Automotive Fasteners and Sealing Techniques for Vehicle Assemblies

1. Chapter 9 Fasteners, Gaskets, Seals, and Sealants

2. Contents (9 Topics) • Fasteners • Washers • Machine screws • Sheet metal screws • Nonthreaded fasteners

3. Contents • Torquing bolts and nuts • Thread repairs • Removing damaged fasteners • Gaskets and seals

4. Fasteners • Devices that hold the parts of a car together • Thousands of fasteners are used in vehicles

5. Automotive Fasteners

6. Bolts and Nuts • Bolt • metal rod with external threads on one end and a head on the other • when a bolt is threaded into a part other than a nut, it can also be called a cap screw • Nut • has internal threads and a six-sided outer shape

7. Bolts and Nuts When a nut is screwed onto a bolt, a powerful clamping force is produced

8. Bolt Dimensions

9. Bolt Dimensions

10. Thread Types • There are three basic types of threads used on fasteners: • Coarse threads • UNC-Unified National Coarse • Fine threads • UNF-Unified National Fine • Metric threads • SI

11. Thread Direction • Bolts and nuts come in right- and left-hand threads • Right-hand threads • fastener must be turned clockwise to tighten • Left-hand threads • fastener must be turned counterclockwise to tighten • letter L may be stamped on fastener

12. Bolt Grade • Also called tensile strength • Refers to the amount of pull a fastener can withstand before breaking • Bolt head markings specify the tensile strength of the bolt • U.S. customary bolts are marked with lines • Metric bolts are marked with numbers

13. Bolt Designation Number Gives information about the bolt

14. Bolt Designation Number Used when purchasing new bolts

15. Bolt Designation Number

16. Nut Types Common types of nuts used in vehicles

17. Castle Nut andCotter Pin Cotter pin keeps the nut from turning and possibly coming off

18. Washers • Used under bolt heads and nuts • Two basic types of washers used: • flat washers • lock washers

19. Washer Types • Flat washer • increases the clamping surface under the fastener • prevents the bolt or nut from digging into the part • Lock washer • prevents the bolt or nut from becoming loose under stress and vibration

20. Washer Types • Lock tabs or lock plates • perform the functions of both flat washers and lock washers • increase clamping surface area and secure the fastener

21. Washer Types A. Plain flat washer B. Split lock washer C. Toothed lock washer D. Lock plate

22. Machine Screws • Similar to bolts, but they normally have screw-type heads • Threaded along their full length • Used to secure parts when clamping loads are light • Available in various head shapes

23. Sheet Metal Screws • Also called tapping screws • Commonly used on plastic and sheet metal parts such as body trim, dashboard panels, and grills • Use tapering threads that are widely spaced

24. Sheet Metal Screws Basic types of tapping screws

25. Nonthreaded Fasteners Numerous types of nonthreaded fasteners, such as snap rings, clips, and adhesives, are used in the assemblyof a vehicle

26. Snap Ring • Fits into a groove in a part and commonly holds shafts, bearings, gears, pins, and other similar components in place • Snap ring pliers are needed to remove and install a snap ring • special jaws grasp the snap ring

27. Snap Ring Types

28. Keys and Set Screws • Key • fits into a keyseat (slot) cut into a shaft and a keyway cut into the mating part • Set screw • normally used to lock a part onto a shaft • not as strong as a key

29. Keys and Set Screws A. KeyB. Set screw

30. Splines • Series of slots cut into a shaft and a mating part • Allow the gear or collar to slide on the shaft but still not rotate • Used in manual transmissions, clutches, and drive shaft yokes

31. Splines

32. Adhesives • Special glues widely used in vehicles • Used to hold body moldings, rubber weather stripping, and body emblems • Some stay soft and pliable while others dry hard • Some take hours to dry while others dry in seconds • Observe all directions and safety precautions when using adhesives

33. Torquing Bolts and Nuts It is very important that bolts and nuts are tightened properly–this is called torquing

34. Torque Specifications • Tightening values given by the auto manufacturer • Normally given for all precision assemblies, such as engines, transmissions, and differentials • Factory specifications should be used • general bolt torque chart may be used if factory specs are not available

35. Bolt Torque Chart

36. Torque-to-yield • Requires a specific bolt torque, followed by turning the bolt a specific number of degrees • Procedure stretches the bolt to its correct yield point, preloading the fastener • New bolts may be required each time

37. Torque Stretch • Determined by measuring bolt length change while torquing the bolt • when building a racing engine, you can “mike” connecting rod bolts to measure the length before and after tightening • Too much stretch indicates bolt weakness • Not enough stretch may indicate thread problems affecting torque

38. Bolt Tightening Sequence • Used to make sure that parts are fastened evenly • Creates an even, gradual clamping force along the entire mating surface of the parts • Crisscross pattern is often recommended

39. Bolt Tightening Sequence Service manual pattern for a cylinder head

40. Bolt Tightening Sequence Service manual pattern for wheel lug nuts

41. Torque Wrench Rules • Keep a steady pull on the wrench • Clean fastener threads • Avoid using swivel joints • When reading a torque wrench, look straight down at the scale • Use manufacturer’s specifications when available

42. Torque Wrench Rules • When manufacturer’s specs are not available, use general specs in a crisscross pattern • To avoid a false reading, pull only on the handle • Tighten bolts and nuts in four steps • Retorque when required • some assemblies must be retightened after operation and heating

43. Thread Repairs Threaded holes in parts can become damaged, requiring repairs. A technician must be capable of repairing damaged threads quickly and properly

44. Minor Thread Repairs Minor damage can be repaired with a thread chaser or thread file

45. Major Thread Repairs • Badly smashed or stripped threads may be repaired with either a tap or die • Tap • threaded tool for cutting internal threads in holes • Die • cuts external threads on metal rods, bolts, shafts, and pins

46. Tap and Die

47. Using a Tap and Die • Hold the handle squarely with the work • Back the handle off to clean metal out of the threads • Use a taper tap to start the threads • Use a plug tap and a bottoming tap to cut the threads to the bottom of a blind hole

48. Tap and Die Rules • Never force a tap handle or the tool may break • Keep the tap and die well oiled to ease cutting • Use coarse threads when threading or tapping into soft metal, like aluminum • coarse threads will hold better than fine threads

49. Tapping Oversize • When threads cannot be restored, the hole can be drilled and tapped oversize • Use a “drill and tap size chart” to choose a drill bit and tap • Drill the hole one size larger than the original hole • Cut new threads in the drilled hole • Use a larger bolt in the threaded hole

50. Thread Repair Insert • Used when the use of an oversize hole and fastener is not acceptable • Takes place of damaged internal threads • Allows the use of the original-size bolt