Modern Automotive Technology PowerPoint for by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

Chapter 9 Fasteners, Gaskets, Seals, and Sealants

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

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

Fasteners Devices that hold the parts of a vehicle together Thousands of fasteners are used in vehicles

Automotive Fasteners

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 six-sided outer shape

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

Bolt Dimensions

Bolt Dimensions

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

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

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

Gives information about the bolt Bolt Description Gives information about the bolt

Used when purchasing new bolts Bolt Description Used when purchasing new bolts

Bolt Description

Common types of nuts used in vehicles Nut Types Common types of nuts used in vehicles

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

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

Washer Types Flat washer Lock 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

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

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

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

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

Sheet Metal Screws

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

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

Snap Ring Types

Keys and Set Screws Key Set screw 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

Keys and Set Screws A. Key B. Set screw

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

Splines

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

Torquing Bolts and Nuts It is very important that bolts and nuts be tightened properly—this is called torquing

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

Bolt Torque Chart

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

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

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

Bolt Tightening Sequence 9 5 1 4 8 10 6 2 3 7 Service manual pattern for a cylinder head

Bolt Tightening Sequence Service manual pattern for wheel lug nuts

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

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

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

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

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

Tap and Die

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

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

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

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

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

Insert allows the use of the original-size bolt Using an Insert Insert allows the use of the original-size bolt

Damaged threads before a repair Using an Insert Damaged threads before a repair Installed insert

Removing Damaged Fasteners 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

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

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

Removal Methods Using a screw extractor A. Drill a hole B. Tap the extractor into the hole C. Unscrew the extractor and bolt

Use rust penetrant to help ease turning and prevent fastener breakage Removal Methods Use rust penetrant to help ease turning and prevent fastener breakage

Gaskets and Seals Used between parts to prevent leakage of engine oil, coolant, transmission fluid, and other fluids

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

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

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

Sealers Gaskets are often coated with a sealer to help prevent leakage and to hold the gasket in place during assembly

Types of Sealers

Form-in-Place Gaskets Used instead of conventional fiber or rubber gaskets Two common types are: room temperature vulcanizing (RTV) sealer anaerobic sealer

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

Commonly recommended where two different gaskets join RTV Sealer Commonly recommended where two different gaskets join

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

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

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

Both anaerobic and RTV sealers are used on this water pump Using Sealers Both anaerobic and RTV sealers are used on this water pump

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

Seal lip faces the fluid and keeps it inside the part Seal Application Seal lip faces the fluid and keeps it inside the part

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

Inspect shafts for wear and burrs Seal Rules Inspect shafts for wear and burrs

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

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

O-Ring Seal Normally, the O-ring seal is coated with system fluid before installation

Specially-shaped seal that fits down into a groove formed in the part Synthetic Seal Specially-shaped seal that fits down into a groove formed in the part