22 Cylinder Head, Valve Train & Block Practice Questions & Answers

1. 1. A diesel engine loses coolant with no external leak, and the coolant reservoir bubbles steadily whenever the engine runs. Which test best confirms that combustion gases are entering the cooling system?

   • A.A cooling system pressure test held at the cap's rated value
   • B.A coolant condition check made with a refractometer sample
   • C.A chemical block test that draws vapor from the filler neck✓ Answer
   • D.A radiator cap test comparing opening pressure to the rating

   A chemical block tester pulls air from above the coolant through a fluid that changes color in the presence of combustion gas, so it identifies combustion leakage into the coolant rather than merely proving a leak exists. A pressure test shows only that the system will not hold pressure, and a cap test or refractometer reading says nothing about combustion gas.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area A/B — inspect for coolant contamination and diagnose cylinder head gasket failure (combustion leak testing)Report a problem with this question

2. 2. A diesel loses coolant with no external leak. After removing an injector, the technician finds coolant standing on top of that piston. Tech A says a leaking injector sleeve (cup) in the cylinder head can put coolant straight into the cylinder. Tech B says the sleeve should be replaced and the head pressure tested to verify the repair. Who is right?

   • A.Neither Tech A nor Tech B
   • B.Tech B only
   • C.Both Tech A and Tech B✓ Answer
   • D.Tech A only

   The injector sleeve is the thin tube that isolates the injector from the coolant jacket, so when it cracks or its seals fail, coolant enters the cylinder and the oil with no external leak. The task list calls for replacing the sleeve and seals and then pressure testing the head to verify the repair before reassembly, which makes both technicians correct.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — inspect and replace injector sleeves and seals; pressure test to verify repairReport a problem with this question

3. 3. A diesel cylinder head has been resurfaced once before. It now checks 0.004 in (0.10 mm) out of flat against a 0.002 in (0.05 mm) limit, and its measured thickness is already below the manufacturer's minimum. What should the technician do?

   • A.Replace the head, since it is under minimum thickness✓ Answer
   • B.Fit a thicker head gasket to make up the metal removed
   • C.Resurface it and shim the injectors back to protrusion spec
   • D.Resurface it again and recheck flatness with a straightedge

   Diesel heads carry a published minimum thickness because removing metal changes injector or nozzle protrusion, valve-train geometry and piston-to-valve clearance, so the resurfacing allowance is small or nonexistent. Once measured thickness is under that minimum the head is not serviceable, and no gasket or shim restores the material already cut away.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — measure cylinder head thickness; check mating surfaces for warpage and flatnessReport a problem with this question

4. 4. Before a diesel cylinder head goes back on, the technician wants to confirm the water jackets are free of cracks. Which procedure does that?

   • A.Fill the ports with solvent and watch the face for seepage
   • B.Run a cranking compression test and compare the cylinders
   • C.Seal the coolant passages and pressure test the head in hot water✓ Answer
   • D.Pull a vacuum on the intake ports and watch the gauge decay

   Blocking the coolant passages, applying regulated air pressure and submerging the head in heated water makes escaping bubbles reveal a crack, and the heat opens cracks that stay closed when the head is cold. A vacuum test checks valve sealing, solvent seepage is unreliable, and a compression test cannot be run on a head that is off the engine.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — inspect cylinder head for cracks and damage; pressure test passagesReport a problem with this question

5. 5. During a short-block rebuild the technician measures piston protrusion above the deck at every cylinder with a dial indicator. What does that measurement determine?

   • A.Which grade of select-fit rod bearing shell is needed
   • B.How much metal may be cut from the block deck surface
   • C.Which thickness grade of head gasket the engine needs✓ Answer
   • D.How much end play the crankshaft thrust bearing allows

   Many diesels are built with graded head gaskets, and the grade is chosen from the greatest measured piston protrusion so that clearance and compression stay in spec: more protrusion calls for a thicker gasket. Grades are identified by notches or holes at the gasket edge, and on a V engine the left and right gaskets are not interchangeable.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — determine required cylinder head gasket thickness by measuring piston protrusionReport a problem with this question

6. 6. Read carefully: this question asks for the exception. All of these are correct practice when installing a diesel cylinder head with torque-to-yield head bolts EXCEPT:

   • A.tightening in the sequence the manufacturer specifies
   • B.applying the final step as a torque value plus an angle
   • C.cleaning and chasing the threaded holes in the block beforehand
   • D.reusing the original bolts because they look straight and unstretched✓ Answer

