Observation

Most candidates did not attempt this question. It is of the opinion that they either found it hard or simply found other questions easier. Notwithstanding, the candidates that attempted the question did it satisfactorily. The solutions of the question are given below.

Solution

(A) The Importance of Valve Clearance

Valve clearance is provided to ensure the complete closure of the valve. It also enhances the expansion of valve stem and the effectiveness of pushrod and rocker arm.
It also ensures good engine performance and efficiency in power generation.

(B)

Induction
Inlet valve opens and exhaust valve closes. The piston moves down the cylinder and the mixture is admitted into the combustion chamber.

Compression
The two valves close while the piston moves up to compress the mixture in the cylinder.

Power
At this stage, the piston is at TDC, with both valves closed. The spark plug fires, causing burning and subsequent gas expansion that pushes the piston down the cylinder.

Exhaust
Exhaust valve opens and piston moves up the cylinder to expel the burnt gases.