I85PREP
⌘ K
Maharashtra HSC Scooter & Motorcycle Servicing (Bifocal) study materials
Maharashtra HSC Scooter & Motorcycle Servicing (Bifocal) study resources

Maharashtra HSC Scooter & Motorcycle Servicing (Bifocal) practice questions

One question at a time. Build your Maharashtra HSC Scooter & Motorcycle Servicing (Bifocal) understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Workshop safety, hand tools, special tools, and measuring instruments

While using a pedestal grinder to sharpen a tool in a two-wheeler workshop, which personal protective item is most important for the eyes?

  1. Cotton hand gloves
  2. Safety goggles Correct answer.
  3. Ear plugs
  4. Leather apron

Explanation

Safety goggles with side protection shield the eyes from flying abrasive particles and metal chips produced by the grinding wheel. Other PPE items protect different parts of the body and do not prevent eye injury. Eye protection must be worn even for a short grinding job.

Question 2Workshop safety, hand tools, special tools, and measuring instruments

A lead-acid battery is being charged in the workshop. Which gas is released that can form an explosive mixture and must be kept away from sparks or flames?

  1. Oxygen
  2. Hydrogen Correct answer.
  3. Nitrogen
  4. Carbon dioxide

Explanation

During charging, a lead-acid battery electrolyses water and releases hydrogen, which is flammable and can accumulate in an enclosed space. The charging area must therefore be ventilated and free of naked flames or sparks. Oxygen is also released, but hydrogen is the gas chiefly associated with the explosive hazard.

Question 3Workshop safety, hand tools, special tools, and measuring instruments

Which spanner has a closed, multi-point head that surrounds all six flats of a nut and is preferred where access allows?

  1. Ring spanner Correct answer.
  2. Adjustable spanner
  3. Pipe wrench
  4. Open-end spanner

Explanation

A ring spanner grips all six corners of a hexagonal nut, so the load is spread and the risk of rounding the nut is reduced. An open-end spanner contacts only two flats, while an adjustable spanner can slip if it is not snug. A pipe wrench is intended for pipes and will damage a finished nut.

Question 4Workshop safety, hand tools, special tools, and measuring instruments

When tightening a cylinder-head nut to the specified torque with a click-type torque wrench, what is the correct practice?

  1. Lubricate the threads with any oil available to reduce friction
  2. Use the torque wrench as a breaker bar to loosen the nut first
  3. Apply a steady pull until the wrench clicks, then stop Correct answer.
  4. Set the wrench to the highest scale and estimate the click

Explanation

A click-type torque wrench signals when the set torque is reached, so the operator should pull steadily and stop at the click to avoid over-tightening. It should not be used for loosening because this can damage the internal mechanism. Thread lubrication must follow the manufacturer's specification, since friction changes the actual clamp load.

Question 5Workshop safety, hand tools, special tools, and measuring instruments

The jaws of a metric vernier caliper are closed and the vernier zero lies 0.04 mm to the right of the main-scale zero. The caliper is then used to measure a part and the observed reading is 12.36 mm. What is the corrected measurement?

  1. 12.32 mm Correct answer.
  2. 12.36 mm
  3. 12.44 mm
  4. 12.40 mm

Explanation

When the vernier zero lies to the right of the main-scale zero with the jaws closed, the zero error is positive. A positive zero error is subtracted from the observed reading. Therefore the corrected reading is 12.36 − 0.04 = 12.32 mm.

Question 6Workshop safety, hand tools, special tools, and measuring instruments

A metric outside micrometer has a spindle pitch of 0.5 mm and a thimble with 50 equal divisions. The barrel shows 7.5 mm and the thimble division on the reference line is 24. What is the reading?

  1. 7.50 mm
  2. 7.74 mm Correct answer.
  3. 7.24 mm
  4. 7.98 mm

Explanation

The least count is pitch divided by thimble divisions, so 0.5 ÷ 50 = 0.01 mm. The thimble contributes 24 × 0.01 = 0.24 mm. Adding this to the barrel reading gives 7.50 + 0.24 = 7.74 mm.

Question 7Workshop safety, hand tools, special tools, and measuring instruments

To check the tappet clearance of a four-stroke motorcycle engine with a specified clearance of 0.10 mm, which measuring tool is most suitable?

