1.
Doughnut
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A doughnut or donut is a type of fried dough confectionery or dessert food. The doughnut is popular in countries and prepared in various forms as a sweet snack that can be homemade or purchased in bakeries, supermarkets, food stalls. Doughnuts are usually deep-fried from a dough, and typically either ring-shaped or without a hole. Other types of batters can also be used, and various toppings and flavorings are used for different types, such as sugar, chocolate, or maple glazing. In addition to flour, doughnuts may also include such ingredients as water, leavening, eggs, milk, sugar, oil/shortening, the two most common types are the ring doughnut and the filled doughnut—which is injected with fruit preserves, cream, custard, or other sweet fillings. A small spherical piece of dough may be cooked as a doughnut hole, once doughnuts have been fried, they may be glazed with a sugar icing, spread with icing or chocolate, or topped with powdered sugar or sprinkles or fruit. Other shapes include rings, balls, and flattened spheres, as well as ear shapes, twists, Doughnut varieties are also divided into cake and yeast-risen type doughnuts. Donuts are often accompanied by coffee when they are purchased at shops or fast food restaurants. This smaller piece of dough can be cooked and served as a hole or added back to the batch to make more doughnuts. A disk-shaped doughnut can also be stretched and pinched into a torus until the center breaks to form a hole, alternatively, a doughnut depositor can be used to place a circle of liquid dough directly into the fryer. There are two types of ring doughnuts, those made from a dough for raised doughnuts, or those made from a special type of cake batter. Yeast-raised doughnuts contain about 25% oil by weight, whereas cake doughnuts oil content is around 20%, cake doughnuts are fried for about 90 seconds at approximately 190 °C to 198 °C, turning once. Yeast-raised doughnuts absorb more oil because they take longer to fry, about 150 seconds, cake doughnuts typically weigh between 24 g and 28 g, whereas yeast-raised doughnuts average 38 g and are generally larger, and taller when finished. After frying, ring doughnuts are often topped, raised doughnuts are generally covered with a glaze. Cake doughnuts can also be glazed, or powdered with confectioners sugar, or covered with cinnamon and they are also often topped with cake frosting and sometimes sprinkled with coconut, chopped peanuts, or sprinkles. Doughnut holes are small, bite-sized doughnuts that were made from the dough taken from the center of ring doughnuts. Traditionally, doughnut holes are made by frying the dough removed from the portion of the doughnut. Consequently, they are smaller than a standard doughnut and tend to be spherical
2.
Rope
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A rope is a group of yarns, plies, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting, as a result, they cannot be used for pushing or similar compressive applications. Rope is thicker and stronger than similarly constructed cord, line, string, fiber rope is made from fiber, whereas wire rope is made from wire. Rope may be constructed of any long, stringy, fibrous material, synthetic fibre ropes are significantly stronger than their natural fibre counterparts, but also possess certain disadvantages, including slipperiness. Common natural fibres for rope are manila hemp, hemp, feathers, linen, cotton, coir, jute, straw, synthetic fibres in use for rope-making include polypropylene, nylon, polyesters, polyethylene, Aramids and acrylics. Some ropes are constructed of mixtures of several fibres or use co-polymer fibres, wire rope is made of steel or other metal alloys. Ropes have been constructed of fibrous materials such as silk, wool, and hair. Rayon is a fibre used to make decorative rope. The twist of the strands in a twisted or braided rope serves not only to keep a rope together, without any twist in the rope, the shortest strand would always be supporting a much higher proportion of the total load. Rope is of paramount importance in fields as diverse as construction, seafaring, exploration, sports, theatre, and communications, to fasten rope, many types of knots have been invented for countless uses. Pulleys redirect the force to another direction, and can create mechanical advantage so that multiple strands of rope share a load. Winches and capstans are machines designed to pull ropes, such ropes normally use a kernmantle construction, as described below. Static ropes, used for example in caving, rappelling, and rescue applications, are designed for minimal stretch, the UIAA, in concert with the CEN, sets climbing-rope standards and oversees testing. Any rope bearing a GUIANA or CE certification tag is suitable for climbing, climbing ropes, however, do cut easily when under load. Keeping them away from sharp rock edges is imperative, rock climbing ropes come with either a designation for single, double or twin use. A single rope is the most common and it is intended to be used by itself, single ropes range in thickness from roughly 9mm to 11mm. Smaller ropes are lighter, but wear out faster, double ropes are thinner ropes, usually 9mm and under, and are intended for use as a pair. These ropes offer a margin or security against cutting, since it is unlikely that both ropes will be cut, but they complicate belaying and leading
3.
