Effective with engine serial number 4D-14120, the blower assembly for the 4-53 engine has been revised by
the-use of a new longer drive gear pilot and the addition of a drive coupling spacer (Fig. 15). Tighten the 5/16-
24 drive gear pilot bolt to 25-30 lb ft (34-41 Nm) torque. Prior to the above change; a shorter drive coupling
was used and,-no spacer was required.,
The coupling is placed on the upper rotor gear on the in-line
Secure the cam retainer to the coupling with four 1/4-28 bolts and tighten them to 14-18 lb ft
Figure 15. Current Pilot and Spacer
Used on 4-53 Blower
18. Remove the bolts and washer used to temporarily secure the rear end plate to the 4-53 engine blower.
Then install the rear end plate cover and gasket and secure the cover and 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.
Examine the inside of the blower for any foreign material. Also revolve the rotors by hand to be sure that they
turn freely. Then install the blower on the engine as follows:
Affix a new blower-to-block gasket on the side of the cylinder block. Use Scotch Grip Rubber
Adhesive No. 1300, or equivalent, only on the block side of the gasket.
Install the seal and clamp on the blower rear end plate cover.
Slide one end of the blower drive shaft into the drive cam.
Position the blower on the side of the cylinder block. Use care so
that the blower gasket is not damaged or dislocated during installation of the blower.
Secure the blower to the cylinder block with bolts and washers. Tighten the bolts to 55-60 lb ft
(75-81 Nm) torque,
Slide the seal and clamp back against the blower drive gear support and tighten the clamp to
hold the seal in place.
Check the backlash between the blower drive gear and the camshaft gear. The backlash
should be 0.003 to 0.007 inch.
Install the air shutdown housing as outlined in Air Shutdown Housing.