Enstrom TH-28/480 Series. Maintenance Manual (2020)

Table 9-1. Main Rotor Hub Assembly

Inspection Requirements

P/N

Fig. 9-4, 9-5

Part Name

Inspection*

Serviceable Limits*

Repair Limits

Repair or Action

Item #

28-14224-1, -3,

12 & 18

Spline Adapters

Spline wear

.0015 on side

Not Repairable

Replace Adapter

-5

(Cont’d)

Nicks, scratches, or

.010 deep

≤ .010 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Adapter

28-14280-1, -3,

Upper Hub

Spline Adapter Bore

+.0005

Not Repairable

Replace Upper Hub

-5

3.624 to 3.625

U Block Bearing Bores

+.0008

Not Repairable

Replace Upper Hub

2.4986 to 2.4994

Recesses for the DU

+.0005

Not Repairable

Replace Upper Hub

washers parallel to the

upper surface within

.001

Damper Bolt Bushing

+.0005

Not Repairable

Replace Bushing

Dia. .3747 to .3757

Threads for walking

None Allowed

Not Repairable

Replace Heli coil

beam brackets

(crossed or missing)

Nicks, scratches, or

None Allowed

≤ .010 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Upper Hub

Rev. 26

MM-9-21

Feb 28/2020

Table 9-1. Main Rotor Hub Assembly

Inspection Requirements

P/N

Fig. 9-4, 9-5

Part Name

Inspection*

Serviceable Limits*

Repair Limits

Repair or Action

Item #

28-14223-1

Spacer

Dowel Hole Dia. .3125

+.0005

Not Repairable

Replace Spacer

Bolt Hole Dia.

+.002

Not Repairable

Replace Spacer

.313 to .318

Nicks, scratches, or

.030 deep

≤ .030 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Spacer

28-14281-1, -3,

Lower Hub

Spline Adapter Bore

+.0005

Not Repairable

Replace Lower Hub

-5

3.624 to 3.625

U Block Bearing Bores

+.0008

Not Repairable

Replace Lower Hub

2.4986 to 2.4994

Recesses for the DU

+.0005

Not Repairable

Replace Lower Hub

washers parallel to the

lower surface within

.001

Damper Bolt Bushing

+.0005

Not Repairable

Replace Bushing

Dia. .3747 to .3757

Nicks, scratches, or

None Allowed

≤ 0.10 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Lower Hub

* All dimensions are in inches.

Rev. 26

MM-9-22

Feb 28/2020

D. Place the spacer (16) and shim (34), if installed, on the lower hub plate and align the

bolt holes.

NOTE

Ensure the DU washers are seated in the recessed areas of the upper hub

plate.

E. Lubricate the bearing bores of the upper hub plate and install the upper hub plate

onto the U-blocks.

F. Lubricate the dowel pins (13) and install by tapping them into the center hole of the 3-

hole bolt pattern. Install the pins until they are slightly recessed from the surface of the hub

plate.

NOTE

The upper spline adapter has the wider flat surface on top side of the splines

while the lower adapter has a rib extending from the lower end of the splines.

CAUTION

The phasing marks on the upper spline adapter must be aligned with one of the

pitch change bellcrank mount brackets. Using a felt marker, mark a line on the

outboard edge of the hub plates in line with the spline phasing marks to aid in

installing the lower spline adapter.

G. Insert bolts in the upper spline adapter (12) as guides and install the adapter onto the

upper hub plate.

H. Carefully turn the hub assembly over and position on wood blocks.

Install the lower spline adapter (18) and align the phasing mark with the upper

adapter phasing marks.

J. Turn the hub assembly over and install the center hub bolts (11) in the holes adjacent

to the pitch change bellcrank mount bracket holes. Install the washers and nuts and torque the

hardware.

K. Install the pitch change bellcrank mount brackets (3). Torque the through bolts (2).

Torque and lockwire (.032) the other bolts (1).

L. Set the rotational drag of the U-blocks as follows:

(1) Place the hub assembly on a hub stand with the lower end of the U-blocks up.

(2) Install a DU washer (7) into the recess of the hub plate with the chamfer in board

toward the hub plate.

(3) Install shims (8) approximately .025 inch/0.6 mm thick and the lower U-block nut

(9). Tighten the nut using tool (T-0003).

Rev. 26

MM-9-23

Feb 28/2020

(4) Rotate the U-block to one of the stops and install a hinge pin into the retention

pin hole until the inside edge of the flange is 7.1 inches/18 cm from the center of

the universal block.

(5) Place a wire loop around the hinge pin against the flange. Attach a spring scale

to the wire loop and pull to check the drag. The drag tolerance with the nut

torqued is 4-10 pounds/1.8-4.5 kg.

(6) Add or subtract shims as required to obtain the proper drag.

(7) Place the locking key (10) into the slot on the nut that is aligned with the notch in

the U-block and secure with the washer and screw.

Turn the hub assembly over on the stand.

Install the upper U-block nuts (5) as follows:

NOTE

If the hub is equipped with oil lubricated flapping bearings, shims may be

required between the bearing and the lock washer to prevent the universal

block from protruding above the nut. The oil reservoir flange must seat flush

against the nut.

(1) Install the lock washer (6) and nut on the U-block.

(2) Torque the nut to 20 ft-lbs/27.3 Nm using tool (T-0051).

(3) Tap down on the upper nut with a plastic mallet and re-torque the nut to seat the

bearing. Repeat the process until the nut will not move while being re-torqued.

(4) Bend the tab on the lock washer that aligns with the recess in the nut into the

nut.

(5) If the main rotor hub assembly is equipped with grease lubricated flapping

bearings, install the dust cover (4) and secure.

(6) If the main rotor hub assembly is equipped with oil lubricated flapping bearings:

a. Install new O-rings (31) on the reservoir (29). Lubricate the O-rings with MIL-

PRF-23699 and (Figure 9-5, 29).

b. Install the reservoir (29) onto the universal block (15) using a twisting motion

until the base of the reservoir seats flat against the universal block.

CAUTION

Ensure the reservoir is fully seated into the universal block before installing the

screws. Do not attempt to seat the reservoir into the universal block by using

the screws. The reservoir will distort and crack.

c. Install the dust cover (4) and secure.

Rev. 20

MM-9-24

Apr 25/13

9-15. Disassembly - Retention Assembly (Figure 9-7)

NOTE

If replacing the tension-torsion straps only, proceed to paragraph 9-19.1.

NOTE

For Lamiflex equipped aircraft, the blade grip, lamiflex bearing, and lamiflex

bearing shims can be removed with the retention assembly installed on the hub

assembly.

Lamiflex equipped aircraft:

(1) Remove the main rotor blade (para. 9-34) and disconnect the pitch change link

from the pitch change bellcrank (para. 12-93) if the retention assembly is

installed on a hub assembly.

CAUTION

Use brass protector plates in the vise jaws to prevent from damaging the

retention assembly.

(2) Clamp the retention assembly vertically in a vise if removed from the hub

assembly.

(3) Remove the dust cover (18) from the blade end of the retention assembly.

Inspect for brass residue (chips or flakes) from the lamiflex bearing, if equipped.

(4) Remove the cotter pin (17) from the retention nut (16) and remove the nut. Use

tool (T-0013) if the nut cannot be removed by hand.

(5) Remove the shims (15), lamiflex bearing (14), and nylatron strap (5), if not

bonded to the spindle, from the spindle (3).

(6) Pull the blade grip (13) from the spindle. If required, tap the grip with a plastic

mallet to aid in removal.

CAUTION

If the lamiflex bearing wears through the nylatron strap, inspect the spindle for

damage. The maximum depth allowed is .020"/0.51 mm. Blend the damage

out before installing a new nylatron strap.