Hoist (device)
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A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be operated, electrically or pneumatically driven and may use chain. The load is attached to the hoist by means of a lifting hook, the basic hoist has two important characteristics to define it, Lifting medium and power type. The lifting medium is either wire rope, wrapped around a drum, or load-chain, the power can be provided by different means. Common means are hydraulics, electrical and air driven motors, both the wire rope hoist and chain hoist have been in common use since the 1800s, however mass production of an electric hoist did not start until the early 1900s and was first adapted by Germany. A hoist can be built as one unit, designed for cost-effective purchasing and moderate use, or it can be built as a built-up custom unit, designed for durability. The built-up hoist will be more expensive, but will also be easier to repair. Package units were regarded as being designed for light to moderate usage. Built-up units are designed for heavy to severe service, but over the years that market has decreased in size since the advent of the more durable packaged hoist. A machine shop or fabricating shop will use an integral-package hoist, while a Steel Mill or NASA would use a unit to meet durability, performance. NASA has also seen a change in the use of package hoists, the NASA Astronaut training pool, for example, utilizes cranes with packaged hoists. The more commonly used hoist in todays worldwide market is an electrically powered hoist and these are either the chain type or the wire rope type. See the Hoists Manufacturers Institute site for true life calculation which is based on load, in todays modern world for the North American market there are a few governing bodies for the industry. The Overhead Alliance is a group that represents Crane Manufacturers Association of America, Hoist Manufacturers Institute and these product counsels of the Material Handling Industry of America have joined forces to create promotional materials to raise the awareness of the benefits to overhead lifting. The members of group are marketing representatives of the member companies. Common small portable hoists are of two types, the chain hoist or chain block and the wire rope or cable type. Chain hoists may have a lever to actuate the hoist or have a loop of operating chain that one pulls through the block which then activates the block to take up the main lifting chain. For a given rated load wire rope is lighter in weight per unit length, the lift chain of a chain hoist is far larger than the liftwheel over which chain may function
4.
Bicycle lock
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A bicycle lock is a security device used to deter bicycle theft, generally by fastening the bicycle to a fixed object, e. g. a bike rack. Quick-release levers - common on most bicycle wheels and seatpost fasteners - are a challenge for theft preventions. Unless both wheels and frame are secured, wheels can be removed separately, an optimal locking method will secure the frame as well as both wheels — either to a fixed object or to each other. Locking devices vary in size and security, the most secure tending to be the largest, heaviest and least portable, thus, like other security equipment, bicycle lockers must balance the competing interests of security, portability, and cost. Some are made of expensive materials chosen for their acceptable strength. An alternate defense is the provision of bicycle lockers or a cage in which the whole bicycle is locked. A bike locker is not a bicycle lock, test standards that rate the effective security of bicycle locks are provided by Thatcham and Sold Secure in the United Kingdom, ART in the Netherlands, SSF in Sweden, and VDS in Germany. A U-lock is a metal ring in the shape of the letter U. The U part of the lock attaches to a crossbar section, to lock the bicycle, one locks it physically to some other object, such as a bike rack, parking meter or other pole installed securely in the solid ground. Merely locking the frame to the wheel is not recommended because, although it cannot be rolled away. U-locks are more secure than most other kinds of locking mechanism because they are resistant to cutting with high-leverage hand tools such as bolt cutters. However, most are still vulnerable to at least one type of exploit, for instance, if there is enough space for a thief to fit a jack into the U, the jack can produce enough leverage to break the lock. Another common brute force method to break open U-locks is to use a length of pipe to twist the lock open. Like all locks, U-Locks are vulnerable to power such as portable angle grinders. A quality U-lock will advertise the materials hardness, its resistance to prying, for a time, many U-locks used a cylindrical pin tumbler lock. However, most cylindrical locks can be picked by thieves using a common disposable Bic pen, U-locks with cylindrical pin tumblers should be avoided, though most manufacturers no longer offer them. A very similar type of lock, often referred to as an O-lock and this lock may be more protective as it does not leave space for thieves to insert tools like a car jack which would burst a normal u-lock. A chain lock is a chain with a lock and it often has a key or a combination lock attached to it
5.
Jewellery
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Jewellery or jewelry consists of small decorative items worn for personal adornment, such as brooches, rings, necklaces, earrings, and bracelets. Jewellery may be attached to the body or the clothes, for many centuries metal, often combined with gemstones, has been the normal material for jewellery, but other materials such as shells and other plant materials may be used. It is one of the oldest type of archaeological artefact – with 100, historically, the most widespread influence on jewellery in terms of design and style have come from Asia. Jewellery may be made from a range of materials. Gemstones and similar such as amber and coral, precious metals, beads, and shells have been widely used. In most cultures jewellery can be understood as a symbol, for its material properties, its patterns. Jewellery has been made to nearly every body part, from hairpins to toe rings. The word jewellery itself is derived from the jewel, which was anglicised from the Old French jouel. In British English, Indian English, New Zealand English, Hiberno-English, Australian English, both are used in Canadian English, though jewelry prevails by a two to one margin. Numerous cultures store wedding dowries in the form of jewellery or make jewellery as a means to store or display coins, alternatively, jewellery has been used as a currency or trade good, an example being the use of slave beads. Many items of jewellery, such as brooches and buckles, originated as functional items. Jewellery can also symbolise group membership or status, wearing of amulets and devotional medals to provide protection or ward off evil is common in some cultures. These may take the form of symbols, stones, plants, animals, body parts, in creating jewellery, gemstones, coins, or other precious items are often used, and they are typically set into precious metals. Alloys of nearly every metal known have been encountered in jewellery, bronze, for example, was common in Roman times. Modern fine jewellery usually includes gold, white gold, platinum, palladium, titanium, most contemporary gold jewellery is made of an alloy of gold, the purity of which is stated in karats, indicated by a number followed by the letter K. American gold jewellery must be of at least 10K purity, many whimsical fashions were introduced in the extravagant eighteenth century. Cameos that were used in connection with jewellery were the attractive trinkets along with many of the objects such as brooches, ear-rings. Some of the necklets were made of pieces joined with the gold chains were in and bracelets were also made sometimes to match the necklet
6.
Hudson River Chain
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These defenses along the Hudson River were overseen by the Highlands Department of the Continental Army. The most significant and successful was the Great Chain, constructed from West Point in 1778, the huge links for the chains were forged at iron works in Orange County, New York. Both the Americans and British knew that passage on the Hudson River was strategically important to the war effort. Americans worked to devise plans to slow or block ship passage on the river, planning to attack ships by cannons. The largest and most important project was the chain at West Point. Creating more obstructions on the river enabled the shore batteries to work their cannons against the enemy, the logs were intended to pierce and sink any British ships that passed over it. An opening was left for the passage of American ships, after the British learned of the opening from a local resident, they successfully passed through the barrier several times. The British captured Fort Washington on November 16,1776 and Fort Lee on November 20, Fort Clinton had been built just south of Popolopens Kill and also on the West Bank. In November 1776, a faulty link broke under stress induced by the river tides, after the British captured forts Montgomery and Clinton on October 6,1777, they dismantled the chain and raided upriver as far as Kingston. Governor Clinton, one of the committee assigned by the New York Convention to devise means of defending the Hudson, was heartened as the British never attempted to run ships through the chain and he concluded that the basic idea of obstructing the river seemed sound. After Captain Machin recovered from wounds from battle with the British, he work on the stronger Great Chain at West Point. Another chevaux-de-frise was constructed across the Hudson between Plum Point and Pollepel Island, north of West Point, the defenses were never fully completed, and its importance was overshadowed by completion of the Great Chain at West Point the following year. In the spring of 1778, a heavy chain supported by logs was stretched across the Hudson from West Point to Constitution Island. It was constructed at the Stirling Iron Works, in Warwick, Orange County, the task was completed in six weeks. The Hudson Rivers narrow width and sharp turns at West Point created adverse sailing conditions, the Army took advantage of this by constructing The Great Chain in 1778 as an obstacle to the movement of British ships north of West Point. The distinctive S-Curve of the Hudson at this point forced any large ship to tack in order to navigate it, American soldiers positioned the chain to impede the progress of a ship should it attempt to turn into the east-west channel against the strong current and frequently unfavorable winds. Part of the estuary of the Lower Hudson River, this area is subject to significant tides, cannons were placed in forts and artillery batteries on both sides of the river to destroy ships when they slowed to a halt against the obstacle. When finally completed, the 600 yards chain contained huge iron links, the links were carted to New Windsor, where they were put together, and floated down the river to West Point on logs late in April
7.
