Rev. A Sept 18, 2007 3- 1

Transmissions

Model S64F Helicopter

3- 2Rev. A Sept 18, 2007

Main Gear Box

3- 3Rev. A Sept 18, 2007

“F” Main Gear box

The main gearbox (M/G/B) is mounted behind the engines and changes the angle of drive from the engine to the main rotor head, and reduces the engine 9000 rpm.

The main gearbox contains a four-stage gear reduction system to drive the main rotor head at a ratio of 48.609 to 1 for a final main rotor speed of 185 rpm, and to drive the tail rotor head at 850 rpm

3- 4Rev. A Sept 18, 2007

“F” Main Gear Box Schematic

3- 5Rev. A Sept 18, 2007

“F” Main Gear Box

A free wheeling unit at each MGB input allows for single- engine operation and auto-rotation.

The accessory section, located at the rear of the transmission upper housing, contains mounting pads for A/C generators, rpm sensor, APU, and hydraulic pumps.

A tail take-off (T.T.O.) gear in the transmission is coupled to the T.T.O. flange for tail rotor drive.

3- 6Rev. A Sept 18, 2007

Rear Cover Accessory System Schematic

3- 7Rev. A Sept 18, 2007

Right Hand Accessory The right hand accessory provides a location for

additional hydraulic pumps to operate: 2nd stage pump, Hoist pump and Auxiliary pump.

The 2nd stage hydraulic pump operates the primary flight controls.

The hoist hydraulic pump pad operates additional equipment such as the auxiliary pump or the hoist pump.

3- 8Rev. A Sept 18, 2007

Right Hand Accessory

Auxiliary Pump

2nd stage Pump

(24132 kPa)

(20684 kPa)

3- 9Rev. A Sept 18, 2007

Free Wheeling unit

The two 2nd stage input pinion gears have a roller-ramp type clutch which permits the freewheel units in the gearbox to disengage the main rotor and tail rotor drive shafts when the relative main rotor rpm exceeds relative engine rpm such as during auto rotation, at engine shutdown, and single engine operation

3- 10Rev. A Sept 18, 2007

Free Wheeling Unit Assembly

Clutch & Freewheel Housing

3- 11Rev. A Sept 18, 2007

Accessory Section Rear coverThe main gearbox accessory section is located on the rear of the main gearbox.

Mounted on the rear cover are the:

1.Number 1 and number 2 electrical generators.2.The first stage hydraulic pump3.The utility hydraulic pump4.Oil Cooler pump5.The tachometer Generator.6.The A.P.U. Drive gear.

3- 12Rev. A Sept 18, 2007

Rear cover Accessory Section

(1b) No 2 generator

(1a) No.1 generator

Oil filler

(5) Tachometer (6) A.P.U. Input

Tail Take off coupling (4) Oil Cooler Pump

(3) Utility

(2) 1st stage

Oil filter

3- 13Rev. A Sept 18, 2007

Rear Cover Accessory System Schematic

3- 14Rev. A Sept 18, 2007

Accessory Drive NotesNote: Tach. Generator (5), oil cooler pump (4), and the tail take-off coupling will not be operating during A.P.P. operations.

Note: It is important to keep this operation to a minimum to

reduce the possibility of damage or failure of freewheel rollers.

3- 15Rev. A Sept 18, 2007

Tail Take Off A tail take-off freewheel unit is incorporated in the rear cover

accessory section of the main gearbox. When the auxiliary power plant (A.P.P.) is operating, the # 1

& 2 generators (1a & 1b), utility hydraulic pump (3), 1st stage pump(2), and oil pump are operating; thus, providing the aircraft with electricity, hydraulics, and the main gearbox with oil flow.

When the aircraft turbine engine(s) are operating and the main rotor is spinning at 185 revolutions per minute (rpm), the A.P.U. is no longer driving the accessory section. The accessory section is now being driven by the aircraft engine(s) through the main gearbox.

3- 16Rev. A Sept 18, 2007

Tail Take-off Assembly (T.T.O)

Free Wheel Gear

3- 17Rev. A Sept 18, 2007

APU Drive

Clutch

Drive Shaft

3- 18Rev. A Sept 18, 2007

Auxiliary Power Unit

The Auxiliary Power Unit (A.P.U.) provides temporary power for the aircraft.

The A.P.U. drives the centrifugal type clutch assembly mounted on the lower aft section of the rear cover.

The clutch couples the A.P.U. to the main gearbox by engaging when the A.P.U. is operating at approximately 75% and disengaging when the M/G/B speed (rpm) becomes faster than that of the A.P.U.