(7) Peel the nylatron strap (5) from the spindle if bonded to the spindle.

(8) Remove the O-ring (12) and DU washer (11) from the spindle.

(9) Remove the retaining ring (10) from the spindle.

Rev. 26

MM-9-27

Feb 28/2020

(10) Remove the hinge pin alignment pin from the ear of the spindle using a small

punch.

(11) Install a press tool between the seal (6) and the bearing (7) on the spindle.

Using a hydraulic press, press the bearings (7 & 9) and spacer (8) from the

spindle.

(12) Remove the seal (6).

NOTE

Removal/replacement of the retention stops are necessary only if the stops are

damaged or the adhesive has loosened.

(13) Remove the retention stops (1 & 4).

(14) Remove the cap from the bore of the spindle (2).

(15) Remove the planipetal weight (22) and the pitch horn (21) from the blade grip.

Tension-Torsion Strap equipped aircraft:

NOTE

There are two different Tension-Torsion Strap Retention Assemblies used on

the TH-28/480 Series. The 28-14381-1 Retention Assembly uses an O-ring at

the outboard end of the spindle assembly to prevent grease leakage from the

retention assembly. The 28-14381-3 Retention Assembly uses a seal installed

in the blade grip to prevent grease leakage from the retention assembly.

NOTE

If equipped with STC SH03465CH tension-torsion straps, refer to Table 2-2 for

manufacturer installation instructions and instructions for continued airworthiness.

(1) Remove the retention assembly from the main rotor hub (para. 9-14).

CAUTION

Use brass protector plates in the vise jaws to prevent from damaging the

retention assembly.

(2) Clamp the retention assembly vertically in a vise.

(3) Remove the dust cover (18) from the blade end of the retention assembly.

(4) Remove one of the retaining rings (31) securing the pin in the lug at the

outboard end of the retention assembly. Remove the pin (30) and the remaining

retaining ring.

(5) Pull the blade grip (28) from the spindle.

Rev. 26

MM-9-31

Feb 28/2020

NOTE

Only remove the seal from the blade grip if replacing a defective seal or blade

grip.

(6) Remove the O-ring (27) from the spindle (28-14381-1 Retention Assembly).

Remove the seal (33) from the grip (28-14381-3 Retention Assembly).

NOTE

The pin used to secure the tension-torsion strap at the inboard end is not

secured with retaining rings.

(7) Remove the spindle from the vise and push the tension-torsion strap (25) back

through the spindle.

(8) Remove the pin (23) from the cylinder (24) and separate the tension-torsion

strap from the cylinder.

(9) Remove the retaining ring (10) from the spindle.

NOTE

Do not remove the cylinder alignment pin from the spindle unless required.

(10) If required, remove the flapping pin alignment pin from the ear of the spindle and

the cylinder alignment (32) pin using a small punch.

(11) Install a press tool between the seal (6) and the bearing (7) on the spindle.

Using a hydraulic press, press the bearings (7 & 9) and spacer (8) from the

spindle.

(12) Remove the seal (6).

NOTE

Removal/replacement of the retention stops are necessary only if the stops are

damaged or the adhesive has loosened.

(13) Remove the retention stops (1 & 4).

(14) Remove the hardware securing the lug to the blade grip and remove the lug

(29).

(15) Remove the pitch horn (21) from the blade grip.

MM-9-32

Feb 9/01

Table 9-2. Retention Assembly

Inspection Requirements*

P/N

Fig. 9-7

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

40NBC20-

Bearing

O.D. 3.2492 to 3.2500

No Tolerance

Not Repairable

Replace Bearing

52YZP

Allowed

I.D. 2.4993 to 2.5000

No Tolerance

Not Repairable

Replace Bearing

Allowed

Ratcheting or

Not Repairable

Replace Bearing

roughness

None Allowed

28-14261-1

Spacer

Length 3.061 to 3.062

-.001

Not Repairable

Replace Spacer

Ends parallel

Within .0012 FIM

Not Repairable

Replace Spacer

32NBC20-

Bearing

O.D. 2.7494 to 2.7500

No Tolerance

Not Repairable

Replace Bearing

44YZP

Allowed

I.D. 1.9993 to 2.0000

No Tolerance

Not Repairable

Replace Bearing

Allowed

Ratcheting or

roughness

None Allowed

Not Repairable

Replace Bearing

28-14313-1

DU Washer

Thickness .090 to.093

-.003

Not Repairable

Replace Washer

28-14279-3

Blade Grip

Blade retention bolt

+.0005

Not Repairable

Replace Blade Grip

bore Dia. .875 to .876

Large bearing bore Dia.

+.0018

Not Repairable

Replace Blade Grip

3.2512 to 3.2522

Small bearing bore Dia.

+.0011

Not Repairable

Replace Blade Grip

2.7511 to 2.7519

Rev. 17

MM-9-35

Jun 24/11

Table 9-2. Retention Assembly

Inspection Requirements*

P/N

Fig. 9-7

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14279-3

Blade Grip (Cont'd) Thru bore Dia. 1.5145

+.0015

Not Repairable

Replace Blade Grip

to 1.5165

Drag link ear width .745

-.001

Not Repairable

Replace Blade Grip

to .747

Threads (crossed or

None Allowed

Not Repairable

Replace Blade Grip

missing)

Nicks, scratches, or

None Allowed

≤ .010 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Blade Grip

28-14320-15

Lamiflex Bearing

Thickness .770 to .790

(See Note)

Not Repairable

Replace Bearing

External to internal tab

±.5°

Not Repairable

Replace Bearing

angle 15°

Column separations

None Allowed

Not Repairable

Replace Bearing

(see Note and also

SDB T-054)

28-14335-1

Nut

Thrust face for flatness

.0015

Not Repairable

Replace Nut

Threads (rolled or

None Allowed

Not Repairable

Replace Nut

missing)

Note: Lamiflex bearings that are found swelled from grease contamination should be cleaned with denatured alcohol and checked for delamination. If the

bearing is swelled beyond the limits (.790” thick), they may still be serviceable if they can be reinstalled in accordance with para. 9-18 and do not

cause binding in the controls.

Any bearing that shows evidence of bulging around the outer circumference of the elastomer segments, excessive axial swelling, visual

delamination of the segments or the expulsion of shim fragments on the outside diameter, should be replaced by an airworthy bearing prior to the

next flight.

Rev. 26

MM-9-36

Feb 28/2020

Table 9-2. Retention Assembly

Inspection Requirements*

P/N

Fig. 9-7

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14007-1 &-3

Blade Retention Bolt

O.D. .8738 to .8745

-.0002

Not Repairable

Replace Bolt

Threads

None Allowed

Not Repairable

Replace Bolt

(crossed or missing)

Nicks, scratches, or

None Allowed

≤ .010 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Bolt

28-14283-1

Drag Link

Distance between

 001

Not Repairable

Replace Link

blade grip ears .748

Distance between

± .0005

Not Repairable

Replace Link

blade root ears .564 to

.566

Retention bolt hole Dia.

