Question 1

Which of the following reasons best explains why diesel engine cylinder heads use more head bolts per cylinder?

Accepted Answer

Diesel engines have higher cylinder pressures compared to gasoline engines, necessitating more head bolts per cylinder to ensure a secure and tight seal to withstand these pressures.

Question 2

The purpose of a variable intake swirl mechanism is to __________.

Accepted Answer

A variable intake swirl mechanism is designed to improve the mixing of air and fuel in the combustion chamber, which can lead to more complete combustion and thus reduce particulate emissions.

Question 3

Which of the following cylinder head valve train arrangements can provide the highest injection pressures?

Accepted Answer

Overhead camshaft arrangements allow for more precise control of valve timing and higher injection pressures due to their direct actuation of the valves, reducing the complexity and friction associated with pushrod systems.

Question 4

Excessively worn valve train components are more commonly found on which valve actuation mechanism?

Accepted Answer

Exhaust valves are subjected to higher temperatures and pressures than intake valves, which leads to increased wear.

Question 5

The most common valve angle for poppet valves is ______.

Accepted Answer

The most common valve angle for poppet valves is 45° because it provides a good balance between flow efficiency and sealing capability.

Question 6

While examining a valve spring from an engine that is being overhauled, technician A says that valve springs should be checked for free length and cracks. Technician B says the spring should be checked for compressed spring pressure, nicks, and straightness. Who is correct?

Accepted Answer

Both technicians are correct. Valve springs should be checked for free length, cracks, compressed spring pressure, nicks, and straightness to ensure they are in good condition and functioning properly.

Question 7

When adjusting the valve clearances on the engine, technician A says the valves are closed when the valve lifter or follower is on the inner base circle of the camshaft lobe. Technician B says that valves are always adjusted when closed while the lifter or follower is on the camshaft lobe outer base circle. Who is correct?

Accepted Answer

Technician A is correct because the valves are closed when the valve lifter or follower is on the inner base circle of the camshaft lobe, which is the correct position for adjusting valve clearances.

Question 8

Technician A says that before reusing any head bolt, it should be inspected for nicks and pitting. Technician B says the service manual should be consulted before reusing because some bolts can only be used once. Who is correct?

Accepted Answer

Both technicians are correct. Head bolts should be inspected for damage before reuse, and the service manual should be consulted as some bolts are designed for single use only.

Question 9

While discussing variable valve timing in diesel engines, technician A says that only dual overhead camshafts (DOHCs) use variable valve timing. Technician B says variable valve timing is not commonly used in diesel engines. Who is correct?

Accepted Answer

Variable valve timing is not as commonly used in diesel engines as it is in gasoline engines, due to the different combustion processes and engine design priorities.

Question 10

Valve overlap occurs during _____________.

Accepted Answer

Valve overlap occurs at the end of the exhaust stroke and the beginning of the intake stroke, allowing for better scavenging of exhaust gases and improved intake of the air-fuel mixture.

Question 11

A valve failure with a break between the head and stem was likely caused by _______.

Accepted Answer

The answer of A valve failure with a break between...

Question 12

Which valve guide in a turbocharged diesel engine will more likely not have valve stem seals?

Accepted Answer

The answer of Which valve guide in a turbocharged diesel...

Question 13

Technician A says that the cam gear rotates two times faster than the crank gear. Technician B says the cam gear rotates at half the engine speed. Who is correct?

Accepted Answer

The camshaft rotates at half the speed of the crankshaft in a four-stroke engine, so Technician B is correct.

Question 14

Technician A says that rear geartrains are used on engines because they operate with less noise. Technician B says that rear geartrains are used because they have less wear than a front geartrain mechanism. Who is correct?

Accepted Answer

Rear geartrains are used on engines because they operate with less noise and have less wear than a front geartrain mechanism.

Question 15

Technician A says that overhead cam engines with unit injectors can provide the greatest actuation force for the highest injection pressures. Technician B says that pushrod engines that use a low-mounted camshaft can provide the same force as an overhead camshaft engine to its unit injectors. Who is correct?

Accepted Answer

Technician A is correct because overhead cam engines can provide greater actuation force due to their direct actuation of the injectors, which is beneficial for achieving higher injection pressures. Pushrod engines, on the other hand, have more components between the camshaft and the injectors, which can reduce the force transmitted.

Question 16

The maximum allowable warpage for a cylinder head is approximately ___________.

Accepted Answer

The maximum allowable warpage for a cylinder head is typically around 0.004-0.006 inches, which is a common specification for maintaining proper sealing and engine performance.

Question 17

Which of the following is the most common method for achieving consistent head gasket clamping force on today's diesel engines?

Accepted Answer

The torque-turn method is commonly used to achieve consistent clamping force by tightening bolts to a specified torque and then turning them a specific angle.

Question 18

While installing a cylinder head, technician A says the threads in cylinder head bolts must be lubricated before installation. Technician B says that only the underside of the bolt head requires lubrication and that the threads only need be clean. Who is correct?

Accepted Answer

The answer of While installing a cylinder head, technician A...

Question 19

Technician A says that fiber gaskets are the best and most commonly used gaskets in modern diesel engines. Technician B says that MLS gaskets are now the most commonly used head gaskets. Who is correct?

Accepted Answer

MLS (Multi-Layer Steel) gaskets are the most commonly used head gaskets in modern diesel engines due to their durability and ability to withstand high pressures and temperatures.

Question 20

Technician A says that whether combustion gases are leaking into the engine can be detected by measuring whether fuel hydrocarbons are present in the coolant. Technician B says that excessive gas pressure in the cooling system can indicate a head gasket leak. Who is correct?

Accepted Answer

Excessive gas pressure in the cooling system can indicate a head gasket leak, as combustion gases may enter the cooling system, causing increased pressure. Measuring hydrocarbons in the coolant is not a standard method for detecting combustion gas leaks.

Quiz 6: Cylinder Heads and Valve Train Mechanisms