WORK BOOK Power Transmission Group Automotive Aftermarket Contents Introduction Page High mechanical output on demand, completely independent of wind or water power – the spread of the steam engine un- Introduction 3 leashed the industrial revolution in the factories. The individual production machines were driven via steel shafts mounted on Timing belts 4 the ceiling of the building, pulleys and flat drive belts made of Function 5 leather. Design/materials 6 Profiles/handling 9 The first cars and motorcycles also used this power transmis- Maintenance and replacement 10 sion principle. However, the flat belts in this application were Changing the timing belt 12 soon replaced by something better: the V-belt with its trapezoi- Timing chains 13 dal cross-section transmitted the necessary forces with a signifi- Tools 14 cantly lower pretension and became the accepted standard for ancillary component drives. Timing belt drive components 18 Idlers and guide pulleys 19 The multi V-belt, a further development of the V-belt, has been Tensioners 20 taking over automotive applications since the early 1990s. Its Water pumps 22 long ribs enable it to transmit even greater loads. Its flat design allows multiple units to be incorporated and driven at the same V-belts and multi V-belts 26 time. This gives new impetus to the ever more compact design Function, handling 27 of engines. Timing belts have been used for synchronous pow- Design, materials, profiles 28 er transmission to drive the camshaft in automotive engines – V-belts since the 1960s. – multi V-belts – Elastic multi V-belts The next generations of the old transmission belts are now Maintenance and replacement 34 high-tech products. To ensure that they function properly, the Tools 36 other belt drive components, such as tensioning pulleys, idlers and water pumps, must also be capable of withstanding the Multi V-belt drive components 40 very demanding requirements. Our aim in this publication is to Torsional vibration dampers 41 expand your technical knowledge relating to belt drives in pas- Idlers and guide pulleys, senger car engines and help you in making correct diagnoses. tensioners 42 Overrunning alternator pulleys 44 Tools 46 Appendix 48 Fault patterns for idlers, tensioners and pulleys Adrian Rothschild Service 50 Head of Product Management EMEA Automotive Aftermarket 4 5 Timing belts Function Timing belts guarantee absolutely synchronous power transmission The timing belt transmits the rotary mo- The valves have to be opened and then In a four-stroke engine (intake – compres- since a positive-fit connection is created between the drive pulley and tion of the crankshaft to the camshafts. closed again in precisely defined time sion – power – exhaust) the valves may Their cams operate transmission ele- windows in order for the combustion only open with every second revolution the belt by means of the teeth. In internal combustion engines they are ments such as tappets, rocker arms or chamber to be filled with gas or the fuel/ of the crankshaft to generate the four used to drive camshafts, fuel injection pumps, balancer shafts and cam followers, which ultimately transfer air mixture and for the exhaust gases to strokes. the motion to the valves. Starting from be effectively discharged. If actuated at In this case, therefore, the crankshaft and water pumps. the camshaft, the valves are therefore the wrong time, the engine does not de- camshaft rotate in the ratio 2:1. In other opened and then closed again through liver the required power and serious en- words, the camshaft rotates at half the the force of the valve springs. This pro- gine damage can be caused if the valves speed of the crankshaft. cess enables the charge exchange pro- collide with the piston. cess in four-stroke internal combustion engines to take place. Camshaft pulley Camshaft pulley The valve timing is driven by the camshaft pulleys. The intake and exhaust valves open alternately with every rota- tion of the camshaft. The opening intervals must be precisely adhered to. If incorrect positions occur, the valves can collide with the piston in the worst-case scenario. Idler Valve timing (See also the graphic on p.8 > camshaft “Operation of a 4-stroke engine” .) > valve spring > valve stem with plate Tensioning pulley Water pump pulley Crankshaft pulley Idler The crankshaft pulley drives the timing belt. In a four- stroke engine this has only half as many teeth as the camshaft pulleys. As a result of this 2:1 gear Crankshaft pulley reduction ratio the cam- shafts rotate at exactly half the speed of the crankshaft. Configuration example Timing-belt drives come in many different variants. Timing belts 6 7 Timing belt design Fabric backing A timing belt is made up of four main components: Highly stressed timing belts are reinforced > Polyamide fabric on the back of the belt with a temperature- > Elastomer body resistant polyamide fabric which also in- > Tension members creases the wear resistance of the edges. > Fabric backing (depending on