  1. Feeler gauge Correct answer.
  2. Vernier caliper
  3. Outside micrometer
  4. Dial bore gauge

Explanation

A feeler gauge is a set of thin blades of known thickness that is inserted between the rocker and valve stem to check tappet clearance. The specified blade should pass with a slight drag while the next size should not enter. Vernier calipers and micrometers measure external dimensions, and a bore gauge measures internal diameters.

Question 8Workshop safety, hand tools, special tools, and measuring instruments

A sealed ball bearing is pressed into a motorcycle wheel hub and only the inner race is accessible from the back. Which special tool is most suitable for removing it without damaging the hub?

  1. Flat screwdriver and mallet
  2. Bench vice and hammer
  3. Blind bearing puller Correct answer.
  4. Cold chisel and punch

Explanation

A blind bearing puller expands inside the bearing so it can be pulled out when the outer face is not accessible. A slide hammer is commonly attached to provide the extraction force. Hammering with a screwdriver, chisel or punch can damage the bearing seat and the hub.

Question 9Workshop safety, hand tools, special tools, and measuring instruments

To measure lateral runout of a motorcycle front brake disc, which setup is correct?

  1. Vernier caliper held against the disc edge while the wheel is rotated by hand
  2. Steel rule placed across the disc and gap checked with a feeler gauge while locked
  3. Dial indicator on magnetic base, plunger perpendicular to disc, wheel rotated Correct answer.
  4. Micrometer used on the disc thickness while the wheel is spinning

Explanation

A dial indicator continuously shows small changes in position as the disc rotates, so it is the correct instrument for runout. The magnetic base holds the indicator steady, and the plunger must contact the disc surface perpendicular to it. A caliper, micrometer or steel rule does not give a continuous runout reading during rotation.

Question 10Workshop safety, hand tools, special tools, and measuring instruments

When checking the primary winding resistance of a motorcycle ignition coil with a digital multimeter, which condition gives a valid measurement?

  1. Engine cranking while the meter is set to AC volts across the connected coil
  2. Engine running and coil connected to the ignition circuit
  3. Ignition off, coil disconnected, meter set to the lowest ohms range Correct answer.
  4. Ignition on, meter set to DC volts, coil connected

Explanation

Resistance must be measured with the component isolated and no power applied, otherwise the meter reading is affected by parallel circuits or the meter itself may be damaged. The ignition should be off, the coil disconnected and the meter set to the lowest suitable ohms range. The meter's own small test current then gives the coil resistance directly.

Question 11Workshop safety, hand tools, special tools, and measuring instruments

A small petrol spill near a motorcycle fuel tank catches fire in the workshop. Which immediate action is correct?

  1. Use a CO2 or dry-powder extinguisher Correct answer.
  2. Play a water hose jet onto the flames
  3. Throw dry cotton waste over the flames
  4. Blow the flames away with the air line

Explanation

Petrol is a Class B flammable-liquid fire, and a water jet can spread the burning fuel instead of putting it out. A CO2 or dry-powder extinguisher smothers the flames by excluding oxygen, which is the correct first action for a small spill fire. Compressed air would supply oxygen and scatter the fire, while dry cotton waste is itself flammable.

Question 12Workshop safety, hand tools, special tools, and measuring instruments

Which hand tool is designed specifically to remove and refit the circlip that retains a bearing in a motorcycle gearbox?

  1. Long-nose pliers
  2. Side-cutting pliers
  3. Adjustable mole wrench
  4. Circlip pliers Correct answer.

Explanation

Circlip pliers have small hardened tips that engage the lug holes of an internal or external circlip so it can be compressed or expanded without distortion. Long-nose pliers may grip the clip but often slip and damage the lugs or the gearbox bore. Side-cutting pliers are for cutting wire, and a mole wrench does not fit circlip lugs.

Question 13Workshop safety, hand tools, special tools, and measuring instruments

Which instrument is most suitable for measuring a motorcycle cylinder bore to detect wear and taper to within 0.01 mm?

  1. Steel rule
  2. Outside micrometer
  3. Dial bore gauge Correct answer.
  4. Feeler gauge

Explanation

A dial bore gauge is set with an outside micrometer and then used inside the bore, so it shows small changes in diameter directly on its dial. An outside micrometer cannot enter the bore, a feeler gauge measures gaps rather than diameters, and a steel rule has far too coarse a scale. With practice the bore gauge can resolve 0.01 mm wear and taper readings.