   A torque-to-yield bolt is deliberately stretched past its elastic limit as it is tightened, so its clamping ability cannot be judged by appearance and the manufacturer's procedure governs whether it is replaced or measured. Chasing the threads, following the tightening sequence and finishing with torque plus angle are all required steps.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — install cylinder head per manufacturer procedure; inspect threaded holes, studs and bolts for serviceabilityReport a problem with this question

7. 7. A high-mileage diesel uses oil and puffs blue smoke at start-up and after a long idle, but measured crankcase pressure is normal. Tech A says worn valve guides and stem seals can pull oil down the stems and account for the smoke. Tech B says the piston rings must be worn out. Who is right?

   • A.Both Tech A and Tech B
   • B.Neither Tech A nor Tech B
   • C.Tech B only
   • D.Tech A only✓ Answer

   Worn guides and stem seals let oil drain down the stems into the ports while the engine sits, which burns off as blue smoke at restart and after idling. Normal crankcase pressure argues against worn rings, because rings that pass enough oil to smoke also pass combustion gas into the crankcase and raise that pressure.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B/C — inspect valves, guides and seals; crankcase pressure (blowby) test as a ring-condition indicatorReport a problem with this question

8. 8. On a diesel that requires periodic valve adjustment, several exhaust valve clearances measure well below the specified value. What is the most likely result if this is not corrected?

   • A.The valves are held slightly open and burn from lost seat contact✓ Answer
   • B.The valve train clatters and the rocker faces wear quickly
   • C.The cam lobes lose oil film and the followers scuff under load
   • D.The valves close hard and pound the seats into recession

   An exhaust valve sheds most of its heat through contact with its seat, so clearance below specification holds the valve slightly off the seat as parts expand and the valve overheats and burns. Excessive clearance is the condition that produces noise and accelerated valve-train wear, not burned valves.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — adjust valve clearance; inspect valves and valve seatsReport a problem with this question

9. 9. A four-valve-per-cylinder diesel uses a valve bridge (crosshead) over each pair of valves. One bridge is reinstalled without being adjusted. What is the likely result?

   • A.The rocker unloads at high speed and the pushrod bends
   • B.The bridge guide wears and lash grows at both valves
   • C.One valve of the pair takes most of the lift and can burn✓ Answer
   • D.Both valves of the pair open late and the engine loses power

   The bridge adjusting screw squares the bridge so the rocker load is split evenly and both valves lift together. Left unadjusted the bridge sits crooked, one valve receives most of the lift and closes onto its seat unevenly, and that valve overheats and burns while the other may not seal.

   Source: ASE Automobile Study Guide, Test A9 Task List, Area B — inspect, replace and adjust valve bridges (crossheads) and guidesReport a problem with this question

10. 10. After fitting a rebuilt injector, the technician measures nozzle tip protrusion below the fire deck and finds it greater than the specified value. Which action corrects it?

    • A.Fit a copper sealing washer of the next greater thickness✓ Answer
    • B.Fit a thinner washer so the injector seats deeper
    • C.Torque the injector hold-down clamp to a higher value
    • D.Machine the fire deck until the protrusion comes in

    Nozzle protrusion is set by the thickness of the copper sealing washer under the injector, so a thicker washer lifts the injector and reduces protrusion that is too great. Protrusion controls spray targeting and the sealing of the tip in its seat, and it is corrected with washer selection rather than clamp torque or machining.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area B — measure injector tip, nozzle or prechamber protrusion to specificationReport a problem with this question

11. 11. A diesel cranks at normal speed but is badly down on power, and cranking compression is low and nearly equal on every cylinder. Which of these could be the cause?

    • A.One head gasket has failed between two cylinders
    • B.One injector sleeve is leaking coolant into a bore
    • C.A valve bridge on a single cylinder is misadjusted
    • D.The timing gear train is out of time by one tooth✓ Answer

    A fault that lowers compression on every cylinder by a similar amount has to act on something all cylinders share, and mistimed cam-to-crank gearing shifts valve events on all of them at once. A failed gasket, a misadjusted bridge or a leaking sleeve is a single-cylinder or two-cylinder fault and would show up as one low reading.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area B — inspect and time the drive gear train (gear, chain and belt systems)Report a problem with this question

12. 12. A cylinder bore is being checked for taper and out-of-round with a dial bore gauge. Which procedure gives valid readings?

