69) The auto ignition in a spark ignition engine means

automatic ignition of the charge at the end of compression

ignition induced by the passage of a spark

ignition of the charge before the passage of flame front

ignition induced to supplement the process of normal combustion

Answer is:

ignition of the charge before the passage of flame front

Explanation:

Auto ignition is defined as the self-ignition of the vapors emitted by a liquid heated above its ignition temperature.

The auto ignition in a spark ignition engine means

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70) It is necessary to maintain the valve clearance as they

reduce the resistance to sliding that occurs between the cam and the tappet.

allow for lengthening of the valve owing to the heat of combustion

increase the speed at which the valves move up and down

make the crankshaft turn smoothly

Answer is:

allow for lengthening of the valve owing to the heat of combustion

Explanation:

It is necessary to maintain the valve clearance as they allow for lengthening of the valve owing to the heat of combustion.

71) If the valve clearances are excessively large, the problem that can arise is

overheating of the engine

incomplete valve closure

fouling of spark plug by gasoline

none of these

Answer is:

incomplete valve closure

72) The valve tappet clearance is measured by

screw pitch gauge

engineering scale

feeler gauge

vernier caliper

Answer is:

feeler gauge

Explanation:

Feeler gauges are used:
– To check the gap between the mating parts
– To check and set the spark plug gaps
– To set the clearance between the fixture (setting block) and the cutter/tool for machining the jobs
– To check and measure the bearing clearance, and for many other purposes where a specified clearance must be maintained.