Explore topic-wise InterviewSolutions in .

The correct CHOICE is (d) ENGINE speed

To explain I would say: Metallic particle on INSULATOR tip, eroded electrode indicates that the plug as RUNNING overheated this may arise due to weak mixture, defective cooling system, loose-fitting causing the exhaust gases to leak.

Correct choice is (b) BURNING of fuel on the PLUG

The explanation is: The carbon deposits due to the burning of petrol on the spark plug are recognized by their black color and dry, fluffy nature. The main CAUSE for this is due to a defective fuel system delivering extra rich MIXTURE.

The correct option is (b) Contacts must CLOSE WITHOUT bounce

Easy explanation: The essential requirements of a good spark PLUG is to PROVIDE very high resistance to current leakage,gas tightness, resistance to corrosion, electrode temperature should be maintained between certain LIMITS.

The correct OPTION is (a) Semiconductor

Best explanation: SURFACE discharge plug is a special type of spark plug where the space between the plug ELECTRODES is filled with some semiconductor material. Thus the spark has to jump ACROSS this material instead of air in the ordinary plugs.

Right OPTION is (b) Twice the value of four-stroke

The best I can EXPLAIN: The frequency of firing in the two-stroke engine is twice the value for four-stroke engines. THEREFORE expected spark plug LIFE in a motorcycle with two-stroke engines is only half the life in case of CARS that always have four-stroke.

The correct choice is (a) Nickel

For EXPLANATION: The GROUND electrode is USUALLY FORMED of nickel or sometimes an alloy of nickel and manganese. The addition of manganese is about 2.5-3.5 percent which improves the tensile strength and the resistance to the SULFUR attack at high temperatures.

Correct choice is (b) 0.6-0.1

Easy explanation: The correct spark plug gap size is SPECIFIED by the manufacturers VARIES in general from 0.6 to 1millimeter. For the new spark plug, the gap is GENERALLY 0.6 millimeters, but with use it is increased, thus requiring higher VOLTAGE for the spark to JUMP across it.

The correct choice is (a) Low carbon steel

The best explanation: The BODY SHELL is generally made of low carbon steel. The body is FORMED by impact extrusion. The threads are cold rolled to provide a low friction profile. Porcelain was used initially for INSULATION, but this has a disadvantage of brittleness and low resistance.

The correct OPTION is (c) 3

The explanation: The battery winding consists of 200-300 turns of thick wire of TOTAL RESISTANCE about 3 ohms while the secondary is made up of a large number of turns about 15,000-20,000 of fine wire.

Correct option is (a) Prevents the hot gas from LEAKING

Easiest explanation: The body shell serves to HOUSE the electrodes and the insulator. A gas-tight seal is NECESSARY to PREVENT the hot gas from leaking between the insulator and the body shell and between the insulator and the center ELECTRODE.

Right answer is (b) Insulator tip

The best I can explain: The insulator nose length is the DISTANCE from the firing end of the insulator to the POINT where the insulator meets the metal SHELL. The insulator tip is the hottest part of the spark PLUG, which makes the tip TEMPERATURE, the main factor in pre-ignition and fouling.

The correct CHOICE is (a) ATTACK rate

For EXPLANATION: The ignition timing during acceleration should have a SUFFICIENT attack rate to keep up with the timing requirement. Attack rate is the maximum permissible NUMBER if degree per second, change which may be as high as possible in some high-performance engines.

Right answer is (b) 2

For EXPLANATION: In a COMPLETE vacuum control type there are two vacuum openings in the carburetor. One is at the venturi and the other one is just on the atmospheric SIDE of the THROTTLE when the same is closed.

Correct option is (d) Computerized ADVANCE CONTROL

To EXPLAIN: The computerized advance control uses a computer with memory, a timing map, which contains spark advance values for all combustion of speed, LOAD, and other conditions. Based upon the signals received from various sensors, the ECU SENDS the signal to the ignition coil at the precise moment indicated in the timing map.

Right option is (a) SPEED

The explanation: The centrifugal advance MECHANISM takes care of speed only and not the load conditions, which are looked after by the vacuum advance mechanism. Further, the vacuum advance is independent of centrifugal advance and this mechanism is when the engine is running under light load and moderate-high speed.

Correct answer is (d) RETURN spring

The best explanation: A return spring on the vacuum SIDE of the diaphragm keeps the advance UNIT at zero advance if no vacuum is applied as during IDLING. However, when the throttle is opened the vacuum is applied which moves the diaphragm against the return spring.

