Question 1

The camshaft makes ________ for every revolution of the crankshaft.

Accepted Answer

The camshaft makes one half revolution for every full revolution of the crankshaft. This is because the camshaft operates the engine's valves and needs to open and close them once for every two crankshaft revolutions (in a four-stroke engine).

Question 2

Flat-bottom valve lifters rotate during operation because of the ________ of the camshaft.

Accepted Answer

The taper of the lobe on the camshaft causes the flat-bottom valve lifters to rotate during operation. This design ensures even wear on the lifter and cam lobe surfaces.

Question 3

If lift and duration remain constant and the lobe center angle decreases, then ________.

Accepted Answer

When the lobe center angle decreases, the camshafts are positioned closer together, which increases the period during which both the intake and exhaust valves are open simultaneously, thus increasing valve overlap.

Question 4

Which timing chain type is also called a "silent chain"?

Accepted Answer

Morse and flat link chains are both referred to as "silent chains" because of their quiet operation compared to other types of chains, such as roller chains.

Question 5

Two technicians are discussing variable valve timing. Technician A says that changing the exhaust valve timing helps reduce exhaust emissions. Technician B says that changing the intake valve timing helps increase low-speed torque. Who is right?

Accepted Answer

Both technicians are correct. Changing the exhaust valve timing can indeed help reduce exhaust emissions by ensuring more complete combustion. Adjusting the intake valve timing can increase low-speed torque by optimizing the air-fuel mixture's entry into the combustion chamber at lower speeds.

Question 6

Many technicians always use new pushrods because ________.

Accepted Answer

Pushrods are hollow and it is difficult to clean all the dirt out of the center.

Question 7

A DOHC V-6 has how many camshafts?

Accepted Answer

A DOHC (Dual Overhead Camshaft) V-6 engine has two camshafts per cylinder bank, totaling four camshafts.

Question 8

The intake valve opens at 39° BTDC (before top dead center) and closes at 71° ABDC (After bottom dead center). The exhaust valve opens at 78° BBDC (before bottom dead center) and closes at 47° ATDC (after top dead center). Which of these is correct regarding this cam timing?

Accepted Answer

The answer of The intake valve opens at 39° BTDC...

Question 9

Hydraulic valve lifters can make a ticking noise when the engine is running if ________.

Accepted Answer

The answer of Hydraulic valve lifters can make a ticking...

Question 10

Hydraulic lifters or hydraulic lash adjusters (HLA) may not bleed down properly and could cause an engine miss if ________.

Accepted Answer

Hydraulic lifters rely on the correct viscosity of oil to function properly. Using the wrong SAE-rated engine oil can affect the lifters' ability to maintain proper clearance, leading to issues like engine miss.

Question 11

Technician A says that the pushrods should be rotating while the engine is running if the camshaft and lifters are okay. Technician B says that the camshaft rotates at one-quarter the crankshaft speed. Who is right?

Accepted Answer

Technician A is correct because pushrods typically rotate slightly due to the design of the camshaft and lifters, indicating proper operation. Technician B is incorrect because the camshaft rotates at half the speed of the crankshaft, not one-quarter.

Question 12

Technician A says that silent chains are quieter than roller chains and do not stretch with use. Technician B says that on overhead valve engines, the camshaft is usually placed in the block above the crankshaft. Who is right?

Accepted Answer

The answer of Technician A says that silent chains are...

Question 13

Which term is used to describe the number of degrees of crankshaft rotation for which the valve is lifted off the seat?

Accepted Answer

Duration is the term used to describe the number of degrees of crankshaft rotation for which the valve is lifted off the seat. It measures how long a valve remains open during the engine cycle.

Question 14

Technician A says that valve overlap is the number of crankshaft degrees that both valves are closed. Technician B says that valve overlap is the number of degrees that both valves are open. Who is right?

Accepted Answer

Valve overlap refers to the period during the engine's cycle when both the intake and exhaust valves are open at the same time. This occurs near the end of the exhaust stroke and the beginning of the intake stroke. Technician B is correct.

Question 15

Camshafts turn at which of these?

Accepted Answer

Camshafts in a four-stroke engine turn at half the speed of the crankshaft. This is because for every two revolutions of the crankshaft, the camshaft completes one revolution, ensuring that the intake and exhaust valves open and close once per cycle.

Question 16

If the exhaust valve opens at 57° before BDC (before dead center) and closes at 29° after TDC (top dead center), what is the exhaust valve duration in degrees?

Accepted Answer

The exhaust valve duration is calculated by adding the degrees before BDC to the degrees after TDC and then adding 180° (the degrees from BDC to TDC). So, 57° + 29° + 180° = 266°.

Question 17

What determines the amount of valve overlap?

Accepted Answer

Valve overlap is determined by the camshaft design, which dictates when the intake and exhaust valves open and close in relation to the position of the piston.

Question 18

Valve lifters are designed in which of these ways?

Accepted Answer

Valve lifters are often dome-shaped to assist in rotation, which helps in even wear and proper functioning.

Question 19

On an engine with variable cam timing, the cam timing can be changed by use of ________.

Accepted Answer

Variable cam timing engines can use either a spline cam phaser or a vane cam phaser to adjust the cam timing.

Question 20

Two technicians are discussing an engine with an interference design. Technician A says if a valve remains open when its cylinder reaches TDC, the piston may strike the valve. Technician B says if a valve remains open when its cylinder reaches TDC, valvetrain damage can result. Which technician is correct?

Accepted Answer

Both technicians are correct. In an interference engine design, if a valve remains open as the piston reaches Top Dead Center (TDC), the piston can strike the valve, potentially causing damage to the valve, piston, and other components, which includes the valvetrain.

Quiz 32: Camshafts and Valve Trains