Performing Gas Engine Tune Up

A blown head gasket also causes a low reading during a wet compression test. The
gasket has burned away and compression pressure leaks between the cylinder block
and head. Low or no compression in two adjacent cylinders is probably due to a blown
head gasket between the two cylinders.
Whatever the cause—rings, pistons, cylinder walls, valves, gaskets—the cylinder head
must be removed to correct the trouble. The exception is an improper valve adjustment
that holds the valves slightly off their seats. Valves are adjusted with the cylinder head
in place.

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ASSESSMENT TASKS:

These assessment tasks should be completed when you are confident that you can
check/replace fuel filter and air cleaner. Assessment needs to conform to the rules of
evidence. Therefore:
• You will need to participate and complete the learning activities
• You will demonstrate tasks to the required standard

• You will answer oral and written questions
• You will complete the assessment tool

OBSERVATION CHECKLIST:

Self Component Trainer’s check
check
Competent Not yet
competent

Compression test is performed properly.

Results of compression tests are reported to
instructor.

Engine components are cleaned.

Tools are properly used and stored.

Work area is cleaned.

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PERFORMANCE TEST

Learner's Name Date
Competency: Perform Gas Engine Tune Up
Test Attempt
1st 2nd 3rd

Directions: OVERALL EVALUATION

CALL YOUR INSTRUCTOR, ask Level PERFORMANCE LEVELS
your instructor to assess your Achieved
performance in the following critical
task and performance criteria 4 - Can perform this skill without supervision
below. and with initiative and adaptability to problem
situations.
You will be rated based on the
overall evaluation on the right side. 3 - Can perform this skill satisfactorily without
assistance or supervision.

2 - Can perform this skill satisfactorily but
requires some assistance and/or supervision.

1 - Can perform parts of this skill satisfactorily,
but requires considerable assistance and/or
supervision.

Instructor will initial level achieved.

PERFORMANCE STANDARDS Yes No N/A
For acceptable achievement, all items should receive a "Yes" or "N/A"
response.
1. Functions of tune-up equipment are identified and explained
2. Major steps in tuning-up an engine are enumerated
3. Valve tappet clearance is set
4. Checking and adjustment is performed
5. Spark plug clearance is adjusted
6. Spark plug is tested
7. Fuel filter and air cleaner are replaced
8. Fuel filter is free of sediments and impurities
9. Ignition breaker is tested and replaced
10. Condenser is tested and replaced

11. Fuel mixture and idle rpm is adjusted

12. Advanced timing is checked

13. Compression test is performed

14. Compression test result is interpreted and appropriates
recommendations is prescribed

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Learner’s diary

DIARY NOTES

Record important dates, jobs undertaken and other workplace events that will assist you in providing
further details to an Assessor.

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 1 : Identify and explain the functions of tune-up equipment and enumerate
the major steps in tuning-up an engine

Performance Criteria:

1.1. Functions of tune-up equipment are identified and explained
1.2. Major steps in tuning-up and engine are enumerated.
Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
Trainer’s signature:.......................................................................
Date:.............................................................................................

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 2 : Measure/adjust valve tappet clearance

Performance Criteria:

2.1 Valve tappet clearance is set
2.2 Checking and adjustment is performed
Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 3 : Test spark plug

Performance Criteria:

3.1 Spark plug clearance is adjusted.
3.2 Spark plug is tested.
3.3 Spark plug test result analyzed and appropriate recommendations are

prescribed.
Comments:

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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
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Date:.............................................................................................

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 4 : Check/replace fuel filter and air cleaner

Performance Criteria:

4.1. Fuel filter and air cleaner are replaced.
4.2. Fuel filter is free of sediments and impurities.
Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
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Date:.............................................................................................

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 5 : Test and replace ignition breaker

Performance Criteria:

5.1. Ignition breaker is tested and replaced
5.2. Condenser is tested and replaced
Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
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Date:.............................................................................................

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 6 : Check/adjust ignition distributor setting

Performance Criteria:

6.1. Ignition distributor is checked
6.2 Ignition distributor setting is adjusted
Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
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Date:.............................................................................................

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 7 : Set fuel mixture and idle rpm

Performance Criteria:

7.1. Fuel mixture and idle rpm is adjusted
7.2. Advanced timing is checked

Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
Trainer’s signature:.......................................................................
Date:.............................................................................................

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Record of Achievement

Module : Performing Gas Engine Tune Up

LO 8 : Perform compression test

Performance Criteria:

8.1. Compression test is performed.
8.2. Compression test result is interpreted and appropriates recommendations is

prescribed.

Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
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Terms and Definitions

Air cleaner:
A device which filters the air entering the engine to remove airborne impurities, dust,
dirt, and bumblebees. Also called air filter.

BDC:
Acronym for " bottom dead center."

Breaker-triggered transistorized ignition:
A transistorized ignition system whose distributor is the same as that of a coil ignition
system, but whose contact breaker switches only the control current of the transistor,
not the primary current. Usually not fitted as original equipment.

Carbon fouling:
The situation that occurs when the two electrical terminals of the spark plug are
coated with carbon causing a reduction in efficiency leading to intermittent firing or
complete failure.

