the piston. Install the collar and nut onto the piston rod to
verify that the inside diameter fits and rotates freely. Run the piston nut down by
hand until the rod threads protrude to verify freedom of thread engagement.
Remove nut and collar.
4.
Check piston rings to determine wear (see “Determining Ring Wear:” on page
5-32). Replace piston rings as required.
5.
Clamp the piston rod in Torque Fixture D-0961. See Figure 5-21 on Page 5-28.
6.
Apply a thin coat of Never-Seez, regular grade, to piston rod shoulder and rod
collar locating band, and collar face in contact with the piston, then slide collar
onto rod.
7.
Apply a thin coat of Never-Seez, regular grade, to the piston rod threads at the
piston end, then slide piston onto rod and collar.
NOTE: IF ONE END OF SINGLE PIECE PISTONS ARE MACHINED 0.001 IN. (0.03 mm)
UNDERSIZE ACROSS A 3/4 IN. (20 mm) WIDE BAND (FOR MANUFACTURING
PURPOSES); THIS IS THE HEAD END OF THE PISTON.
8.
Apply a thin coat of Never-Seez, regular grade, to the piston nut threads and
piston mating face. Install nut and hand tighten to make up the piston and rod
assembly.
9.
Use the piston turning/piston nut torquing tool and a torque wrench to tighten the
piston nut. The two dowels on the turning tool fit holes in the nut and two 5/16-18
x 1-1/4 in. bolts should be used to secure the tool to the nut. Tighten the piston
nut to the recommended torque in Table 1-12 on page 1-16.
10. After tightening nut, the piston rod should not protrude more than 0.010 in. (0.25
mm) past the piston face.
11.
Apply a thin coat of Never-Seez, Regular Grade, to two new Allen set screws.
Two new Allen key wrenches are 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 permanently deformed by tightening past its
yield point (twisted through an additional 15° arc). A piece of heavy wall tubing
or equal of a proper inside diameter to fit over the Allen wrench is required to
extend the “handle” end of the wrench to achieve proper tightening. The Allen
wrenches used must conform to ASME B18.3 requirements for hexagonal keys.
12. Use a 60° center punch to prick-punch the piston nut, within 1/16 in. (1.5 mm) of
the set screw threads, to stake the set screws in place. Prick-punch marks
should deform the nut to lock the set screws without deforming the set screw.
The staked piston nut must not exhibit any cracks or torn material that might
