PT6T removal and installation

PT6T Removal and Installation By Greg Napert February 1999 For the average helicopter technician, an engine change is not a very common event. In the case of the Pratt & Whitney PT6T Twin-Pac® installation, if the engines are operated...

Typical Twin-Pac removal from Bell Model 412 Helicopter
1. Cap all open lines and fittings. Cover both section air inlet and exhaust ducts to prevent foreign objects from entering.
2. Use standard precautions for use of the maintenance hoist; do not stand under powerplant during removal procedure.
3. Preservation should be accomplished, if applicable before powerplant is removed.
4. Turn off all electrical power and disconnect battery.

1. Open and hinge forward the forward pylon fairing, remove the forward transmission fairing.
2. Disconnect anti-collision light electrical connector at top panel. Remove the upper pylon cowling.
3. Release and remove left and right engine inlet fairings.
4. Open and remove left and right engine lower cowls.
5. Open engine upper cowls, disconnect starter-generator cooling ducts, fire detection element lead wires, and FM antenna and remove left and right engine top and side cowl assemblies.
6. Remove left and right reduction gearbox inspection doors and side panels.
7. Remove left hand combining gearbox top cowl with side cowl attached.
8. Disconnect oil filler hose and oil vent hose from oil filler adapter.
9. Remove right hand combining gearbox top cowl with the center panel and side cowl attached.
10. Remove top portion of cooler support cowl.
11. Disconnect ejector drain tubes, vent hoses and remove vent tube and bolts securing ejector to brackets.
12. Remove screws and hardware securing firewall, upper aft, and remove ejector and firewall section.
13. Remove main drive shaft and, using T101588 or 412-20-001-101 holding wrench, remove engine drive shaft adapter.
14. Remove screws to detach center section of aft firewall, and center firewall through, disconnect lines to differential switch and remove centerline firewall. Aft firewall center section will be removed with powerplant.
15. Remove upper section of induction baffle, disconnect air management valve electrical connector, disconnect engine wash hose at spray ring, disconnect vent line and remove transition duct as an assembly.
16. Remove screws, detach and flex left and right inboard ears of lower middle firewall and induction baffle forward to allow clearance and secure with lockwire.
17. Remove screws to allow removal of panels from lower middle firewall. remove access doors from aft cabin bulkhead at each side of pylon, in cabin and disconnect bonding strip from each tach generator.
18. Drain engine oil and disconnect engine control tubes, electrical connections, fuel, oil, bleed air and drain lines as required.
19. Loosen clamps and slide oil cooler blower boots aft.
20. Install Engine sling, SWE13833, attach a hoist using the fifth hole from the rear, and take up the slack.
21. Disconnect right forward engine mount vertical tube at lower end and left forward vertical tube upper end. Remove bolts and disconnect powerplant from bipod and tripod mounts.
22. Lift engine clear of helicopter after checking all lines, electrical wiring and linkages are disconnected.
23. Remove right forward engine mount vertical tube from accessory gearbox.
24. Position powerplant to engine stand and secure engine mount pads with locking pins.
25. Ensure stand position locks are applied and remove sling.

Typical Twin-Pac installation
1. Transfer from removed powerplant any parts not provided on replacement assembly. Such parts include exhaust ducts, aft center firewall section, manual fuel control levers and oil filler adapter, and vent hoses.
2. Install engine sling, SWE 13833, attach a hoist, using the fifth hole from the rear, and take up slack.
3. Remove pins and lift powerplant from stand.
4. Install left and right forward engine mount vertical tube upper end to fitting. Bolt heads should be positioned forward for the front engine deck fittings and bolt heads inboard for upper fittings on the accessory gearbox.

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