Power Mechanics Paper 1 Questions and Answers - KCSE 2021 Past Papers

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SECTION A (40 marks)

Answer all the questions in this section in the spaces provided.

1. State one reason for studying power mechanics. (1 mark)
2. Outline six components of a marketing plan of a business plan. (3 marks)
1. List four contents of a first aid box. (2 marks)
2. Make a sketch of a double cut flat file. (2 marks)
1. Name four hydraulic tools used in a power mechanic workshop. (2 marks)
2. Identify four parts of a motor vehicle that are made of cast iron. (2 marks)
1. Explain the energy conversion processes that takes place in the braking system of a vehicle. (2 marks)
2. Explain two characteristics of wing nuts as locking devices. (2 marks)
1. State two functions of an air cleaner. (2 marks)
2. Identify four causes of low compression in a spark ignition single cylinder engine. (2 marks)
1. Outline four methods used in engine cooling systems. (2 marks)
2. Explain the term 'back flushing' with respect to engine cooling system. (2 marks)
1. State four desirable properties of a clutch centre plate lining material. (2 marks)
2. State three requirements that should be observed to achieve effective soft soldering. (3 marks)
1. Explain the function of the filler rod during gas welding. (2 mark)
2. Outline two essential practices observed when soft soldering in order to achieve high quality joints. (2 marks)
1. State two disadvantages of a riveted shoe lining over a bonded shoe lining. (2 marks)
2. State one function of tyre tread.(1 mark)
1. Explain one advantage of coil springs over leaf springs in vehicle suspension systems. (2 marks)
2. Explain the purpose of ball joints in the steering system. (2 marks)

SECTION B (60 marks)

Answer question 11 on the A3 paper provided and any other three questions from this section in the spaces provided.
Candidates are advised to spend not more than 25 minutes on question 11.

Figure 1 shows an isometric drawing of a bracket.
On the 43 paper provided, draw FULL SIZE, in first angle orthographic projection the following views:
1. Front Elevation in the direction of arrow W
2. End elevation in the direction of arrow X
3. Plan (15 marks)
Figure 2 shows a diagram of a multicylinder engine.
1. Identify the type of engine by:
  1. type of fuel used (1 mark)
  2. arrangement of the cylinders (1 mark)
  3. arrangement of the valves (1 mark)
2. Name the parts labelled A to F. (3 marks)
3. Explain the operation of the valve system of this engine. (9 marks)
1. State the meaning of the following designation on a tyre: 205/65R15/94T (5 marks)
2. Figure 3 shows a component of the suspension system.
  1. Name the component. (1⁄2 mark)
  2. Identify the parts labelled G, H, I, J and K. (2½ marks)
  3. Explain the operation of the component under each of the following road conditions:
    1. Pitch (5 marks)
    2. Bounce (2 marks)
1. Outline six regular maintenance checks carried out on water cooling systems. (3 marks)
2. With the aid of a labelled diagram, explain the operation of an impeller water pump. (12 marks)
1. 1. Differentiate between clutch slip and clutch judder. (4 marks)
  2. List five causes of clutch slip when the clutch is engaged. (5 marks)
2. Explain the term 'coupling point with respect to a torque convertor. (1 mark)
3. Outline five drive transmission conditions that can be achieved by the planetary gear set of an automatic gearbox. (5 marks)