The A.P.U. drives the accessory gear box at 8,000 rpm The tail take off is driven at 8,025 rpm by the MGB.

3- 19Rev. A Sept 18, 2007

Spline Warning

The Spline adapters help eliminate gear spline wear and thus increase gear life.

Spline adapters are inserted into many of the accessory drive gears.

All hydraulic pumps that do not use spline adapters need to be removed from the main gearbox to grease the internal drive splines every Phase 4 (150 hrs.).

Warning: Only use special tools to insert and remove adapters

3- 20Rev. A Sept 18, 2007

Spline adapter pictures

The spline adapters (vespals) are made from phenolic plastic.

3- 21Rev. A Sept 18, 2007

Thomas Coupling

The Thomas couplings are mounted between the engine drive shafts and input flanges of the main gearbox input housings.

The Thomas couplings absorb engine torque and engine to gearbox vibrations.

The Thomas couplings are dynamically balanced and must be replaced as an assembly.

The outer three washers can be replaced if damaged or lost. All replacement washers must be the exact same weight.

3- 22Rev. A Sept 18, 2007

Thomas Coupling Heavy Mark

Heavy Mark

3- 23Rev. A Sept 18, 2007

Thomas Coupling notes

Any damage to the disks or other components of the coupling may cause excessive vibration and the coupling must be replaced.

When replacing Thomas Coupling input flange use anti-seize on splines

Thomas couplings and engine high-speed shafts will be identified with a residual heavy mark.

It is important to remember to off set these marks 180 degrees (Or as close to 180º as possible.)

3- 24Rev. A Sept 18, 2007

MGB Lubrication Description Lubrication is accomplished by a self-priming wet sump

system. The oil pump, attached to the main gearbox sump,

circulates oil for main gearbox lubrication and cooling.

3- 25Rev. A Sept 18, 2007

F-Gear Box Lubrication Schematic

3- 26Rev. A Sept 18, 2007

Oil Filter and Strainer Description The gearbox has an oil filter and oil strainer or screen. A magnetic chip detector on the bottom of the sump and

oil strainer assembly is part of the chip detector warning system.

Note: F Model has an additional chip detector inside the oil strainer.

3- 27Rev. A Sept 18, 2007

Oil Filter

The oil filter consists of a cover, bowl, bypass valve, and cartridge with filter elements. Filter elements can be bronze mesh or Monel mesh. Both are 40 micron nominal.

It is mounted on the lower right side of the main gearbox accessory cover, and it filters all main gearbox oil between the oil pump and oil cooler.

3- 28Rev. A Sept 18, 2007

Oil Filter Installation

3- 29Rev. A Sept 18, 2007

Oil Filter Bypass

If the filter becomes clogged, a bypass valve opens, allowing the oil to bypass the filter.

The oil cartridge should be removed, and the filter elements should be cleaned and inspected every 150 hrs.

3- 30Rev. A Sept 18, 2007

Oil strainer Description

A strainer in the lower part of the main gearbox consists of a sleeve, retainer, and screen.

A chip detector is mounted inside the strainer. The strainer prevents large particles from entering the pump and causing damage.

The strainer may be removed and inspected without draining the main gearbox by turning the outer sleeve 90º

Note: The Strainer should be removed, inspected, and cleaned every 150 Hrs. with the oil filter.

3- 31Rev. A Sept 18, 2007

Oil Strainer Installation

3- 32Rev. A Sept 18, 2007

Oil Pump

3- 33Rev. A Sept 18, 2007

Oil Pressure

Main Gear Box Oil is Mobil 626. The main gearbox oil pressure normal operating range is 50-

65 psi (345-448 kPa). The oil pressure is adjusted at the oil pump which is located on the sump.

A pressure transmitter located on the aircraft transmission deck sends an electrical signal to the Pressure Indicator located in the cockpit.

3- 34Rev. A Sept 18, 2007

MGB Pressure Transmitter

Pressure Transmitter

3- 35Rev. A Sept 18, 2007

Oil Pressure Warning

When oil pressure at the furthest point from the pump drops below 13-17 psi (90-117 kPa). the low oil warning switch on the main gearbox actuates, causing the caution “trans oil press” light to illuminate.

The switch is located on the lower front right side at the lower MGB support.

3- 36Rev. A Sept 18, 2007

Oil Temperature

The main gearbox temperature indicating system consists of an indicator, a resistance bulb located on the main gearbox sump, just after the oil screen, and circuit breakers.

The temperature resistance bulb converts the temperature of the oil system to an electrical signal supplied to the “trans oil temp” indicator at the center of the instrument panel.

