jcb JS70, Service Manual

Page: 248 / 385

77 - 2
Ram Piston Head Nut (cont’d)
Due to the high piston nut tightening torques used on the
rams, it is necessary to use a special rig (consisting of the
special tools shown in the Tables) for ram piston head nut
fitting and removal (see Section 1 -
Service Tools ).
As shown in illustrations A and B , the rig uses a modified lift
ram C acting on a heavy-duty ring spanner D to loosen or
tighten the piston nut. Hydraulic power to operate the rig
may be obtained from a suitable hydraulic power pack
(maximum pressure required 150 bar (2175 lb/in
2
) or from
the auxiliary circuit of a JCB machine equipped with quick-
release couplings. In either case, small bore hoses
E (Part
No. 892/00137 - 2 off) must be used to connect the rig to
the power source to limit the speed of operation of ram
C . In
addition F , test point (Part No. 892/00262) and pressure
gauge (Part No. 892/00279) should be fitted in the line to the
piston side of the ram
C to measure the tightening pressure
being applied.
See Table 1 on the following page for details of the pressure
necessary to achieve the required tightening torques. The
torque settings themselves are given on Table 2 of the same
page.
Nut Removal
It is assumed that the ram has been removed from the
machine, hydraulic piping removed and the piston rod
assembly separated from the cylinder.
Note: Before using the nut removal/fitting rig, operate the rig
cylinder over its full range for 5 or 6 strokes to remove all air
from the cylinder.
1 Install the piston rod assembly in the
dismantling/assembly rig with the piston rod supported
by block
J .
2 Secure the eye end of the piston rod to the rig at
position
G , using a suitable pivot pin.
3 Fit a ring spanner to the piston nut and connect it to the
eye end of ram
C at position H .
4 Power the ram slowly downwards, noting the pressure
at which the piston nut first moves on the piston rod.
(The pressure should be 1.0 to 1.5 times the tightening
pressure for the particular size).
5 Remove the piston nut.
6 Remove the piston rod assembly from the rig and then
proceed with dismantling as detailed earlier for
individual rams.
Nut Fitting
Before assembly ensure that all components have been
thoroughly cleaned and all new seals, backing rings and ‘O’-
rings are available. Smear all seals, etc. with hydraulic fluid.
1 Assemble the piston rod components as detailed earlier
for individual rams.
2 Install the piston rod assembly in the nut removal/fitting
rig with the piston rod supported by block
J .
3 Secure the eye end of the piston rod to the rig at
position
G , using a suitable pivot pin.
4 Fit a ring spanner to the piston nut and connect it to the
eye end of ram
C at position K .
5 Using the rig, tighten the piston head nut H to the
torque specified for individual rams by powering the
ram slowly downwards. The torque required is indicated
by gauge
F (see Table 1 on following page).
6 Remove the piston rod assembly from the rig and insert
into the ram cylinder as detailed earlier for individual
rams.
Section E Hydraulics
9803/6020
Section E
77 - 2
Issue 1
Hydraulic Rams