Mazda Training manual - part 245

 

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Mazda Training manual - part 245

 

 

 
4 – VALVE TRAIN 

 

65

Piston Engine Fundamentals

TC010-05-01S

VALVE ADJUSTMENT

 

 
When a valve closes, there must be a small amount of clearance between 
the end of the valve stem and the rocker arm. This clearance is called by 
various names such as valve lash, tappet clearance, or valve clearance. 
 
Engines that have solid lifters require periodic valve adjustments to make 
sure the clearance is correct. The proper valve clearance eliminates noise 
and excess friction. 
 
In some engines, the clearance is adjusted by using shims, which are small 
metal disks that come in various thicknesses. Figure 46 shows a tappet 
and adjustment shim. By changing the thickness of the shim, the technician 
adjusts the valve clearance. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Valve Clearance

 

 

The purpose of valve clearance is to make sure that the valve can close 
tightly against its seat during compression and combustion. With no 
clearance, the valve can be held slightly off its seat, causing compression 
pressure to leak past the valve. When the valve remains partially open, 
the valve head does not transfer heat to the seat, and combustion gases 
will gradually burn the valve away. 

 

On the other hand, if there is too much clearance, the valve train parts can 
hammer against each other, causing a ticking noise often called ticking 
valves. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 46. In 
some engines, a 
shim is used to 
adjust the valve 
clearance.

 

 

Adjustment 
shim

 

Tappet

 

 

 
4 – VALVE TRAIN 

 

66

Piston Engine Fundamentals

TC010-05-01S

Answers to 
Review 
Exercise 5

 

 
1. face

 

2. valve 

guide

 

3. heat

 

4. working 

height

 

5. C 

(DOHC)

 

6. A 

(OHV)

 

7. B 

(SOHC)

 

8. timing 

belt, 

timing chain

 

9. B, D

 

 
 
FIGURE 47. 
Hydraulic lash 
adjusters auto- 
matically adjust 
valve clearance. 
 

Camshaft

 

Bucket-type 

hydraulic 

lash 

adjusters 

(HLAs) 

 

HYDRAULIC LASH ADJUSTERS (HLA) 
 
On other engines, the valve clearance is adjusted automatically by 
hydraulic lash adjusters (HLAs)

. HLAs eliminate the need for manual valve 

adjustments. 
 
 
Description and Operation

 

 
The HLA is mounted above the valve stem. A bucket-type HLA is 
positioned between the top of the valve stem and the camshaft, as shown 
in Figure 47. In this design, the camshaft directly contacts the top of the 
HLA. In some engines, a rocker arm-mounted HLA fits between the valve 
stem and the rocker arm. (Rocker arm-mounted HLAs are described on 
page 68.) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
4 – VALVE TRAIN 

 

67

Piston Engine Fundamentals

TC010-05-01S

Bucket-Type HLA

 

 

The bucket-type HLA, shown in Figure 48, has a bucket body that contains 
two oil chambers. Movement of oil between these two chambers is 
controlled by a check ball and spring. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As the oil moves from one chamber to the other, a spring-controlled 
plunger moves up and down, and contacts the top of the valve stem. 

 

 

 

 

 

 

 

 

FIGURE 48. A 
bucket-type HLA 
has two oil 
chambers, a 
check ball, and a 
plunger. 
 

Bucket 
body 
Body 

Plunger 
spring 

Check ball 
cage 

Check ball 

Check ball 
spring 

Plunger 

 

 
4 – VALVE TRAIN 

 

68

Piston Engine Fundamentals

TC010-05-01S

 

 
 
 
 
 
 

FIGURE 49. 
Rocker arm- 
mounted HLAs 
are positioned 
between the 
valve stem and 
the rocker arm. 

 

Rocker 
arms

 

HLAs

 

Camshafts

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Rocker Arm-Mounted HLA

 

 

Rocker arm-mounted HLAs operate much like bucket-type HLAs, except 
that the top of the HLA contacts the rocker arm, rather than the camshaft. 
Figure 49 shows how rocker arm-mounted HLAs are positioned in a DOHC 
engine. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
An HLA mounted on a rocker arm does not have a bucket body, but the 
check ball, plunger, and body work the same way to maintain a valve 
clearance of 0. 

 
 

Regular Oil Changes

 

 

Because the plunger and body of the HLA fit so closely together, regular 
oil changes according to the maintenance schedule are very important. 
Even small particles of dirt can clog an HLA, resulting in a ticking noise. 
Regular oil changes help prevent HLA noise. 
 

 

 

 

 

 

 

 

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