+.0002

Not Repairable

Replace Link

(2 places) .3745 to

.3750

Nicks, scratches, or

None Allowed

≤ .010 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Link

Rev. 26

MM-9-37

Feb 28/2020

Table 9-2. Retention Assembly

Inspection Requirements*

P/N

Fig. 9-7

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14278-1

Pitch Arm

Pitch change link bolt

+.001

Not Repairable

Replace Arm

and mount bolt hole

Dia. (5 places) .312 to

.315

Nicks, scratches, or

None Allowed

≤ 0.10 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Arm

4143010-5

Planipetal Weight

Nicks, scratches, or

None Allowed

≤ .010 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Planipetal

Weight

28-14382-19,&

23, 30

Retention Pin

O.D. .747 to .749

-.002

Not Repairable

Replace Pin

-21

Nicks, scratches, or

None Allowed

≤ .005 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Replace Pin

Rev. 26

MM-9-38

Feb 28/2020

Table 9-2. Retention Assembly

Inspection Requirements*

P/N

Fig. 9-7

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14383-13, &

Cylinder

O.D. 2.101 to 2.100

-.002

Not Repairable

Replace Cylinder

-15

Pin bore .750 to.751

-.002

Not Repairable

Replace Cylinder

Index groove width

+.005

Not Repairable

Replace Cylinder

.125 to .129

Nicks, scratches, or

None Allowed

≤ .005 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Cylinder

ECD084-1

Tension-Torsion

Broken wires

None Allowed

Not Repairable

Replace Strap

Strap

Notify Enstrom

Strap bulge

Notify Enstrom

Cracks in urethane

Notify Enstrom

coating

Delamination of

Notify Enstrom

urethane coating

Swelling from grease

None Allowed

Not Repairable

Replace strap if swollen.

contamination

Clean strap with

denatured alcohol

Cracks in strap

None Allowed

Not Repairable

Replace Strap

bushings

Rev. 17

MM-9-39

Jun 24/11

Table 9-2. Retention Assembly

Inspection Requirements*

P/N

Fig. 9-7

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

ECD084-1

Tension-Torsion

Fretting corrosion on

.002 deep over 25%

Not Repairable

Replace Strap

Strap

bushing flange

of total flange area

(Cont'd)

Fretting corrosion in

.002 deep over 25%

Not Repairable

Replace Strap

bushing bore

of bore area

AA-ECD-084-480

Tension-Torsion

Refer to manufacturer’s instructions for continued airworthiness (ref. Table 2-2)

Strap

28-14385-11,

Spindle

Cylinder bore Dia.

+.003

Not Repairable

Replace Spindle

-13 & -15

2.102 to 2.106

Inspect remainder of spindle following the inspection criteria listed earlier in this table

28-14386-1 & -3

Blade Grip

O-ring bore Dia. 2.016

+.002

Not Repairable

Replace Blade Grip

to 2.018

Inspect the remainder of the blade grip following the inspection criteria listed earlier in this table

28-14386-5

Blade Grip

Seal bore Dia. 2.249 to

+.002

Not Repairable

Replace Blade Grip

2.250

Inspect the remainder of the blade grip following the inspection criteria listed earlier in this table

28-14384-13

Lug

Pin bore Dia. .750 to

+.002

Not Repairable

Replace Lug

.751

Nicks, scratches, or

None Allowed

≤ .005 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Lug

Rev. 26

MM-9-40

Feb 28/2020

(7) Lubricate (MIL-PRF-81322) the bearing surface and install the bearing (9) using

a plastic mallet.

NOTE

Ensure the bearings are seated firmly against the spindle shoulders.

(8) Install the retaining ring (10).

(9) Install the DU washer (11) with the chamfered side of the washer facing the

bearings.

(10) Install the O-ring (12) on the spindle and seat against the DU washer.

(11) Install tool (T-0036) behind the seal with the chamfered side of the tool toward

the large radius of the spindle.

(12) Lubricate (MIL-PRF-81322) the bore of the blade grip and install the grip (13) on

the spindle. Tap the grip onto the spindle with a plastic mallet until the seal in

seated in the grip.

(13) Remove tool (T-0036) and tap the blade grip until fully seated on the spindle.

(14) Install the nylatron strap (5) inside the lamiflex bearing (14). Ensure that the

ends of the nylatron do not overlap.

(15) Install the lamiflex bearing (14) and nylatron strap (5) onto the spindle. Install the

tabs on the bearing into the notches in the spindle and the grip.

(16) Install the nut (16) and torque until the grip is fully seated on the spindle.

Release the torque on the nut.

(17) Shim (15) the nut until the cotter pin hole in the nut aligns with the hole in the

spindle when the nut is tightened (5-15 in-lbs/0.6-1.7 Nm).

NOTE

Add or subtract shims until the cotter pin hole in the nut aligns with the hole in

the spindle when the nut is tightened finger tight. Do not under tighten the nut to

align the holes. Do not over tighten the nut to align the holes.

CAUTION

The shims must be installed with the O.D. of the shims concentric to the O.D. of

the nut and the lamiflex bearing. Improper alignment of these shims can cause

wear to the inner surfaces of the main rotor blade grip (Figure 9-9).

(18) Install the nut on the spindle and tighten until finger tight.

Rev. 25

MM-9-42

Aug 22/16

(19) Install the cotter pin after the nut has been properly shimmed and torqued. Bend

the cotter pin ends to secure.

CAUTION

To prevent lamiflex bearing damage, do not over-rotate the grip with the pitch

change links disconnected.

(20) Install the dust cover (18).

(21) Install the flapping pin alignment pin into the spindle ear if it was removed.

(22) Install the pitch arm and Planipetal weight onto the blade grip. Install the

hardware and torque to 75 in-lbs/8.5 Nm. Lockwire the hardware (.032) in

horizontal pairs.

(23) If the retention assembly is installed on the hub assembly, connect the pitch

change link to the pitch change bellcrank (para. 12-96) and install the main rotor

blade (para. 9-38).

(24) Perform a maintenance test flight (para. 4-61).

Tension-Torsion Retention Assembly, P/N 28-14381-1

(1) If installing new retention stops (1 & 4), follow the procedures in paragraph 9-

18,A,1.

CAUTION

Use brass protector plates in the vise jaws to prevent from damaging the

retention assembly.

(2) Clamp the spindle in a vise in the vertical position.

(3) If removed, apply a small amount of Loctite⁷ 635 (green) to the alignment pin

(32) and press the alignment pin into the spindle until the end is slightly

recessed from the seal surface.

(4) Lubricate (MIL-PRF-81322) the seal surface of the spindle and install the seal

(6) with the spring side facing toward the ears of the spindle.

(5) Lubricate (MIL-PRF-81322) the bearing surface and install the bearing (7) using

a plastic mallet.

(6) Install the spacer (8).

(7) Lubricate (MIL-PRF-81322) the bearing surface and install the bearing (9) using

a plastic mallet.

Rev. 26

MM-9-43

Feb 28/2020

NOTE

Ensure the bearings are seated firmly against the spindle shoulders.

(8)

Install the retaining ring (10).

(9)

Install the tension-torsion strap (25) into the cylinder (24) so that the chamfer on

the cylinder is facing inboard (center of main rotor hub) and install the retention

pin (23).

(10)

Install the tension-torsion strap into the spindle and ensure the groove in the

cylinder engages the pin in the spindle.

(11)

Install the O-ring (27) on the spindle.

(12)

Install tool (T-0036) behind the seal with the chamfered side of the tool toward

the large radius of the spindle.

(13)

Install the lug (29) onto the end of the blade grip. Apply Loctite⁷ 222MS to the

threads of the hardware and install the hardware and torque.

(14)

Lubricate (MIL-PRF-81322) the bore of the blade grip and install the grip (28) on

the spindle. Tap the grip onto the spindle with a plastic mallet until the seal in

seated in the grip.

(15)

Remove tool (T-0036) and tap the blade grip until fully seated on the spindle.

(16)

Install one of the retaining rings (31) into the lug. Align the tension-torsion strap

to the lug and install the retention pin (30). Install the other retaining ring.

(17)

Install the dust cover (18).

(18)

Apply a bead of silicone sealant (732-RTV) around the perimeter of the cylinder

assembly (24) to form a seal between the cylinder and the spindle.

(19)

Install the flapping pin alignment pin into the spindle ear if it was removed.

(20)

Install the retention assembly onto the main rotor hub assembly (para. 9-19).

