 The valve stem moves up and down inside the passage called a guide, which is fitted in the engine-block.the head of the valve called valve face, is generally ground to a 45-degree angle, so as to fit properly on the valve seat in the block and prevent leakage

The poppet valve is fundamentally different from slide and oscillating valves; instead of sliding or rocking over a seat to uncover a port, the poppet valve lifts from the seat with a movement perpendicular to the plane of the port.The main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication.