Threaded Fasteners, Torque, and Repair CH 6.2 Threaded Fasteners, Torque, and Repair

Introduction (1 of 2) Tools and equipment are very important to an efficient and effective shop operation. Provide means for work to be undertaken on vehicles Purchase, use, and maintenance is very important to overall performance of any shop.

Introduction (2 of 2) Always use tools and equipment the way they are designed to be used. Identify the most effective tools to do the task. Inspect the tool before using it. Use it correctly. Clean and inspect it after you use it. Store it in the correct location.

Fasteners and Torque (1 of 3) Fasteners are designed to secure parts that are under various tension and sheer stress. Lug studs and lug nuts are examples of fasteners withstanding sheer stresses. Fasteners come in a variety of diameters and hardnesses. Defined in grades

Fasteners and Torque (2 of 3) Fasteners with screw threads are designed to be tightened to a specific rating. The material they are made from Their size The thread type

Fasteners and Torque (3 of 3) Overtightened fastener Could become damaged or break Undertightened fastener Could come loose over time Torque is a way of defining how much a fastener should be tightened.

Bolts, Studs, and Nuts (1 of 8) Designed for heavier jobs than screws Made of metal or metal alloys

Bolts, Studs, and Nuts (2 of 8) Cylindrical piece of metal Has a hexagonal head on one end A thread cut into the shaft at the other end

Bolts, Studs, and Nuts (3 of 8) Hexagonal nut threads onto the bolt thread Hexagonal heads are designed to fit tools such as combination wrenches and sockets Stud Does not have a fixed hexagonal head Has a thread cut on each end Used to attach throttle body to intake manifold Can have different threads on each end

Bolts, Studs, and Nuts (4 of 8) Can have either standard or metric threads Thread diameter Measured across outside of threads Fractions of an inch for standard-type fasteners Millimeters for metric-type fasteners

Bolts, Studs, and Nuts (5 of 8) Thread pitch The coarseness of any thread Measured in threads per inch (tpi)

Bolts, Studs, and Nuts (6 of 8) Thread pitch (cont’d) Each bolt diameter in the standard system can have one of two thread pitches: Coarse (UNC) (3/8 – 16) Fine (UNF) (3/8 – 24) Measured by distance between peaks of threads in millimeters in the metric system

Bolts, Studs, and Nuts (7 of 8) Length Measured from end of bolt to bottom of head Listed in inches or millimeters Grade Relates to its strength Higher grade number, higher tensile strength

Bolts, Studs, and Nuts (8 of 8) The Society of Automotive Engineers certifies fasteners. Have a rating scale from grade 1 to grade 8 Most general-purpose bolts used are grade 5. Bolts under higher stresses are a higher grade. Must replace original bolt with a bolt of same grade

Torque Specification (1 of 2) Level of tightness that bolts and nuts need to be tightened to Many nuts need to be tightened to specific level. Bolts and nuts are often marked with grade to tell you their strength. Determines how much torque can safely be applied to them

Torque Specification (2 of 2) Once bolts are tightened, you must ensure they stay tight. A locking washer A locking chemical compound A nylon locking device built into the nut

Torque Charts Torque specification for bolts and nuts will usually be contained within shop manuals. Manufacturers also produce torque charts. Most charts include: Bolt diameter Threads per inch Grade Maximum torque setting for dry and lubricated bolts and nuts

Torque Wrenches (1 of 7) Also known as a tension wrench Used to tighten fasteners to predetermined torque

Torque Wrenches (2 of 7) Designed to tighten using drive on end Fits with any socket and accessory of the same drive size, found in an ordinary socket set When torque is specified, it is important to follow specifications.

Torque Wrenches (3 of 7) Torque value Amount of twisting force applied to a fastener by torque wrench Specified in: Foot-pounds (lb-ft) Inch-pounds (in-lb) Newton meters (Nm)

Torque Wrenches (4 of 7) Torque wrenches come in various types. Beam style Uses spring steel beam that flexes under tension A smaller fixed rod indicates amount of torque on a scale mounted to the bar. Amount of deflection of the bar coincides with the amount of torque on the scale. Must be positioned directly above the scale

Torque Wrenches (5 of 7) Clicker Uses an adjustable clutch inside that slips (clicks) when the preset torque is reached The higher the torque, the louder the click. The lower the torque, the quieter the click. It is easy to miss the click and overtighten, break, or strip the bolt.

