Switchable Tappets

The switchable tappets are installed on the intake valves, in bores in the cylinder heads. The cylinder heads incorporate engine oil galleries along the inboard and outboard sides of the bores. The inboard oil galleries (between the tappets and the spark plug/fuel injector bores) supply an oil feed to the locking pins in the switchable tappets. The outboard oil galleries (over the inlet ports) supply an oil feed to the hydraulic lash adjusters in the switchable tappets.

Each switchable tappet consists of inner and outer tappets, which can operate independently or be locked together by locking pins. A hydraulic lash adjuster on the bottom of the inner tappet locates on the intake valve stem.

In low lift, the intake valve lift is controlled by the inner tappets, which run on the center lobes of the intake camshafts. The outer tappets run on the outer lobes of the intake camshafts, and move up and down the inner tappets without affecting the valve lift. The lost motion springs keep the outer tappets in contact with the outer lobes. Movement of the inner tappets is transferred to the intake valves through the hydraulic lash adjusters.

In high lift, engine oil is supplied to the locking pins, which lock the outer tappets to the inner tappets. Intake valve lift is controlled by the outer tappets, which run on the outer lobes of the intake camshafts. Movement of the outer tappets is transferred to the intake valves through the locking pins, the inner tappets and the hydraulic lash adjusters.