3- 37Rev. A Sept 18, 2007

Hot Oil Warning

The main gearbox hot oil warning system consists of a caution panel capsule, (Trans Oil Hot ), temperature Plug Stat

Switch, signal adapter unit, and a circuit breaker. The temperature Plug Stat Switch is located in the secondary

manifold above the right hand input. The Temperature Plug Stat Switch actuates when oil temperature is over 121 ºC illuminating the caution-advisory

panel “Trans Oil Hot” light. When the oil temperature drops below 121ºC the light will go

off.

3- 38Rev. A Sept 18, 2007

Temperature Plug Stat Switch

Temperature Switch Location

3- 39Rev. A Sept 18, 2007

Chip Detectors

The electrical chip detectors provide an indication of metal accumulation in the main gearbox.

The chip detectors are located on the bottom of the oil sump and in the strainer assembly.

The two chip detectors are wired together in parallel.

3- 40Rev. A Sept 18, 2007

Chip Detector DiagramChip Detector Diagram

MGB SumpChip Detector

MGB ScreenChip Detector

Caution Panel

Press to TestOn Left Main

Gear Leg

3- 41Rev. A Sept 18, 2007

Oil Screen Chip DetectorWhen enough conductive material bridges the contacts

of the magnetic detector, a ground is provided, allowing current to actuate a relay that illuminates the “Chip Main Trans” light capsule on the caution-advisory panel.

3- 42Rev. A Sept 18, 2007

Types of Chip Plug ContaminationKind of Metal Quantity and/or Size Action Required Notes

Steel Fine hair-like particles None Result of normal wear (may have exaggerated appearance because of presence of oil).

Particles in splinter or granular form.

Do serviceability check. Replace gear box if necessary.

Usually indicates failure.

Tin, Lead, or Cadmium Particles not over 0.0005 inch thick (.00127 mm).

None Component plating material only.

Particles over 0.0005 inch thick (.00127 mm).

Do serviceability check.

Aluminum or Magnesium Particles in granular form. Do serviceability check. Result of using mallets and drifts during assembly.

Copper or Bronze Particles in granular form. Do serviceability check. May indicate too much wear of thrust washers.

Phenolic Particles in granular form. None Result of using mallets and drifts during assembly.

Silver Particles in flake or splinter form

None Component Plating material only.

Baked Resin Coating Total area of 0.062 in.2

(1.5748 mm2) (i.e.) 0.25 in. (6.35mm)

More than 0.062 in.2 (1.5748 mm2)

Do serviceability check.

Remove gear box from service.

3- 43Rev. A Sept 18, 2007

Oil Cooler

3- 44Rev. A Sept 18, 2007

Oil Cooler

The oil cooler has a thermostatic bypass valve, which will cause the oil to flow into the radiator core when the oil temperature exceeds 70C.

Also, oil will bypass the core if pressure exceeds 50 psi (345 kPa) differential.

Note: Oil cooler assembly must be removed with the main gearbox if the M/G/B is removed for making metal.

3- 45Rev. A Sept 18, 2007

MGB Input

3- 46Rev. A Sept 18, 2007

Input Seal Replacement

3- 47Rev. A Sept 18, 2007

Rotor Brake

3- 48Rev. A Sept 18, 2007

Rotor Brake

The rotor brake is a hydraulic disc-type rotor, which has replaceable brake linings (pucks).

The rotor brake housing is mounted on the left side of the main gearbox with the brake disc rotating through it.

The rotor brake is capable of stopping the main rotor in about 45 seconds from 100% NR with both engines shut-off.

The hand pump lever to activate the brake is located in the cockpit overhead.

3- 49Rev. A Sept 18, 2007

Rotor Brake

Rotor Brake Assemble

Rotor Brake Disc

3- 50Rev. A Sept 18, 2007

Rotor Brake Shaft Seal

A face-type (carbon) seal is used the rotor brake shaft.

The carbon seal consists of two matched components: the seal assembly and the seal mating ring.

The mating surfaces of the carbon element and the ring are lapped to extremely close fit, providing the sealing action.

3- 51Rev. A Sept 18, 2007

MGB Operational Check

New, overhauled or repaired main gearboxes receive a full load run-in at the factory and require no further break-in run.

However, an operational check is required in addition to the pilot pre-flight check to ensure proper installation and that the lubrication system is working properly.

3- 52Rev. A Sept 18, 2007

Allowable Leakage

Leaking from the main gearbox may be caused by worn or poorly installed seals, gaskets, or shims.

Total oil leakage from all sources must not exceed a drop in oil level on the dipstick from full to midway between “Full” and “Add” in 10 flight hours.

Note: Oil level should be checked 30 minutes after engine or A.P.U. shutdown.