Engine Top End Construction - Chapter Review

What is a bare cylinder head normally made of?

• A. Aluminum or cast iron.

• B. Brass or cast iron.

• C. Cast iron or steel.

• D. Magnesium or aluminum.

Answer explanation

A bare cylinder head is typically made of aluminum or cast iron due to their favorable properties such as lightweight and good thermal conductivity, making option A the correct choice.

A valve guide is a separate sleeve forced into a hole machined in the cylinder head.

• integral

• welded

• pressed-in

• forged

Answer explanation

A valve guide is typically a pressed-in component, meaning it is inserted into the cylinder head hole with force to ensure a tight fit. This distinguishes it from integral or welded types, which are not separate sleeves.

The most common valve seat angles are

• 45° and 35°

• 45° and 30°

• None of the above

• 25° and 35°

Answer explanation

The most common valve seat angles are 45° and 30°. These angles are widely used in engine design for optimal sealing and performance, making this the correct choice.

An interference angle is a 1/2° – 1° difference between the valve seat face angle and the angle of the valve face.

• True

• False

Answer explanation

The statement is true. An interference angle refers to the small difference, typically between 1/2° and 1°, between the valve seat face angle and the valve face angle, which is crucial for proper sealing.

Identify the two different types of valve guides and seats, as well as the related components in the following illustration.

​ ​ ​ ​ ​

a

b

c

d

e

f

g

Cylinder Head

Integral valve seat

Integral valve guide

Pressed-in valve seat

Valve Stem

Valve Face

Pressed-in valve guide

A stellite valve is often used in engines designed to burn __________ fuel.

Answer explanation

A stellite valve is often used in engines designed to burn unleaded gasoline fuel due to its resistance to wear and corrosion, making it suitable for high-performance applications.

A stellite valve seal is shaped like a cup and can be made of neoprene rubber or plastic.

• True

• False

Answer explanation

The statement is false because a stellite valve seal is typically made of stellite, a cobalt-chromium alloy, not neoprene rubber or plastic.

A valve spring shield is normally used with an O-ring type oil seal.

• True

• False

Answer explanation

True. A valve spring shield is designed to work with an O-ring type oil seal, providing additional support and preventing oil leakage, which is essential for proper engine function.

What is valve spring free length?

• The circumference of the valve spring.

• The length of the valve spring when fully compressed in the valve train.

• The length of the valve spring when removed from the engine.

• The diameter of the valve spring.

Answer explanation

Valve spring free length refers to the length of the valve spring when it is not under any compression, specifically when it is removed from the engine. This measurement is crucial for ensuring proper spring function.

Valve ______ occurs when the valve fails to close entirely at high engine speeds because the spring is too weak.

• clatter

• runaway

• spark

• float

Answer explanation

Valve float occurs when the valve does not close completely at high engine speeds due to a weak spring, leading to performance issues. This term specifically describes the failure of the valve to seat properly.