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ASE H2 Diesel Engines (Transit Bus) study materials
ASE H2 Diesel Engines (Transit Bus) study resources

ASE H2 Diesel Engines (Transit Bus) practice questions

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Question 1General Engine Diagnosis

A transit bus with a diesel engine cranks normally but will not start. Which of the following is the most useful first check on a diesel engine?

  1. Inspect the turbocharger vanes
  2. Verify that fuel is reaching the injectors Correct answer.
  3. Measure the compression ratio
  4. Test the glow plug relay

Explanation

A diesel needs fuel delivered at the right pressure and timing to fire; confirming fuel delivery at the injectors quickly separates a fuel problem from a compression or air problem. Compression ratio is a design value and cannot be measured directly as a first step. Turbocharger and glow plug checks come after basic fuel and air delivery are confirmed.

Question 2General Engine Diagnosis

A diesel engine in a transit bus produces white smoke and runs rough immediately after a cold start, then clears as it warms. Which condition best explains this?

  1. Excess fuel from a leaking injector
  2. Insufficient heat for complete combustion during warm-up Correct answer.
  3. Air trapped in the fuel supply line
  4. Coolant entering the combustion chamber

Explanation

Cold diesel engines have low compression heat, so some fuel does not fully burn and appears as white vapor that clears as the engine warms. Coolant intrusion typically produces persistent white steam and coolant loss. A leaking injector and air in the fuel usually cause symptoms that do not clear simply with warm-up.

Question 3General Engine Diagnosis

Which instrument is used to measure the rotational speed of a diesel engine during diagnosis?

  1. Pyrometer
  2. Manometer
  3. Hydrometer
  4. Phototachometer Correct answer.

Explanation

A phototachometer or optical tachometer reads engine rpm from a reflective target or rotating component. A manometer measures pressure, a hydrometer measures electrolyte specific gravity, and a pyrometer measures temperature.

Question 4General Engine Diagnosis

A bus operator reports low power and black smoke under load. A boost gauge shows turbo boost is well below specification. Which is the most likely cause?

  1. Worn valve stem seals
  2. Faulty coolant temperature sensor
  3. Low battery voltage
  4. Restricted air intake or leaking charge-air piping Correct answer.

Explanation

Low boost with black smoke indicates the engine is over-fueled relative to available air, commonly from an intake restriction or a charge-air leak. A coolant sensor, valve stem seals, and battery voltage do not directly reduce turbo boost. Black smoke results from an air-deficient rich mixture.

Question 5General Engine Diagnosis

During a cylinder balance test on a diesel engine, disabling one injector produces no change in engine speed or sound. What does this indicate?

  1. The engine is running too lean overall
  2. That cylinder is contributing little or no power Correct answer.
  3. The turbocharger is overboosting
  4. The injection pump timing is retarded

Explanation

If cutting out a cylinder does not change engine speed or sound, that cylinder was not contributing power, pointing to a fault in that cylinder's fuel, compression, or air. Timing, overall mixture, and boost affect all cylinders and would not isolate a single dead cylinder.

Question 6General Engine Diagnosis

Which of the following best describes the purpose of a compression test on a diesel engine?

  1. To check the turbocharger shaft speed
  2. To confirm injector pulse width
  3. To measure the fuel rail pressure
  4. To verify each cylinder can generate enough heat to ignite fuel Correct answer.

Explanation

Diesel ignition depends on compression heat, so a compression test verifies each cylinder can build enough pressure and temperature to ignite fuel. Fuel rail pressure, turbo speed, and injector pulse width are measured with other tools and are unrelated to a compression test.

Question 7General Engine Diagnosis

A diesel engine has excessive blue-gray smoke and high oil consumption. Which condition is the most likely cause?

  1. A clogged fuel filter
  2. Worn piston rings or valve guides allowing oil into the cylinders Correct answer.
  3. Retarded injection timing
  4. A faulty thermostat

Explanation

Blue-gray smoke with oil consumption indicates oil is entering the combustion chamber, typically past worn rings or valve guides. A clogged fuel filter causes power loss and hard starting, retarded timing causes white smoke and poor power, and a thermostat affects temperature regulation only.

Question 8General Engine Diagnosis

A scan tool shows a diagnostic trouble code for the intake air temperature sensor circuit. How does this sensor input most directly affect engine operation?

