Page 6. AURTTA003 Use and maintain basic mechanical measuring devices
THE IMPERIAL SYSTEM
This system of units of measurement was used prior to the metric system being introduced in 1966. It is essential that the motor mechanic is fully conversant with both the Imperial system and SI units.
Linear Measurements With the English system the unit of measurement of length is the inch (" or in).
Accuracy For greater accuracy the inch is further divided into:
a. Decimals, eg 0.200" ; or
5 b. Fractions, eg /8"
Decimals of One-Inch Decimals are expressed as follows:
0.200" zero point two inch, or two hundred thou(sandth) of an inch 0.0003" three tenth of a thou(sandth) of an inch 1.889" one point eight eight nine inch
Fractions of an Inch Fractions of an inch are indicated as follows:
1 /2" half (an) inch
1 /4" (a) quarter (of an) inch
3 2 /16" two and three sixteenth of an inch
The fractions and multiples thereof in use are:
1 1 1 1 1 1 /2" /4" /8" /16" /32" /64"
When to use Decimal or Common Fractions 1 Fractions are generally used where an accuracy no greater than ± /32" is required. For greater accuracy, such as required for various fits and tolerances, decimals of an inch are used.
Measuring Tools One of the most important of all hand processes is accurate measurement. Many tools and devices have been designed for this purpose. Some of them are simple and inexpensive, others are more intricate and may cost a considerable amount. However, each measuring tool, whether cheap or expensive, has its definite uses.
This underpinning knowledge deals with some of the simple and inexpensive measuring tools such as rules and calipers. Their degree of importance is very high because the accuracy which can be achieved with these tools depends entirely on the amount of skill and experience of the user. It is essential that these skills are fully developed before precision measuring tools are used.
AUR20716 – Certificate II in Automotive Vocational Preparation ©Copyright LAPtek Pty. Ltd. Page 12. AURTTA003 Use and maintain basic mechanical measuring devices
TASK 1: REVIEW QUESTIONS – MEASUREMENT AND MEASURING TOOLS
How: Complete the following questions to display to your instructor your understanding of measurements and measuring tools. 1. State the name of the two systems used for measurement. i) ......
ii) ......
1 1 1 2. Starting from /16" and raising in increments of /16", write the fractions from /16" up to 2", 1 1 3 1 e.g. /16", /8", /16", /4" etc. up to 2"......
......
...... 3. How are imperial rules generally graduated?
......
...... 4. How are metric rules graduated?
......
...... 5. When taking a measurement using a rule, why do you use the rule on its edge?
......
...... 6. Why do you not use a steel rule as a scraper, screwdriver or cleaning tool?
......
...... 7. Explain where you would use a try square or a combination square...... 8. Explain where you use the following calipers. Inside Caliper: ......
......
Outside Caliper: ......
......
AUR20716 – Certificate II in Automotive Vocational Preparation ©Copyright LAPtek Pty. Ltd. Page 16. AURTTA003 Use and maintain basic mechanical measuring devices
STRAIGHT EDGE Straight edges are manufactured from steel or aluminium and are available up to a length of 1.8 metres. The straight edge is surface ground, with a bevelled edge finished to an accuracy of .03mm (.001") per 30 centimetres. The straight edge is used to check cylinder heads, cylinder blocks and manifolds for distortion.
Using a Straight Edge Clean the cylinder head then place the straight edge on the cylinder head bevel side down. Use a set of feeler gauges to check for clearance between the straight edge and the cylinder head.
To correctly inspect the cylinder head for distortion you must check diagonally, longitudinally and transversely. (Refer to diagram below). Check cylinder head surface using a straight edge
TASK 3: USE A STRAIGHT EDGE AND FEELER GAUGE
Check cylinder head and block surfaces How: On your engine check your cylinder head and cylinder block surfaces with a straight edge and feeler gauge and compare to manufacturer specifications. Check diagonally, longitudinally and transversely.
Checking cylinder head
Engine model: ......
Makers Specification: Maximum cylinder head distortion: ......
Maximum cylinder block distortion: ......
Cylinder head Cylinder block
1...... 1......
2...... 2......
3...... 3......
4...... 4......
5...... 5......
6...... 6......
AUR20716 – Certificate II in Automotive Vocational Preparation ©Copyright LAPtek Pty. Ltd.