(21)

Install the pitch arm onto the blade grip. Install the hardware and torque to 75 in-

lbs/8.5 Nm. Lockwire the hardware (.032) in horizontal pairs.

Tension-Torsion Retention Assembly, P/N 28-14381-3

(1) If removed, install the grease seal (33) into the blade grip using the following

procedure:

a. Place the replacement seal on the seal installation tool (T-0149-11) with the

open face against the tool.

b. Place the blade grip over the seal installation tool.

Rev. 26

MM-9-44

Feb 28/2020

c. Place tool T-0149-13 onto the blade grip and using a press or other suitable

device, press the seal into the blade grip seal bore.

d. Remove the installation tools.

(2) If required, bond the covers for the cylinder and lug (not shown in Figure 9-8)

using the following procedure:

a. Remove residual adhesive from the cover and cylinder/lug as required.

b. Slightly abrade the bonding surfaces of the cover and cylinder/lug.

NOTE

Follow the mixing and application instructions for the DP420 adhesive or the

DP420 will not cure or adhere properly.

c. Bond the cover to the cylinder/lug using DP420 adhesive. Allow the DP420

adhesive to cure for 24 hours.

d. Apply a light bead of silicone sealant (732-RTV) around the cover.

(3) If installing new retention stops (1 & 4), follow the procedures in paragraph 9-

18,A,1.

CAUTION

Use brass protector plates in the vise jaws to prevent from damaging the

retention assembly.

(4) Clamp the spindle in a vise in the vertical position.

(5) If removed, apply a small amount of Loctite⁷ 635 (green) to the alignment pin

(32) and press the alignment pin into the spindle until the end is slightly

recessed from the seal surface.

(6) Lubricate (MIL-PRF-81322) the seal surface of the spindle and install the seal

(6) with the spring side facing toward the ears of the spindle.

(7) Lubricate (MIL-PRF-81322) the bearing surface and install the bearing (7) using

a plastic mallet.

(8) Install the spacer (8).

(9) Lubricate (MIL-PRF-81322) the bearing surface and install the bearing (9) using

a plastic mallet.

NOTE

Ensure the bearings are seated firmly against the spindle shoulders.

Rev. 26

MM-9-46

Feb 28/2020

(10)

Install the retaining ring (10).

(11)

Install tool (T-0036) behind the seal with the chamfered side of the tool toward

the large radius of the spindle.

(12)

Remove the spindle from the vise and insert the grip installation pilot tool (T-

0149-12) into the spindle.

(13)

Lubricate (MIL-PRF-81322) the seal surface on the adapter in the outboard end

of the spindle.

(14)

Lubricate (MIL-PRF-81322) the bore of the blade grip and install the grip (28) on

the spindle. Tap the grip onto the spindle with a plastic mallet until the seal in

seated in the grip. Remove the pilot tool (T-0149-12) and the seal tool (T-0036)

from the spindle.

(15)

Install the lug (29) onto the end of the blade grip. Apply Loctite^® 222MS to the

threads of the hardware and install the hardware and torque.

(16)

Install the tension-torsion strap (25) into the cylinder (24) so that the chamfer on

the cylinder is facing inboard (center of main rotor hub) when the tension-torsion

strap is installed in the spindle and install the retention pin (23).

(17)

Lubricate (MIL-PRF-81322) the portion of the inner spindle bore (3) that contacts

the O.D. of the cylinder (24).

(18)

Install the tension-torsion strap into the spindle and ensure the groove in the

cylinder engages the pin in the spindle.

(19)

Install one of the retaining rings (31) into the lug. Align the tension-torsion strap

to the lug and install the retention pin (30). Install the other retaining ring.

(20)

Install the dust cover (18).

(21)

Apply a bead of silicone sealant (732-RTV) around the perimeter of the cylinder

assembly (24) to form a seal between the cylinder and the spindle.

(22)

Install the flapping pin alignment pin into the spindle ear if it was removed.

(23)

Install the retention assembly onto the main rotor hub assembly (para. 9-19).

(24)

Install the pitch arm onto the blade grip. Install the hardware and torque to 75

in-lbs/8.5 Nm. Lockwire the hardware (.032) in horizontal pairs.

(25)

Service the blade grip.

a. Purge lubricate the retention assembly (para. 4-35).

b. Ensure the seal (6) is not dislocated from the blade grip. If it has moved,

remove the purge screw from the top of the blade grip. Insert the blade of a

flathead screwdriver between the seal and the spindle. Carefully work the

seal back into the grip. It is normal if grease is displaced out of the purge

hole as the seal is pushed back into place. Reinstall the purge screw.

Rev. 26

MM-9-47

Feb 28/2020

9-19. Installation - Retention Assembly (Figure 9-6)

NOTES

Grease bearings (grease lubricated) prior to installation through the small hole

in the bearing. When reinstalling removed bearings, purge old grease and refill

the bearings with new grease.

480, S/N 5003, 5014 and subsequent, have flapping bearings installed in the

universal blocks using the shimming procedure in paragraph 9-24, B or C.

A. Use the following procedure to install a retention assembly if the flapping bearings are

installed in the universal blocks using the shimming procedure in paragraph 9-24, B or C.

NOTE

Installing a pilot (Refer to Figure 9-13) will keep the spacer and shims in the

proper location while installing the hinge pin.

(1) Lubricate the O.D. of the hinge pin (2) (MIL-PRF-81322, grease lubricated

flapping bearings; MIL-PRF-23699, oil lubricated flapping bearings).

(2) Install the sleeves into the seals if equipped with oil lubricated flapping bearings.

NOTE

Install the shims (if installed) behind the DU washers in the same position as

previously installed.

NOTE

If new parts are installed in the flapping axis, begin with a 0.005” shim and

follow the shimming procedure in para. (7)a.

(3) Install the shims (4) and DU washers (3) on each side of the U-block with the

chamfered side inboard toward the U-block.

NOTE

Ensure that the correct retention assembly is being installed on the universal

block.

(4) Carefully slide the retention assembly into position over the DU washers and U-

block.

NOTE

The pilot tool (Figure 9-13) will be pushed out as the hinge pin is pushed into

the assembly while keeping the shims in the correct place.

(5) Install the hinge pin through the spindle and U-block. Align the roll pin slot in the

hinge pin with the roll pin and seat the hinge pin. Tap the roll pin flush with the

hinge pin if it protrudes from the hinge pin.

Rev. 26

MM-9-48

Feb 28/2020

(6) Lightly lubricate (MIL-PRF-81322; MIL-PRF-23699) the back of nut (6) and

install the lock washer (5) and nut (6) on the hinge pin.

CAUTION

Excessive torque could shear the roll pin installed in the head of the hinge pin.

(7) Insert a long punch into the damper-rod end attach holes in the flapping pin.

Torque the nut (6) using tool (T-0051-3) to 150 ft-lb/204.5 Nm. The nut may be

torqued to 175 ft-lb/238.6 Nm for aligning one of the lock washer tabs. While

torqueing the nut, pull against the punch to avoid shearing off the roll pin that

locates the head of the pin against the spindle arm side of the retention

assembly.

NOTE

If new parts are installed in the flapping axis, follow the shimming procedure in

para. (7)a below.

a. Check the flapping bearing drag resistance at the flapping pin. Initially, the grip

should not stay up. If the retention assembly stays up, remove shims in 0.005-

inch increments until the retention assembly will drop with no resistance when

nut is torqued.

(8) Bend one of the tabs on the lock washer into a slot in the nut.

(9) Install the main rotor damper (para. 9-31), connect the pitch change link to the

pitch change bellcrank and the pitch horn (para. 12-96), and install the main

rotor blade (para. 9-38).