  1. It controls the alternator charge rate
  2. It sets the transmission shift point
  3. It influences fuel delivery calculations for air density Correct answer.
  4. It regulates the cooling fan clutch

Explanation

Intake air temperature is used with manifold pressure to calculate air density and mass, which the ECM uses to schedule fuel delivery. It does not control charging, transmission shifting, or the fan clutch.

Question 9General Engine Diagnosis

A diesel engine overheats only when the bus is climbing a long grade under full load. Which cause is most consistent with this symptom?

  1. A low coolant level at all times
  2. A restricted radiator or failing fan drive under high heat load Correct answer.
  3. An inoperative coolant temperature gauge
  4. A stuck-open thermostat

Explanation

Overheating only under high load points to a cooling system that cannot reject enough heat when demand peaks, such as a restricted radiator or a fan drive that fails to engage. A stuck-open thermostat causes overcooling, a constant low coolant level causes overheating at all times, and a faulty gauge is a display issue, not a real heat rejection problem.

Question 10General Engine Diagnosis

Which of the following is a correct safety practice before performing a compression test on a diesel engine?

  1. Remove the radiator fan
  2. Disable the fuel injection and ignition sources and wear eye protection Correct answer.
  3. Run the engine at high idle to warm the tester
  4. Open the cooling system pressure cap

Explanation

Disabling fuel delivery prevents the engine from starting or injecting fuel during cranking, and eye protection guards against high-pressure fuel spray and debris. Warming the engine at high idle, opening the pressure cap, and removing the fan are not required steps and can create hazards.

Question 11General Engine Diagnosis

A diesel engine idles smoothly but misfires and loses power as load increases. Fuel supply pressure at the injectors drops below specification under load. Which is the most likely cause?

  1. A worn turbocharger wastegate actuator
  2. A faulty glow plug controller
  3. A restricted fuel filter or weak lift pump Correct answer.
  4. An open thermostat

Explanation

A restriction in the fuel supply or a weak lift pump limits fuel volume, which shows up as pressure loss and misfire as demand rises with load. The glow plug controller, thermostat, and wastegate actuator do not control fuel supply pressure.

Question 12General Engine Diagnosis

What does a diesel engine's electronic control module use as the primary input to determine injection timing and quantity?

  1. Fuel tank level
  2. Crankshaft position and camshaft position signals Correct answer.
  3. Vehicle speed only
  4. Ambient light level

Explanation

Crank and cam position signals tell the ECM where the pistons are and which stroke each cylinder is on, which is essential for timing and sequencing injection. Vehicle speed, ambient light, and fuel level do not determine injection timing or quantity.

Question 13General Engine Diagnosis

A diesel engine produces a steady knock that is worse at idle and decreases as engine speed increases. Which condition is the most likely cause?

  1. A worn injector nozzle with poor atomization Correct answer.
  2. A leaking exhaust manifold gasket
  3. An overcharged battery
  4. A loose accessory drive belt

Explanation

Poor atomization from a worn nozzle causes delayed ignition and a diesel knock that is often most noticeable at idle and may lessen at higher speed as cylinder conditions change. A belt, exhaust leak, and battery charge do not produce a combustion knock.

Question 14General Engine Diagnosis

When checking for air in a diesel fuel system, where is air most likely to enter?

  1. At the exhaust manifold
  2. On the pressure side of the injection pump
  3. Inside the combustion chamber
  4. At the suction side fittings and filter seals Correct answer.

Explanation

The fuel supply line from tank to lift pump operates under suction, so loose fittings, cracked lines, or bad filter seals can draw air in. The pressure side leaks fuel out rather than drawing air in, and the combustion chamber and exhaust manifold are not part of the fuel supply path.

Question 15General Engine Diagnosis

A transit bus diesel engine has a hard-start condition only when cold, but starts easily when warm. Which check is most appropriate first?

  1. Rear axle gear ratio
  2. Transmission fluid level
  3. Alternator output at high idle
  4. Glow plug or intake heater operation Correct answer.

Explanation

Cold-only hard starting points to the cold-start assist system, so verifying glow plug or intake heater operation is the logical first check. Transmission fluid, axle ratio, and alternator output do not change with engine temperature in a way that explains cold-only starting difficulty.

Question 16General Engine Diagnosis

Which test best identifies a weak cylinder on a diesel engine without disassembly?

  1. Fuel tank vent test
  2. Cooling system pressure test
  3. Cylinder balance or contribution test Correct answer.
  4. Battery load test

Explanation

A cylinder balance or contribution test disables each cylinder in turn and observes the change in speed or power, isolating the weak cylinder. Battery load, cooling system pressure, and fuel tank vent tests evaluate other systems and cannot identify a weak cylinder.

