Five free practice questions on cylinder head and valve train: content area B of the ASE A9 Light Vehicle Diesel Engines test, 5 of its 50 scored questions (10%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A light-duty diesel's aluminum cylinder head is off for a gasket replacement. Its deck is eaten away in pits around several coolant passages, while the deck around the combustion chambers is clean and smooth. What does this pitting point to?
- Coolant with spent corrosion inhibitors
- Combustion gas cutting past the fire rings
- Head bolts torqued past the specification
- Oil seeping between the gasket and deck
Show the answer
A. Correct. Coolant protects aluminum only while its inhibitors last; once they are used up, the coolant attacks the metal it touches, around the coolant passages. Test the coolant's condition and the system for stray voltage, and repair or replace the head if the pits reach the gasket's sealing areas.
Why not the others
B. Combustion leaks erode the deck at the edges of the combustion chambers, and those areas are clean here. Pitting confined to the coolant passages points to coolant that has lost its corrosion protection.
C. Over-torqued bolts can distort the deck or pull threads, but they do not eat pits into the metal around the coolant passages. That pattern comes from coolant whose inhibitors are used up.
D. Engine oil does not corrode aluminum, and a seep would not single out the coolant passages. Pits around the coolant passages come from coolant that no longer protects the metal.
ID A9-B-005 · Task A9-B-3 (ASE task list)
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On a light-duty V8 diesel, each bank's injector wiring runs under the valve cover and leaves through a sealed pass-through connector in the cover. Right after both covers were removed and refitted to reseal them, the ECM sets an injector circuit DTC for one cylinder. Any of these could cause it EXCEPT:
- a slight oil seep at the gasket's outer edge.
- a wire pinched between the cover and the head.
- a pass-through connector not fully latched.
- a terminal left loose at that cylinder's injector.
Show the answer
A. Correct. Oil seeping out at the outside of the gasket is a leak to fix, but it cannot open or short an injector circuit right after the job. Each of the other faults disturbs the wiring the cover work handled, which is why a circuit DTC that appears right after a valve cover job sends the technician back under the cover first.
Why not the others
B. This could: wiring caught under the cover's sealing edge can be cut through or shorted to the head as the cover is tightened. An external oil seep, by contrast, does nothing to the circuit.
C. This could: a pass-through connector that is not fully latched can lose contact at one injector's terminals and set a circuit DTC. An oil seep at the gasket's outer edge cannot.
D. This could: an injector terminal or connector disturbed while the harness was moved, and not secured, opens the circuit or makes it intermittent. An external oil seep does not affect the circuit.
ID A9-B-010 · Task A9-B-8 (ASE task list)
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On some overhead-camshaft diesels, the gear that drives one camshaft from the other is made in two halves that a spring twists against each other. What does this split (scissor) gear do?
- Slips to save the valves if a piston hits
- Varies valve timing as engine speed rises
- Takes up backlash to quiet the gears
- Lets each camshaft be timed on its own
Show the answer
C. Correct. One half meshes normally and the spring-loaded half is twisted against the mating teeth, so there is no free play for the diesel's sharp torque pulses to rattle through. During installation the halves are commonly wound up and held with a pin or bolt that is removed once the gears are in mesh.
Why not the others
A. The spring is not a slip clutch; it holds the two halves against both faces of the mating teeth. A gear that slipped would lose valve timing, and the split gear's job is to take up backlash and keep the mesh quiet.
B. Varying valve timing is a cam phaser's job; the scissor gear's spring only removes backlash and does not change the camshafts' timing. Its purpose is quiet gear mesh.
D. Both camshafts stay locked in time with each other through the gear mesh; the spring only takes up the free play between the teeth. Its job is quiet, rattle-free gear mesh.
ID A9-B-013 · Task A9-B-11 (ASE task list)
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On many diesel cylinder heads, the injector fits into a thin copper or stainless steel sleeve that passes through the coolant jacket. What is the sleeve's main job?
- Damping injector vibration to quiet the engine
- Holding the injector down against firing pressure
- Insulating the injector so its tip runs hotter
- Sealing the injector's bore from the coolant
Show the answer
D. Correct. The sleeve is the wall between the coolant jacket and the injector's bore: it keeps coolant out of the bore and the cylinder, and its thin wall still lets the coolant draw heat from the injector's tip. A leaking sleeve lets coolant into the cylinder or combustion gas into the coolant.
