Definition of tappet in US English:



  • A lever or projecting part on a machine that intermittently makes contact with a cam or other part so as to give or receive motion.

    • ‘Contact between the cams and the tappets in the valve train span the mixed and boundary regions.’
    • ‘Very small roller cam followers are installed in the cylinder head to operate the valves instead of the conventional bucket-type tappets, and here friction is cut by about 70 per cent.’
    • ‘The barrier valve furthermore has a tappet, which engages the support body and is movable relative to the armature and carries a closing body of a seat valve.’
    • ‘The 16-valve has twin, chain-driven, overhead camshafts and hydraulic tappets, while the 8-valve format uses a single camshaft.’
    • ‘The real breakthrough in lifter design for street and moderate competition applications was the marriage of roller tappets with hydraulic lifters.’


Mid 18th century: apparently an irregular diminutive of tap.