    • A.Measure below the ridge with the gauge at any angle
    • B.Measure once at mid-stroke in the thrust direction
    • C.Measure at several depths and at 90 degrees apart at each depth✓ Answer
    • D.Measure at the bottom of travel where wear is worst

    Taper is the difference between readings taken at different depths and out-of-round is the difference between two readings 90 degrees apart at the same depth, so both numbers require several depths and two axes. Wear is greatest at the top of ring travel, not at the bottom, because that is where pressure and heat are highest and lubrication is poorest.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — inspect and measure cylinder walls for wear and damage (taper and out-of-round)Report a problem with this question

13. 13. Piston ring end gap is being checked during a diesel rebuild. Which statement describes correct practice?

    • A.The ring is measured on the piston with the piston in the bore
    • B.The ring is squared in the bore with a piston before measuring✓ Answer
    • C.The ring is squared against the block deck before measuring
    • D.The ring is measured in its groove with a feeler blade at the top

    End gap is meaningful only when the ring sits perpendicular in the bore it will run in, so it is pushed down with a piston crown and then measured with a feeler gauge. A gap below specification lets the ends butt as the ring grows with heat, which scuffs the bore and can break the ring.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — check ring end gap and install rings on pistonsReport a problem with this question

14. 14. A used piston is being reused. With a new ring in its groove, a feeler gauge shows side clearance well above the specified limit. What does that indicate?

    • A.The ring end gap was filed too wide when it was fitted
    • B.The aro is the wrong diameter for that cylinder bore
    • C.The cylinder wall is worn past the taper service limit
    • D.The ring groove is worn and the piston should be replaced✓ Answer

    Side clearance is measured between a new ring and the groove, so the ring thickness is known good and an excessive reading can only come from a groove worn wider by ring pounding. A worn groove lets the ring flutter instead of sealing, which raises blowby and oil consumption, and the cure is a new piston rather than a new ring.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — check ring-to-groove fit (side clearance); inspect and measure pistonsReport a problem with this question

15. 15. A wet-sleeve diesel is torn down and two liners are pitted through from the coolant side. Tech A says vibration of the liner collapsing vapor bubbles against its outer wall causes that pitting. Tech B says depleted coolant additive lets the pitting go on unchecked. Who is right?

    • A.Both Tech A and Tech B✓ Answer
    • B.Tech A only
    • C.Tech B only
    • D.Neither Tech A nor Tech B

    Combustion flexes a wet liner, and the outward motion forms low-pressure vapor bubbles in the coolant that collapse violently against the liner wall, hammering metal away in a process called cavitation erosion. The supplemental coolant additive maintains a protective film on that surface, so once the additive is depleted the pitting continues until it perforates the liner, which makes both technicians correct.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C/D — cylinder liner inspection and coolant condition/contamination checks (cavitation erosion)Report a problem with this question

16. 16. A connecting rod bearing is removed and the wear is heaviest along one edge of the shell and tapers away across its width. What does this pattern point to?

    • A.Bearing clearance was excessive from a worn journal
    • B.Dirt was carried in the oil supplied to that bearing
    • C.The engine ran at low oil pressure for a long time
    • D.The rod or its bore is not square to the crankshaft journal✓ Answer

    Wear that is heavy on one edge and tapers across the shell means the load was concentrated at one side, which happens when the rod is bent or its bore is not parallel to the journal. Dirt leaves embedded particles and scratches spread over the whole surface, and low pressure or excess clearance wipes the overlay evenly rather than on one edge.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — read piston, rod-bearing and main-bearing wear patterns; check bearing bore and bushing conditionReport a problem with this question

17. 17. Main bearings are being fitted to a diesel block that uses select-fit grades. Tech A says standard-size shells are always correct as long as the crankshaft has not been reground. Tech B says the grade codes marked on the block and crankshaft may be ignored once the measured clearance is under the maximum. Who is right?

    • A.Tech A only
    • B.Neither Tech A nor Tech B✓ Answer
    • C.Tech B only
    • D.Both Tech A and Tech B

    On a select-fit engine the factory sorts blocks and crankshafts into grades and marks them, and the shell thickness is chosen from those codes so the clearance lands inside a narrow window. Standard shells are not automatically right on an unground crankshaft, and clearance has a minimum as well as a maximum, so neither technician is correct.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — determine proper select-fit components (pistons, connecting rod and main bearings)Report a problem with this question

18. 18. During a diesel rebuild the technician finds one piston cooling jet bent out of alignment. Why must this be corrected before the engine is assembled?

