Chapter 6 Fasteners PDF

Chapter 6 Fasteners  Objectives Identify the various fasteners used in vehicle construction Remove and install bolts and nuts properly Explain when specific fasteners are used in vehicle construction Explain bolt and nut torque values Summarize the use of chemical fa...

Chapter 6 Fasteners  Objectives Identify the various fasteners used in vehicle construction Remove and install bolts and nuts properly Explain when specific fasteners are used in vehicle construction Explain bolt and nut torque values Summarize the use of chemical fasteners Identify hose clamps  Introduction Fasteners are the thousands of bolts, nuts, screws, clips and adhesives that hold a vehicle together Must be able to identify and use fasteners properly Each fastener is engineered for a specific application Always replace a fastener with exactly the same type that was removed from the original equipment manufacture (OEM) assembly  Bolts Bolt is a shaft with a head on one end and threads on the other Cap screw is a high-strength bolt Bolts and cap screws are named after the body part they hold – Fender bolt, hood hinge bolt, etc. Also named after the shape and head drive configuration  Bolts (continued) Bolt head is used to tighten the bolt Socket wrench fits over the bolt head Some metric/SAE sockets are very close in size Improper wrench or socket size could strip or round off the both you are working on – This could damage your tools or even cause an injury if the tool slips off Figure 6-1. Bolt measurements are needed when working. Study each dimension of both USC and metric bolts  Bolts (continued) Bolt length is measured from the end of the threads to the bottom of the bolt head Bolt length does not including the bolt head itself Bolt diameter, or bolt size, is measured around the outside of the threads Bolt head size is the distance across the flats of the bolt head Head size is given in fractions, like wrench size – Common head sizes are 7/16, ½ and 9/16 – Common metric sizes are 8 mm, 10 mm, 13 mm  Bolts (continued) Both thread pitch is a measurement of thread coarseness Bolts and nuts can have coarse, fine, and metric threads Bolt threads are measured with a thread pitch gauge Two common metric threads are coarse and fine and can be identified by the letters SI and ISO Do not accidentally interchange thread types or the bolt, or the part threads will be ruined  Bolts (continued) Bolts and nuts are available in right- and left- hand threads Turn right-hand threads clockwise to tighten Turn left-hand threads counterclockwise to tighten Left-hand threads have notches or a letter “L” stamped on them (A) Thread pitch gauge. The thread pitch gauge is fit against threads. Threads that match the gauge equal the pitch number printed on the gauge. Figure 6-3. Gauges can be used to tell thread, bolt or nut sizes.  Bolt Strengths or Grades Bolt strength is the amount of tightening force that should be applied Bolts are made from different materials – Have degrees of hardness for different situations Bolt grade markings are lines or numbers on top of the head to identify hardness and strength Hardness or strength of metric bolts is indicated by a property class indicator on bolt head  Bolt Strengths or Grades (continued) Bolt strength markings are given as lines, more lines means more strength Metric bolt strength markings are numeric – Higher number means more strength Tensile strength is the amount of pressure bolt can withstand before breaking when pulled apart The harder the bolt, the greater tensile strength  Torque Torque is a measurement of the turning force applied when tightening a fastener Over-tightening can stretch or break a bolt Under-tightening can allow bolt or nut to loosen and fall out Torque specifications are tightening values for a specific bolt or nut, given by the manufacturer  Torque (continued) Torque wrench measures torque values General bolt torque chart gives a general torque value for the size and grade of bolt Bolt threads should be lubricated for accurate results – Refer to repair manual to see if threads should be lubricated or dry Tightening sequence or torque pattern ensures that parts secured by several bolts are clamped down evenly Figure 6-5. When tightening several bolts that hold one part, a wheel, for example, always use a crisscross pattern. This will prevent part warpage and damage.  Torque (continued) Tighten fasteners in a crisscross pattern Tighten the fastener in steps, beginning at half- torque then continue to ¾ torque, and then full torque at least twice Be careful when tightening bolts and nuts with air wrenches – Easy to stretch or break a bolt in an instant Air wrench can spin the bolt or nut so fast that it can hammer the fastener past its yield point, stripping the threads or breaking the bolt  Nuts Nut uses internal threads and an odd shaped head and is tightened onto a bolt Castellated or slotted nuts are grooved on top to a safety wire or cotter pin can be installed into a hole in the bolt Castellated nuts are used with the studs that hold wheel bearings in position Self-locking nuts produce friction when threaded onto a bolt; top of the nut can be crimped inward  Nuts (continued) Sometimes locking nuts must be replaced after being removed Front wheel drive spindles sometimes use self- locking nuts Jam nuts hold larger nuts in place – Tightened against other nut to prevent loosening  Nuts (continued) Wing nuts have two arms for turning by hand – Used when a part must be removed frequently for service or maintenance, such as for air cleaners Acorn nuts are closed on one end for appearance, to keep water/debris off the threads Body nut has a washer formed onto the nut to distribute the clamping force of the thin body panel or trim piece to prevent warpage Figure 6-7. Body nuts are specially designed for specific holding applications.  Thread Repair Collision repair technician must frequently repair damaged threads Tap is a tool for cutting inside threads in holes Die cuts threads on the outside of bolts or studs Special t-handles fit over tap or die for turning  Thread Repair (continued) Hold tool perfectly square to cut good threads Oil threads then rotate tap or die about one-half turn Back it out about one-fourth of a turn – Cleans out metal shavings and prevents tool breakage Helicoil repairs badly damaged threads, and allows the original bolt size to be used  Washers Washers prevent damage to surface of parts and provide better holding power Flat washers prevent smaller bolt heads from pulling through sheet metal and plastic Wave washers add a spring action to keep parts from rattling and loosening Body or fender washers have large outside diameter for the size hole in them – Have better holding power on thin metal and plastic parts Copper or brass washers prevent fluid leakage  Washers (continued) Spacer washers allow for the adjustment of parts Fiber washers prevent vibration or leakage but cannot be tightened to a great extent Finishing washers have a curved shape for appearance Split lock washers are used under nuts to prevent loosening by vibration Shakeproof or teeth lock washers have teeth or bent lugs that grip both the work and the nut  Screws Screws hold nonstructural parts on a vehicle Machine screws are threaded their full length and are relatively weak Set screws have an internal drive head for an Allen wrench and hold parts onto shafts Sheet metal screws and self-tapping screws have pointed or tapered tips Trim screws have a washer attached Headlight aiming screws have a plastic adapter  Nonthreaded Fasteners Square keys, Woodruff keys prevent gears, cams and pulleys from turning on their shafts Taper pins are used to locate and position matching parts Dowel pins are used to position and align the parts of an assembly Cotter pins prevent bolts and nuts from loosening Snaprings hold parts onto shafts, and pop rivets hold two pieces of sheet metal together Figure 6-11. Keys and set screws are both used to align parts on shafts. (A) Key and keyway. (B) Set screw application  Hose Clamps Hose clamps hold radiator hoses Also hold heater hoses or other hoses into their fittings  Adhesives Epoxy is a two part bonding agent that dries harder than adhesive – Does not shrink when hard and is waterproof and heat-resistant at moderate temperatures Trim adhesive is used to install trim pieces onto the body surface Trim adhesive dries to a pliable rubber-like consistency and will bond plastics, metal, rubber and other materials to painted surfaces  Summary Fasteners make up the thousands of bolts, nuts, screws, clips, and adhesives that literally hold a vehicle together Bolt strength indicates the amount of torque or tightening force that should be applied Nonthreaded fasteners do not use threads – Keys, snaprings, pins, clips, adhesives