ASE A9 Cylinder Head and Valve Train — Questions and Answers
Question 1: When checking a diesel cylinder head for warpage, which method is correct?
- Lay a straightedge on the machined surface and use a feeler gauge to measure gaps lengthwise, crosswise and diagonally (Correct answer)
- Measure the thickness of the head at the center only with a dial caliper
- Press a bearing plastigage strip across the deck and measure its width
- Spray the surface with dye penetrant and look for linear indications
Correct answer: Lay a straightedge on the machined surface and use a feeler gauge to measure gaps lengthwise, crosswise and diagonally
Flatness is verified by placing a precision straightedge on the deck and sliding feeler gauges under it. Readings are taken along the length, across the width and diagonally.
Head warpage is measured with a machinist's straightedge and feeler gauges. Check several positions: along the length, across the width and diagonally, and compare the largest gap to the manufacturer's flatness limit. Dye penetrant finds cracks, not warpage. Plastigage measures bearing clearance. A single caliper reading of thickness says nothing about flatness. If the head exceeds the limit, it must be resurfaced, if that is allowed, or replaced.
Question 2: Why must a diesel cylinder head's thickness be measured before it is resurfaced?
- To confirm the valve guides are still the correct length
- To make sure removing material will not drop it below the minimum thickness specification (Correct answer)
- To calculate the correct head gasket torque
- To determine the correct coolant capacity of the engine
Correct answer: To make sure removing material will not drop it below the minimum thickness specification
Each resurfacing removes metal from the deck. Going below the minimum specified thickness can alter combustion chamber geometry, injector protrusion and valve-to-piston clearance, and can weaken the head.
Manufacturers publish a minimum head thickness, or a maximum material removal amount. A head machined below that limit changes compression ratio, injector tip protrusion and the clearance between valves and pistons. It also weakens the casting and can disturb the timing-gear or camshaft geometry on some designs. Measure the thickness first. If the head is already near the limit, replace it rather than machining it.
Question 3: A diesel engine has coolant in the oil but no external leaks, and the head gasket has been ruled out. What is the best way to test the cylinder head for cracks?
- Perform a compression test on each cylinder
- Check the cranking vacuum at the intake manifold
- Pressure test the head's coolant passages after plugging all ports, and check for leaks (Correct answer)
- Bench test the injectors on a nozzle tester
Correct answer: Pressure test the head's coolant passages after plugging all ports, and check for leaks
Plugging the water ports and applying air or water pressure to the coolant passages shows leaks through cracks into the oil, intake, exhaust or cylinder areas.
Cracks usually form between valve seats, injector bores or the water jacket and an oil gallery. To test, remove the head, seal the coolant openings with plates and apply regulated pressure, then submerge the head in warm water or watch for dripping. Bubbles or leaks show the crack location. A compression test shows sealing problems but cannot find coolant passage cracks.
Question 4: After a valve job on a diesel engine, which measurement most directly shows whether the valve was sunk too deeply into the head?
- Valve spring free height
- Valve stem height or valve recession measured from the deck or the spring seat (Correct answer)
- Pushrod runout
- Rocker arm shaft diameter
Correct answer: Valve stem height or valve recession measured from the deck or the spring seat
Valve stem height, or recession relative to the deck, shows how far the valve has moved into the head as the seat and face are ground. Excess recession can change spring installed height and compression.
Grinding the valve face and seat lowers the valve into the head. Measure the valve stem tip height, or the recession of the valve face below the deck, and compare it with the specification. Too much recession can lead to incorrect installed spring height, poor flow and altered compression. Specifications often allow a maximum amount, after which the valve or seat insert must be replaced.
Question 5: Which valve spring measurement shows that a spring is bent or distorted rather than weak?
- Squareness, checked against a square on a flat surface (Correct answer)
- Spring pressure at installed height
- Free length
- Spring wire diameter
Correct answer: Squareness, checked against a square on a flat surface
Standing the spring on a flat surface next to a square and measuring the gap at the top shows if it is out of square. Free length and pressure show weakness or shortening, not leaning.
Springs must be inspected for free length, squareness and load. To check squareness, put the spring on a flat plate against a machinist's square and rotate it, then measure the gap at the top. A spring out of square more than the specification, often around 1/16 inch, can cause side loading, uneven wear on the valve guide and valve stem and eventual spring failure. Replace springs that fail any of the tests.
Question 6: A diesel engine has tight valve lash on the exhaust valves, below specification. What is the most likely result if it is not corrected?
- The valve will not close fully and can burn from lack of heat transfer to the seat (Correct answer)
- Excessive valve noise at idle
- Reduced valve spring pressure
- Higher oil pressure
Correct answer: The valve will not close fully and can burn from lack of heat transfer to the seat
If lash is too tight, the valve can be held slightly off its seat as parts expand with heat. This lets hot gas leak past and prevents the valve from cooling through the seat, so it burns.