(10) Lubricate the U-block lead lag and flapping bearings (if the flapping bearings are

grease lubricated) (para. 4-31).

(11) Lubricate the retention assembly (para. 4-35).

(12) Service the flapping bearing reservoir if equipped with oil lubricated flapping

bearings (para. 4-21).

(13) Perform a maintenance test flight (para. 4-61).

B. Use the following procedure to install a retention assembly until the flapping bearings

are installed in the universal blocks using the shimming procedure in paragraph 9-24,B or C.

(1) Lubricate the O.D. of the hinge pin (2) (MIL-PRF-81322, grease lubricated

flapping bearings; MIL-PRF-23699, oil lubricated flapping bearings).

Rev. 26

MM-9-49

Feb 28/2020

(2) Install the DU washers (3) on each side of the U-block with the chamfered side

inboard toward the U-block.

(3) Carefully slide the retention assembly into position over the DU washers and U-

block.

(4) Install the hinge pin through the spindle and U-block. Align the roll pin slot in the

hinge pin with the roll pin and seat the hinge pin. Tap the roll pin flush with the

hinge pin if it protrudes from the hinge pin.

(5) Install the lock washer (5) and nut (6) on the hinge pin.

CAUTION

Excessive torque could shear the roll pin installed in the head of the hinge pin.

(6) Torque the nut to 50-100 ft-lbs/68.2-136.4 Nm using tool (T-0051-3). Ensure the

retention assembly does not remain in the up-stop position.

a. Check the flapping bearing drag resistance at the flapping pin. Initially, the grip

should not stay up. If the retention assembly stays up, remove shims in 0.005-

inch increments until the retention assembly will drop with no resistance when

nut is torqued.

NOTE

Shims may be installed as required on the inboard side of the DU washers to

avoid excessive torque in obtaining the flapping preload. All three retention

assemblies should have an equal flapping preload.

(7) Lubricate the U-block lead lag and flapping bearings (para. 4-35) and re-check

the retention assembly in accordance with para. 9-19, B, (6). Reshim and

retorque the nut, if required.

(8) Bend one of the tabs on the lock washer into a slot in the nut when the proper

preload has been obtained.

(9) Install the main rotor damper (para. 9-31), connect the pitch change link to the

pitch change bellcrank and the pitch horn (para. 12-96), and install the main

rotor blade (para. 9-38).

(10) Lubricate the retention assembly (para. 4-35).

(11) Perform a maintenance test flight (para. 4-61).

Rev. 26

MM-9-50

Feb 28/2020

9-19.1 Tension-Torsion Strap (Figure 9-7)

9-19.2 Tension-Torsion Strap - Removal

NOTE

The following procedure is performed for changing the tension-torsion straps.

The blade grip does not need to be removed from the spindle when changing

the tension-torsion straps.

A. Remove the retention assembly from the main rotor hub (para. 9-14).

B. Remove the dust cover (18) from the blade end of the retention assembly.

C. Remove one of the retaining rings (31) securing the pin in the lug at the outboard end

of the retention assembly. Remove the pin (30) and the remaining retaining ring.

D. Using a non-metallic scraper remove the silicone sealant from the cylinder (24) and

the spindle.

NOTE

The pin used to secure the tension-torsion strap at the inboard end is not

secured with retaining rings.

E. Push the tension-torsion strap (25) back through the spindle.

F. Remove the pin (23) from the cylinder (24) and separate the tension-torsion strap

from the cylinder.

9-19.3 Tension-Torsion Strap - Installation

A. Install the tension-torsion strap (25) into the cylinder (24) so that the chamfer on the

cylinder is facing inboard (center of main rotor hub) when the tension-torsion strap is installed in

the spindle and install the retention pin (23).

B. Lubricate (MIL-PRF-81322) the portion of the inner spindle bore (3) that contacts the

O.D. of the cylinder (24).

C. Install the tension-torsion strap into the spindle and ensure the groove in the cylinder

engages the pin in the spindle.

D. Install one of the retaining rings (31) into the lug. Align the tension-torsion strap to

the lug and install the retention pin (30). Install the other retaining ring.

E. Verify proper installation of both retaining rings (31) Install the dust cover (18).

F. Apply a bead of silicone sealant (732-RTV) around the perimeter of the cylinder

assembly (24) to form a seal between the cylinder and the spindle. Reinstall Retention

assembly (para. 9-19).

Rev. 26

MM-9-51

Feb 28/2020

9-20. Universal Block

9-21. Disassembly - Universal Block (Figure 9-4 or 9-5)

A. Remove the upper and lower bearings and DU washers from the universal block (U-

block).

B. Remove the sleeves and seals from the flapping bearing bore if equipped with oil

lubricated flapping bearings.

NOTE

Flapping bearings can be removed from the universal blocks using the Flapping

Bearing Removal/Installation Tool (Grease Lubricated), T-0151-1, or Flapping

Bearing Removal/Installation Tool (Oil Lubricated), T-0162-1, when the

universal blocks are installed on the aircraft.

C. Press the flapping bearings, spacer, and shims from the bore of the U-block.

D. Remove the screws and stop pads if visual damage appears on the blocks.

E. Remove the grease fittings if equipped with grease lubricated flapping bearings.

F. Remove the drain plug if equipped with oil lubricated flapping bearings.

9-22. Inspection - Universal Block

A. See Table 9-3 for the detailed inspection requirements of the universal block

assemblies.

9-23. Repair - Universal Block

A. Repair or replace the components of the universal block assembly as required in

accordance with Table 9-3.

9-24. Assembly - Universal Block (Figure 9-4 or 9-5)

A. If removed, install the stop blocks (21).

NOTE

Index mark the universal blocks and retention assemblies (spindles) as sets.

Rev. 26

MM-9-52

Feb 28/2020

Table 9-3. Universal Block Assembly

Inspection Requirements*

P/N

Fig. #

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14251-1 & -2

Fig. 9-4, 21

Stop Pad

Visual damage (cracks,

None Allowed

Not Repairable

Replace Stop(s)

Fig. 9-5, 20

chips, etc.)

ECD092-1

Fig. 9-4, 22

Bearing

O.D. 2.4994 to 2.5000

No Tolerance

Not Repairable

Replace Bearing

Fig. 9-5, 21

Allowed

ECD092-3

Fig. 9-5, 21A

I.D. 1.7493 to 1.7500

No Tolerance

Not Repairable

Replace Bearing

Allowed

Ratcheting or

Not Repairable

Replace Bearing

roughness

None Allowed

28-14236-1

Fig. 9-4, 23

DU Washer

Flatness

.005

Not Repairable

Replace Washer

Fig. 9-5, 22

Thickness .090 to.093

-.003

Not Repairable

Replace Washer

28-14117-11 or -

Fig. 9-4, 15

U-Block

Bore Dia. 2.4988 to

+.0002

Not Repairable

Replace U-Block

2.4996

Fig. 9-5, 15

Bearing Surface O.D.

-.0002

Not Repairable

Replace U-Block

1.7488 to 1.7494

Bearing Surfaces

.001 FIM

Not Repairable

Replace U-Block

concentric

Threads (crossed or

None Allowed

Not Repairable

Replace U-Block

missing)

Nicks, scratches, or

None allowed at the

≤ .030 deep

Blend and polish out

corrosion

radius of the bearing

smooth

spindle

Cracks

None Allowed

Not Repairable

Replace U-Block

Rev. 26

MM-9-53

Feb 28/2020

Table 9-3. Universal Block Assembly

Inspection Requirements*

P/N

Fig. #

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14235-1

Fig. 9-4, 24

Spacer

Ends parallel

.0015 FIM

Not repairable

Replace Spacer

28-14233-2

Fig. 9-6, 2

Flapping Pin

Threads (crossed or

None Allowed

Not Repairable

Replace Pin

missing)

Damper bolt hole Dia.