Question 14Workshop safety, hand tools, special tools, and measuring instruments

A motorcycle has been raised on a hydraulic jack for rear wheel removal. What is the correct safety practice before the mechanic reaches under the machine?

  1. Ask a helper to hold the handlebars steady
  2. Leave the jack handle in the raised position
  3. Place rigid axle stands under the frame Correct answer.
  4. Lower the jack until the tyre just touches the floor

Explanation

A hydraulic jack can creep or lose pressure, so it must never be the only support while anyone works underneath. Rigid axle stands placed under a strong frame or swingarm point give positive mechanical support. A helper holding the handlebars does not prevent the machine dropping, and lowering the jack or relying on the handle position does not remove the crush hazard.

Question 15Workshop safety, hand tools, special tools, and measuring instruments

How should a click-type torque wrench be stored after a cylinder-head tightening job?

  1. Coat the scale with oil and store it with a socket fitted
  2. Set the scale to maximum to keep the spring compressed
  3. Leave it at the last tightening value and hang it up
  4. Set the scale to its lowest setting before storing Correct answer.

Explanation

A click-type wrench uses an internal spring, and leaving it compressed at a high setting causes the spring to take a set that spoils calibration. The correct practice is to wipe the tool clean, set it to the lowest scale value and store it in its case. Leaving it at the working torque, hanging it up, or oiling the scale can all disturb accuracy or attract dirt.

Question 16Workshop safety, hand tools, special tools, and measuring instruments

A motorcycle flywheel is to be separated from the tapered end of the crankshaft. Which special tool is used for this job?

  1. Valve spring compressor
  2. Clutch holding tool
  3. Bearing puller
  4. Flywheel puller Correct answer.

Explanation

A flywheel puller screws into or bolts onto the flywheel and uses a hardened centre screw to push the flywheel off the crankshaft taper without levering on the crankcases. A bearing puller has arms for bearings, a valve spring compressor works on cylinder-head springs, and a clutch holding tool locks the clutch but does not pull the flywheel. Using a general puller or a hammer can bend the crankshaft.

Question 17Workshop safety, hand tools, special tools, and measuring instruments

During an engine overhaul, which method is used to check the big-end bearing clearance of a motorcycle connecting rod?

  1. Read the clearance with a dial indicator on the piston crown
  2. Insert a feeler gauge between the rod and the crank web
  3. Use plastigauge between the bearing and the crankpin Correct answer.
  4. Measure the rod length with a vernier caliper

Explanation

Plastigauge is a soft plastic strip placed on the crankpin; when the rod is assembled and tightened to specification, the strip is crushed and its width is compared with a scale to give the bearing clearance. A feeler gauge cannot reach the big-end bearing, a vernier caliper measures external length rather than oil clearance, and a dial indicator on the piston does not read bearing clearance.

Question 18Workshop safety, hand tools, special tools, and measuring instruments

A taper-fitted component on a motorcycle is to be separated without damaging its soft alloy surface. Which tool is appropriate?

  1. Centre punch
  2. Steel cold chisel
  3. Hammer used directly on the alloy
  4. Brass drift Correct answer.

Explanation

A brass drift is softer than steel and is used with a hammer to transmit shock to the taper without cutting or peening the alloy surface. A cold chisel or centre punch is hardened and will dig into and damage the component. Striking the alloy directly with a hammer can crack or deform it.

Question 19Workshop safety, hand tools, special tools, and measuring instruments

Before electric welding a patch onto a motorcycle petrol tank, which preparation is essential for safety?

  1. Wash only the outside of the tank with soapy water
  2. Close the fuel cap tightly and weld in a well-ventilated area
  3. Fill the tank completely with petrol and keep the cap open
  4. Drain the fuel and purge the tank with water or an inert gas Correct answer.

Explanation

Even an apparently empty tank can hold explosive petrol vapour, so the tank must be drained and purged with water or an inert gas before any heat is applied. Welding a tank that still contains fuel or vapour can cause an explosion. External washing alone leaves vapour inside, and keeping petrol in the tank or sealing the cap does not remove the hazard.

Question 20Workshop safety, hand tools, special tools, and measuring instruments

A dial bore gauge is being used to check a motorcycle cylinder for wear. How is taper measured correctly?

  1. Take one reading at mid-stroke and call it the taper value
  2. Measure the bore with a vernier caliper and subtract the ring gap
  3. Take one reading at the top and compare it with the piston
  4. Measure at several heights in two directions and compare Correct answer.