Valve lash provides room for thermal expansion of the valve train. When the clearance is too small, the valve train can hold the valve open slightly when hot. Combustion gases then leak past, the face overheats because it cannot transfer heat to the seat, and the valve can burn or the seat can be damaged. Loose lash on the other hand makes ticking noise and reduces valve lift. Always adjust lash with the engine at the specified temperature and the correct cylinder position.
Question 7: While inspecting a pushrod, a technician rolls it on a flat surface and sees it wobble. What does this indicate?
- The pushrod is bent and must be replaced (Correct answer)
- The pushrod is operating correctly
- The cam lobe is excessively worn
- The lifter is collapsed
Correct answer: The pushrod is bent and must be replaced
A straight pushrod rolls smoothly on a flat surface. Wobble or a visible gap means it is bent, and a bent pushrod must be replaced.
Pushrods are inspected by rolling them across a flat plate or by using a dial indicator while rotating them in V-blocks. Any visible wobble or runout beyond the specification means the rod is bent. Bent pushrods often result from valve train interference, a stuck valve or incorrect lash. Also inspect the ends for wear and check the oil passage in hollow pushrods for blockage. Always find the cause of the bend before reassembling.
Question 8: A technician measures a valve stem with a micrometer and the valve guide bore with a small-hole gauge. Which condition does excessive stem-to-guide clearance most commonly cause?
- Hard starting from low compression pressure caused by a weak starter
- Oil consumption and blue smoke as oil is drawn past the valve stem (Correct answer)
- Higher boost pressure
- Stuck injectors
Correct answer: Oil consumption and blue smoke as oil is drawn past the valve stem
Worn guides let oil pass between the stem and guide, particularly on the intake side, burning in the cylinder and producing blue smoke. It also causes the valve to seat unevenly.
Stem-to-guide clearance is determined by subtracting the stem diameter from the guide bore. Too much clearance allows the valve to rock, which causes uneven seat contact and wear, and lets oil be pulled past the stem seal. The result is oil consumption and blue smoke. The fix is to replace or repair the guide, and then reface the valve and grind the seat concentric to the new guide.
Question 9: What is the correct way to tighten diesel cylinder head bolts that are torque-to-yield?
- Reuse them and tighten to the torque value in one step in any order
- Use new or approved bolts and follow the specified sequence and torque-plus-angle procedure (Correct answer)
- Add thread sealant to each bolt and tighten them to maximum torque
- Tighten them from the outside to the center in one pass
Correct answer: Use new or approved bolts and follow the specified sequence and torque-plus-angle procedure
Torque-to-yield bolts stretch permanently when tightened, so they are generally replaced and the manufacturer's sequence, torque steps and angle procedure must be followed.
Torque-to-yield (stretch) bolts are tightened by torque followed by a specified angle of turn, which stretches them into the plastic zone to give accurate and uniform clamping load. They cannot be relied on to give the same clamping load when reused, so follow the service information on replacement. Tighten in the published sequence, usually from the center outward in a spiral, in several stages. Also clean and lubricate threads only as the manufacturer states.
Question 10: A technician installs a new injector sleeve and measures injector tip protrusion. Why is this measurement important?
- It sets the fuel injection timing
- It controls the fuel pressure in the rail
- It ensures the nozzle tip is positioned correctly in the combustion chamber for spray pattern and proper cooling (Correct answer)
- It adjusts the valve lash
Correct answer: It ensures the nozzle tip is positioned correctly in the combustion chamber for spray pattern and proper cooling
Protrusion affects where fuel is sprayed in the combustion chamber and how well the tip is cooled. Incorrect protrusion can cause poor combustion, smoke or a damaged injector or piston.
Injector tip protrusion is measured from the head's combustion face to the nozzle tip using a gauge or depth tool. Too little or too much protrusion changes the spray target, and can lead to poor combustion, smoke, higher temperature at the tip or carbon buildup. It is also affected by head thickness after resurfacing and by the thickness of the injector seat washer or sleeve. Adjust with shims or correct components as specified.
ASE A9 Cylinder Head and Valve Train
When checking a diesel cylinder head for warpage, which method is correct?
What Practice Test Geeks adds beyond an AI chat for ASE A9
An AI chatbot can quiz you, but it can't reproduce the exam conditions or keep your record. Here you get:
- A timed, full-length ASE A9 mock exam — 60 questions in 75 minutes with a 70% pass mark, modeled on the official exam's question count and time limit, followed by a score report broken down by exam domain.
- A fixed ASE A9 question bank: the same test every attempt, so your score is comparable from one try to the next instead of changing with every regenerated quiz.
- Progress saved on your device: completed tests, scores and missed questions stay in My Progress, so you can retake only what you got wrong.
- A printable ASE A9 cheat sheet you can print or save as a PDF.
- ASE A9 flashcards built from the same question bank.
These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy
Sources & references
Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy
- ase.com — Eligibility, exam format, renewal, time limit, registration deadline, retake policy, score release, score validity, test delivery, fees · verified Nov 2026