[www.oto hui.com]chapter34measuringfasteners

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.

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