Explanation

Cylinder taper is found by measuring the bore at several heights and in two directions at right angles, then comparing the largest and smallest readings. A single reading at the top or mid-stroke cannot show taper, and comparing with piston diameter checks clearance rather than bore shape. Vernier caliper readings are too coarse, and ring end gap does not measure bore taper.

Question 21Workshop safety, hand tools, special tools, and measuring instruments

A two-wheeler mechanic is about to use a cold chisel whose struck end has spread into a mushroom-shaped lip. What is the correct workshop practice?

  1. Hold the chisel with pliers and continue until the lip breaks off.
  2. Strike the mushroomed end with a larger hammer to flatten it.
  3. Use the chisel as it is, provided heavy leather gloves are worn.
  4. Dress the mushroomed end on a bench grinder to restore a slight chamfer before use. Correct answer.

Explanation

A mushroomed head can spall and send sharp metal fragments toward the user or bystanders. The safe practice is to grind the head back to the original contour with a slight chamfer, then check the cutting edge and handle. Gloves do not protect against flying chips, and continuing to use the chisel risks injury.

Question 22Workshop safety, hand tools, special tools, and measuring instruments

A mechanic uses a click-type torque wrench with a crows-foot extension fitted at 90° to the wrench handle to tighten a motorcycle engine mounting nut to 40 N·m. How should the wrench be set?

  1. Set it to 40 N·m, because a crows-foot at 90° does not change the effective lever length. Correct answer.
  2. Set it above 40 N·m, because the extension absorbs part of the applied torque.
  3. Set it below 40 N·m, because the crows-foot increases the lever length.
  4. Set it to 40 N·m only if the crows-foot is shorter than 50 mm; otherwise recalculate.

Explanation

Torque is force multiplied by the perpendicular distance from the fastener axis. With the crows-foot at 90° to the wrench handle, the added length is perpendicular to the applied force and does not increase the lever arm, so the wrench setting stays at 40 N·m. Correction is needed when the extension lies along the handle and increases effective length.

Question 23Workshop safety, hand tools, special tools, and measuring instruments

A steel stud has broken off flush with the surface of an aluminium motorcycle engine casing. The threads are not seized. Which removal method is correct?

  1. Weld a large nut to the casing around the stud and turn the nut.
  2. Grip the flush end with locking pliers and twist it anticlockwise.
  3. Centre-punch the stud, drill a pilot hole, and use a screw extractor. Correct answer.
  4. Cut a slot in the stud with a chisel and turn it with a flat screwdriver.

Explanation

A screw extractor is designed to grip the inside of a drilled pilot hole and turn the broken stud out without crushing the surrounding thread. The hole must be centred and drilled smaller than the stud's minor diameter, and penetrating oil can help. This avoids damaging the aluminium casing.

Question 24Workshop safety, hand tools, special tools, and measuring instruments

A motorcycle cylinder bore is checked with a dial bore gauge at several levels. At one level the gauge, zeroed on a 54.00 mm setting ring, reads +0.06 mm in the thrust direction and +0.02 mm in the axial direction. Which conclusion is correct?

  1. The cylinder out-of-round at that level is 0.08 mm.
  2. The cylinder taper at that level is 0.04 mm.
  3. The cylinder out-of-round at that level is 0.04 mm and must be compared with the service limit. Correct answer.
  4. The piston-to-bore clearance is 0.06 mm, so the bore is serviceable.

Explanation

Out-of-round, or ovality, is the difference between the largest and smallest diameters measured at the same bore level and in perpendicular directions. Here 0.06 mm minus 0.02 mm gives 0.04 mm, so the reading shows ovality, not taper. Taper is found by comparing sizes at different levels along the bore, and clearance requires the actual piston diameter.

Question 25Two-wheeler engine construction, operation, lubrication, and cooling

In a small two-stroke scooter engine, the lubricating oil is mixed with the petrol before the mixture enters the engine. What is the main reason for this arrangement?