+.0015

Not Repairable

Replace Pin

.5005 to .5015

O.D. 1.7486 to 1.7492

-.0005

Not Repairable

Replace Pin

Longitudinal scores or

.011 deep

≤ .011 deep

Blend and polish out

scratches

smooth

Radial Scores

None Allowed

Not Repairable

Replace Pin

28-14233-3

Fig. 9-6, 2

Flapping Pin

O.D. 1.7488 to 1.7494

-.0005

Not Repairable

Replace Pin

Inspect the remainder of the flapping pin following the inspection criteria listed for the -2 flapping pin

W-09

Fig. 9-6, 5

Lock Washer

Tangs

None Allowed

Not Repairable

Replace Washer

(deformed or cracked)

N-09

Fig. 9-6, 6

Nut

Threads

None Allowed

Not Repairable

Replace Nut

(crossed or missing)

4143011-11

Fig. 9-5, 23

Spacer

Ends parallel

.0015 FIM

Not Repairable

Replace Spacer

4143011-13

Fig. 9-5, 26

Sleeve

Ends parallel

.0015 FIM

Not Repairable

Replace Spacer

* All dimensions are in inches.

MM-9-54

Feb 9/01

9-25. Dampers

9-26. Removal - Dampers (Figure 9-16)

A. Remove the bolt (5) connecting the damper to the retention assembly.

B. Pivot the damper and remove the spacers (7) from between the damper bearing and

the hinge pin.

NOTE

If the center bolt head in the pitch change bellcrank is orientated over the

inboard pivot bolt, hardware removal is not necessary.

C. If required, remove the nut and washers from the pitch change bellcrank center pivot

bolt. Remove the bolt until the end is flush with the mounting bracket.

D. Remove the inboard pivot bolt (1) from the hub and remove the damper.

9-27. Disassembly - Dampers (Figure 9-17)

NOTE

The following procedure only applies to the hydraulic main rotor dampers, P/N

28-14375-“X”.

A. Secure the damper assembly in a vise.

B. Insert a punch through the rod end (20) hole. Pull on the punch to pull the rod end

assembly to expose 1.0 inch/25 mm of the piston shaft (6) and install tool T-0005.

C. Reposition the damper in the vice so that the vice jaws grip tool T-0005.

D. Remove the lockwire from the locking tab (18) and loosen the jam nut (19) and back it

out as far as the threads on the rod end (20) will allow which will withdraw the locking tab from

the piston shaft (6).

NOTE

If the rod end was not previously assembled with epoxy, but there is evidence

of threadlocker (Loctite Red 271, or equivalent) it may be necessary to heat the

rod end assembly to remove the jam nut.

WARNING

Use protective gloves when handling heated parts.

D. If required, heat the rod end assembly (250°F/121°C). Remove the rod end.

E. Remove the damper from the vice.

F. Remove the reservoir plugs (26) and pour the fluid from the reservoir (21).

Rev. 26

MM-9-62

Feb 28/2020

G. Remove the hardware (16) and (28) securing the reservoir to the damper and remove

the reservoir.

H. Remove the sleeves (27) and O-rings (25).

CAUTION

The relief valves are adjusted and set at the factory. Return defective valves to

the factory.

If removal of the valve assemblies (22) is required, place the reservoir back in a vise.

Remove the valve caps (23) and remove the valves.

CAUTION

Remove all burrs from the piston shaft to prevent damage to the brass sleeve

and seals during end cap removal.

J. Remove the hardware (16) and (17) that secures the end cap (10) to the damper

housing (1). Rotate the end cap approximately 45° using a plastic mallet and remove the end

cap by tapping outward on its corners.

K. Pour the fluid from the damper housing.

L. Tap the piston (6) out of the housing using a nylon drift and remove the O-ring or Seal

Pack (9) from the piston.

CAUTION

Do not damage the I.D. of the sleeves during seal and wiper removal.

M. Remove the seals (14) and wipers (15) from the brass sleeves (5 & 12) in the end cap

and damper housing.

N. Install tool (T-0095) between the ears of the damper housing and press the bushing

(3) out using a suitable size drift.

O. Inspect the bushing faces (2) for fretting and wear. Do not remove the bushings (2)

unless replacement is required.

Rev. 26

MM-9-63

Feb 28/2020

9-28. Inspection - Dampers

A. See Table 9-4 for the detailed inspection requirements for the damper assemblies.

9-29. Repairs - Dampers

A. Replace leaking seals or O-rings on hydraulic dampers as required.

B. Repair or replace the detailed parts of the hydraulic damper assembly as required in

accordance with Table 9-4.

9-30. Assembly - Dampers (Figure 9-17)

NOTE

The following procedure only applies to the hydraulic main rotor dampers, P/N

28-14375-“X”.

CAUTION

Do not damage the I.D. of the sleeves during seal and wiper installation.

A. Install the seals (14) and wipers (13) into the end cap and damper housing as follows:

(1) Install the seals in the inboard groove of the brass sleeves (5 &12) with the O-

ring side toward the piston. Ensure the seal has the O-ring installed in it.

(2) Install the wiper in the outboard groove of the brass sleeves with the lip of the

wiper facing outboard.

B. If the bushings (2) where removed, install tool (T-0095) between the ears of the

damper housing (1). Using an arbor press, install the bushings into the housing. If new

bushings are installed, they must be line reamed with a ½ in. line reamer.

C. Lubricate (L-45/SF96-20) the O.D. of the bushing (3). With tool (T-0095) installed,

press the bushing into the housing.

D. Place the damper housing in a vise with the bore up.

NOTE

Ensure the components are free of dirt and contamination prior to assembly.

CAUTION

Do not damage the O-rings or seals during the assembly process.

E. Lubricate (L-45/SF96-20) the bore of the housing.

Rev. 26

MM-9-66

Feb 28/2020

F. Install the O-ring or Seal Pack using the following procedure:

(1) If O-ring is installed, lubricate (L-45/SF96-20) the O-ring (9) and install on the

piston (6).

(2) If seal pack is installed, install the seal pack onto the piston using tool T-0160-1.

Using wood blocks or other suitable devices to protect the piston shaft from

damage, clamp the piston vertically in a vise. Install the installation sleeve (T-

0160-3) onto the piston. Lubricate (L-45/SF96-20) the seal ring and install on the

piston using the expanding sleeve and pilot (T-0160-9). Remove the tools.

G. Install the piston into the damper housing (1) using the following procedure:

(1) Clamp the damper housing vertically in a vice. Install the installation collar tool

T-0610-7 onto the damper housing. Install the piston into the collar with the

threaded end up and tap with a plastic mallet until the seal pack is into the

damper housing. Remove the collar and tap the piston with the plastic mallet

until the piston is bottomed in the housing.

H. Fill the housing with damper oil (L-45/SF96-20) and install the O-ring (9) into the

recess in the damper housing.

Lubricate (L-45/SF96-20) the seal and wiper in the end cap (10). Install the end cap

on the piston shaft and gently tap the cap to seat it onto the damper housing.

J. Install the hardware (16 & 17) securing the end cap to the housing. Torque the bolts

in a cross pattern.

K. If the relief valves (22) have been removed for cleaning or replacement, install the

valves in the reservoir and torque to 350 in-lbs/39.8 Nm.

L. Install new O-rings (24) onto the valve caps (23) and install the valve caps.

M. Reposition the damper to the horizontal position with the reservoir ports up.

N. Install new O-rings (25) on the sleeves and install the sleeves (27) into the reservoir

ports in the damper housing.

O. Align the ports in the reservoir (21) with the sleeves in the damper housing and install

the reservoir. Install the securing hardware and torque.