finish) In addition, there are a few special cases, for instance: > Timing belts which run in oil and enable a slimmer engine Elastomer body design. Their components are specially equipped for this This consists of a tough, fiber-reinforced poly- application environment and are resistant to oil and con- mer with embedded tension members. HNBR taminants in the oil such as particulates, fuel, condensation (hydrogenated nitrile butadiene rubber) elas- and glycol. tomers are used for demanding drives with tough requirements relating to temperature, aging resistance and dynamic strength. This > Double-sided timing belts which allow positive-fit drive on material is highly resistant to aging and can be both sides (e.g. for balancer shafts) used up to approx. 140 °C. Tooth fabric The polyamide fabric protects the teeth against wear and shear forces. Fabrics con- taining PTFE are used where the load de- > Timing belts with a ribbed reverse for driving ancillary mands are high. components Tension members These are mainly made of high-strength glass fibers which are particularly longitudinally stable and capable of withstanding reverse flexing. To ensure that the belt runs neutrally, fibers with clockwise and counterclockwise twists are embedded in pairs. Broken glass fibers impair the belt’s load ca- pacity to such an extent that a sudden failure may occur. For that reason, do not crimp or twist timing belts. Timing belts 8 9 Operation of a 4-stroke engine: The engine only runs properly if the rotary movements of the crankshaft and the camshafts are synchronized. Profiles Handling The first timing belts used a trapezoidal bles uniform distribution of the forces Timing belts are high-performance com- shape which was already in use in indus- acting on the tooth and avoids tension ponents which are required to work relia- trial applications (L profile). As require- spikes. The pitch (t) is the distance be- bly over a long service life under extreme ments relating to noise properties and tween two teeth and is generally 8 mm operating conditions. Correct handling of load transmissions increased, curved or 9.525 mm for camshaft belts. the belts is very important to avoid dam- tooth shapes (HTD and STD profiles) be- aging them before use. came established. The circular shape ena- Storage – Cool (15–25°C) and dry. – No direct exposure to sunlight and heat. Profile Scale 2:1 – In the original packaging. t 1st stroke (intake) identification – Not near highly flammable, aggressive HTD: High Torque Drive; profile which is media such as lubricants and acids. optimized for the transmission of high loads, LA – Maximum of 5 years (see use-by date such as for diesel engines with a high fuel on packaging). injection pressure STD: Super Torque Drive; noise optimized, HTD therefore mainly for gasoline engines Fitting – Follow automaker’s fitting instructions. There are a large number of variations of – Use specified special tools. Never use these tooth shapes. For example, a groove STD force, e.g. with a tire lever or similar, on the tooth head can result in better noise when fitting the belt around the pul- properties since only two linear areas of leys. This will destroy the glass cord contact occur between the tooth head and tension members. the belt pulley when meshing with the pul- – Do not crimp or twist. Never bend leys rather than full-surface contact. around a smaller diameter than the 2nd stroke (compression) crankshaft belt pulley. This will damage the glass cord tension members. – If necessary, set the manufacturer- specified belt tension using a tension tester. Twisting the belt through 90 de- grees is only permissible for a very small number of vehicles and must not be assumed to be generally applicable. – Protect the belt against the effects of Play safe oil (including oil mist) and other service ! fluids such as coolant, fuel and brake fluid. Do not use any sprays or chemi- cals to reduce belt noise. > Only fit timing belts that have been correctly stored and are 3rd stroke (power) not out-of-date. > Only use timing belts with the correct profile. > Never crimp or twist timing belts as this will damage the tension members. > When fitting, follow the automaker’s instructions and the handling tips given above. > Always use the specified special tools. 4th stroke (exhaust) Timing belts 10 11 Maintenance and replacement Problem Typical fault pattern Cause Solution Timing belts are maintenance-free, i.e. they do not Timing belt snapped ➀ Foreign objects in drive ➀ Remove foreign objects, check components for damage require retensioning. They endure high levels of stress and change, if necessary; change belt as a result of the high temperatures in the engine com- ➁ Contamination from coolant, oil or other fluids ➁ Eliminate any leaks, clean belt pulleys, change belt partment and the constant flexing and are subject to ➂ Pretension too high ➂ Change belt, set correct tension ➃ Belt crimped before or during fitting ➃ Change belt and fit correctly aging and constant wear.