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8/13/2019 [Www.oto Hui.com]Chapter34MeasuringFasteners
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Measuring tools
Modern engines use thinner casting and require
more precise measuring
Selectively fit engines
All parts are measured and marked according to sizeThen selectively assembled for optimum clearance
Copyright 2003 Gary Lewis - Dave Capitolo
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Tolerance limits
The minimum and maximum allowable diameters
Specified clearance
Difference in diameters formating parts
Specified clearance of
replacement part should
be used
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Example of tolerance limits for crankshaft and housing bore
Standard shaft size 1.9995/2.0005 in. Housing bore diameter 2.1245/2.1250 in.
Clearances
Difference between shaft OD and bearing ID
Minimums and maximums
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Minimum bearing clearance
Minimum bearing ID +2.0015 in.Maximum crankshaft diameter - 2.0005 in.
Minimum bearing clearance .001 in.
Maximum bearing clearance
Maximum bearing ID +2.0020 in.Minimum crankshaft diameter - 1.9995 in.
Maximum bearing clearance .0025 in.
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To find valve guide diameter
Minimum clearance .0015 in.Maximum stem diameter +.3415 in.
Valve guide diameter .3430 in.
Or
Maximum clearance .0025 in.
Minimum stem diameter +.3405 in.
Valve guide diameter .3430 in.
Example of valve stem clearance
Valve stem diameter .3405 - .3415 in.
Stem-to-guide clearance .0015 - .0025 in.
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Example from book
Pin diameter .9000
Pin bore diameter .9005Clearance at room temp .0005
Pin diameter with 250F change .9013
Pin bore with 250F change .9032
Clearance with 250F change .0019
Heat during machining
Rough and finish machiningMeasuring tools at room temperature
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Units of measure for linear measurement
1 mm = .03937
.1 mm = .003937
.01 mm = .0003937
.001 mm = .00003937
To convert inches to millimetersInches times 25.4 or
Inches divided by .03937
To convert millimeters to inches
Millimeters divided by 25.4 or
Millimeters times .03937
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Measuring tools
Outside micrometer
Inside micrometer
Depth micrometer
Telescoping gauge
Split ball gauge
Dial indicator
Dial bore gauge
Calipers
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Outside micrometer
Screw pitch of 1/40 or .025 for inch micrometer
One inch of travel
Screw pitch of .50 mm for metric micrometers
Resolution limit of .0001 for inch micrometers
Resolution limit of up to .001 mm for metric
Calibrated with standards or gauge blocks
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Depth micrometer
Used for measuring deck clearance, stepped flywheels
One inch of travel
Screw pitches same as outside micrometer
Resolution limit of .001 for inch micrometers
Scales are read in reverse order
Calibrated with gauge blocks and surface plate
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Inside micrometer
Used for measuring cylinder bores, housing bores
One inch of travel
Screw pitches same as outside micrometer
Used more often with transfer measurements
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Transfer measurement
Adjust inside micrometer to size
Other tools include telescoping and split ball gauges
Measure with an outside micrometer
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Dial indicators
Resolution limits printed on dial face
Read TIR (total indicator reading)
Used for checking straightness of cams and cranks
Check out-of-roundness first
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Dial bore gauge
Used for cylinder bores and main bores
Set up in a setting fixture or outside micrometer
Uses comparative measurement
Measure differences in the size that was set
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Surface finish
Crank journals 10 AA micro inches
Cylinder bores 10-15 AA for moly rings
25-30 AA for iron and chrome
Head and block deck surfaces 2060 AA micro inches
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Fastener terminology
Major diameter - Largest thread diameter
Minor diameter - Smallest thread diameter
Pitch - Distance between threads
Threads per inch - Number of thread in a linear inch
Grade - A system of grading fastener strength
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Threaded fasteners
Bolts, machine screws, and capscrews stretch
when tightened
Fasteners have an elastic limit, then fracture occurs
Below elastic limit, fasteners can be tightened repeatedly
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Fastener strength
Cross section of threads Minor diameter effects strength
As pitch increases on external threads, crossection
decreases
As pitch increases on internal threads, crossection
increases
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Fastener strength
Heat treatment
Low strength fasteners are made of low carbon mild steel
High strength fasteners have added carbon for heat treating
SAE fasteners have marks for strengthMetric fasteners have numbers for strength
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Thread identification
Outside diameter of the threads with a micrometer
Measure pitch with thread pitch gauge (threads per inch)
For the machine screw 10-32
Diameter: 10 x .013 + .060 = .190 in.Pitch: 32 threads per inch = .031 in.