P. Temporarily install the damper bearing (20) and place the damper in the damper

fixture (T-0057). Position the piston approximately .5 inches/13 mm. from the bottomed

position.

Q. Fill the reservoir with damper oil (L-45/SF96-20). Install the servicing/bleeding tools

(T-2896) (Refer to Figure 4-5) and cycle the tools until the entrapped air is removed. Remove

the servicing/bleeding tools and install the reservoir plugs (26) with new O-rings (25) installed.

R. Remove the damper from the fixture and wipe down to remove the damper oil.

Rev. 26

MM-9-67

Feb 28/2020

S. Install the damper rod end bearing assembly.

NOTE

The rod end bearing assembly may have been previously treated with ACF-50 or

MIL-PRF-23377 Type I Class 2C or Class N epoxy primer corrosion inhibitor per

SDB T-058. If continuing use of ACF-50, removal of prior ACF-50 application is

unnecessary. If changing from ACF-50 to epoxy primer, ACF-50 residue must be

removed before reinstallation. For helicopters S/N 5242 and subsequent, the rod

ends are treated with epoxy primer at the time of manufacture.

(1)

Remove the nut.

(2)

For new epoxy primer application, remove any ACF-50 residue from the threads

of the rod end and the interior threads of the piston with a suitable solvent.

(3)

If applying a touch-up of epoxy primer, remove any loose epoxy primer residue

from the threads of the rod end and the interior threads of the piston with a

brush and a small amount of solvent.

CAUTION

Do not allow the epoxy primer to dry prior to assembly of the rod end.

CAUTION

Mask the bearing area prior to applying epoxy primer to avoid damaging

the bearing.

NOTE

Follow the manufacturer’s instructions for corrosion inhibitor application.

(4) Apply the applicable corrosion inhibitor to the entire thread length of the rod end,

as required.

NOTE

Installing the nut will tend to wipe away corrosion inhibitor that was freshly

applied. Re-apply to ensure complete coverage.

(5) Install the jam nut.

(6) Re-apply corrosion inhibitor to the threads below the jam nut, as required.

(7)

Install the damper rod end bearing assembly until the distance between the

outboard edge of the jam nut (19) and the center line of the damper bearing

equals 1.050 in. ± .005 in./26.7 mm ± .13 mm (Figure 9-20).

(8) Re-apply corrosion inhibitor to the threads above the jam nut, as required.

Rev. 26

MM-9-68

Feb 28/2020

NOTE

The locking key must be aligned with the piston slots for the jam nut to seat

against the piston shaft.

T. Hold the damper bearing with a wrench and tighten the jam nut when the correct

position is set. Lockwire (.032) the jam nut to the locking key (18). Position the locking key

towards the top of the damper.

U. Lockwire (.032) the end cap bolts (17) in pairs and the valve caps (23) to the reservoir

bolts (28) in pairs. Lockwire (.025) the bleed plugs (26) in a pair.

9-31. Installation - Dampers (Figure 9-16)

A. Install the damper onto the main rotor hub.

B. Install the chamfered washer (3) onto the inboard pivot bolt (2) with the chamfer

against the bolt head.

C. Install the inboard pivot bolt through the hub plates and damper. Install the washer

(3) and nut (4) but do not torque.

CAUTION

On hydraulic dampers, the locking key in the piston shaft must be on the top

side to prevent interference with the hinge pin.

D. Install the spacers (7) on each side of the damper bearing and slide the damper

bearing into the hinge pin.

E. Align the damper bearing and spacers with the hinge pin. Install a washer (6) on the

bolt (5) and install the bolt. Install two washers (6) and the nut (8). Torque to 450-500 in-

lbs/45.5-56.8 Nm and install a cotter pin (9).

F. Torque the inboard pivot bolt to 190 in-lbs/21.6 Nm.

G. If the washers and nut were removed from pitch change bellcrank center bolt in

accordance with step C, remove the center pivot bolt, turn the bolt 180°, and reinstall the bolt

and install washers and nut. Torque to 40 in-lbs/4.5 Nm and cotter pin.

H. Perform a maintenance test flight (para. 4-61).

Rev. 26

MM-9-69

Feb 28/2020

Table 9-4. Hydraulic Damper Assembly

Inspection Requirements*

P/N

Fig. 9-17

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14357-3 or -5

Housing

Sleeve bore Dia.

+.0002

Not Repairable

Replace Housing

1.1250 to 1.1255

Flanged bushings in

1/3 of total face light

2 of total face light

Blend and polish to

the ears for excessive

fretting

remove

fretting

Obstructions in the flow

None Allowed

Clear with compressed air

ports

Threads (crossed or

None Allowed

Not Repairable

Replace Housing

missing)

Security of the chrome

No movement

Not Repairable

Replace Housing

sleeve in the bore of

allowed

the housing

Surface scratches

None Allowed

≤ .020 deep

Blend and polish out

smooth

28-14277-1 or

Bushing

O.D. .4995 to .5005

-.0005

Not Repairable

Replace Bushing

28-14359-17

(28-14277-1)

O.D. .4994 to .4999

(28-14359-17)

I.D. .3747 to .3757

+.0005

Not Repairable

Replace Bushing

(28-14277-1)

I.D. .3765 to .3775

(28-14359-17)

Nicks and scratches

.005 deep

≤ .005 deep

Blend and polish out

smooth

Rev. 26

MM-9-73.1

Feb 28/2020

Table 9-4. Hydraulic Damper Assembly

Inspection Requirements*

P/N

Fig. 9-17

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-14356-3 or -5

5 & 12

Sleeve

O.D. 1.1260 to 1.1265

-.0002

Not Repairable

Replace Sleeve

Piston shaft bore Dia.

+.002

Not Repairable

Replace Sleeve

.749 to .751

28-14356-3 or -5

5 & 12

Sleeve

O.D. to I.D.

.002 FIM

Not Repairable

Replace Sleeve

(Cont=d)

concentricity

28-14370-15,

Piston

Piston shaft O.D. .746

-.001

Not Repairable

Replace Piston

-17

to .748

Nicks or scratches in

None Allowed

≤ .5" long and

Blend and polish out

surface

≤ .005 deep

smooth

Obstruction in the flow

None Allowed

Clear with compressed air

restrictor

Concentricity

.001 FIM

Not Repairable

Replace Piston

Threads

None Allowed

Not Repairable

Replace Piston

(crossed or missing)

28-14265-3

End Cap

Sleeve bore Dia.

+.0002

Not Repairable

Replace Cap

1.1250 to 1.1255

Obstructions in the fluid

None Allowed

Clear with compressed air

port

Nicks, scratches, or

None Allowed

≤ .020 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Cap

ECD091-1

Damper Bearing

Radial Play

.007

Not Repairable

Replace Bearing

Axial Play

.005

Not Repairable

Replace Bearing

Rev. 26

MM-9-73.2

Feb 28/2020

Table 9-4. Hydraulic Damper Assembly

Inspection Requirements*

P/N

Fig. 9-17

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

ECD091-1

Damper Bearing

Threads

None Allowed

Not Repairable

Replace Rod End

(Cont’d)

(crossed or missing)

Threads

None Allowed

Not Repairable

Replace Rod End

(damage or corrosion)

28-14366-1

Reservoir

Obstructions in the flow

None Allowed

Clear with compressed air

ports

Threads

None Allowed

Not Repairable

Replace Reservoir

(crossed or missing)

Nicks, scratches, or

.020 deep

≤ .020 deep

Blend and polish out

corrosion

smooth

Cracks

None Allowed

Not Repairable

Replace Reservoir

If the valves are

None Allowed

removed, valve threads

Flush with cleaning

and ports for

solvent and dry with

contamination

compressed air

28-14368-1, -2

Plug

Threads

None Allowed

Not Repairable

Replace Plug

(crossed or missing)

28-14369-1

Sleeve

O.D. and I.D. for nicks

None Allowed

Not Repairable

Replace Sleeve

or scratches

AN814-2DL

Plug

Threads

None Allowed

Not Repairable

Replace Plug

(crossed or missing)

O-Rings, Wiper, and

Inspect for obvious

None Allowed

Not Repairable

Replace as required

Seals

defects

* All dimensions are in inches.

