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Thielert TAE125-02-99 gearbox removal

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For those interested in the inside of a Thieliert TAE125 (now Continental CD155) here are some photos of a gearbox removal and clutch check.  The engine is out of my SQ2000 project described elsewhere.

The TAE125 engine is based on a Mercedes OM640 engine however it is heavily modified with custom aluminium block, custom sump, flywheel and fuel injection.

The gearbox exterior looks conventional for a PSRU with the exception of the hydraulic propeller controller which includes an oil pressure pump and ECU controller governor. Propeller flange is a Rotax style 80MM PCD suitable for constant speed MTU propeller. 

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The gearbox is removed via the peripheral M8 hex capscrews and two M5 screws just below the propeller flange. The flywheel is then revealed which is custom Thielert (not Mercedes O640)

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The flywheel still contains a clutch plate which drives the gearbox. The design is arranged to absorb the power pulses from the high compression Diesel via slippage of the clutch plate.  Many Thielert failures have been caused by the plate either slipping (oil or contaminant) or burning. The design differs from other PSRU (eg Rotax) which normally retain a flywheel and rubber power coupling which is used to transmit power.  As the engine has no clutch pedal, the clutch plate is permanently retained by a twist locking ring. To remove, the clutch spring must be compressed by inserting 4 specially slotted M8 screws.

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Once the screws are in, the clutch plate can be rotated anticlockwise and released. 

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The clutch plate and clutch can then be removed and inspected.

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Once the clutch is out, the flywheel can be seen. Its clear it is NOT standard Mercedes and is a custom lightweight flywheel made by Thielert. Later Continental CD155 models have a dual mass flywheel however these earlier engines have a conventional 'single mass' style. 

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The clutch spring itself is a giant Belleville washer. Not individual springs. Its marked with it KN setting which is important in the correct 'slippage' for the clutch.

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The clutch plate is conventional Sachs although it is marked with a TAE part number so perhaps the friction material is custom.

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Looking at the gearbox side it is a standalone PSRU with conventional spline to mate to the clutch plate.

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From the above dissembly, its clear that Thielert have customised the design of the drivetrain extensively to reduce weight and account for the high torque of their Diesel motor.   The PSRU design is unique in many ways and illustrates the difficulty of engineering a PSRU with a high torque engine. 

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