be timed. When properly positioned, the blower rotors run with a slight clearance between the rotor lobes and
with a slight clearance between the lobes and the walls of the housing.
The clearances between the rotors may be established by moving one of the helical gears out or in on the shaft
relative to the other gear by adding or removing shims between the gear hub and the rotor spacers.
It is preferable to measure the clearances with a feeler gage comprised of two or more feelers, since a
combination is more flexible than a single feeler gage. A specially designed feeler gage set J 1698-02 for the
blower clearance operation is available. Take measurements from both the inlet and outlet sides of the blower.
Measure the clearance between the rotor lobes and the housing as shown in Fig. 11. Take
measurements across the entire length of each rotor lobe to be certain that a minimum clearance of 0.004 inch
exists at the air outlet side of all blowers and a minimum clearance of 0.0075 inch exists at the air inlet side of
the blower (Fig. 12).
Measure the clearance between the rotor lobes, across the length of the lobes, in a similar
manner. By rotating the gears, position the lobes so that they are at their closest relative position (Fig. 12).
The clearance between the lobes should be a minimum of 0.009 inch.
Measure the clearance between the end of the rotor and the blower end plate as shown in
Fig. 13. Refer to the chart for the required minimum clearances.
Push and hold the rotor toward the end plate at which the
clearance is being measured.
Figure 11. Measuring Rotor Lobe to Housing Clearance
After timing the rotors, complete assembly of the blower.
14. Remove the bolts and washers used to temporarily secure the front end plate to the housing. Then
install the front end plate to the blower with six bolts and special washers and two reinforcement plates and
tighten the bolts to 20-25 lb ft (27-34 Nm) torque.
The current front and rear end plate gaskets on the 4-53 engine
blower are identical and may be used in either position.
Formerly these gaskets were not interchangeable.
BLOWER ROTOR END CLEARANCES