  1. Oil is needed mainly to cool the spark plug and piston crown
  2. The crankcase has no oil sump to draw from Correct answer.
  3. Petrol thins the oil so that it burns without smoke
  4. A separate oil pump cannot be fitted to a two-stroke engine

Explanation

In a two-stroke engine the crankcase is part of the induction and scavenging path, so it cannot hold a standing body of oil that a pump could pick up. The lubricant must therefore be carried with the fuel-air charge, either as a petrol-oil premix or through an oil-injection system that feeds into the intake, so that it reaches the main bearings, big-end bearing and cylinder wall as a mist. After doing its work the oil passes out with the exhaust, which is why two-stroke oils are blended to burn cleanly and leave little deposit.

Question 26Two-wheeler engine construction, operation, lubrication, and cooling

Air-cooled two-wheeler cylinders are cast with thin fins around the barrel and head. What is the purpose of these fins?

  1. They guide the piston and keep it square in the bore
  2. They stiffen the barrel so that piston slap is reduced
  3. They trap a layer of hot gas that insulates the barrel
  4. They increase the surface area for heat transfer to air Correct answer.

Explanation

Cooling fins work by conduction followed by convection: heat flows from the hot metal into the fin, and the fin's large exposed area gives the surrounding air more surface from which to carry that heat away. The thinner and more closely spaced the fins, the greater the area, provided air can actually flow between them without the gaps choking. Fins play no part in locating the piston or in controlling piston slap.

Question 27Two-wheeler engine construction, operation, lubrication, and cooling

In a four-stroke motorcycle engine, in which stroke are both valves closed, the charge being compressed, and the spark occurring near the end of the stroke?

  1. Exhaust stroke
  2. Intake stroke
  3. Power stroke
  4. Compression stroke Correct answer.

Explanation

During the compression stroke the piston rises from bottom dead centre with both the intake and exhaust valves held shut, squeezing the trapped charge into the combustion chamber. The spark is timed to occur slightly before the piston reaches top dead centre, so ignition takes place near the end of this stroke. In the power stroke that follows, both valves also remain closed, but combustion has already begun, so the spark does not occur near its end.

Question 28Two-wheeler engine construction, operation, lubrication, and cooling

A mechanic sets the tappet clearance on a four-stroke engine much smaller than the manufacturer's specification. What is the most likely consequence?

  1. Ignition timing retards as the cam chain slackens
  2. Tappet noise increases because the gap has become too wide
  3. Valve lift increases and volumetric efficiency rises
  4. The valve cannot seat fully and compression leaks Correct answer.

Explanation

Tappet clearance allows for the expansion of the valve stem and the rest of the valve train as the engine reaches working temperature. If the gap is set too small, the valve is held slightly off its seat once the parts expand, so hot gases escape past the valve face during firing. This causes loss of compression, rough idling and eventually burning or warping of the valve and seat.

Question 29Two-wheeler engine construction, operation, lubrication, and cooling

In a piston-ported two-stroke engine, how is the timing of the transfer port related to the exhaust port?

  1. The transfer port opens after the exhaust port and closes before it Correct answer.
  2. The transfer port opens before the exhaust port and closes after it
  3. The transfer port opens only after the piston passes bottom dead centre
  4. Both ports open and close at exactly the same instant

Explanation

As the piston descends, the exhaust port is uncovered first, so the burnt gases blow down and cylinder pressure falls. A little later the transfer port is uncovered and the fresh charge from the crankcase enters, and on the upstroke the transfer port is covered again before the exhaust port closes. This overlap lets the incoming charge continue to fill the cylinder and slightly supercharge it after the exhaust has been sealed.

Question 30Two-wheeler engine construction, operation, lubrication, and cooling

A four-stroke commuter motorcycle is described as having a wet-sump lubrication system. What does this mean?

  1. Oil is carried in a separate tank and returned by a scavenge pump
  2. Oil is splashed only by the crankshaft and is never pumped
  3. Oil is mixed with petrol before it enters the crankcase
  4. Oil is stored in a sump beneath the crankshaft Correct answer.

Explanation

In a wet-sump system the engine oil is held in a sump forming part of the crankcase below the crankshaft, and a pump draws it up, forces it through the filter and oil galleries to the bearings and cylinder head, after which it drains back to the sump. A dry-sump engine, by contrast, keeps its oil in a separate tank and uses a return pump, which allows a shallower crankcase. Splash-only lubrication has no pressure feed and is found on small engines rather than modern four-stroke motorcycles.

Question 31Two-wheeler engine construction, operation, lubrication, and cooling

Which piston ring has the main job of scraping surplus oil from the cylinder wall and returning it to the crankcase?

