Thieves stole the face, hands and pendulum of a Victorian station clock worth more than £5,000.
The clock, which dates from the 1860s, was originally from the high level station in East Grinstead.
It had hung on platform one at the Bluebell Railway's Sheffield Park station since the early Sixties.
In Thursday night's theft, all the inner workings were taken, leaving only the case which was firmly attached to the wall.
The distinctive face had the letters LBSCR inscribed on it, standing for London, Brighton and South Coast Railway.
Bluebell curator John Potter said: "Railway clocks have assumed astronomical value."
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