Auto Mechanics Paper 2,May/June 2011
 Questions: 1 2 3 4 5 Main
Weakness/Remedies
Strength

Question 2

The data of engine valve timing is as follows:

-               inlet valve opens 6' before top dead centre;

-               inlet valve closes 35' after bottom dead centre;

-               exhaust valve opens 38' before bottom dead centre;

-               exhaust valve closes 5' after top dead centre.

Draw the valve timing diagram.

(b)    Calculate:
(i)    The overlap;
(ii)   The total period the inlet valve remained closed after bottom dead centre;
(iii)   The total period the exhaust valve was opened during the operation.

&nb
OBSERVATION

Most of the candidates who attempted this question did not draw the valve timing diagram. Some who drew it did not use the required instrument. Only one centre performed well throughout the country. The correct diagram is shown below.

Part (b) of the question was not also well answered by the candidates. The required working statement for each is as follows;
(b)(i)   Valve overlap =6' +5'= 11'.
(ii) Total period the inlet valve remained closed after bottom dead centre
=360' _  (6'+180'+35')
=360' _ 221'
=139'.
(b) (ii) Total period the exhaust valve was opened during the operation = 38' + 180' +5'
= 223'