Mazda Training manual - part 239

 

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Mazda Training manual - part 239

 

 

 
3 – SHORT BLOCK 

 

41

Piston Engine Fundamentals

TC010-05-01S

Oil Rings

 

 

Oil rings help lubricate the cylinder walls and control the flow of oil. Oil is 
constantly sprayed or splashed onto the walls of the cylinders, where it 
keeps the metal parts from wearing against each other. Oil also helps cool 
the cylinder, and it washes carbon and dirt particles from the cylinder 
walls. 

 

So much oil is on the walls of the cylinders that it won’t all fit into the small 
clearance next to the piston when the compression rings scrape the walls. 
To provide a place for the extra oil to go, the oil ring is usually segmented  
— made of three pieces — as shown in Figure 28. 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
As the oil is scraped, it flows behind the expander ring to holes in the ring 
groove. These holes direct the oil to the open space inside the piston skirt, 
where it eventually drains back into the crankcase. 

 

The expander ring is a steel ring installed between the two oil rings. These 
oil rings are made of more flexible material than compression rings. The 
expander ring holds the oil rings tightly against the cylinder wall, improving 
their ability to scrape the oil. 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 

FIGURE 28. Oil 
rings are 
usually made of 
three pieces, or 
segments. 
 

Oil rings 

Expander 

ring 

 

 
 
 
 
 

 
 
 
 

 
3 – SHORT BLOCK 

 

42

Piston Engine Fundamentals

TC010-05-01S

REVIEW EXERCISE 4

 

 
Fill in the words that correctly complete these sentences. Check your answers with the 
answer key on page 44.

 

 
1.      The part that attaches the piston to its connecting rod is called the 

___________________ . 

 
2.      When the pin bore is not drilled directly in the center of the piston, it is called an 

___________________ pin bore. 

 
3.   Cam-ground pistons have a slightly ___________________ shape. 
 
4.   The piston rings that scrape the cylinder walls and seal the combustion chamber are 

called ___________________ rings. 

 
5.      The expander ring is usually part of the ___________________ ring on a piston. 
 
6.      Which of these symptoms would you expect to find in an engine that has worn or 

damaged piston rings? More than one answer may be correct. 

 

A.  excessive oil consumption 
 
B.    blue smoke in exhaust 
 
C.  leaking coolant 
 
D.  high idle 

 

 
4 – VALVE TRAIN 

 

43

Piston Engine Fundamentals

TC010-05-01S

Engines have passages that let the air-fuel mixture into the cylinders and let exhaust gases 
out after the mixture has burned. These passages, called valve ports, must be sealed very 
tightly during parts of the four-stroke cycle. 
The valves must open and close the ports at precise times. 
 
The engine parts that open and close the valves are called the valve train. This section 
describes how the valve train operates. 
 
 
 
OBJECTIVES

 

 
 
After completing this section, you will be able to: 
 

•  Identify the important parts of the cylinder head and gasket and describe their 

functions. 

 

•  Identify important parts of valves and describe how they operate. 
 

•  Describe the advantages of multi-valve engines. 
 

•  Describe how the valve seals against the valve seat. 
 

•  Describe how valve guides hold the valve in the cylinder head. 
 

•  Identify important parts of the valve spring and retainer assembly. 
 

•  Describe the differences among OHV, SOHC, and DOHC valve trains. 
 

•  Identify the four types of Mazda camshaft drives. 
 

•  Describe how camshafts are designed. 
 

•  Describe the differences between manual valve adjustment and automatic valve 

adjustment. 

 

•  Describe how pushrods and rocker arms transfer motion to the valves. 

 
4 – VALVE TRAIN 

 

44

Piston Engine Fundamentals

TC010-05-01S

Answers to 
Review 
Exercise 4

 

 
1. piston 

pin

 

 
2. offset

 

 
3. oval

 

 
4. compression

 

 
5. oil

 

 
6.  A and B

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
FIGURE 29. The 
cylinder head 
contains the 
valve train 
components and 
spark plugs.

 

 

Right cylinder 

head for V-6 

engine 

Intake port 

Valve 

Spark plug 

Exhaust port

 

CYLINDER HEAD

 

 
The cylinder head bolted on top of the cylinder block, forms the roof of the 
combustion chamber. The cylinder head: 
 
•  Seals the tops of the cylinders. 
 
•  Holds the spark plugs. 
 
•  Provides seats, guides, and ports for the intake and exhaust valves. 
 
•  Holds the valve train. 
 
•  Provides mountings for the intake and exhaust manifolds. 
 
 
Construction

 

 
Like the cylinder block, the cylinder head is made of cast iron or aluminum 
alloy. The intake and exhaust manifolds are mounted to the cylinder head, 
against the valve ports, shown in the side of the head in Figure 29. Most 
V-6 or V-8 engines have two cylinder heads, one for each bank of 
cylinders. (This drawing shows the right cylinder head on a typical V-6 
engine.) The top part of the cylinder head is manufactured so that the 
valve rocker arms and/or other parts of the valve train can be mounted on 
it. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

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