Mazda Training manual — part 246

4 – VALVE TRAIN

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Piston Engine Fundamentals

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PUSHRODS (OHV)

In an OHV engine, pushrods transfer the lifting motion from the camshaft
and lifters to the valves. Pushrods are made of stiff steel tubing, with cups
or balls on the ends to mate with the lifters and rocker arms.

The pushrods flex slightly in normal operation, and this flexing is taken into
account when the cam lift is designed. On some engines, pushrods come
in varying lengths to provide an initial clearance adjustment with hydraulic
lifters.



ROCKER ARMS

The rocker arm reverses the direction of lift from the pushrod or camshaft
to the valve. Mazda engines use shaft-pivoted rocker arms, as shown in
Figure 50. The rocker arm is made of aluminum, and a pivot is drilled out
so the rocker arm can run on a hollow rocker arm shaft.

FIGURE 50.
Rocker arms are
fitted to shafts.

Rocker arm
shaft

Shaft-pivote
d rocker arm

Valve

Pushrod

4 – VALVE TRAIN

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Piston Engine Fundamentals

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REVIEW EXERCISE 6

Fill in the words that correctly complete these sentences. Check your answers with the
answer key on page 73.

1. The space between the end of the valve stem and the rocker arm is called

_________________________________.

2. A(n) __________________ uses oil pressure and a plunger to eliminate the need for

manual valve adjustments.

3. In an OHV engine, the ______________________ transfers the lifting motion from the

camshaft and lifters to the valves.

4. A ___________________________ changes the direction of pushrod or camshaft

motion.

5. A ticking noise from the top of the engine at one half crankshaft speed may be caused

by:

A. excessive valve clearance
B. worn cylinders
C. a clogged HLA
D. carbon build-up

5 – LUBRICATION SYSTEM

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The lubrication system provides a steady supply of pressurized oil to the moving parts of
the engine. Lubrication reduces friction and keeps parts from wearing against each other.
Oil also helps cool, clean, and reduce noise by constantly recirculating the engine oil
through an external filter. This section describes how the lubrication system works.



OBJECTIVES

After completing this section, you will be able to:

•

Identify important parts of the lubrication system and describe how they operate.

•

Describe how oil flows through the lubrication system.

•

Describe the differences between rotor-type and gear-type oil pumps.

•

Describe how the oil filter traps dirt and debris in the oil.

•

Describe the materials used in oil seals and gaskets.

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FIGURE 51. The
lubrication
system provides
a steady supply
of pressurized
oil to moving
engine parts.

Oil pan

Oil strainer

Oil pump

Oil filter

SYSTEM COMPONENTS

Some important parts of the lubrication system are shown in Figure 51.
These parts are described in the following paragraphs.