  1. Second compression ring
  2. Piston pin circlip
  3. Top compression ring
  4. Oil control ring Correct answer.

Explanation

The oil control ring sits at the bottom of the ring pack and has a sharp scraping edge plus slots or holes behind it, so as the piston moves it removes excess oil from the bore and passes it back down to the sump. This keeps the amount of oil reaching the combustion chamber small, limiting oil consumption and carbon deposit. The two upper rings are compression rings, sealing combustion gas and helping to conduct heat from the piston to the cylinder wall.

Question 32Two-wheeler engine construction, operation, lubrication, and cooling

A forced-air-cooled scooter engine uses a fan driven by the crankshaft. During long idling in stationary traffic, the cylinder head temperature climbs even though the fan is turning. What is the best explanation?

  1. The thermostat shuts off coolant flow at low engine speeds
  2. Fan speed falls with engine speed, cutting air flow Correct answer.
  3. The fan stops turning whenever the scooter is stationary
  4. Idling makes the mixture so rich that carbon coats the fins

Explanation

A crankshaft-driven cooling fan delivers air flow in proportion to engine speed, so at idle the volume of air passing over the fins is small just when the engine is still producing heat. Heat removal therefore falls behind heat generation and the head temperature rises. This is why stationary idling for long periods is discouraged on air-cooled machines, and why some designs use a thermostatically switched electric fan instead.

Question 33Two-wheeler engine construction, operation, lubrication, and cooling

In a two-stroke engine, the fresh charge carrying lubricating oil passes through the crankcase on its way to the cylinder. How does the big-end roller bearing still receive oil?

  1. Oil is thrown up from a sump at the bottom of the crankcase
  2. Oil splashes across from the gearbox onto the crank assembly
  3. Oil mist carried by the charge deposits on the bearing surfaces Correct answer.
  4. A pressure pump forces oil through drillings in the crankshaft

Explanation

The fuel-air-oil mixture is drawn into the sealed crankcase, and turbulence in the scavenging flow turns the oil into a fine mist that wets the crankcase walls, the main bearings, the connecting rod and the big-end rollers. On engines with oil injection, additional oil is sprayed into the intake or the crankcase to supplement this mist. Because there is no pressurised circuit in the crankcase, the oil film is thin and depends heavily on the correct oil grade and mixing ratio.

Question 34Two-wheeler engine construction, operation, lubrication, and cooling

An engine oil is labelled SAE 20W-50. What does this designation tell the technician?

  1. It contains 20% winter additive and 50% mineral base oil
  2. It meets SAE 20 when cold and SAE 50 when hot Correct answer.
  3. It must be changed from SAE 20 in winter to SAE 50 in summer
  4. It has a viscosity index of 20 measured at 50 degrees Celsius

Explanation

In a multigrade designation the figure before the W is the low-temperature viscosity grade determined in a cold-cranking test, and the figure after the W is the viscosity grade measured at 100 degrees Celsius. A 20W-50 oil therefore behaves like an SAE 20 oil when cold, so it cranks and circulates easily, yet it retains the thickness of an SAE 50 oil at operating temperature, protecting the bearings under load. It is a single oil used all year, not two oils changed with the season.

Question 35Two-wheeler engine construction, operation, lubrication, and cooling

In a four-stroke motorcycle engine, the piston moves down the cylinder with the inlet valve open and the exhaust valve closed. Which stroke is this?

  1. Power (expansion) stroke
  2. Compression stroke
  3. Exhaust stroke
  4. Intake (suction) stroke Correct answer.

Explanation

In the intake stroke the piston descends while the inlet valve is open and the exhaust valve is closed. The increasing cylinder volume lowers the pressure, so the air-fuel mixture is drawn in. Compression and power occur with the piston rising or just after top dead centre, and exhaust occurs with the exhaust valve open.

Question 36Two-wheeler engine construction, operation, lubrication, and cooling

In a two-stroke scooter engine fitted with a reed valve at the inlet, what is the main function of the reed valve?

  1. It controls the flow of coolant to the radiator.
  2. It regulates the pressure of oil in the main gallery.
  3. It admits mixture to the crankcase and stops backflow. Correct answer.
  4. It opens and closes the exhaust port at the correct time.

Explanation

The reed valve is a one-way valve at the inlet. It opens when crankcase pressure falls below inlet pressure, and it closes when the descending piston pressurises the crankcase, preventing the charge from being pushed back into the carburettor.

