Repair
This section gives the procedures and data necessary to repair the main rotor hub assembly as follows:
All packings and seals
Unserviceable hardware
Curled or damaged shims
Worn or damaged parts
Mechanical and corrosion damage
Refinish surfaces as required
Standard Repairs
Yoke Grips and bearings
Trunnion, pillow blocks, and bearings
Strap pin
Blade bolts
Preliminary requirements
Consumables, materials and expendables
Safety conditions
Main Procedures
Replace procedures
Refer to the 505-CMM for the items that must be replaced, or items which cannot be repaired.
Self-locking nuts are unserviceable when tare torque is not present.
Replace all packings, seals, washers, unserviceable self-locking nuts, and attaching hardware.
Replace shims that have curled or damaged laminations.
Replace cracked, broken, or distorted parts, or parts that have damaged threads.
Replace parts that exceed allowable wear or damage limits.
Replace blade bolt cap if damaged.
Replace trunnion if cracked or if mechanical and corrosion damage limits are exceeded.
Visually inspect bushings, thrust washers, and adjusting screws for damage that would render parts unserviceable.
Replace trunnion bearing inner race if spalled, brinelled, or discolored due to overheating. Replace inner race and trunnion if damaged due to race turning on spindle of trunnion.
Replace bearings if spalled or discolored due to overheating, roller is broken, or operation is rough.
Replace latch nut or blade bolt nuts if cracked, damaged, or corroded.
Replace pillow block if cracked or if damaged beyond limits.
Refer to the manufacturer instructions for the mixing ratio, pot life, and curing time of the adhesive.
Replace pillow block pads as follows:
Lightly abrade bonding surfaces on the pillow block with a 400 grit Abrasive cloth or paper. Clean with MEK and dry with a clean lint free cloth.
Abrade the light brown side of new pillow bloc pads with a 100 or 150 grit Abrasive cloth or paper. Clean with aliphatic naphtha and let the pads air dry.
Apply a 0.003 to 0.008 inch (0.08 to 0.20 mm) thick layer of Adhesive to the bonding surfaces of the pillow block or pillow block pads, as applicable.
Locate the pillow block pads on the inboard and outboard sides of the pillow block, respectively, and within 0.030 inch (0.76 mm) of the hole center.
Bond the pillow block pads to the pillow block and remove excess adhesive before complete cure.
Refinish the pillow block in accordance with DMC-505-A-62-20-01-00A-257A-B, as required.
Replace grip bearings if any of the following conditions is found:
Broken or rough rollers.
Spalling, scoring, flaking, brinelling, or discoloration.
Pits larger than 0.008 inch (0.20 mm).
Cluster of three pits or more within an area of 0.25 inch (6.3 mm) diameter with any one pit larger than 0.004 inch (0.10 mm).
Replace any part with defects for which no damage limits are specified.
Cleanup of allowable damage
This section gives information on the repair of negligible and/or allowable mechanical and corrosion damage to main rotor hub parts and the description of the surface treatment after their repair:
Repair allowable mechanical and corrosion damage to the main rotor hub parts (Limits charts)
Trunnion and pillow blocks
strap fittings, strap pins, and radius ring
strap bolts and latches
blade bolts and plug
excluder retainers
pitch horns
static stops
mast nut and cone set
Repair steel parts as follows
Polish out acceptable damage using fine India stone.
Apply brush-on cadmium plating solution to all previously plated and repaired steel surfaces (BHT-ALL-SPM, Chapter 3, Standard Practices Manual). Do not cadmium plate threaded areas.
Repair aluminum parts as follows:
Polish out acceptable damage using a 400 to 600 grit silicon carbide abrasive cloth or paper.
Apply chemical chromate conversion material to all repaired and bare aluminum surfaces (BHT-ALL-SPM, Chapter 3, Standard Practices Manual).
Dress out minor damage to blade bolt nuts and latch nuts.
Standard Repairs
This section gives the procedures and data necessary to repair damage and also gives the permitted damage for the following parts:
Yoke
Grips
Trunnion
Pillow blocks
Strap pin
Blade bolts
Yoke
Repair yoke as follows:
Polish out minor scratches and damage on noncritical areas with Crocus cloth
Longitudinal scratches on spindle, not more than 0.002 inch (0.050 mm) deep, do not need to be completely removed. Surface burrs must be removed with a Crocus cloth. Clean up minor damage to threads.
Pillow block bore damage must be removed by sanding in a circular motion with a 400 grit Abrasive cloth or paper. Final polish surface until scratch free with a fine Abrasive pad. Make sure that all nicks, scratches, and tool marks are removed.
Damage to bearing and spacer journals and mating fillet radii must be removed by sanding with a 400 grit Abrasive cloth or paper and Abrasive pad.
Damage to other surfaces must be removed by sanding with a 400 grit Abrasive cloth or paper and Abrasive pad. Make sure that all nicks, scratches, tool marks, and corrosion pitting are removed. Touch up surfaces where plating has been damaged or where repairs were done. Apply Cadmium plating solution where required.
Apply Epoxy polyamide primer (C-204) to yoke (12, Figure 1) as required.
After primer has cured, examine the yoke pillow block bores with inside micrometer for minimum I.D. of 2.6242 inches (66.655 mm). Sand as required without penetrating primer to get set dimension.
Within 8 hours of primer application, apply two coats of light gull gray Polyurethane coating (C-245), color code 36440 per FED-STD-595, to yoke (12) center section (Figure 17).
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