Right choice is (d) Carburetor

Easy explanation: In a vacuum advance TYPE one side of the DIAPHRAGM is open to the atmosphere while the other side is SUBJECTED to the vacuum from the carburetor. A return spring on the vacuum side of the diaphragm keeps the advance UNIT at zero advance if no vacuum is applied as during IDLING.

The correct option is (d) 34-38

The EXPLANATION: In general the crankshaft degree of ADVANCEMENT in a centrifugal advance type varies between 34 and 38 crankshaft degrees, including the initial TIMING,which is usually about 8-degree bottom dead center.

The correct choice is (a) 2

The explanation: The distributor shaft is ACTUALLY in TWO pieces connected through centrifugal ADVANCE arrangement, which consist of two centrifugal WEIGHTS. These weights are pinned and connected with the breaker PLATE using spring.

Right choice is (c) Nitrogen oxides (NOx)

To explain: Nitrogen oxides (NOx) emission increases with an increase in ignition advance. However, emission of CO is not much AFFECTED by ignition timing, rather the same is INFLUENCED by air/fuel RATIO. And there is very little EFFECT of ignition advance on hydrocarbon.

Right option is (c) ENTROPY

Explanation: The various factors affecting the ignition advance are the nature of fuel, ENGINE speed, load, engine temperature, compression ratio, engine COOLANT and intake air temperature, TURBO boost pressure. WHEREAS entropy has no role in the ignition advance.

Correct option is (B) Turbulence

Easy explanation: For engines with higher SPEED REQUIRES more IGNITION advancement but the turbulence increases with speed, which improves the RATE of combustion, requiring lesser advance. The net requirement, however, remains the increased advance at higher speed.

Right option is (a) High voltage

Easiest explanation: Used spark PLUGS MAY require a fairly higher voltage to fire than the new plugs because of the increase in the gap and rounding off of the center ELECTRODE. In a given engine the HIGHEST ignition voltage is required during part THROTTLE acceleration.

Correct option is (C) Paper

To explain I WOULD say: The distributor proper consist of a rotor and a cap, both of these are made of bakelite. APART from the bakelite, the other material used is alkyl PLASTIC phenol RESIN, fiberglass-reinforced polyester resin plastic.

Correct choice is (b) Condenser

The EXPLANATION: Condenser is a kind of plastic CONTAINER in which the energy due to the inertia of the current flowing during the CONTACT period is stored. The condenser ABSORBS EXCESS energy during the break period.

Right OPTION is (d) Contacts should open with fling

Easy explanation: The essential requirements of a good CONTACT BREAKER are the contact must open and close at the correct time, the contacts must close without bounce, the CORROSION of the points should be MINIMUM. Whereas the contacts must open without fling.

Right answer is (B) Negative

Explanation: The advantage of negative earth type is that comparatively less voltage is required for the electrons to JUMP from the central electrode which is HOTTER than the outer electrode. Further, the CENTER electrode is made negative CONCERNING the earth, thus the plug life is increased.

The correct option is (a) 0.35-0.45

For explanation: The contact breaker gap is between 0.35 to 0.45 MILLIMETERS. In CASE the gap is too small the points will not OPEN for the period which is sufficient for the coil to FUNCTION. This will cause the points to burn rapidly and the engine to misfire at all the speeds.

The CORRECT choice is (a) Ballast resistor

The explanation: When the engine is running at a SLOW speed, the CONTACT breaker POINT is closed for a comparatively longer period. This causes overheating of the induction coil. To avoid this a ballast RESISTANCE is inserted in the primary circuit of the coil.

Right CHOICE is (c) Paper

To explain I would say: The voltage difference between the adjacent turns is SMALL, only think insulation is required and enameled wire is used. However, there is sufficient voltage drop between the LAYERS and for this purpose, the paper is used for insulation.

Correct answer is (d) Step up the voltage

For EXPLANATION I would say: The ignition coil is simply a transformer with certain characteristics making it suitable for its special USE but impairing to some EXTENT its efficiency as a transformer. It serves to SET up the LOW battery voltage to high voltage.

Correct option is (d) ENGINE speed

Easy explanation: The voltage at which spark occurs is called breakdown voltage and it depends upon so many factors LIKE the GAP, polarity and condition of plug electrodes, condition of plug INSULATION, moisture on the distributor cap, and spark PLUGS.

The CORRECT option is (c) Breakdown voltage

Explanation: A battery of 12 VOLTS is generally preferred. However, a very high voltage surge of about 25,000 volts in modern engines for ignition PURPOSES. The actual high voltage at which the spark occurs is called the breakdown voltage.