Question 37Two-wheeler engine construction, operation, lubrication, and cooling

In a liquid-cooled scooter engine, what is the job of the coolant pump?

  1. To circulate coolant through the engine and radiator Correct answer.
  2. To maintain pressure in the lubrication circuit
  3. To open the thermostat when the engine is cold
  4. To cool the coolant before it returns to the engine

Explanation

The coolant pump is mechanically driven, usually from the crankshaft or camshaft, and forces coolant through the cylinder and head jackets. The heated coolant then passes to the radiator, where airflow removes heat before the coolant returns to the pump.

Question 38Two-wheeler engine construction, operation, lubrication, and cooling

A four-stroke engine runs at 6000 rpm. At what speed does its camshaft rotate?

  1. 6000 rpm
  2. 3000 rpm Correct answer.
  3. 1500 rpm
  4. 600 rpm

Explanation

A four-stroke cycle needs two crankshaft revolutions to complete, while the camshaft makes only one revolution in that time. The camshaft therefore turns at half the crankshaft speed, so at 6000 rpm it turns at 3000 rpm.

Question 39Two-wheeler engine construction, operation, lubrication, and cooling

A motorcycle has a wet clutch that shares the engine oil. Which oil marking is most important to ensure the clutch does not slip?

  1. SAE 20W-50
  2. JASO MA or MA2 Correct answer.
  3. ISO VG 46
  4. API SN

Explanation

A wet clutch runs in the same oil as the engine, so the oil's friction characteristics affect clutch grip. JASO MA and MA2 are motorcycle-specific ratings that ensure adequate friction for wet clutches, whereas some energy-conserving car oils can make the clutch slip.

Question 40Two-wheeler engine construction, operation, lubrication, and cooling

In a piston-ported two-stroke engine, what is the main purpose of the crankcase being sealed and compressed by the underside of the piston?

  1. To raise the compression ratio of the engine above the design value
  2. To force lubricating oil into the gearbox
  3. To pressurise the charge for transfer to the cylinder Correct answer.
  4. To operate the exhaust power valve

Explanation

In a two-stroke engine the crankcase is part of the induction system and is sealed from the gearbox. As the piston descends, it compresses the charge in the crankcase; this pressure then pushes the charge through the transfer ports when they are uncovered.

Question 41Two-wheeler engine construction, operation, lubrication, and cooling

What is the function of the relief valve in a motorcycle engine's lubricating oil pump circuit?

  1. It opens the oil passage to the cylinder head only at high speed.
  2. It filters metal particles from the oil before the bearings.
  3. It stops oil flow when the engine is cold.
  4. It limits peak oil pressure by bypassing excess oil. Correct answer.

Explanation

A positive-displacement oil pump can generate more pressure than the bearings need, especially when the oil is cold. The relief valve opens at a preset pressure and diverts excess oil back to the sump or pump inlet, protecting seals and hoses.

Question 42Two-wheeler engine construction, operation, lubrication, and cooling

Some small four-stroke motorcycle engines use a centrifugal oil filter on the crankshaft. How does it remove dirt from the oil?

  1. It uses a magnet to attract metallic and non-metallic particles.
  2. It burns the dirt when the oil reaches operating temperature.
  3. It traps particles in a paper element that is replaced at every service.
  4. It spins the oil so heavy particles are thrown onto the bowl wall. Correct answer.

Explanation

A centrifugal filter uses the rotation of the engine or a spinning bowl to separate dirt. Dense particles move outwards and collect on the bowl wall, while cleaner oil flows to the bearings; the bowl is cleaned at service.

Question 43Two-wheeler engine construction, operation, lubrication, and cooling

In a two-stroke engine, the squish band is the narrow flat area of the cylinder head around the combustion chamber. What is its main effect?

  1. It delays the opening of the exhaust port.
  2. It holds the head gasket in position and prevents coolant leaks.
  3. It increases the volume of the combustion chamber at top dead centre.
  4. It creates turbulence in the charge near top dead centre. Correct answer.

Explanation

The squish band forces the outer part of the charge towards the centre as the piston nears top dead centre. This creates turbulence that mixes fuel and air and speeds combustion, reducing the risk of detonation.

Question 44Two-wheeler engine construction, operation, lubrication, and cooling

A four-stroke motorcycle engine has a blocked crankcase breather. Which problem is most likely to result?