MARKING SCHEME

1	To equip the power mechanics graduates with skills and attitudes for gainful employment. To make power mechanics graduates employers Acquisition of knowledge Informed consumer/producer Identification of business opportunities. (1x1 = 1mark) Customer analysis Competition analysis Market size and share analysis Pricing strategy Advertising and promotion strategy Distribution strategy Sales strategy Any 6 x 1⁄2 ( 3 marks)	(4marks)
2	Bandage Spirit Ant-septic Pain killers Scissors/razor blade Cotton wool Gloves Any 4 x 1⁄2 ( 2 marks) Sketch = 1 mark Double cut=1⁄2 mark Flat = 1⁄2 mark	(5 marks)
3	Hydraulic jack Bottle jack Cranes Car lifts Portable cranes Hydraulic press Any 4 x 1⁄2 = 2 marks) Piston Cylinder head Cylinder block Drum (brakes) Housing of slave cylinder Crankshaft (4x1⁄2 = 2 marks)	(4 marks)
4	Kinetic - hydraulic mechanical heat - mechanical - pneumatic 1⁄2 mark 1⁄2 mark 1⁄2 mark 1⁄2 mark can be easily rotated by hand it is used where frequent adjustment is required.	(4 marks)
5	To clean the air as it enters the engine To silence air movement To act as a flame trap Any 2 x 1 = (2 marks) Valve not closing Burnt valve or seat Compression rings broken Cylinder wall worn out Cylinder head warped Any 4 x 1 = (4 marks)	(6 marks)
6	Water cooled Air cooled Oil cooled Coolant cooled Hybrid cooled/combined Thermosiphon Pressured Any 4 x 1⁄2 (2 marks) It is the act of forcing pressurized water to pass through the outlet pipe of the radiator to dislodge the sediments inside the tubes. (2 marks)	(4marks)
7	high coefficient of friction good heat sink heat resistant no additional noise caused long life Any 4 x 1⁄2 (2 marks) surfaces to be joined must be thoroughly cleaned usage of the correct flux applying adequate heat using the correct type of solder cleaning the soldered surface to remove flux after soldering Any 3 x 1 = (3 marks)	(5 marks)
8	The filler rod provides additional metal in completing the welding, because the composition of filler metal is the same as that of the metals to be welded. surfaces to be joined must be thoroughly cleaned usage of the correct flux applying adequate heat using the correct type of solder cleaning the soldered surface to remove flux after soldering Any 2x 1 = (2 marks)	(4 marks)
9	less friction surface as a result of the riveting nail holes (1 mark) they may not wear further than to the depth of the rivet (1 mark) the rivets can score the drum weaker joint Any 2 x 1 = (2 marks) Gives tyre a good road grip Discharge water and dirt Cool the tyre Any 2 x 1 = (2 marks)	(4 marks)
10	energy stored per unit volume is almost double than that of leaf spring there is no noise problem because it is one unit unlike the leaf spring that has several leaves and bushes that wear. Any 1 x 2= (2 marks) It allows both angular and rotational movement between steering linkages. (2 marks)	(4 marks)
11	Marks distribution Front elevation 4 faces x 1 4 marks 1 semicircle 1⁄2 marks Subtotal 41⁄2 marks End elevation 3 faces x 1 3 marks 2 hidden details (2 x 1⁄2) 1 marks Subtotal..... 4 marks Plan 4 faces x 1 4 marks 4 hidden details (4x½) 2 marks Subtotal.................. 6 marks Correct elevation 1⁄2 mark Total (15 marks)	(15marks)
12	Diesel (1 mark) Vertical inline (1 mark) Overhead camshaft (1 mark) A. Camshaft B. Piston C. Injector nozzle D. Injector pump E. Sump F. Timing belt Any 6 x 1⁄2 (3 marks) As the engine run, crankshaft drives camshaft through the timing chain (1) When the camlobe is in upright position, it pushes the pushrod upwards (1) The pushrod, through the tappet (1), pushes the rocker arm (1) Since the rocker arm is pivoted about the rocker shaft, it compresses the valve sprint (1) and pushes the valve downwards to open it (1) When the cam rotates to the horizontal position, the valve spring the systemin releases pressure and relaxes (1), releasing pressure on the system and allowing the valve to assume its closed (1) position	(6 marks)
13	2.05: This is the width of tyre (1 mark) 65: It's the height/width ratio (1 mark) R: Radial tyre (1 mark) 15: Diameter of tyre in inches (1 mark) 94T: 94 load index T = Speed Code (1 mark) Subtotal (5 marks) Hydrolastic displacer unit 1⁄2 mark G - damper valve 6 H - rubber diaphragm 8 I - rubber spring 2 J - tampered piston 5 K - interconnecting pipe 2½marks Pitch When the vehicle experiences a sudden upward movement of the front wheel it causes the diaphragm to displace the fluid through the damper (1) This forces fluid along the pipe (1) to the rear unit where it will move the diaphragm and raise the rear unit of the car to (1) the level of the front. When the front wheel descends, the fluid is returned and the vehicle settles back to its normal riding position (1). During this sequence, the fluid has to pass the damper valve in each unit, so restriction to fluid flow at the valves and in the pipeline damps out any pitch oscillation tendency (1) Bounce When the vehicle bounces it causes the four wheels to deflect at the same time (1) All the hydraulic units will then perform at the same time similarly to the outer units by stiffening the system (1)
14	Top up with soft water only Check the water level Examine the rubber hoses and replace if they are dry and cracked Check the tightness of the clips Check all joints and pipes for leaks and renew if in poor state Check the thermostat and radiator pressure cap for proper operation Any 6 x 1⁄2-3 marks Drawing 6 main parts = 6 x ½ = 3 Labelling 6 parts = 6 x 1⁄2 = 3 Operation The impeller is rotated by the pulley when the engine starts (1) Water which is at the centre of the impeller is impelled along the blades by the centrifugal force (1) The water is then thrown off the edge of the impeller and directed to the outlet by the casing (1) The centre of the impeller that has low pressure is refilled with the water displaced from the radiator (1). Circulation continues as long as the impeller is rotated. If the thermostat valve is closed, the water leaving the pump is returned to the pump inlet through an internal or external bypass (1) (12 marks)
15	Clutch slip - refers to the tendency of the clutch to slip or spin, especially when accelerating. It generates a lot of heat and wear of clutch disk facing. (2 marks) Clutch judder - refers to the tendency of the clutch to grab or when engaged and release sporadically Causes of clutch slip while engaged. Incorrect pedal adjustment Broken or weak pressure linkages Broken engine mount Worn friction disc linings Warped clutch disk Oil/grease on lining Any 5 x 1 = 5 marks Coupling point - refers to when the turbine is turning nearly at the same speed as the pump. Increase speed and decrease torque (overdrive) Decrease speed and increase torque (reduction) Reverse the direction of rotation (reverse) Act as a solid shaft (direct drive) Disconnect the driving shaft from the driven shaft (neutral) Any 5 x 1 (5 marks)	14 marks