2. 3
Fasteners, Sealants, and Gaskets

3. Learning Objectives
Identify fasteners used on small gas engines and implements.
Remove and install various fasteners correctly.
Repair or produce internal and external threads.
Properly select and install fasteners.
Remove, select, and install gaskets correctly.

4. Threaded Fasteners Thread
Inclined plane that circles the cylindrical bolt or hole
Incline of bolt or screw thread must be the same as incline of thread in nut or threaded hole into which it is placed

5. Bolts Hold parts together by squeezing them between the head and a nut
Holes bolt passes through is not threaded
Shank is unthreaded portion of bolt near head
Shank should pass all the way through top part and partially through second component

6. Bolts
Should be long enough to pass through parts, washers and nut, and protrude 1 ½ to 2 threads beyond nut

7. Nuts

8. Nuts Hexagon nut Square nut Jam nut
Loosened or tightened with standard sockets or box-end wrenches
Square nut
Found on older implements
Jam nut
Used with hexagon nut to produce locking condition

9. Nuts Castle nut Used when axial clearance is required
Used on bolts or shafts when a component turns or pivots on it
Cotter pin used to prevent nut from turning

10. Nuts Acorn nut Wing nut Lock nut Provides smooth, neat appearance
Can be tightened or loosened by hand
Lock nut
Reduces tendency for vibration or motion to loosen nut

11. Bolt and Nut Terminology
Bolt size
Bolt head size
Bolt length
Thread pitch
Thread length

12. Bolt Grades Minimum tensile strength of bolt
Bolt head markings indicate bolt grade
On SAE bolts, number of marks is two less than grade number
Grade 1 and 2 bolts have no markings
Metric bolts are marked with 5D, 8G, 10K, or 12K

13. Bolt Grades
Load applied to bolt during tightening coupled with external load could exceed tensile limit of bolt
When bolt reaches its load limit, it exceeds its elastic limit and begins to stretch plastically
A bolt that stretches plastically will not return to its original length or shape when load is released

14. Thread Terminology

15. Thread Types Unified National Coarse (UNC) series
For general use
Should not be subjected to vibration
Unified National Fine (UNF) series
For work where vibration is a factor
Metric (M) series
Formed with a 60° angle

16. Thread Types Right-handed thread Left-handed thread
Turned clockwise to tighten
Left-handed thread
Turned counterclockwise to tighten
The letter L may be stamped on the fastener

17. Thread Fit Class 1 fit Class 2 fit Class 3 fit
Largest manufacturing tolerance
Used where ease of assembly is desirable
Class 2 fit
Used on largest percentage of threaded fasteners
Class 3 fit
Will be tight when assembled

18. Thread Designations
Series of numbers and letters used to describe a bolt or thread
Standard designation ½-13 UNC-2A  1
Metric designation M-10  1.5  25

19. Screws
Hold parts together by passing through one part and threading into another

20. Screw Types Machine screws Cap screws Set screws Self-tapping screws
Used in threaded holes
Cap screws
Similar to bolts but smaller in diameter
Set screws
Secure rotating components
Self-tapping screws
Cut threads

21. Screw Head Types

22. Tightening and Loosening Threaded Fasteners
Right-handed threads
Turned clockwise for tightening and counterclockwise for loosening
Left-handed threads
Turned counterclockwise for tightening and clockwise for loosening
Bolts, nuts, and screws on engines should be tightened to specific torque

23. Removing Broken Fasteners
If fastener protrudes from hole, use vise grips or pipe wrench
If fastener breaks off flush with hole, it can be driven out with hammer and small punch
If fastener breaks off even with or below surface of hole, it can be removed using a screw extractor

24. Using a Screw Extractor

25. Chasing Threads Threading tap used to recut damaged threads
A taper tap should be used to chase a through hole
Damaged bolt or screw threads can be chased with a threading die

26. Internal Thread Repair

27. Tapping New Threads Before tapping, a new hole must be drilled
Proper hole diameter obtained from tap drill chart
Start tap straight in hole
Use cutting fluid
Tap wrench should be turned counterclockwise two-thirds of a turn and then reversed one-third of a turn to break and clear chips.
Continue through or to bottom of hole