  1. The camshaft drive chain will lose tension and jump teeth on the sprockets.
  2. The engine oil will become too cold to circulate through the galleries.
  3. The spark plug will fire earlier than the ignition timing setting.
  4. Crankcase pressure rises and oil may be forced past seals and gaskets. Correct answer.

Explanation

The crankcase breather vents blow-by gases that leak past the piston rings into the crankcase. If it is blocked, pressure builds up and can push oil past the crankshaft seals, gaskets and dipstick, causing leaks and oil consumption.

Question 45Two-wheeler engine construction, operation, lubrication, and cooling

In a liquid-cooled motorcycle engine, what is the main job of the thermostat?

  1. To drive the coolant pump whenever the engine is running
  2. To remove heat from the coolant by switching the cooling fan
  3. To filter metal particles out of the coolant before it reaches the radiator
  4. To keep coolant from circulating through the radiator until the engine reaches normal operating temperature Correct answer.

Explanation

The thermostat is a temperature-controlled valve. While the engine is cold it keeps coolant flowing through the bypass or block, and once operating temperature is reached it opens to allow radiator flow. This helps the engine warm up quickly and maintain a stable temperature.

Question 46Two-wheeler engine construction, operation, lubrication, and cooling

What is the purpose of the spring-loaded pressure cap on a motorcycle radiator?

  1. It mixes extra antifreeze into the coolant when pressure falls
  2. It stops the coolant from expanding as the engine warms up
  3. It raises the coolant boiling point by holding system pressure Correct answer.
  4. It pumps coolant through the radiator while the engine is off

Explanation

The pressure cap seals the cooling system and allows it to operate above atmospheric pressure, which raises the boiling point of the coolant. This helps prevent boiling and cavitation around the hot combustion chamber and cylinder head. A separate spring valve releases pressure only if it becomes excessive.

Question 47Two-wheeler engine construction, operation, lubrication, and cooling

What is the main function of the cylinder head gasket in a liquid-cooled four-stroke motorcycle engine?

  1. To guide the piston as it moves up and down in the bore
  2. To seal combustion gases and coolant passages between head and cylinder Correct answer.
  3. To conduct heat from the piston to the cooling fins
  4. To set the valve clearance when the head is tightened

Explanation

The head gasket is clamped between the cylinder block and cylinder head. It must seal high-pressure combustion gases as well as coolant and oil passages, while withstanding heat and movement. A failed gasket can cause compression loss, overheating, or mixing of coolant and oil.

Question 48Two-wheeler engine construction, operation, lubrication, and cooling

A spin-on oil filter on a motorcycle engine contains a bypass valve. What is the purpose of this valve?

  1. It traps particles smaller than the filter paper can catch
  2. It increases oil pressure when the engine is cold
  3. It lets oil bypass a blocked filter or thick cold oil Correct answer.
  4. It drains oil back to the sump when the engine stops

Explanation

The bypass valve is spring-loaded and opens when the pressure difference across the filter becomes too high. This can happen with a clogged filter or with very thick oil during a cold start. It allows unfiltered oil to reach the bearings rather than starving the engine of lubrication.

Question 49Two-wheeler engine construction, operation, lubrication, and cooling

In a four-stroke motorcycle engine, what is the job of the valve stem seal?

  1. To transfer heat from the valve head to the spring
  2. To keep the valve seated on its seat when the engine is hot
  3. To limit oil from running down the guide into the combustion chamber Correct answer.
  4. To adjust the valve clearance as the stem expands

Explanation

The valve stem seal fits around the valve stem at the top of the guide. It controls the small amount of oil needed for lubrication while preventing excess oil from being drawn into the intake port or combustion chamber. Worn stem seals commonly cause blue smoke at startup and increased oil consumption.

Question 50Two-wheeler engine construction, operation, lubrication, and cooling

Why must a piston ring be fitted with a specified end gap in the cylinder bore?

  1. To let oil pass the ring and reach the combustion chamber
  2. To allow for thermal expansion of the ring when hot Correct answer.
  3. To make the ring press harder against the wall when cold
  4. To let combustion gas escape past the ring and reduce pressure

Explanation

A piston ring runs much hotter than the cylinder and expands as it warms up. The specified end gap provides room for this expansion so the ring ends do not butt together and scuff or break the ring and bore. Too small a gap can cause seizure, while too large a gap increases blow-by and oil consumption.