Measuring tools Modern engines use thinner casting and require more precise measuring

1. 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

2. Tolerance limits • The minimum and maximum allowable diameters • Specified clearance • Difference in diameters for • mating parts • Specified clearance of • replacement part should • be used

3. 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

4. Maximum bearing inside diameter • Maximum housing bore +2.1250 in. • Bearing thickness -.0615 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. • Bearing thickness -.0615 in. • Min bearing inside diameter 2.0015 in.

5. 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.

6. Example of valve stem clearance • Valve stem diameter .3405 - .3415 in. • Stem-to-guide clearance .0015 - .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.

7. Thermal expansion • Engines are assembled at room temperature • An error at room temperature may cause problems at • operating temperature • Coefficient of thermal expansion • Iron and steel .000006 in. Aluminum .000012 in.

8. 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

9. 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

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

11. Outside micrometer • Screw pitch of 1/40” or .025” for inch micrometer • Screw pitch of .50 mm for metric micrometers • One inch of travel • Resolution limit of .0001” for inch micrometers • Resolution limit of up to .001 mm for metric • Calibrated with standards or gauge blocks

12. Depth micrometer • Used for measuring deck clearance, stepped flywheels • Screw pitches same as outside micrometer • One inch of travel • Resolution limit of .001” for inch micrometers • Scales are read in reverse order • Calibrated with gauge blocks and surface plate

13. Inside micrometer • Used for measuring cylinder bores, housing bores • Screw pitches same as outside micrometer • One inch of travel • Used more often with ‘transfer’ measurements

14. Transfer measurement • Adjust inside micrometer to size • Measure with an outside micrometer • Other tools include telescoping and split ball gauges

15. Dial indicators • Resolution limits printed on dial face • Used for checking straightness of cams and cranks • Read TIR (total indicator reading) • Check out-of-roundness first

16. Dial bore gauge • Used for cylinder bores and main bores • Uses ‘comparative’ measurement • Set up in a setting fixture or outside micrometer • Measure differences in the size that was set

17. Calipers • Dial and digital calipers • Lack of rigidity limits accuracy to .002” • Easy to read

18. Surface finish • Crank journals 10 AA micro inches • Head and block deck surfaces 20–60 AA micro inches • Cylinder bores 10-15 AA for moly rings • 25-30 AA for iron and chrome

19. 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

20. 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

21. Necked down bolt • Example of a bolt that has been necked down. Tightening • past its elastic limit

22. 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

23. 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

24. 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.