FMC M12-HD, Operation & Maintenance Manual, Page: 11 / 20

F M C M 1 2 - H D O P E R A T I O N A N D M A I N T E N A N C E M A N U A L
11
•
Install new piston (42) and piston o-ring (45) into
the piston sub-assembly as shown (70). Note that
the piston o-rings cannot be seen in the
assembled view.
•
Torque the piston nut (44) to 250 ft-lbs.
•
Use a small amount of oil to lubricate the OD of
the piston, then insert the piston sub-assembly
(70) into the front end of the piston cylinder as
shown. Use a press or rubber mallet to drive the
piston to the approximate center of the piston
cylinder.
•
Install new cylinder o-rings (50) in the piston
cylinder. Use a dab of grease to hold the o-
ring in the groove.
•
Place the piston-cylinder assembly into the
counterbore of the fluid end and push in firmly
until it is seated at the base of the
counterbore.
•
Slide the cylinder clamp (48) over the cylinder
and into position over the cylinder studs.
•
Install and tighten the cylinder hex nuts (46)
and washers (47). Torque the nuts to 125 ft-
lbs in three stages to prevent cocking of the
cylinder.
•
Use a wrench on the flats of the piston
extension (40) to twist and pull it up to proper
position in the crosshead extension (52). If the
assembly is properly aligned, the quill on the
end of the piston extension should easily slide
into the bore of the crosshead extension.
•
Reconnect the plunger clamp assembly and
torque the hex bolts (59) to 5 ft-lbs.
•
Reconnect liner wash piping that was removed
for service (if equipped) and replace the cradle
cover.