by
Russell Krick
Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only
(9 Topics)
 Fasteners
 Washers
 Machine screws
 Sheet metal screws
 Nonthreaded fasteners
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 Torquing bolts and nuts
 Thread repairs
 Removing damaged fasteners
 Gaskets and seals
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 Devices that hold the parts of a vehicle
together
 Thousands of fasteners are used in
vehicles
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Automotive Fasteners
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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, usually, a sixsided outer shape
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Bolts and Nuts
When a nut is screwed onto a bolt, a
powerful clamping force is produced
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Bolt Dimensions
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Bolt Dimensions
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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
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Thread Direction
 Bolts and nuts come in right- and lefthand 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
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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
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Bolt Description
Gives information about the bolt
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Bolt Description
Used when purchasing new bolts
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Bolt Description
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Nut Types
Common types of nuts used in vehicles
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Castle Nut and
Cotter Pin
Cotter pin keeps the nut from turning and
possibly coming off
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 Used under bolt heads and nuts
 Two basic types of washers are used:
 flat washers
 lock washers
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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
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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
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Washer Types
A. Plain flat washer
C. Toothed lock washer
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B. Split lock washer
D. Lock plate
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 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
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 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
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Sheet Metal Screws
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Numerous types of nonthreaded
fasteners, such as snap rings, clips, and
adhesives, are used in the assembly
of a vehicle
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Snap Ring
 Fits into a groove in a part and
commonly holds shafts, bearings,
gears, pins, and other components in
place
 Snap ring pliers are needed to remove
and install a snap ring
special jaws grasp the snap ring
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Snap Ring Types
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Keys and Set Screws
 Key
 prevents a part from turning on its shaft
 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
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Keys and Set Screws
A. Key
B. Set screw
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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
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Splines
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Adhesives
 Special glues widely used in vehicles
 Used to hold body moldings, rubber
weather stripping, and body emblems
 Some stay soft and pliable; others dry
hard
 Some take hours to dry; others dry in
seconds
 Observe all directions and safety
precautions when using adhesives
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It is very important that bolts and
nuts be tightened properly—this is
called torquing
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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
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Bolt
Torque
Chart
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Torque-to-Yield
 Requires a bolt to be tightened to a
specific torque and then turned an
additional number of degrees
 Procedure stretches the bolt to its
correct yield point, preloading the
fastener for better clamping under
varying conditions
 New bolts may be required each time
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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
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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
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Bolt Tightening
Sequence
10
9
6
5
2
1
3
7
4
8
Service manual pattern for a cylinder head
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Bolt Tightening
Sequence
Service manual pattern for wheel lug nuts
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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
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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
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Threaded holes in parts can become
damaged, requiring repairs. A technician
must be capable of repairing damaged
threads quickly and properly.
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Minor Thread Repairs
 Minor thread damage includes nicks,
partial flattening, and other less serious
problems
 Minor damage can be repaired with a
thread chaser or a thread file
 the thread chaser is run through or over
the threads to restore them
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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
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Tap and Die
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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 the
hole
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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
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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
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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
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Using an Insert
A. Drill the hole
oversize
B. Tap the hole
oversize
C. Mount the
insert on a
mandrel
D. Thread the
insert into the
hole
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Using an Insert
Insert allows the use of the original-size bolt
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Using an Insert
Damaged threads
before a repair
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Installed insert
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 An automotive technician must be able
to remove broken bolts, screws, and
studs, as well as fasteners having
rusted or rounded-off heads
 Specific tools and methods are needed
for removing problem fasteners
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Removal Methods
 Grasp a rusted or rounded head with
locking pliers
 Use a stud puller or stud wrench
 removes studs and bolts broken off above
the surface of the part
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Removal Methods
 Cut a slot in the fastener with a
hacksaw or weld on a nut to grasp
 Use a hammer and punch
 angle the punch so that blows from the
hammer can drive out the broken
fastener
 Drill a hole almost as large as the
inside diameter of the threads
 use a tap or punch to remove the thread
shell
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Removal Methods
Using a screw extractor
A. Drill a hole
B. Tap the extractor into the hole
C. Unscrew the extractor and bolt
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Removal Methods
Use rust penetrant to help ease turning
and prevent fastener breakage
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Used between parts to prevent leakage of
engine oil, coolant, transmission fluid, and
other fluids
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Gaskets
 Soft, flexible material placed between
parts to prevent leakage
 Made of fiber materials, rubber,
neoprene (synthetic rubber), cork,
treated paper, or thin steel
 When parts are fastened together, the
gasket material fills small gaps, dents,
or scratches in the mating surfaces
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Gasket Rules
 Inspect for leaks before disassembly
 Be careful not to damage mating
surfaces while removing parts
 Clean off old gaskets carefully
 Wash and dry parts thoroughly
 Compare the new gasket to the shape
of the mating surface
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Gasket Rules
 Use a sealer if specified
 When assembling, start all bolts by
hand
 Tighten fasteners in steps
 Use a crisscross tightening pattern
 Do not overtighten fasteners
 apply only the specified torque
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Sealers
Gaskets are often coated with a sealer to
help prevent leakage and to hold the
gasket in place during assembly
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Types of Sealers
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Form-in-Place Gaskets
 Used instead of conventional fiber or
rubber gaskets
 Two common types are:
 room temperature vulcanizing (RTV)
sealer
 anaerobic sealer
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RTV Sealer
 Also called silicone sealer
 Dries in contact with air
 Used to form a rubber-like gasket on
thin, flexible flanges
 Available in tubes
has a shelf life of one to two years
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RTV Sealer
Commonly recommended where two
different gaskets join
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Using RTV Sealer
 Apply in a continuous bead that is
approximately 1/8” (3 mm) wide
 Circle all mounting holes
 Torque components in place while the
RTV is still wet to the touch
 within about 10 minutes of application
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Anaerobic Sealer
 Cures to a plastic-like substance in the
absence of air
 Designed for tightly fitting, thick parts
 Used between two smooth, true
surfaces
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Using Anaerobic
Sealer
 Apply in a continuous bead that is
approximately 1/16"–3/32" (1.5 mm–
2 mm) wide
 Circle all mounting holes
 Torque components in place within 15
minutes of sealer application
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Using Sealers
Both anaerobic and
RTV sealers are
used on this water
pump
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Seals
 Prevent leakage between a stationary
part and a moving part
 Found in engines, transmissions,
power steering units, and any part
containing fluid and moving parts
 Made of synthetic rubber molded onto
a metal body
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Seal Application
Seal lip faces the fluid and keeps it
inside the part
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Seal Rules
 Inspect the seal for leakage before
disassembly
 if the seal is leaking, look for a bent shaft,
misaligned seal housing, or damaged
parts
 Remove the old seal carefully, without
scratching the seal housing
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Seal Rules
Inspect shafts for wear and burrs
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Seal Rules
 Compare the old seal to the new seal
 make sure the inner and outer diameters
match before installation
 Install the new seal correctly
 coat the outside with an approved sealer
 coat the inner lip of the seal with system
fluid
 install the seal with the sealing lip toward
the inside of the part
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O-Ring Seal
 Stationary seal that fits into a groove
between two parts
 When the parts are assembled, the
synthetic rubber seal is partially
compressed to form a leakproof joint
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O-Ring Seal
Normally, the O-ring seal is coated with
system fluid before installation
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Synthetic Seal
Specially-shaped seal that fits down into a
groove formed in the part
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