Torque Wrenches (6 of 7) Dial Turns a dial that indicates torque based on torque being applied You have to be able to see the dial to know how much torque is being applied. Many have a movable indicator that is moved by the dial and stays at the highest reading. Once the proper torque is reached, the indicator can be moved back to zero.

Torque Wrenches (7 of 7) Electronic Uses a spring steel bar with electronic strain gauge to measure amount of torque applied Torque wrench can be preset to desired torque. Torque is displayed when the torque fastener is being tightened . Usually gives audible signal when it reaches the preset torque Torque wrenches fall out of calibration over time or if they are not used properly.

Using Torque Wrenches (1 of 2) Used to apply a specified amount of torque to a fastener Various methods used to indicate that correct torque has been reached Audible sound Visual signal Some must be observed while torquing the fastener.

Using Torque Wrenches (2 of 2) Support head of torque wrench with one hand. It is best to not use extensions; use a deep socket instead.

Torque-to-Yield and Torque Angle (1 of 3) If threads are rusty, rough, or damaged: Twisting force required to tighten increases Tightening a rusty fastener to a particular torque will not provide as much clamping force as a smooth fastener torqued the same amount. When bolts are tightened, they are also stretched.

Torque-to-Yield and Torque Angle (2 of 3) Torque-to-yield (TTY) bolts Designed to provide a consistent clamping force when torqued to yield point or just beyond The torque does not increase very much, or at all, once yield is reached. TTY bolts generally require torquing procedure called torque angle. In virtually all cases, TTY bolts cannot be reused because they have been stretched into their yield zone and likely fail if retorqued.

Torque-to-Yield and Torque Angle (3 of 3) A more precise method to tighten TTY bolts Multistep process Bolts are first torqued in the required pattern using a standard torque wrench. They are further tightened an additional specified angle (torque angle) using an angle gauge, providing further tightening.

Thread Repair (1 of 6) Aim of thread repair is to restore thread to a condition that restores fastening integrity.

Thread Repair (2 of 6) Thread file The least invasive and reshapes the thread If threads are not too badly damaged, can clean them or a restoring tool can be used to reshape Each thread file has eight different sets of file teeth that match the bolt you are working on and file the bolt in line with the threads. Will remove any distorted metal from threads Only file until the bad spot is reshaped. Tool looks like an ordinary tap and die set.

Thread Repair (3 of 6) Thread insert For threads that have substantial damage Thread insert is a sleeve with both internal and external threads. Internal thread on the insert matches original damaged thread size. Hole is made larger and a larger thread is cut. Thread matches external thread on insert. Thread insert can be screwed and secured into prepared hole.

Thread Repair (4 of 6) Make sure tools are clean and in good condition and are suitable for thread repair. Determine type and size of thread to be repaired. Thread removal includes: Removal of a broken bolt Restoration of internal and external threads Use of thread insert to repair an internal thread

Thread Repair (5 of 6) To remove a broken bolt Inspect the site. Select correct size of extractor and drill designated hole size in center of broken bolt. Use a center punch to mark the bolt. Once hole is drilled, insert extractor and turn counterclockwise.

Thread Repair (6 of 6) To remove a broken bolt: Flutes on extractor should grab inside of bolt. Don’t exert too much force if bolt is really stuck. Once broken bolt is removed, run lubricated tap or thread restoring tool of correct size and thread pitch through hole to clean up any rust or damage.

Summary (5 of 30) Torque defines how much a fastener should be tightened. Bolts, nuts, and studs use threads to secure each part; these threads can be in standard or metric measures. Thread pitch refers to the coarseness of the thread; USCS bolts, nuts, and studs are measured in threads per inch (tpi), classified as coarse (UNC) or fine (UNF).

Summary (6 of 30) Fasteners are graded by tensile strength (how much tension can be withstood before breakage). SAE rates fasteners from grade 1–8; always replace a nut or bolt with same grade. Torque specification indicates level of tightness each bolt or nut should be tightened to; torque charts list torque specifications for nuts and bolts.

Summary (7 of 30) Torque (or tension) wrenches tighten fasteners to correct torque specification. Torque value—the amount of twisting force applied to a fastener by the torque wrench—is specified in foot-pounds, inch-pounds, or newton meters. Torque wrench styles are beam, clicker, dial, and electronic. Each gives indication when proper torque is achieved.

Summary (8 of 30) Bolts that are tightened beyond their yield point do not return to their original length when loosened. Torque-to-yield (TTY) bolts can be torqued just beyond their yield point, but should not be reused. Torque angle can be used to tighten TTY bolts and requires both a torque wrench and an angle gauge.

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