Question 17General Engine Diagnosis

A diesel engine's exhaust shows continuous black smoke even at moderate load, and fuel economy has dropped. Which condition is most likely?

  1. A worn pilot bearing
  2. A small coolant leak into one cylinder
  3. Over-fueling from a faulty injector or incorrect calibration Correct answer.
  4. A clogged crankcase breather

Explanation

Continuous black smoke indicates unburned carbon from an over-rich mixture, commonly caused by over-fueling from a faulty injector or incorrect calibration. A small coolant leak gives white smoke, a pilot bearing is a driveline component, and a clogged breather causes crankcase pressure and oil leaks.

Question 18General Engine Diagnosis

A technician measures high crankcase pressure on a diesel engine. Which condition is the most likely cause?

  1. A faulty fuel shutoff solenoid
  2. An open thermostat
  3. A restricted air filter
  4. Worn piston rings or scored cylinder walls Correct answer.

Explanation

High crankcase pressure results from combustion gases blowing past worn rings or scored cylinder walls into the crankcase. A restricted air filter causes low power and black smoke, a fuel shutoff solenoid affects starting and shutdown, and an open thermostat affects temperature.

Question 19General Engine Diagnosis

Which of the following describes the correct way to verify turbocharger boost pressure on a diesel engine?

  1. Read battery voltage at idle
  2. Check coolant pH
  3. Measure fuel pressure at the tank
  4. Compare manifold boost pressure to specification at a specified load and rpm Correct answer.

Explanation

Boost is verified by measuring manifold pressure at a defined operating point and comparing it to the manufacturer's specification. Fuel pressure at the tank, coolant pH, and battery voltage do not reflect turbocharger boost.

Question 20General Engine Diagnosis

A diesel engine starts, runs briefly, then shuts down. A scan tool shows the ECM is commanding fuel off after startup. Which area should be investigated first?

  1. The starter solenoid
  2. The turbocharger compressor wheel
  3. The engine protection or safety shutdown inputs Correct answer.
  4. The radiator cap rating

Explanation

If the ECM commands fuel off after startup, an engine protection input such as low oil pressure, high coolant temperature, or a shutdown signal is likely triggering the command. Turbo compressor condition, radiator cap rating, and the starter solenoid do not cause the ECM to cut fuel after the engine starts.

Question 21General Engine Diagnosis

A diesel engine's oil pressure warning triggers at idle when hot but clears at higher rpm. Which is the most likely cause?

  1. Worn engine bearings or a weak oil pump Correct answer.
  2. An overfilled crankcase
  3. A faulty glow plug
  4. A clogged air filter

Explanation

Low oil pressure at hot idle that rises with rpm indicates excessive bearing clearance or a pump that cannot maintain pressure at low speed. Overfilling, a clogged air filter, and a glow plug fault do not cause low oil pressure.

Question 22General Engine Diagnosis

Which condition would cause a diesel engine to produce a rhythmic misfire at a steady speed that is traceable to one cylinder?

  1. A worn driveshaft center bearing
  2. A partially clogged fuel tank vent
  3. A faulty injector on that cylinder Correct answer.
  4. A loose alternator belt

Explanation

A single-cylinder rhythmic misfire points to a fault affecting that cylinder, such as a faulty injector. A tank vent restriction affects the whole fuel system, a belt affects accessories, and a driveshaft bearing is a driveline noise source.

Question 23General Engine Diagnosis

A diesel engine's valve clearance is found to be too tight on several cylinders. What is the most likely effect?

  1. The engine will run cooler
  2. Valves may not seat fully, causing compression loss and possible burning Correct answer.
  3. Turbo boost will increase
  4. Fuel economy will improve

Explanation

Excessively tight valve clearance holds valves off their seats during part of the cycle, causing compression loss, rough running, and the risk of burned valves. It does not reduce operating temperature, improve economy, or raise boost.

Question 24General Engine Diagnosis

Which of the following is the correct procedure for reading diagnostic trouble codes on a modern electronically controlled diesel engine?

  1. Use a scan tool connected to the diagnostic connector to retrieve active and stored codes Correct answer.
  2. Disconnect the batteries and count alternator pulses
  3. Ground the fuel solenoid and watch the injector light
  4. Remove the ECM and inspect the circuit board

Explanation

Modern diesel engines store diagnostic trouble codes in the ECM, and a scan tool connected to the diagnostic link retrieves active and stored codes with descriptions. Counting alternator pulses, grounding the fuel solenoid, or removing the ECM are not valid or safe methods.

