gears, using a suitable dial indicator. Backlash shall be
(7) Replace all gaskets and seals.
0.0005 inch to 0.0025 inch with new gears, or a maxi-
(8) Inspect threaded openings and hardware for
mum of 0.0035 inch with used gears. Replace the gears
damaged threads. Chase damaged threads with the
if backlash exceeds 0.0035 inch.
correct size tap or die. Replace all damaged hardware.
(10) After the blower rotors and gears have been
f. Reassembly. Refer to figure 3-19 and reassemble
installed, the blower rotors must be timed. When prop-
the blower assembly as follows:
erly positioned, the blower rotors run with a slight
(1) Press two teflon oil seals (30) in counterbores
clearance between the rotor lobes and walls of the
of each end plate (29) as follows:
(a) Place the plate on the bed of an arbor press.
(11) The clearance between the rotors may be es-
(b) Lubricate the outside diameter of the new
tablished by moving one of the helical gears out or in
seal and using a suitable installer tool, press the seal
on the shaft relative to the other gear by adding or re-
(lip facing down) into the counterbored hole until the
moving shims (22) between the gear hub and the rotor
shoulder on the installer tool contacts the plate.
(12) It is preferable to measure the clearance with
The seal must be positioned below the fin-
a feeler gage comprised of two or more feelers, since a
ished face of the place within 0.002 to 0.008
combination is more flexible than a single feeler gage.
Take measurements from both the inlet and outlet
(2) Place front end plate on two wood blocks and
sides of the blower.
install the rotors (31) in the end plate, gear end up. In-
(13) Measure the clearance between the rotor
stall the housing (32) over the rotors and, making sure
lobes and the housing as shown in figure 3-21. Take
that the oil seals are properly positioned on the rotors,
measurements across the entire length of each rotor
install the rear end plate over the blower housing.
lobe to be certain that a minimum clearance of 0.004
(3) Attach two thrust washers (27) to the front
inch exists at the air outlet side (B, fig. 3-20) and a
end plate with bolts (26).
clearance of 0.0075 inch exists at the inlet side (A, fig.
(4) Attach three spacers (25) and thrust plate (24)
to front end plate with bolts (23). Tighten bolts to 7-9
(14) Measure the clearance between the rotor
lbft of torque and check clearance between thrust
lobes, across the length of the lobes. Rotate the gears
plate and thrust washers. The clearance shall be
until the lobes are at their closest relative position (C,
fig. 3-20). The clearance between the lobes should be a
(5) Position the rotors so that the missing serra-
minimum of 0.010 inch.
tions on the gear ends of the rotor shafts are 90°
(15) Measure the clearance between the end of the
apart. This is accomplished by positioning the rotors in
rotors and the front end plate as shown in figure 3-22.
a "T" shape with the missing serrations in the upper
The clearance should be a minimum of 0.006 inch.
rotor facing to the left, and the missing serrations in
the lower rotor facing the bottom (fig. 3-20). Install
Push and hold the rotor toward the end plate
the shim (22, fig. 3-19) and spacers (21) in the counter-
at which the clearance is being measured.
bore in rear face of rotor gears (19 and 20). Place gears
(16) Measure the clearance between the end of the
on end of shafts with missing serration in alignment
rotors and the rear end plate in the same manner. The
with missing serrations on shaft.
clearance should be a minimum of 0.009 inch.
(6) Tap the gears lightly with a soft hammer to
(17) Remove the screws (1, fig. 3-19) and washers
seat the gears on the shaft. Then, rotate the gears until
used to temporarily secure the front end plate to the
punch marks on the face of gears match. If the punch
housing. Install gasket (14), cover (13), reinforcing
marks on the face of gears do not match, reposition the
plates (11 and 12) and secure with screws (l). Tighten
screws to 23 lb-ft. of torque.
(7) Wedge a clean cloth between the blower
(18) Assemble the coupling assembly as follows:
rotors. Use the blower rotor gear retaining bolts and
(a) Place the spring support (10) on two blocks
plain washers to press the gears on rotor shafts.
Tighten bolts uniformly until gears are tight against
(b) Position the spring seats in the support,
shoulder on the shafts. Remove gear bolts, plain
apply grease to the springs to hold the leaves together,
washers, and cloth.
then slide the two spring packs (fifteen leaves per
(8) Place pilots (16 and 18) in the counterbore of
pack) in place.
gears (19 and 20) respectively, and start the twelve
(c) Place the drive cam (7) over the end of an in-
point bolt (15) in rotor shaft and start the hex head
stalling tool, insert tool between the spring packs and
bolt (17) in the rotor shaft. Tighten the bolts to 25-30
press the cam in place (fig. 3-23).
lb.-ft of torque.
(19) Position coupling assembly on gear (20).
(9) Measure the backlash between the blower