28. Tapping New Threads

29. Threading Threading is done with a die.
Die is mounted in die stock
Threading procedure is similar to tapping procedure
Diameter of rod being threaded must be same as major diameter of thread

30. Washers Flat washers Lock washers Provide wide bearing surface
Prevent loosening of bolts, screws, or nuts
Kantlink washer
Wide bearing lock washer
Toothed washer

31. Common Washers

32. Pins
Used to retain parts in fixed position or preserve part alignment

33. Retaining Rings Spring steel fasteners that fit into a groove in part
Prevent lateral movement of shafts in hole
Do not prevent the shaft from rotating in hole
Removed and installed with snap ring pliers

34. Retaining Rings
External retaining is placed in groove in surface of shaft
Internal retaining ring fits into groove in hole

35. Keys
Used on shafts that have a component that fits and rotates with the shaft
Recess in shaft is the keyseat
Groove in component is the keyway

36. Adhesives and Sealants
Liquid or Semiliquid
Can be sprayed, brushed, or spread on
Some set up hard, while others remain pliable

37. Thread Adhesives
Prevent nuts, bolts, or screws from loosening during service
Strengths vary from light (removable) to high strength (require applied heat for removal)
Place one drop of adhesive on thread prior to fastening
Cure time varies from 30 minutes to 24 hours

38. Sealants Resistant to oil, water, gas, grease, and salt solutions
Form-in-place sealants
Used in place of conventional gaskets
Room temperature vulcanizing (RTV) sealant
Form-in-place sealant that can be used on both rigid and flexible mating surfaces
Anaerobic sealants
Can be used as a thread locking material or between two machined surfaces

39. Antiseize Compounds
Applied to threaded fasteners and metal components exposed to constant heat
Prevents metal material from being cold welded together
Can be used for exhaust system connections

40. Gaskets Soft pliable material
Used between engine parts to seal and prevent leakage
Type of gasket material depends on functions and conditions of parts being joined

41. Gasket Rules Inspect for leaks before disassembling engine
Do not damage mating surfaces during disassembly
Remove old gasket material carefully
Wash and dry parts thoroughly
Check new gasket fit

42. Gasket Rules Use gasket sealant as directed
Some gaskets do not use sealant
Start all fasteners by hand
Tighten fasteners in small steps
Use a crisscross tightening pattern
Do not overtighten fasteners

43. Bolt Tightening Pattern

44. List five conditions that fasteners are exposed to during engine operation. Heating and cooling, cyclic loading, tensile and shearing loads, corrosion, and vibration

45. What is the most common type of nut used in small engine applications
What is the most common type of nut used in small engine applications? Hexagon nut

46. What is tensile strength
What is tensile strength? Tensile strength is the amount of tension force a fastener can withstand before failing.

47. What is the difference between a machine screw and a cap screw
What is the difference between a machine screw and a cap screw? Machine screws have round heads that accept a screwdriver or Allen wrench. Cap screws have hexagonal heads.

48. What is the difference between tapping and threading
What is the difference between tapping and threading? Tapping is the process of cutting threads in a hole. Threading is the process of cutting threads on an external cylindrical surface.

49. What type of tool should be used to remove a fastener that breaks off below the surface of a hole? A screw extractor

50. How should parts sealed with a gasket be tightened
How should parts sealed with a gasket be tightened? They should be tightened in small steps using a crisscross pattern.

51. Glossary Acorn nuts Anaerobic sealant
Nuts that have an integral cap to cover the sharp thread end of a bolt for safety; named for their resemblance to an acorn.
Anaerobic sealant
A sealant similar to RTV, but can cure in the absence of air. This type of sealant can be used as a thread-locking material or between two machined surfaces.

52. Glossary Antiseize compound Bolt grade Bolt head size
A lubricant applied to threaded fasteners and metal components that are exposed to constant heat to prevent the metal from being cold welded together.
Bolt grade
A grade assigned to a bolt based on the minimum tensile strength specification of the bolt.
Bolt head size
The dimension across the flats of the hexagon.