Question 25Cylinder Head, Valve Train, and Engine Block

In a typical diesel engine, what is the primary function of the valve bridge (crosshead) on a cylinder with two valves per head?

  1. It seals combustion gas at the injector bore
  2. It guides the pushrod in the block
  3. It lets one rocker or pushrod actuate both valves together Correct answer.
  4. It retains the valve spring on the head

Explanation

A valve bridge transfers motion from a single rocker or pushrod to two valves so they open simultaneously. It does not seal combustion gas or guide pushrods. Spring retention is handled by the retainer and keepers.

Question 26Cylinder Head, Valve Train, and Engine Block

Which component directly transfers camshaft lobe motion to a pushrod in a typical bus diesel with an in-block cam?

  1. Valve guide
  2. Valve seat insert
  3. Valve lifter (tappet) Correct answer.
  4. Rocker arm

Explanation

The lifter rides on the cam lobe and transmits that motion up the pushrod to the rocker. The rocker then acts on the valve. Guides and seats locate and seal the valve but do not transfer cam motion.

Question 27Cylinder Head, Valve Train, and Engine Block

What is the purpose of valve lash (clearance) in a mechanical valvetrain?

  1. To allow for thermal expansion so valves fully seat when hot Correct answer.
  2. To keep the pushrod centered in its socket
  3. To reduce oil flow to the rocker shaft
  4. To increase valve lift at high rpm

Explanation

Lash provides room for components to expand as the engine warms so the valve still closes and seats fully. Too little lash can hold a valve off its seat when hot. Lash does not increase lift or meter oil.

Question 28Cylinder Head, Valve Train, and Engine Block

A valve is found with its stem bent and the piston shows a matching impact mark. Which condition most directly explains this?

  1. A worn valve guide seal
  2. Valve-to-piston contact from loss of timing or a stuck valve Correct answer.
  3. Low oil pressure at the rocker shaft
  4. Excessive valve lash on that valve

Explanation

A bent stem with a matching piston mark indicates the valve and piston collided, typically from lost cam timing, a seized valve, or a dropped valve. Lash, seals, and oil pressure do not cause impact bending.

Question 29Cylinder Head, Valve Train, and Engine Block

During a cylinder head inspection, a crack is found between the valve seats. Why is this location especially critical on a diesel head?

  1. It is the coolest part of the head
  2. It is where the injector is mounted
  3. It lies between two high-heat, high-stress sealing areas Correct answer.
  4. It carries no coolant

Explanation

The area between valve seats sees concentrated heat and clamping stress and separates two combustion sealing surfaces. Cracks there can propagate into the seat or water jacket. It is not a cool or unstressed region.

Question 30Cylinder Head, Valve Train, and Engine Block

A technician measures valve recession and finds it beyond the service limit. What is the most likely cause?

  1. Wrong pushrod length
  2. Seat face wear from repeated valve closing impact Correct answer.
  3. Excessively thick valve stem
  4. Over-torqued rocker shaft bolts

Explanation

Recession is the valve sinking into the head as the seat and valve face wear from repeated impact. It reduces valve margin and can affect lash and sealing. Stem thickness, rocker bolt torque, and pushrod length do not cause recession.

Question 31Cylinder Head, Valve Train, and Engine Block

What is the correct purpose of a valve spring retainer and split keepers (locks)?

  1. To seal oil at the top of the guide
  2. To hold the spring compressed and lock the valve to the spring assembly Correct answer.
  3. To adjust valve lash automatically
  4. To center the valve in the seat

Explanation

Keepers seat in a groove on the valve stem and the retainer captures the spring so the assembly stays together. They do not adjust lash or seal oil. Centering is done by the guide and seat.

Question 32Cylinder Head, Valve Train, and Engine Block

A diesel engine has a valve spring with broken coils. Which symptom is most likely?

  1. Misfire and possible valve-to-piston contact at high rpm Correct answer.
  2. Faster cranking speed
  3. Reduced coolant temperature
  4. Higher oil pressure

Explanation

A broken spring can let the valve lose control at speed, causing misfire or contact with the piston. It does not raise oil pressure, speed cranking, or lower coolant temperature. Loss of valve control is the key risk.

Question 33Cylinder Head, Valve Train, and Engine Block

When checking valve lash on a mechanical valvetrain, the engine should be at what condition for a standard cold setting?

