This Hirobo HI0404639 counter gear is an RC-scale replacement part intended for use in pipe drive setups on Eagle-family rotorcraft. The component serves as an intermediate gear in the transmission path, transferring rotation between the pipe drive assembly and the main gearbox elements while remaining within model-scale tolerances.
Compatibility is defined by the part's intended placement in Eagle, Freya, EX and SX platform variants, making it suitable as a service or spare part when the original counter gear shows wear. The 18T designation denotes the tooth count used to match gear mesh and center distances in the pipe drive arrangement.
Installation notes: fit the gear to the counter shaft ensuring correct seating and axial alignment, verify engagement with the mating spur or intermediate gears, and restore any retaining hardware to factory torque where applicable. When replacing this gear, check adjacent bearings and shafts for play that could accelerate tooth wear.
Tuning and maintenance: set gear mesh to a light but full contact pattern to avoid premature wear, inspect tooth faces for chipping after hard landings, and keep lubrication appropriate for model-scale gear trains. Regular inspection and prompt replacement of a worn counter gear help preserve drivetrain efficiency and minimise vibration in flight.
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