4. Transmissions
Model S64F Helicopter
Rev. A Sept 18, 2007 3-

5. Main Gear Box
Rev. A Sept 18, 2007 3-

6. “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 to 1 for a final main rotor speed of 185 rpm, and to drive the tail rotor head at 850 rpm
Rev. A Sept 18, 2007 3-

7. “F” Main Gear Box Schematic
Rev. A Sept 18, 2007 3-

8. “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.
Rev. A Sept 18, 2007 3-

9. Rear Cover Accessory System Schematic
Rev. A Sept 18, 2007 3-

10. 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.
Rev. A Sept 18, 2007 3-

11. Right Hand Accessory Auxiliary Pump 2nd stage Pump (20684 kPa)
Rev. A Sept 18, 2007 3-

12. 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
Rev. A Sept 18, 2007 3-

13. Free Wheeling Unit Assembly
Clutch & Freewheel Housing
Rev. A Sept 18, 2007 3-

14. Accessory Section Rear cover
The main gearbox accessory section is located on the rear of the main gearbox.
Mounted on the rear cover are the:
Number 1 and number electrical generators.
The first stage hydraulic pump
The utility hydraulic pump
Oil Cooler pump
The tachometer Generator.
The A.P.U. Drive gear.
Rev. A Sept 18, 2007 3-

15. Rear cover Accessory Section
Tail Take off coupling (4) Oil Cooler Pump
(3) Utility
(2) 1st stage
Oil filter
(1b) No 2 generator
(1a) No.1 generator
Oil filler
(5) Tachometer (6) A.P.U. Input
Rev. A Sept 18, 2007 3-

16. Rear Cover Accessory System Schematic
Rev. A Sept 18, 2007 3-

17. Accessory Drive Notes
Note: 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.
Rev. A Sept 18, 2007 3-

18. 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.
Rev. A Sept 18, 2007 3-

19. Tail Take-off Assembly (T.T.O)
Free Wheel Gear
Rev. A Sept 18, 2007 3-

20. APU Drive
Drive Shaft
Clutch
Rev. A Sept 18, 2007 3-

21. 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.
Rev. A Sept 18, 2007 3-

22. 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
Rev. A Sept 18, 2007 3-

23. Spline adapter pictures
The spline adapters (vespals) are made from phenolic plastic.
Rev. A Sept 18, 2007 3-

24. 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.
Rev. A Sept 18, 2007 3-

25. Thomas Coupling Heavy Mark
Rev. A Sept 18, 2007 3-

26. 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.)
Rev. A Sept 18, 2007 3-

27. 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.
Rev. A Sept 18, 2007 3-

28. F-Gear Box Lubrication Schematic
Rev. A Sept 18, 2007 3-

29. 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.
Rev. A Sept 18, 2007 3-

30. 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.
Rev. A Sept 18, 2007 3-

31. Oil Filter Installation
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32. 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.
Rev. A Sept 18, 2007 3-

33. 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.
Rev. A Sept 18, 2007 3-

34. Oil Strainer Installation
Rev. A Sept 18, 2007 3-

35. Oil Pump
Rev. A Sept 18, 2007 3-

36. Oil Pressure Main Gear Box Oil is Mobil 626.
The main gearbox oil pressure normal operating range is psi ( 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.
Rev. A Sept 18, 2007 3-

37. MGB Pressure Transmitter
Rev. A Sept 18, 2007 3-

38. Oil Pressure Warning
When oil pressure at the furthest point from the pump drops below psi ( 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.
Rev. A Sept 18, 2007 3-

39. 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.
Rev. A Sept 18, 2007 3-

40. 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.
Rev. A Sept 18, 2007 3-

41. Temperature Switch Location
Plug Stat Switch
Rev. A Sept 18, 2007 3-

42. 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.
Rev. A Sept 18, 2007 3-

43. MGB Screen Chip Detector Press to Test On Left Main Gear Leg
Chip Detector Diagram
Caution Panel
MGB Screen Chip Detector
MGB Sump
Chip Detector
Press to Test On Left Main Gear Leg
Rev. A Sept 18, 2007 3-

44. Oil Screen Chip Detector
When 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.
Rev. A Sept 18, 2007 3-

45. Types of Chip Plug Contamination
Kind 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 inch thick ( mm).
Component plating material only.
Particles over inch thick ( mm).
Do serviceability check.
Aluminum or Magnesium
Particles in granular form.
Result of using mallets and drifts during assembly.
Copper or Bronze
May indicate too much wear of thrust washers.
Phenolic
Silver
Particles in flake or splinter form
Component Plating material only.
Baked Resin Coating
Total area of in.2 ( mm2) (i.e.) 0.25 in. (6.35mm)
More than in.2 ( mm2)
Remove gear box from service.
Rev. A Sept 18, 2007 3-

46. Oil Cooler
Rev. A Sept 18, 2007 3-

47. 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 70C.
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.
Rev. A Sept 18, 2007 3-

48. MGB Input
Rev. A Sept 18, 2007 3-

49. Input Seal Replacement
Rev. A Sept 18, 2007 3-

50. Rotor Brake
Rev. A Sept 18, 2007 3-

51. 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.
Rev. A Sept 18, 2007 3-

52. Rotor Brake Rotor Brake Disc Rotor Brake Assemble 3-
Rev. A Sept 18, 2007 3-

53. 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.
Rev. A Sept 18, 2007 3-

54. 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.
Rev. A Sept 18, 2007 3-

55. 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.
Rev. A Sept 18, 2007 3-