Livery collar
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A livery collar or chain of office is a collar or heavy chain, usually of gold, worn as insignia of office or a mark of fealty or other association in Europe from the Middle Ages onwards. One of the oldest and best-known livery collars is the Collar of Esses, various forms of livery were used in the Middle Ages to denote attachment to a great person by friends, servants, and political supporters. From the collar hung a badge or device indicating the person the livery related to, equally gold collars that had no livery connotations were worn. Livery collars seem to be first recorded in the 14th century, the collar of Esses is first recorded earlier than this, as being given by John of Gaunt, and remained in use by the House of Lancaster throughout the Wars of the Roses. The same collar was worn by Henry IV on the way to his crowning, the inventory shows that Queen Annes collar, was made up of sprigs of rosemary garnished with pearls. The York collar had falcons and fetterlocks, and the Lancaster collar was doubtless that Collar of Esses used by the son, Henry of Bolingbroke, as an earl, duke. The oldest effigy bearing it is that in Spratton church of Sir John Swynford, who died in 1371. Swynford was a follower of John of Gaunt, and the date of his death easily disposes of the theory that the Esses were devised by Henry IV to stand for his motto or word of Soverayne. Many explanations are given of the origin of these letters, in one of Henry VIs own collars the S was joined to the broomcod of the French device, symbolizing the kings claim to the two kingdoms. The kings of the house of York and their chief followers wore the Yorkist collar of suns and roses, with the lion of March. It was presented to ministers and courtiers, and came to represent more a symbol of office by the time of Elizabeth I, the term Collar of SS was preferred by Victorian antiquaries. Since World War II, as SS is usually associated with the Schutzstaffel, besides these royal collars, the 14th and 15th centuries show many private devices. A monumental brass at Mildenhall shows a knight whose badge of a dog or wolf circled by a crown hangs from a collar with edges suggesting a pruned bough or the ragged staff. The Elizabethan artist Nicholas Hilliard was both a goldsmith and miniaturist, and so produced the whole of pieces like the Armada Jewel, given by Queen Elizabeth I of England to a courtier. When the Earl of Rutland returned from an embassy to Denmark, sixteen members of his party were given chains of gold with the James I of Englands picture, during the sixteenth century collars became marks of a specific office or Order, and subsequently remained so. Most British and Irish mayors wear a collar/chain of office, the mayors spouse may have a much smaller version. These are worn over normal clothes when on official duties, following British practice, most Canadian, Australian and New Zealand mayors also wear chains of office. Collars of various devices are worn by the knights of some of the European orders of knighthood
8.
Jewellery chain
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Fine metal chains are used in jewellery to encircle parts of the body, namely the neck, wrists and ankles, and they also serve as points to hang decorative charms and pendants. Unlike industrial or chains for other purposes, jewellery chains or body chains are designed for aesthetic purposes, jewellery chains are typically made from precious metals, mainly gold and silver. Platinum, palladium and steel may also be used and these metals are used because they are not very reactive, keep both their intricate shape and their strength, and require only minimal maintenance to keep their shine. Small lever mechanisms called findings serve as fastenings to enable the chain to be undone and redone, belcher, This is similar to the trace, a belcher chain link is wider than its thickness. Generally the links are round, but the shape of the link can vary, curb, A curb chain is when the links interlock with each other when laid flat. Some more open-link curb chains can only be distinguished from a trace by this method and this style of chain has the greatest variety of widths available, from a few millimetres to over four centimetres. Prince Of Wales, This chain consists of a chain made of small circular links. Spiga, Spiga is formed of small figure-eight links which form a 3D chain that feels almost square, anchor, The anchor chain copies the style of the chain that holds large anchors on ships, an oval link with a dividing bar through the middle. The interlinking sections may be of a curb or trace style, Also a version called Maritime where only every other link is an anchor link. Snake, Snake chain is a very tight-linked chain that has a round or square cross-section and has links that create a slight zigzag look, herringbone, This chain that has the greatest liquid effect, formed from v-shaped links to lie entirely flat. One side can be engraved for greater aesthetics, and thin strands of herringbone can be twisted or even plaited together, briolette, Also known as Box, briolette is similar to a belcher chain except the links are tighter together and are square in shape, hence the name. Bead, Bead chain is formed of small balls of metal joined by small lengths of wire, Also has its own snap over the first link fastening. Larger steel versions are often used to hold ID cards than in jewellery. Fancy, A fancy chain can be anything, any form of metal that can be replicated and joined onto each other to make a chain. Many fancy chains are variations of the styles, for example a trace chain formed of heart-shaped links or a curb chain with every other link set with a gemstone
9.
