KCSE Past Papers 2017 Power Mechanics Paper 1

2. (a) Ensure the plug is properly and safely connected to the tool.

Scale length = Representative fraction x Maximum reading 1/5x 800 = l60mm 1/5 x 800 = l60mm

3. (a) Cleaning tools

(b) i. Grub screw

Often used with keys to prevent a pulley from moving along a shaft.

ii. Pal nut

Is a single threaded nut used lock another nut to prevent it from working loose.

4. (a) i. Tungsten — increases hardness

ii. Chromium — increases strength and hardness (b)b)

Wipers - (Motor)

5. (a)Undersquare engine

Is one where the bore is smaller than the stroke. Therefore the piston travels longer distance per minute to cover a stroke, and thus travels at a higher speed to cover a given RPM.

Oversquare engine

Is one where the bore is larger than the stroke. Therefore, the piston travels a shorter distance per minute to cover a stroke, and thus travels at a lower speed to cover a given RPM.

(b) Causes of cylinder wall wear (2 marks)

Abrasive material from lubricating oil.

6. (a) Battery Radiator Air cleaner Start motor Bell housing

(b) Levers and cables Belts and pulleys Wheels and pulleys Chairs and sprockets Gears Clutches

7. (a) 1. Inlet valve lead

This early opening gives as long as possible time for the intake of fresh charge into the cylinder.

2. Exhaust valve lag

Gives adequate time for the exhaust gases to be cleared from the cylinder.

(b)

8.

(b) i. Castor angle

Is the tilt of the spindle pivot towards the front or the rear of the vehicle from the vertical axis.

ii. It plays an important role in self—centering of the wheels after cornering.

9. (a) Flat base — two piece rim. Flat base divided rim.

Flat base — three piece rim. Semi-drop center rim

(b) i. Backfiring during welding procedures refers to when the flame goes out, producing a loud snapping or popping noise at the nozzle.

10. (a)

(b)

11.

B — Filler cap

C — Water pump/cylinder wall

D — Fan

E — Thermostat

F — Temperature gauge

G — Upper water gallery

H — Water jacket

(b) Operation

When the car starts, the engine is cold and the thermostat shuts off the flow of water to the radiator(1).

Since the water is confined to flow within the engine, it heats quickly as the engine runs hot.

When water reaches a pre-determined temperature, the thermostat opens, allowing free flow of coolant.(')

The hot water leaves the engine through the upper hose to the radia- tor 1).

In the radiator, it passes through the radiator core tubes, which are surrounded by cooling fins,(')through which air is drawn inwards by the low pressure vacuum(' created by the revolving fan(' .

This air cools the hot water as it passes down the radiator core(1).

The cooled water is then drawn into the engine by the water pump ') through the radiator return pipe()1 into the water jackets surrounding(' the cylinders to cool the engine block.

When there is excessive pressure build up in the system, the radiator cup equalizes the internal system pressure with the atmospheric pressure.'

13. (a)

(b) Operational differences between 2 — stroke and 4 stroke cycle engines 2 Stroke 4 Stroke

The uneven expansion and contraction caused by local heating often makes it to crack. This fault is due to the fact that most cast irons are normally in cast forms.

i. Engine stalls after idling or slow speed driving

and High carburetor float level

i. Engine backfires

When the push button is pressed, current flows through the contact points to the electromagnetic coil.

The coil gets energized(1 and attracts the armature,') which moves together with the diaphragm ')which is attached to it. When the armature is attracted, the contact points open, )1 breaking the flow of current.

The coil is the de-energized, thus making armature to be released, 1 And to move back closing the points to start the procedure again.

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