TM 55-1930-209-1 4&P-21
6-12 Blower cleaning, Inspection and repair
Do not use a wire brush or emery cloth for cleaning the blower parts. Handle blower parts
carefully; aluminum parts are easily dented and burred.
a. Cleaning. Clean all parts with cleaning solvent and dry thoroughly.
b. Inspection and Repair
(1) Inspect inside of the blower housing and all finished surfaces for smoothness. Inspect housing for cracks,
breaks, and distortion. Remove all rough spots or burrs with a fine mill file or scraper. Replace a housing that is badly
scored, warped, or cracked.
(2) Inspect rotor lobes for smoothness. Inspect rotor shaft serrations and bearing surfaces for wear or burrs.
Remove all high spots and burrs from rotors with a fine mill file or scraper. Replace defective rotor assemblies.
(3) When washed clean and lubricated with light oil, all bearings should roll smoothly. Replace loose, rough,
or overheated bearings.
(4) The seal lip must be smooth, pliable, and leakproof. Replace all oil seals that have been removed from
housing plates or that are brittle, thin, or cut.
(5) Inspect housing end plates for cracks, breaks, distortion, and other damage. Inspect finished surfaces of
housing plates to see that they are true, smooth, and unscored. Inspect counterbores for bearing and bearing bosses to
see that they are not worn excessively or scored. The bearings must fit the counterbore with a slight push or tap fit.
Remove all burrs or minor local score marks by filing or scraping carefully. Replace housing plates that are cracked,
badly scored or distorted, or have worn bearing counterbores.
(6) Inspect gears for worn splines and for cracked, broken, or worn teeth. Replace damaged or defective
gears. The maximum allowable backlash for gears is 0.0035 inch and the minimum is 0.0005 inch.
(7) Clean all gasket material from mating surfaces. Reassemble the blower with all new gaskets.
6-13 Blower reassembly and installation
The lobes on the upper blower rotor and the teeth on its gear form a right-hand twist. The lower
rotor and its gear twist to the left. Insure that the gear and rotor twists match or the blower
assembly will be damaged during reassembly.
a. Reassembly of the Blower
(1) Install lip type oil seals as follows:
(a) Support blower end plate, finished surface facing up, on wood blocks on the bed of an arbor press.