  1. Cold, with the valve fully closed on the base circle of the cam Correct answer.
  2. At high idle with the governor engaged
  3. Fully warmed and idling
  4. Hot, with the valve partially open

Explanation

Lash is set with the lifter on the cam base circle and the valve fully closed, per the manufacturer's hot or cold spec. Setting on the ramp or lobe gives wrong clearance. Temperature condition must match the published spec.

Question 34Cylinder Head, Valve Train, and Engine Block

What is the purpose of a valve stem seal on a diesel engine?

  1. To retain the valve spring
  2. To seal combustion gas at the seat
  3. To limit oil from running down the guide into the port Correct answer.
  4. To set valve lash

Explanation

The stem seal meters oil at the top of the guide so oil does not get drawn into the intake or exhaust port. It does not retain springs, set lash, or seal combustion at the seat.

Question 35Cylinder Head, Valve Train, and Engine Block

A valve guide is worn beyond limit. Which is the most direct consequence?

  1. Valve stem oil control loss and possible valve seat misalignment Correct answer.
  2. Increased valve spring rate
  3. Reduced injector pop pressure
  4. Higher compression ratio

Explanation

A worn guide lets the valve stem move off center, causing oil control loss and poor seat contact. It does not change spring rate, compression ratio, or injector pop pressure. Misalignment accelerates seat wear.

Question 36Cylinder Head, Valve Train, and Engine Block

Which measurement best indicates valve stem-to-guide clearance?

  1. Stem diameter versus guide bore diameter Correct answer.
  2. Spring free length
  3. Valve margin thickness
  4. Rocker arm ratio

Explanation

Clearance is the difference between stem OD and guide ID, often checked with a dial indicator or bore gauge. Margin, spring length, and rocker ratio describe other features. Clearance controls oil use and valve stability.

Question 37Cylinder Head, Valve Train, and Engine Block

What does a valve seat width that is too narrow typically cause?

  1. Excessive valve lash
  2. Higher oil consumption
  3. Poor heat transfer and possible seat burning Correct answer.
  4. Faster cam wear

Explanation

A narrow seat reduces the contact area for heat transfer from the valve head to the head casting, risking burning and wear. It does not change lash, oil consumption, or cam wear directly. Proper seat width balances sealing and heat flow.

Question 38Cylinder Head, Valve Train, and Engine Block

When installing a cylinder head, what is the correct tightening method for torque-to-yield head bolts?

  1. Torque only the center bolts
  2. Torque to spec once in any order
  3. Tighten cold to half spec and stop
  4. Torque in sequence, then turn a specified angle Correct answer.

Explanation

Torque-to-yield bolts are tightened to a low torque in sequence and then rotated a specified angle to stretch them properly. They are not torqued once in random order. Sequence and angle are critical for even clamping.

Question 39Cylinder Head, Valve Train, and Engine Block

A head gasket shows a failure between two adjacent cylinders. Which condition most likely caused it?

  1. Low coolant level in the radiator
  2. A loose fan belt
  3. Head warpage or insufficient clamping between those cylinders Correct answer.
  4. Wrong oil viscosity

Explanation

A blowout between adjacent cylinders points to lost clamping load or a warped head that lets combustion pressure cross the fire ring. Coolant level, oil viscosity, and belts do not create that pattern. Check head flatness and bolt condition.

Question 40Cylinder Head, Valve Train, and Engine Block

What is the primary reason cylinder head bolts are often replaced rather than reused?

  1. They shrink when cooled
  2. They become magnetized
  3. They are painted and lose color
  4. They stretch permanently and lose clamping ability Correct answer.

Explanation

Torque-to-yield bolts stretch past their elastic limit during tightening and may not hold clamping load if reused. They do not fail because of paint, magnetism, or thermal shrinkage. Always follow the manufacturer's reuse policy.

Question 41Cylinder Head, Valve Train, and Engine Block

A diesel cylinder liner is found with cavitation pitting on the outside. What is the most likely cause?

  1. Abrasive particles in the oil
  2. Vibration-driven coolant bubble collapse against the liner Correct answer.
  3. Excessive valve lash
  4. Too much valve spring pressure

Explanation

Cavitation erosion occurs when vibration creates and collapses coolant vapor bubbles against the liner wall, pitting it. Oil debris, lash, and spring pressure do not cause external liner pitting. Correct coolant chemistry and additives reduce it.

Question 42Cylinder Head, Valve Train, and Engine Block

What is the purpose of a cylinder liner flange (top flange) in a wet-liner engine?