Carbon monoxide:
(CO) A deadly, colorless, odorless, and tasteless gas found in the engine exhaust.
Toxic even in relatively small concentrations. Formed by incomplete burning of
hydrocarbons. Thus at its greatest with a rich mixture.

Carburetor:
Optionally spelled "carburetter" or "carburettor." A device that vaporizes fuel and
mixes it with air in proper quantities and proportions to suit the varying needs of the
engine. A filter screens the air which is drawn into the carburetor. Here the gasoline
mixes with the air and this fuel vapor enters the combustion chamber through the
intake valve where it is compressed and burned.

Combustion chamber:
The volume of the space in the cylinder above the piston with the piston at top dead
center (TDC) in the compression stroke. The head of the piston, the cylinder walls,
and the head form the chamber. Combustion of the fuel-air mixture begins here
when ignited by a spark plug. The design and shape of the combustion chamber can
affect power, fuel efficiency, and emissions of an engine.

Compression check:
Testing the compression in all the cylinders at crankingspeed. All plugs are
removed, the compression gauge placed in one plug hole, the throttlecracked wide
open and the engine cranked until the gauge no longer climbs. The compression
check is a good way in which to determine the condition of the valves, rings, and
cylinders.

Compression gauge:
[1] A gauge used to test the compression in the cylinders. A poor compression
reading can indicate that there is leakage through the valves or the piston rings. In
two stroke engines, it could indicate that there is poor primary compression because
of a leak in the crankshaft seals.
[2] Instrument used to measure positive pressures (pressures above atmospheric
pressures) only. Gauge dial usually runs from 0 to 300 lb. per sq. in. gauge, (psig)
(101.3-2 170 kPa).

Compression tester:
A device which is screwed or pushed into the spark plug hole so that when the
engine is turned over, it measures the amount of compression in that cylinder.

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Cylinder block:
The basic framework of the engine to which other engine parts are attached. It is
usually a casting and includes the engine cylinders and the upper part of the
crankcase.

Detonation:
The action of the fuel charge firing or burning too violently, almost exploding. It
sometimes results in a noise called "pinging." Detonation is caused by autoignition of
the "end gas" i.e., that part of the charge not yet consumed in the normal flame-front
reaction. Detonation occurs because piston motion and compression of the end gas
raise its temperature and pressure to the point where the end gas autoignites. The
pinging or knocking noise is the result of intense pressure waves in the charge which
cause the cylinder walls to vibrate. Also called "fuel knock."

Distributor:
A unit in the ignition system designed to make and break the ignition primary circuit
and to distribute the resultant high voltage to the proper cylinder at the correct time.
The high voltage comes from the coil to the center terminal of the distributor cap and
passes down the rotor. As the rotor turns, contact is made with each successive
terminal on the circumference of the distributor cap. From there, the voltage goes
into the spark plug wires and to the spark plug. Generally when your vehicle has its
timing adjusted, it is the distributor that is adjusted. Also called "ignition distributor."

Drivability:
The general qualitative evaluation of a powertrain's operating qualities, including idle
smoothness, cold and hot starting, throttle response, power delivery, and tolerance
for altitude changes.

Dwell:
[1] In a contact breaker ignition system, the number of degrees the breaker cam
rotates from the time the breaker points close until they open again. Also called the
"dwell angle" or "dwell period."
[2] In a breakerless ignition system, the time during which the electronic control unit
allows current to flow through the primary winding of the coil, which in ignition
systems with a Hall generator is determined by the width of the vanes.

Dwell meter:
An instrument which determines the number of degrees the breaker cam rotates
while the breaker points are closed. Changing the point gap affects the dwell angle.
When the breaker points are correctly gapped, the distributor can give the proper
amount and duration of spark to the spark plugs.

Dynamometer:
An electric or hydraulic machine used to measure the actual engine horsepower
output and torque. An engine dynamometer measures horsepower at the crankshaft
and a chassis dynamometer measures horsepower output at the wheels.

EGR valve:
A part of an EGR system mounted on or near the inlet manifold and controlled by
inlet manifold vacuum, which is usually closed at idle and low speeds, but opens
during acceleration, admitting exhaust gas to the inlet manifold. Most EGR valves
are of the single diaphragm type, some are dual diaphragm valves connected to two
separate vacuum sources to more closely match EGR function to engine loads; for
the same purpose, EGR valves are frequently governed by additional regulating
devices.

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Electrode:
In a spark plug one electrode (the center electrode) is the center rod passing
through the insulator. The side electrode is a rod welded to the shell of the spark
plug. The distance between them is the spark gap.

Emission:
The passing of gases and other toxic substances into the atmosphere.

Engine analyzer:
An electronic engine testing device which (because of its size) used to be placed in
a cabinet or a movable stand. The modern units are often hand-held and are
connected to the vehicle's diagnostic socket (as in the case of the diagnostic read-
out box), which provides data on all aspects of the engine's state of tune

Exhaust-gas analyzer:
An instrument used to measure the exhaust gases (in parts per million, percent,
grams per kilometer, or grams per mile) to determine both combustion efficiency and
the amount of pollutants in the exhaust.