Why not the others
A. The sleeve does nothing to combustion noise, which depends on how the fuel is injected and burns. The sleeve keeps coolant out of the injector's bore while the coolant draws heat from the injector through it.
B. The injector is held down by its clamp or hold-down bolt, not the sleeve. The sleeve separates the coolant from the injector's bore while letting the coolant cool the injector.
C. The sleeve is thin so that coolant can carry heat away from the injector; a hotter tip would coke and fail sooner. Its job is to seal out coolant while passing heat to it.
ID A9-B-016 · Task A9-B-5 (ASE task list)
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Many manufacturers warn against cleaning an aluminum diesel head's gasket surface with an abrasive pad or disc on a power tool. Why?
- It leaves grit that wears the bearings
- It polishes the deck too smooth to seal
- It work-hardens the aluminum so it cracks
- It heats the deck enough to warp the head
Show the answer
A. Correct. Abrasive pads and discs shed fine grit (aluminum oxide from the abrasive, plus metal) that the oil filter does not catch, and it has been known to ruin engine bearings soon after the repair. A spinning pad also cuts soft aluminum unevenly and can round the deck's narrow sealing areas; use the scraper and cleaning method the manufacturer approves.
Why not the others
B. An abrasive disc scratches and gouges the deck rather than polishing it. The concern is abrasive grit carried into the oil, where it wears bearings, plus uneven metal removal that spoils flatness.
C. Light abrasion does not harden aluminum enough to crack it. The real risk is abrasive grit carried into the oil and the bearings, plus uneven metal removal that spoils the deck's flatness.
D. A hand-held pad or disc does not heat a whole aluminum head enough to warp it. The problem is abrasive grit left in the passages and oil, where it wears bearings, and uneven removal of soft metal.
ID A9-B-017 · Task A9-B-1 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | A |
| Q2 | A |
| Q3 | C |
| Q4 | D |
| Q5 | A |
03What area B covers
This content area covers the cylinder head and valve train of a light-duty diesel: head removal, cleaning and crack checks, bolts, studs and threads, deck warpage and corrosion, valves, seats and springs, injector and glow plug sleeves, head gasket selection and bolt torque, pushrods, rockers, lifters and bridges, valve clearance, overhead camshafts and the timing drive.
The ASE test specification calls this content area “Cylinder Head and Valve Train Diagnosis and Repair”. It carries 5 of the 50 scored questions, 10% of the test.
- Clean and inspect the head, bolts and threaded holes
- Check deck flatness, corrosion and cracks
- Inspect valves, guides, seats, springs and seals
- Replace injector and glow plug sleeves
- Choose the head gasket grade and torque the bolts
- Inspect pushrods, rockers, lifters and valve bridges
- Set valve clearance and check camshaft bearing clearance
- Time the gear, chain or belt camshaft drive
04What the questions turn on
Gasket grade from protrusion
Head gasket grade is chosen from the greatest piston protrusion. Clearance is the gasket's compressed thickness minus that protrusion, and only one grade lands inside the range. The thickness before compression does not count, because torquing the head bolts crushes the gasket.
Set valves on compression
Valves are set at top dead center of the compression stroke, both lifters on their base circles. Set during overlap, the clearance grows once the lifters drop. A reading inside the no-adjustment range is left alone; one outside it is reset to nominal.
Sleeves keep coolant out
Injector and glow plug sleeves are the only wall between the coolant jacket and the bore. A leaking sleeve puts coolant in the bore or the cylinder, and a piston crown steam-cleaned of carbon marks the cylinder that is taking in coolant.
Lash, wear and bleed-down
As a valve face and seat wear, the valve sits deeper and its stem rises toward the rocker, so lash shrinks toward zero and the valve can burn. Hydraulic lifters compressed by rocker torque need time to bleed down before the crankshaft is turned.
05The other content areas
The A9 test has six content areas. Each has its own page of free questions:
The ASE A9 Light Vehicle Diesel Engines practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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