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 / in. Housing bore diameter / in. Clearances Difference between shaft OD and bearing ID Minimums and maximums

Maximum bearing inside diameter Maximum housing bore in. Bearing thickness in. Max bearing inside diameter in. Minimum bearing inside diameter Minimum housing bore in. Bearing thickness in. Min bearing inside diameter in.

Minimum bearing clearance Minimum bearing ID in. Maximum crankshaft diameter in. Minimum bearing clearance.001 in. Maximum bearing clearance Maximum bearing ID in. Minimum crankshaft diameter in. Maximum bearing clearance.0025 in.

To find valve guide diameter Minimum clearance.0015 in. Maximum stem diameter in. Valve guide diameter.3430 in. Or… Maximum clearance.0025 in. Minimum stem diameter in. Valve guide diameter.3430 in. Example of valve stem clearance Valve stem diameter in. Stem-to-guide clearance in.

Coefficient of thermal expansion Iron and steel in. Thermal expansion Engines are assembled at room temperature An error at room temperature may cause problems at operating temperature Aluminum 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= ”.01 mm = ”.001 mm = ” To convert inches to millimeters Inches times 25.4 or Inches divided by To convert millimeters to inches Millimeters divided by 25.4 or Millimeters times.03937

Measuring tools Outside micrometer Inside micrometer Depth micrometer Telescoping gauge Split ball gauge Dial indicator Dial bore gauge Calipers

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 AA for moly rings 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 Diameter: 10 x =.190 in. Pitch: 32 threads per inch =.031 in.