53. Glossary Bolt length Bolt size Bolts
The distance from the base of the bolt head to the threaded end of the bolt.
Bolt size
The major (largest) diameter of the bolt threads.
Bolts
Threaded fasteners that hold parts together by squeezing them between the head on one end and a nut on the other end.

54. Glossary Cap screws Castle nut Die-stock
Externally threaded fasteners, similar to machine screws but with a hexagonal head, that are used in threaded bores or with a nut.
Castle nut
A hexagonal nut with a slot cut into the top of each side. Commonly used in conjunction with cotter pins, which prevent the nut from loosening.
Die-stock
Used to hold die while cutting external threads.

55. Glossary Flat washers Form-in-place sealants
Washers that provide a wider bearing surface for a bolt or screw head and/or nut.
Form-in-place sealants
A sealant that can be used in place of conventional gaskets when the exact replacement gasket is not available.

56. Glossary Gasket Grip length
A soft, pliable material, such as fiber, rubber, neoprene (synthetic rubber), cork, treated paper, thin steel, or laminated material, used between engine parts to seal and prevent leakage of engine oil, coolant, compression, and vacuum; acts as a seal.
Grip length
The distance from the base of the bolt head to the thread.

57. Glossary Hexagon nuts Jam nut Kantlink washer
Nuts that have six sides and can be loosened or tightened with standard sockets and box-end wrenches.
Jam nut
A thin nut that is tightened against a plain nut to produce a locking condition.
Kantlink washer
The most common type of lock washer; made of spring steel with beveled ends.

58. Glossary Key Lock nuts Lock washers
A small block inserted between a shaft and hub to fasten a pulley or gear to the shaft.
Lock nuts
A nut designed to create friction to reduce the tendency for vibration or motion to rotate and loosen the nut.
Lock washers
Washers that are designed to prevent loosening of bolts, screws, and nuts.

59. Glossary Machine screws Metric (M) series Pins
Externally threaded fasteners, typically with a rounded head, that are used in threaded bores or with a nut.
Metric (M) series
A type of bolt with threads formed at 60° angles.
Pins
A small metal cylinder used to either retain parts in a fixed position or to preserve alignment of parts.

60. Glossary Retaining rings Room temperature vulcanizing sealant (RTV)
Circular spring steel fasteners that fit externally or internally into a groove in a part.
Room temperature vulcanizing sealant (RTV)
A form-in-place sealant that is also referred to as silicon sealant. Abbreviation is RTV.
Screws
Threaded fasteners that hold parts together by passing through one part and threading into another.

61. Glossary Self-tapping screws Set screw Square nut
Screws with a grooved, tapered point that forms threads in the hole as the screw is turned.
Set screw
A screw that is made from heat-treated, hardened-alloy steel and used to secure such things as pulleys, gears, and shafts.
Square nut
A nut with four sides.

62. Glossary Taper tap Tapping Tensile strength
A tap that has a slender taper at the beginning of the tap that makes it start easier in the threads. Used for tapping through holes.
Tapping
The process of cutting threads in a hole.
Tensile strength
The amount of tension, or pulling, force a material can withstand before failing.

63. Glossary Thread Thread pitch Threading
The helical portion of a screw or bolt, or the helix in a hole that it fastens into.
Thread pitch
The number of threads per inch on U.S. customary fasteners; on metric fasteners it is the distance between each thread measured in millimeters.
Threading
The process of making external threads on an external cylindrical surface.

64. Glossary Through hole Toothed washers
A threaded hole that goes all the way through material.
Toothed washers
Washers made from stamped sheet metal that have internal, external, or external-internal teeth.
United National Coarse (UNC) series
Coarse thread series designation.

65. Glossary United National Fine (UNF) series Wide bearing lock washer
Fine thread series desingation.
Wide bearing lock washer
A washer that combines the characteristics of a flat washer and a kantlink lock washer.
Wing nuts
Nuts that have smooth, thick flanges molded into two sides so the nut can be tightened or loosened by hand.