Presentation on theme: "Measuring tools Modern engines use thinner casting and require more precise measuring Selectively fit engines All parts are measured and marked according."— Presentation transcript:
Measuring tools Modern engines use thinner casting and require more precise measuring Selectively fit engines All parts are measured and marked according to size Then selectively assembled for optimum clearance Copyright 2003 Gary Lewis - Dave Capitolo
Tolerance limits The minimum and maximum allowable diameters Specified clearance Difference in diameters for mating parts Specified clearance of replacement part should be used
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
Maximum bearing inside diameter Maximum housing bore +2.1250 in. Bearing thickness -.0615 in. Max bearing inside diameter 2.0020 in. Minimum bearing inside diameter Minimum housing bore +2.1245 in. Bearing thickness -.0615 in. Min bearing inside diameter 2.0015 in.
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.
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.
Coefficient of thermal expansion Iron and steel.000006 in. Thermal expansion Engines are assembled at room temperature An error at room temperature may cause problems at operating temperature Aluminum.000012 in.
Example from book Pin diameter.9000” Pin bore diameter.9005” Clearance at room temp.0005” Pin diameter with 250° F change.9013” Pin bore with 250° F change.9032 Clearance with 250° F change.0019” Heat during machining Rough and finish machining Measuring tools at room temperature
Units of measure for linear measurement 1 mm =.03937”.1 mm=.003937”.01 mm =.0003937”.001 mm =.00003937” To convert inches to millimeters Inches times 25.4 or Inches divided by.03937 To convert millimeters to inches Millimeters divided by 25.4 or Millimeters times.03937
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
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
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
Transfer measurement Adjust inside micrometer to size Other tools include telescoping and split ball gauges Measure with an outside micrometer
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
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
Calipers Dial and digital calipers Easy to read Lack of rigidity limits accuracy to.002”
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 20–60 AA micro inches
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
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
Necked down bolt Example of a bolt that has been necked down. Tightening past its elastic limit
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
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 strength Metric fasteners have numbers for strength
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.