Fuel filter:
A device that removes impurities from the fuel before it gets to the carburetor. It is
usually found near the carburetor in the fuel line that comes from the fuel pump (in-
line fuel filter), or inside the carburetor ( integral fuel filter) or fuel pump ( integral fuel
filter). This unit must be cleaned or replaced on a regular basis, usually once a year
or it will become clogged and restrict fuel to the carburetor. Without a filter, the jets
and orifices in the carburetor will become clogged.

Fuel mixture:
A mixture of gasoline and air. An average mixture, by weight, would contain 16 parts
of air to one part of gasoline. See air-fuel mixture.

Gapping:
Adjusting the distance between the electrodes of a spark plug or the points of
contact breaker points.

Head gasket:
The gasket at the top of the cylinder and sits between the cylinder and the head. It
keeps the coolant out of the cylinders and retains compression in the cylinder. Also
called cylinder head gasket. Also see blown head gasket

Humidity:
The moisture or dampness in the air. Usually refers to an uncomfortably high level of
humidity.

Idle speed:
This is the speed of the engine with the following conditions: The transmission is in
neutral (or park in automatic transmissions), the engine is fully warmed up, the
choke butterfly is fully open, and there is no extra accessories in operation (i.e., air
conditioner, radio, lights). Also called "idling speed"

Internal combustion engine:
(IC) An engine that burns fuel within itself as a means of developing power (unlike
an external combustion engine such as a steam engine). Although the term "internal
combustion engine" covers all types of reciprocating and rotary engines, it is typically
used with reference to four-stroke gasoline and diesel engines

Insulator:
A unit made of a material that will not conduct electricity. The electricity in a copper
wire covered with a plastic sleeve (insulator) cannot penetrate the sleeve.

Mass airflow meter:
(MAF) device for measuring the mass flow of air into an engine.

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Misfire:
The failure of the fuel charge in one or more engine cylinders to fire or ignite at the
proper time. It can be due to poor compression caused by worn or improperly
adjusted valves, worn piston rings, a faulty head gasket, or in the case of a two-
stroke engine leaking crank seals. It can also be caused by poor ignition due to worn
or dirty spark plugelectrodes, worn or improperly gapped points or spark plugs, poor
fuel delivery, faulty ignition wiring, or faulty distributor components. An easy way to
detect the problem is to put a stiff piece of paper at the end of the tail pipe and
listening for an irregular puffing sound. Also called "missing" or "backfiring."

Preignition:
The fuel charge being ignited before the proper time. Sometimes causes pinging or
detonation. This is the combustion of the fuel-air mixture that is not a result of the spark
plug's firing, but by high pressure, a flame, or a hot surface.

Road test:
A test to check that a car is roadworthy after repair.

Spark plug:
A device containing two electrodes across which electricity jumps to produce a spark
to fire the fuel charge. The center electrode is insulated from the spark plug shell by
means of a molded insulator resembling porcelain. The side electrode protrudes
from the bottom edge of the spark plug shell and is so positioned that there is a gap
between it and the center electrode.

Stoichiometric ratio:
In a spark-ignition engine, the ideal air/fuel mixture ratio of 14.7:1, which must be
maintained on engines with dual-bed and three-way catalytic converters. Also see
air ratio

Tachometer:
(tach) A device used to indicate the speed of the engine in rpm. The tachometer is
mounted on or near the dashboard (some even appear on the hood and others in a
heads-up display on the windshield). It helps the driver to know the optimum rpm for
changing gears on manual transmissions. A tachometer is also a diagnostic device
which a mechanic uses to determine idle speed and other carburetor and running
settings. Also called a "rev counter"

TDC:
Acronym for "top dead center."

Transmission controlled spark:
(TCS) A system to reduce the emission of nitrous oxides by which a vacuum
solenoid and a switch in the transmission system prevents the distributor's vacuum
advance mechanism from operating in the lower gears and at low speed

Tune-up:
The intent of a tune-up is to obtain the maximum performance and economy of the
engine with the lowest possible exhaust emissions so that the vehicle engine will
meet the manufacturer's specifications. It involves checking the components of the
ignition system and cleaning or replacing them; cleaning and adjusting the
carburation or fuel injection system; adjusting the points and timing cleaning and
gapping the spark plugs. Tune-ups should be performed according to the
recommendation of each manufacturer.

Turbocharger:
An exhaust powered turbine super-charger. Turbochargers always use centrifugal-
flow compressors, which operate efficiently at the high rotational speeds produced
by the exhaust turbine.

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Vacuum gauge:
A gauge used to determine the amount of vacuum existing in a chamber.

Valve tappet:
An adjusting screw to obtain the specified clearance at the end of the valve stem
(tappet clearance). The screw may be in the top of the lifter, in the rocker arm, or in
the case of the ball joint rocker arm, the nut on the mounting stud acts in place of a
tappet screw.

Waste gate:
A valve used to limit the boost developed in a turbocharger. A waste gate operates
by allowing some of the engine's exhaust flow to bypass the turbocharger's turbine
section under certain conditions.

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