    • A.Oil pressure will fall and the main bearings run dry
    • B.Oil will fill the crankcase and raise ring blowby
    • C.Oil will miss the piston underside and it can scuff✓ Answer
    • D.Oil will spray the cylinder wall and wash the film off

    The jet is aimed into the piston's cooling gallery or at the underside of the crown, and that oil spray is what carries away the heat of compression ignition from the piston. A misaimed jet leaves the crown without cooling, so the piston overheats, scuffs or cracks, and jet aim and clearance are checked as part of assembly.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — check condition, position and clearance of piston cooling jets (nozzles)Report a problem with this question

19. 19. A diesel engine's viscous crankshaft vibration damper is found leaking and dented. Why does this matter beyond the noise it makes?

    • A.The front crank seal leaks oil and soaks the accessory belt
    • B.The flywheel ring gear wears and the starter grinds
    • C.The crankshaft and gear train absorb torsional vibration✓ Answer
    • D.The drive belt slips and the alternator stops charging

    Each combustion event twists the crankshaft, and the damper's inertia ring absorbs those torsional pulses, which are far stronger on a diesel because cylinder pressures are much higher. With the damper failed the pulses pass into the crankshaft and the timing gear train, and cracked crankshafts and damaged gears follow.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — inspect crankshaft vibration damperReport a problem with this question

20. 20. A dual-mass flywheel is being inspected on a diesel before a new clutch goes in. Which check belongs in that inspection?

    • A.Free play checked by rocking the crank against the ring gear
    • B.Thickness checked with a micrometer at the mounting flange
    • C.End play checked by prying the flywheel away from the block
    • D.Runout checked with a dial indicator on the friction face✓ Answer

    Face runout is measured with a dial indicator sweeping the friction surface with the flywheel bolted up, because runout beyond specification makes the clutch grab and judder no matter how good the new disc is. The inspection also covers cracks and heat checking, ring gear condition and the mounting surfaces.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — inspect flywheel/flexplate and dual-mass flywheel, ring gear, mounting surfaces and runoutReport a problem with this question

21. 21. Main bearing clearance is being checked on a diesel block. Tech A says the bearing bore should be measured with the caps installed but left loose so the bore is not distorted. Tech B says the clearance can be checked with a plastic gauging strip crushed between the journal and the shell. Who is right?

    • A.Neither Tech A nor Tech B
    • B.Tech B only✓ Answer
    • C.Tech A only
    • D.Both Tech A and Tech B

    A bearing bore is only round and to size when the caps are torqued to specification, so measuring with loose caps gives a false reading and Tech A is wrong. Crushing a plastic gauging strip between the journal and the shell and reading its width against the scale is an accepted way to confirm clearance, so Tech B is right.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area C — check main bearing cap fit and bearing clearances (bore measured with caps torqued to specification)Report a problem with this question

22. 22. Read carefully: this question asks for the exception. All of these can raise measured crankcase pressure on a diesel engine EXCEPT:

    • A.worn compression rings letting combustion gas past the piston
    • B.a scored cylinder wall letting gas slip past the ring pack
    • C.a cracked piston passing cylinder pressure into the crankcase
    • D.worn valve guides drawing oil down the stems into the ports✓ Answer

    Crankcase pressure rises when combustion gas escapes past the piston into the crankcase, which is why worn rings, a scored bore and a cracked piston all raise it. Worn valve guides let oil move the other way, down the stems into the ports, so they cause oil consumption and blue smoke without adding gas to the crankcase.

    Source: ASE Automobile Study Guide, Test A9 Task List, Area A/C — perform crankcase pressure (blowby) test; inspect pistons, rings and cylinder wallsReport a problem with this question

Practice questions based on the ASE A9 Light Vehicle Diesel Engines task list. This site is not affiliated with or endorsed by the National Institute for Automotive Service Excellence (ASE). Injection pressures, torque specifications, clearances, glow-plug and heater resistance values, regeneration temperatures and service intervals are set by the engine manufacturer, differ by engine family and model year, and are revised by service bulletin — always work to the service information for the vehicle in front of you, never to a practice test. Emissions and aftertreatment hardware varies by model year and market. Diesel fuel systems operate at pressures that can inject fuel through skin; follow the manufacturer's depressurization and safety procedures. Confirm current test content and registration requirements with ASE before you test. About ASE certification →