Measuring Tools and Systems Chapter 6

Objectives Perform measurements using any of the tools in this chapter Have a working understanding of the metric and English systems of measurement

Introduction Automotive technicians must understand British Imperial (U.S.) system Based on inches, feet, and yards Metric system American manufacturers have changed their tooling to the metric system to be competitive Technicians working on domestic automobiles Need to understand both systems

Metric System Known as the international (S.I.) system Measurement of volume is the liter Unit of weight is the gram Metric equivalent to pounds is kilograms Psi and kilograms per square centimeter measure atmospheric pressure at sea level Temperature measured in degrees centigrade Torque readings are expressed in Newton-meters English system: foot-pounds

Metric System (cont'd.) Metric system based on the number ten Very easy system to use 1/100 (0.01) of a meter is a centimeter (cm) 1,000 meters is a kilometer (km) 1/1000 (0.001) of a meter is a millimeter (mm) Convert inches to millimeters Multiply by 25.4 Convert millimeters to inches Divide by 25.4

Measuring Tools Include: Steel rule: used to make approximate measurements Rulers: measure in metric and fractions of one inch Metric ruler: indicates hundredths and thousands of a meter Thickness gauges (i.e., feeler gauges): measure valve clearance, piston ring side clearance, etc. Plastigage: used to measure oil clearance in bearings and oil pumps

Precision Measuring Tools Vernier calliper Developed in the 17th century Movable scale runs parallel to a fixed scale Measures outside diameter (O.D.) and inside diameter (I.D.) Main scale: divided into inches Vernier scale: divides each .025” section on main scale into 25 parts Measurement combines vernier scale and main scale readings

Micrometer Several advantages Reading a micrometer Clear and easy to read Measure consistently and accurately Built-in adjustment to compensate for wear Reading a micrometer One revolution of thimble advances or retracts the spindle 1/40” Each line on the barrel represents 0.025” A new line is uncovered each thimble revolution Some also have a vernier scale

Metric Micrometer Features One turn of thimble turns spindle 0.5 mm Hub graduated in millimeters Thimble has 50 divisions Read in the same manner as English counterpart Vernier scale reads to 0.002 mm Only five divisions

Combination Digital Mikes and Specialty Micrometers Give both metric and English readings LCD readings taken from the digital readout window accurate to 0.0001 Convertible between inch and metric Specialty micrometers Several types Example: ball micrometer

Inside Micrometers Used to measure: Cylinder bores Main and rod bearing bores Thimble does not move as freely on the barrel as the thimble of an outside micrometer Added friction helps keep the reading from changing Use extension rods to make them the proper size Have handles for use in deep cylinders

Telescoping and Split-Ball Gauges Work in cylinders smaller than about two inches Known as transfer gauges Split-ball gauge Used on small holes such as valve guides Telescoping gauges Used with micrometers Measure cylinders, bearing bores, etc.

Dial Indicators Used to measure: Comparison instruments Movements End play of crankshaft Valve guide wear Valve-in-head depth Cylinder and bearing bores Comparison instruments Measurements compared against known measurement