Chain drive
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Chain drive is a way of transmitting mechanical power from one place to another. It is often used to power to the wheels of a vehicle. It is also used in a variety of machines besides vehicles. The gear is turned, and this pulls the chain putting mechanical force into the system, another type of drive chain is the Morse chain, invented by the Morse Chain Company of Ithaca, New York, United States. Sometimes the power is output by simply rotating the chain, which can be used to lift or drag objects, in other situations, a second gear is placed and the power is recovered by attaching shafts or hubs to this gear. By varying the diameter of the input and output gears with respect to each other, for example, when the bicycle pedals gear rotate once, it causes the gear that drives the wheels to rotate more than one revolution. The oldest known application of a chain appears in the Polybolos. Two flat-linked chains were connected to a windlass, which by winding back and it is here that the flat-link chain, often attributed to Leonardo da Vinci, actually made its first appearance. The chain drive itself was given power via the works of Sus water clock tank and waterwheel. Roller chain and sprockets is an efficient method of power transmission compared to belts. Although chains can be stronger than belts, their greater mass increases drive train inertia. Drive chains are most often made of metal, while belts are often rubber, plastic, urethane, or other substances. Drive belts can slip unless they have teeth, which means that the side may not rotate at a precise speed. Wear on rubber or plastic belts and their teeth is often easier to observe, one problem with roller chains is the variation in speed, or surging, caused by the acceleration and deceleration of the chain as it goes around the sprocket link by link. It starts as soon as the line of the chain contacts the first tooth of the sprocket. This contact occurs at a point below the circle of the sprocket. As the sprocket rotates, the chain is raised up to the circle and is then dropped down again as sprocket rotation continues. This rising and falling of the line is what causes chordal effect or speed variation
10.
Chainsaw
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A chainsaw is a portable, mechanical saw which cuts with a set of teeth attached to a rotating chain that runs along a guide bar. It is used in such as tree felling, limbing, bucking, pruning, cutting firebreaks in wildland fire suppression. Chainsaws with specially designed bar and chain combinations have been developed as tools for use in chainsaw art, specialized chainsaws are used for cutting concrete. Chainsaws are sometimes used for cutting ice, for example for ice sculpture, someone who uses a saw is a sawyer. The origin is debated, but a tool was made around 1830 by the German orthopaedist Bernhard Heine. This instrument, the osteotome, had links of a chain carrying small cutting teeth with the set at an angle. As the name implies, this was used to cut bone, the chain hand saw, a fine serrated link chain which cut on the concave side, was invented around 1783-1785. It was illustrated in Aitkens Principles of Midwifery or Puerperal Medicine, Jeffray claimed to have conceived the idea of the chain saw independently about that time but it was 1790 before he was able to have it produced. In 1806, Jeffray published Cases of the Excision of Carious Joints by H. Park, in this communication he translated Moreaus paper of 1803. Park and Moreau described successful excision of diseased joints, particularly the knee, Jeffray explained that the chain saw would allow a smaller wound and protect the adjacent neurovascular bundle. While a heroic concept, symphysiotomy had too many complications for most obstetricians but Jeffrays ideas became accepted, mechanised versions of the chain saw were developed but in the later 19th Century, it was superseded in surgery by the Gigli twisted wire saw. For much of the 19th century, however, the saw was a useful surgical instrument. The earliest patent for an endless chain saw was granted to Samuel J. Bens of San Francisco on January 17,1905. His intent being to fell giant redwoods, the first portable chainsaw was developed and patented in 1918 by Canadian millwright James Shand. After he allowed his rights to lapse in 1930 his invention was developed by what became the German company Festo in 1933. The company now operates as Festool producing portable power tools, in 1927, Emil Lerp, the founder of Dolmar, developed the worlds first gasoline-powered chainsaw and mass-produced them. World War II interrupted the supply of German chain saws to North America, so new manufacturers sprang up including Industrial Engineering Ltd in 1947, Ltd and part of Outboard Marine Corporation, the oldest manufacturer of chainsaws in North America. McCulloch in North America started to produce chainsaws in 1948, the early models were heavy, two-person devices with long bars
11.
