Course: 01.422 Agriculture Mechanics Technology II
Unit 1: Parts of a Small Engine
Lesson: Dial Caliper Review/Intro to Micrometers
Georgia Performance Standards:
AG-AMII-1: Students will service, maintain, repair, and operate small air cooled engines
o (b) Interpret service and parts manuals for small engines
o (c) Describe the importance of servicing small engines to manufacturer's recommendations
o (f) Identify tools for engine repair.
ELA9RC2: The student participates in discussions related to curricular learning in all subject areas.
ELA12LSV1: The student participates in student-to-teacher, student-to-student, and group verbal
The student understands and acquires new vocabulary and uses it correctly in reading and writing.
ELA10W3: The student uses research and technology to support writing.
MM1A3: The student solves simple equations.
MA1P1: The student solves problems (using appropriate technology).
MA1P3: The student communicates mathematically.
SCSh2: The student uses standard safety practices for all classroom laboratory and field
SCSh3: The student identifies and investigates problems scientifically.
SCSh4: The student uses tools and instruments for observing, measuring and manipulating
scientific equipment and materials.
SP1: The student analyzes the relationships between force, mass, gravity, and motion of objects.
SPS7: The student relates transformations and flow of energy within a system.
1. TSWBAT utilize a dial caliper to measure various parts of an engine.
2. TSWBAT utilize a micrometer to measure various parts of an engine. The student will measure
objects with at least 70% accuracy and will score at least 70% on a worksheet about reading
How do you use a micrometer to take measurements?
Unit Understandings, Themes and Concepts/Primary Learning Goals
Students will learn about the parts of a micrometer and how to properly use a micrometer to measure
various objects. Students will then use this knowledge to measure various parts on an Overhead Valve
Small Engine. The students will review the importance of measurements in regards to servicing engines
to the manufacturer’s specification.
Worksheets from Mr. Beacham
Power Point from Mr. Beacham
Materials and Equipment
Introduction and Mental Set:
Has everyone heard the phrase, "There's more than one way to skin a cat."? Does anyone know where
this saying originated? (It refers to skinning catfish. You know catfish have a really tough skin that is
removed before it is cooked.) What does that mean? (There is more than one way do complete a task;
Lee might skin catfish by just grabbing the skin with his hands, while Joe may use skinning pliers. In the
end, they both have catfish that are ready to be cooked. In other words, they can do things two different
ways and still end up with the same outcome.)
Last week we discussed using dial calipers to measure inner diameter, outer diameter, and depth
of an object. Are there any other ways to take accurate measurements on our engines? (YES!)
Today, we will talk about using a micrometer to take accurate measurements.
Micrometers provide us with another way to take accurate measurements. The micrometers that we
will be working with have an accuracy of 0.0001". Micrometers are available in various sizes, from 0"-1"
up to 35"-36". We will be discussing and using a micrometer that is used to measure the outside
diameter of an object.
There are five main parts of the micrometer: The frame, thimble, sleeve, spindle, and anvil. The frame is
what the parts of the micrometer are on. The thimble is the movable part of the micrometer that has
numbers of it. It is used in reading the measurement. The sleeve is the non-moving part of the
micrometer that has numbers on it. The sleeve is also used in determining the measurement. The
spindle is the movable part of the micrometer that makes contact with the object that is to be
measured. The spindle moves as the thimble spins. The anvil is the stationary part of the micrometer
that makes contact with the object that is being measured.
Now we will work on reading a micrometer. It is very important to write down your work when reading
a micrometer. To read a micrometer, first write down the smallest measurement that can be read on
that particular micrometer. Next, write down the largest reading that can be seen on the sleeve. (The
sleeve is the stationary part with numbers). Next, count the number of lines that you can see that are
past the largest number that you can see on the sleeve. It should be up to 3 lines. Multiply this number
by .25. You do this because there are 3 marks between each number on the sleeve. These marks divide
the distance between numbers into quarters. 0.25 is one quarter. If you can see 3 lines past the last
number on the sleeve, what do you write down? (3X0.25=0.75) (Give examples for 1, 2, and 3 past the
last number on the sleeve) Finally, write down the thimble reading. This is the number on the thimble
that lines up with the horizontal line on the sleeve. When you have written all of these numbers down,
add them to get the reading of the micrometer. We will try one together. Pay attention because you will
be doing this often throughout the week.
Review using micrometers. Go through the power point again. Then, give the students the micrometer
worksheet with 20 readings on it and have them fill it out, showing all work. Review the worksheet on
the board having each student work at least one problem.
Measuring using dial calipers and micrometers and feeler gauges
*Go to lab
*Measure piston diameter: Use micrometer and check with dial caliper
*take 3 measurements and average
*Why is this important? If worn, piston will measure smaller than standard/reject size
*Measure Ring End Clearance: Use feeler gauge
*What is ring end clearance? Distance between the ends of the piston rings
*Why is this important? If there is too much room between the ends of the piston
rings, the engine will burn oil and lose compression
*Trick question: What happens if there is too little room? There can’t be too little
room between the ends.
*Measure valve stem diameter: Use dial caliper and micrometer
*take 3 measurements and average
*What/where are the valve stems? They are the long thin part of the valve.
*What do these do?
*Why is it important that these are the correct size?
*Is maintenance required when the valve stems are larger or smaller than the
*Measure crank journals(Magneto, crankpin, and PTO): Use dial caliper and micrometer
*Take several measurements and average
*Location: On flywheel side: Measure where it fits into the block…against where
counter weights start.
*Importance: Wear will occur against bearing where it fits into the block; throw
off balance of engine if worn
*Take 3 measurements and average
*Location: where connecting rod attaches
*Importance: throw off balance of piston
*Take 3 measurements and average
*Location: fits into crankcase cover
*Importance: Throw off balance and can cause to leak oil if worn
Evaluation: Micrometer Worksheet quiz and lab assessment