A cylindrical engine component that rides directly on the camshaft lobes to actuate the valvetrain. As the cam rotates, the tappet lifts, pushing against a pushrod or directly against the valve stem to open the intake or exhaust valves. When clearance tolerances wear out, they produce a distinct ticking noise.
I can hear a loud tick from the top end, so we probably need to adjust the tappets.
Hydraulic tappets use engine oil pressure to maintain zero clearance and eliminate the need for manual adjustment, whereas solid tappets require regular mechanical gapping with feeler gauges.
Also heard as
- cam follower
- lifter
- valve lifter
Related terms
Pushrod
A metal rod that transfers motion from the camshaft to the rocker arms in overhead valve engines.
Rocker arm
A pivoting lever in a valvetrain that transfers cam or pushrod motion to open a valve.
Overhead valve
An engine design where the intake and exhaust valves sit in the cylinder head above the combustion chamber.