Saw chain
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The saw chain, or cutting chain, is a key component of a chainsaw. It consists of steel held together by rivets, and superficially resembles the bicycle-style roller chain. Its key differences are sharp cutting teeth on the outside of the chain loop, saw chains are used for cutting wood. This may be for harvesting trees for pulp or timber, for tree surgery, whether for hand-held chainsaws, mechanical timber harvesters or chain mortisers, the saw chain has undergone dramatic development since its invention. Modern chains designed for power, high-speed sawing applications will vastly outperform older designs. Saw chains operate by being propelled around a bar, removing material from the kerf by cutting chips from the side. In order to operate properly, the depth to which each tooth cuts must be limited to avoid it binding in the wood. Scratcher chain, like the teeth on a saw, simply uses a multitude of teeth to prevent individual teeth from sinking too far in without undue pressure on the bar. Chipper chain, and all subsequent designs, incorporate a depth gauge on each link to limit depth of cut on each tooth. Individual depth gauges on each tooth also enable the use of skip chain, skip or semi-skip chain has a further reduction in the number of teeth and is used for applications where much debris is produced, such as ripping or cross-cutting very large sections of wood. Skip chain also absorbs less power from the motor per unit length of chain than full-complement chain, very early chainsaws used tooth configurations very similar to conventional hand saws. These were very simple saw teeth following a pattern with no depth gauges as such. They were inefficient and slow in use, and were superseded by chipper chain. They required great skill and a lot of time to sharpen in the leading to extended downtime between sessions. Chipper chain invented by Joseph Cox improved dramatically on the performance of scratcher chain, chipper used a tooth that was curled over the top of the chain, with alternate teeth pointing left and right. Ahead of the tooth was a gauge, which allowed for good clearance around the tooth for chip clearing while limiting the depth of cut. Chipper chains are used for dirty work, since their very large working corner allows the cutter to retain its effective sharpness for a long time in abrasive conditions. Modern chains for use in forestry, tree surgery and firewood cutting come in three basic configurations, the full chisel, the semi-chisel, and the chipper chain
12.
Timing belt (camshaft)
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In an interference engine the timing belt or chain is also critical to preventing the piston from striking the valves. A timing belt is usually a toothed belt -- a drive belt with teeth on the inside surface, a timing chain is a roller chain. Most modern production engines use a timing belt or chain to synchronize crankshaft and camshaft rotation. Timing chains were common on production automobiles through the 1970s and 1980s, when timing belts became the norm, but timing chains have seen a resurgence in recent years. Timing chains are more durable than timing belts – though neither is as durable as direct gear drive – however, timing belts are lighter, less expensive. In the internal combustion engine application the timing belt or chain connects the crankshaft to the camshaft, a four-stroke engine requires that the valves open and close once every other revolution of the crankshaft. It has teeth to turn the camshaft synchronised with the crankshaft, in some engine designs the timing belt may also be used to drive other engine components such as the water pump and oil pump. Gear or chain systems are used to connect the crankshaft to the camshaft at the correct timing. However, gears and shafts constrain the relative location of the crankshaft, even where the crankshaft and camshaft are very close together, as in pushrod engines, most engine designers use a short chain drive rather than a direct gear drive. This is because gear drives suffer from frequent torque reversal as the cam profiles kick back against the drive from the crank, leading to excessive noise, fibre or nylon covered gears, with more resilience, are often used instead of steel gears where direct drive is used. Commercial engines and aircraft engines use steel gears only, as a fibre or nylon coated gear can fail suddenly, a belt or chain allows much more flexibility in the relative locations of the crankshaft and camshafts. Also, timing belts do not require lubrication, which is essential with a chain or gears. A timing belt is an application of a synchronous belt used to transmit rotational power synchronously. Timing belts are typically covered by metal or polymer timing belt covers which require removal for inspection or replacement, engine manufacturers recommend replacement at specific intervals. Indicators that the chain may need to be replaced include a rattling noise from the front of the engine. When an automotive timing belt is replaced, care must be taken to ensure that the valve, failure to synchronize correctly can lead to problems with valve timing, and this in turn, in extremes, can cause collision between valves and pistons in interference engines. This is not a unique to timing belts since the same issue exists with all other cam/crank timing methods such as gears or chains. Timing belts must be replaced at the recommended distance and/or time periods
"Chain". Encyclopædia Britannica. 5 (11th ed.). 1911.
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