Rev. 26

MM-9-73.3

Feb 28/2020

9-32. Main Rotor Blades

9-33. Description - Main Rotor Blades (Figure 9-21)

The main rotor blades are of hollow construction. Upper and lower skins are bonded to

the extruded leading edge spar which is twisted 7.25°. Doublers are bonded to the root end of

the blade for retaining the blades to the main rotor hub. The blades are retained by a single

retention pin to the blade grip and a non-adjustable drag brace connected to the trailing edge of

the blades. Provisions for spanwise and chordwise balance weights are provided in the tip caps

that are bonded in the tip end of the blades. Two tracking tabs are riveted to the trailing edge of

each blade.

9-34. Removal - Main Rotor Blades (Figure 9-22)

NOTE

Lifting the tip of the blade until the blade is parallel to the retention assembly will

allow the retention bolt and the drag brace bolt to be easily removed and will

allow the blade to be removed from the blade grip without spreading the ears of

the grip.

A. Remove the bolt (1) securing the drag link to the rotor blade.

B. Remove the blade retention bolt (2).

C. Carefully slide the blade from the grip.

D. Place the blade into a blade rack or on a suitable device that will prevent the blades

from being damaged.

E. Repeat the process for the other 2 blades.

Rev. 26

MM-9-74

Feb 28/2020

Table 9-5. Tail Rotor Assembly

Inspection Requirements*

P/N

Figure 9-36

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

28-150076-15

Journal

Journal I.D. .4995 to

+.0002

Not Repairable

Replace Journal

.4998

Journal O.D. .7509 to

-.0002

Not Repairable

Replace Journal

.7511

B-1210

Needle Bearing

Bearing O.D. 1.000

-.0002

Not Repairable

Replace Bearing

Visible wear of the

None Allowed

Not Repairable

Replace Bearing

needles

28-150076-13

Thrust Bumper

Thickness .123 to .125

-.002

Not Repairable

Replace Bumper

28-150060-11

Pitch Change Plate

Nicks in edge of plate

None Allowed

 .005 deep

Polish and blend locally not

to exceed .008

Pitch link bolt hole Dia.

+.0005

Not Repairable

Replace pitch change plate

.250 to .251

Return to the factory for

Corrosion

None Allowed

inspection and replating, or

replace pitch change plate

Cracks

None Allowed

Not Repairable

Replace pitch change plate

28-150063-11,

Sleeve

Sleeve I.D. .7878 to

+.0002

Not Repairable

Replace Sleeve

-13

.7882

Sleeve I.D. .7872 to

+.0002

Not Repairable

Replace Sleeve

.7876 (-13)

Sleeve O.D. 1.1245 to

-.0002

Not Repairable

Replace Sleeve

1.1250

Rev. 26

MM-9-113

Feb 28/2020

Table 9-5. Tail Rotor Assembly

Inspection Requirements*

P/N

Figure 9-36

Part Name

Inspection

Serviceable Limits

Repair Limits

Repair or Action

Item #

ECD001-11

Bearing

Bearing O.D. 1.6250

+.0000

Not Repairable

Replace Bearing

-.0005

Visible wear of the

None Allowed

Not Repairable

Replace Bearing

rollers

28-150055-1,

Retainer

Retainer I.D. 1.6250 to

+.0005

Not Repairable

Replace Retainer

-13, -15

1.6255

Retainer I.D. 1.6240 to

+.0005

Not Repairable

Replace Retainer

1.6247 (-15)

Retainer O.D. 2.043 to

-.001

Not Repairable

Replace Retainer

2.044

ECD002-11,

Bearing

Bearing O.D. 2.0467 to

-.0002

Not Repairable

Replace Bearing

-13, -15, -17

2.0472

Bearing Bore Dia.

+.0002

Not Repairable

Replace Bearing

.7870 to.7874

Preload to the thrust

None Allowed

Not Repairable

Replace Bearing

side and check for

roughness or ratcheting

SL61N-5P

Nut

Threads (rolled or

None Allowed

Not Repairable

Replace Nut

missing)

Nicks and burrs on

None Allowed

≤ .10 deep

Blend and polish out

O.D.

smooth

Rounded or burred

Max. 2 slightly

To allow use of the

Blend and polish out

locking tabs

rounded tabs

locknut wrench

smooth

Cracks

None Allowed

Not Repairable

Replace Nut

Rev. 26

MM-9-114

Feb 28/2020

WARNING

Use protective gloves when handling heated parts.

K. Using a heat gun, heat the blade grip (19) to approximately 250°F/121°C.

L. Lubricate (MIL-PRF-81322) the bore of the blade grip. Quickly slide the blade and

grip assembly onto the spindle. Align the pitch link hole in the pitch change plate to the leading

edge of the blade. Align the dowel pins to the center holes in the pitch change plate (the holes

are located in sets of three).

NOTE

Alternately tighten the bolts 1 to 2 turns to pull the pitch change plate and grip

straight together.

M. Start three bolts (25) into the grip and tighten to pull the grip and the pitch change

plate together.

N. Install the rest of the bolts (25). After the blade and grip assembly has cooled, torque

the bolts to 50-70 in-lbs/5.7-8.0 Nm and safety wire (.032) in pairs.

O. Re-heat the blade grip and tap outboard to assure maximum CF (centrifugal force)

position.

P. Torque the blade retention bolt nuts to 75 in-lbs/8.5 Nm (140 in-lbs/15.9 Nm if the

blade and grip assembly has been factory repaired and 5/16 inch bolts installed) after the blade

grip has cooled.

Q. Install the grease fitting into the grip and lubricate the grip (para. 4-39.4) until grease

purges from the pitch change plate from around the spindle.

R. If required, install the opposite blade and grip assembly.

S. Statically balance the tail rotor (para. 9-42).

T. Install the bolts (26), washers (27), and nuts (28) onto the pitch arms if not installed.

9-51. Installation - Tail Rotor Assembly

A. Start a .041 wrap of safety wire around one side of the tail rotor hub.

NOTE

The tail rotor assembly may be rotated 180° or the center hub may be pivoted

180° to obtain the proper installation position of the tail rotor assembly.

Rev. 26

MM-9-123

Feb 28/2020

NOTE

See Figure 9-38. A line drawn through the grease fittings of either end of the

teetering hub (Figure 9-36, 2) (tail rotor hub pivot center line) should align with

the lagging ears of the pitch link retainer. If the tail rotor hub pivot centerline is

centered between the ears of the pitch link retainer, rotate the teeter trunnion

180° to obtain the correct 8° alignment.

B. Install the tail rotor assembly onto the transmission output shaft. Ensure the center

line of the tail rotor hub pivot axis aligns with the inboard side of the pitch change link retainer

ear that lags in the direction of rotation (Figure 9-38).

C. Feed the safety wire through the hole in the teeter stop and install the teeter stop so

that the rubber bumpers align with the flats of the spindle.

D. Install the washer and retaining bolt. Torque the retaining bolt to 300 in-lbs/34.1 Nm

and complete the safety.

E. Connect the pitch change links to the pitch change plates (para. 12-126).

F. Dynamically balance the tail rotor (para. 9-43).

Rev. 22

MM-9-124

Jun 25/14

Enstrom TH-28/480 Series. Maintenance Manual (2020) - page 5