  1. To hold the oil pan
  2. To seal the crankcase breather
  3. To seat the liner and control its protrusion above the deck Correct answer.
  4. To guide the piston rings

Explanation

The flange seats in the block counterbore and sets liner protrusion, which helps seal the head gasket fire ring. It does not seal the breather or guide rings. Protrusion is a critical assembly check.

Question 43Cylinder Head, Valve Train, and Engine Block

A wet cylinder liner shows a coolant leak at its base. Which component is most directly responsible for sealing that area?

  1. The oil pan gasket
  2. The liner O-rings or seal rings in the block Correct answer.
  3. The valve cover gasket
  4. The head gasket

Explanation

Wet liners use O-rings or seal rings at the lower end to keep coolant out of the crankcase. The head gasket seals the top, not the base. Cover and pan gaskets are unrelated to liner coolant sealing.

Question 44Cylinder Head, Valve Train, and Engine Block

What is the primary function of the camshaft in a four-stroke diesel?

  1. To open valves at the correct time relative to the piston Correct answer.
  2. To seal combustion gas
  3. To atomize fuel
  4. To drive the oil pump only

Explanation

The camshaft lobes open the valves in time with the piston and crankshaft through the valvetrain. It does not atomize fuel or seal combustion. Cam timing directly affects breathing and power.

Question 45Cylinder Head, Valve Train, and Engine Block

A camshaft shows severe lobe wear on several lobes. Which is the most likely contributing factor?

  1. Too much valve lash on all valves
  2. Wrong coolant concentration
  3. Loose fan belt
  4. Insufficient lubrication or incorrect oil for the lifter type Correct answer.

Explanation

Lobe wear usually comes from inadequate lubrication, wrong oil, or a lifter that cannot maintain the oil film. Coolant, belt tension, and excess lash do not directly cause lobe scuffing. Correct oil and break-in matter.

Question 46Cylinder Head, Valve Train, and Engine Block

What does camshaft timing refer to in a diesel engine?

  1. The oil pressure at the cam bearings
  2. The angle relationship between the cam and crankshaft Correct answer.
  3. The torque on the rocker bolts
  4. The clearance at the valve guide

Explanation

Cam timing is the angular relationship between the camshaft and crankshaft, which sets when valves open and close relative to piston position. Oil pressure, guide clearance, and bolt torque are separate checks. Incorrect timing can cause piston-to-valve contact.

Question 47Cylinder Head, Valve Train, and Engine Block

A pushrod is found bent. Which is the most likely cause?

  1. Low coolant level
  2. A worn valve stem seal
  3. A valve sticking in its guide or a lifter pumped up too far Correct answer.
  4. Too much valve lash on that valve

Explanation

A stuck valve or an over-pumped lifter can create mechanical interference that bends the pushrod. Excess lash reduces load and would not bend it. Seals and coolant level do not load the pushrod.

Question 48Cylinder Head, Valve Train, and Engine Block

What is the purpose of checking valve stem protrusion (installed height) after a valve job?

  1. To confirm the valve sits at the correct height for spring and lash geometry Correct answer.
  2. To measure oil pressure
  3. To verify the injector timing
  4. To set the cooling fan pitch

Explanation

Installed height affects spring force and lash adjustment range, so it must be correct after grinding seats or valves. It does not set injector timing or oil pressure. Too much height can cause coil bind.

Question 49Cylinder Head, Valve Train, and Engine Block

A diesel engine block is being checked for main bearing bore alignment. Which condition most directly results from misalignment?

  1. Crankshaft binding and uneven bearing wear Correct answer.
  2. Excessive valve lash
  3. Higher injector pop pressure
  4. Faster valve guide wear

Explanation

Misaligned main bores can bind the crankshaft and produce uneven bearing loading and wear. Valve lash, injector pop, and guide wear are not direct results of main bore alignment. The block line bore is a critical machining check.

Question 50Cylinder Head, Valve Train, and Engine Block

A technician is measuring the cylinder head deck for flatness with a straightedge and feeler gauge. Which specification applies to this check?

  1. Maximum allowable warpage across the deck and diagonally Correct answer.
  2. Minimum piston-to-valve clearance
  3. Minimum valve seat contact width
  4. Maximum valve spring installed height

Explanation

Deck flatness is checked with a straightedge placed in several directions, including diagonally, and the largest gap that fits under it is compared with the manufacturer's warpage limit. This confirms the head can seal the gasket across its full surface. The other values are unrelated valvetrain or clearance specs.