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Cylinder Head Gasketed (CHG) joint play predominant role in internal combustion engine and directly affects the engine performance. The main function of cylinder Head Gasketed joint is to seal combustion gases, oil and coolant and avoid entering of outside air into the combustion chamber. Agarwal (2013) studied that gasket sealing purpose preload is to be applied on the cylinder head bolts. Excessive preload on cylinder head bolt will cause extra stresses on crankcase and cylinder head. Cylinder bore deformation also increases which is important engine performing parameter in case of internal combustion engines. Ghasemi (2012) investigated that piston ring conformability with liner decreases with increase in bore deformation which affect engine blow by and lubrication oil consumption. Less preload on cylinder head bolt may defeat gasket sealing function. Combustion gas leakage causes direct engine power loss, oil and coolant leakage may reduce oil and coolant change period and increase friction and thermal stresses respectively. Hence it is very essential to apply adequate and accurate preload on cylinder head bolt.
Alkelani (2007) discussed tightening of a cylinder head bolt in case of torque to yield (TTY) bolt which can be divided into two basic part, where the cylinder head bolt is utilized either in its elastic or plastic region. The most commonly used method of tightening in the elastic region of a bolt is the torque-control method, while tightening a bolt into its plastic region is often done by using the torque and angle method. The pretension for cylinder head bolt is created when a torque is applied, and is generally a percentage of the fastener's yield strength. Proper pretension is necessary to avoid leakage between two parts that are held together and must be higher than the joint separation load.
Toth (2003) discussed a methodology for clevis joint utilizing a screw over its yield point in a controlled fashion, even under simple tightening conditions. The technique predicts elongation of bolt, tightening angle, final torque and preload.
Agarwal (2013) made a study on combustion gas leakage at the piston, rings and liner system which is usually called blow-by. The blow-by is a mixture of combustion gases and oil mist. In some extreme cases blow-by may contribute up to 50% of the total oil consumption of the engine. These blow-by gases are responsible for the engine operation and that is direct power loss of the engine, the economy and ecology expressed through the oil consumption and oil change interval rates. Angular torque method gives perfect sealing of CHG joint and piston rings conformability with cylinder liner is also adequate so that there is very less blow by. To reduce the friction, the piston rings are designed to ride on the layer of an oil film. Bhagavathy (2011) informed that if the bore deformation takes place due to excessive torque, then instead of riding over this film, they scrape it away in to the combustion chamber and out through the exhaust which increases oil consumption and blow by. The less torque in gasket defeats sealing function and leakages occurs.
Bickford John mentioned (1997) there are different types of bolt tightening methods such as tension indicating method, bolt stretch method, torque controlled tightening, and yield controlled tightening, angle torque method. Angle torque method reduces variation of bolt pretension. An attempt is made to develop a methodology for cylinder head bolted joint in this work to reduce the experimentation work which is required in case of angle torque method. The code is developed to estimate cylinder head bolts snug torque and angle torque. This is to achieve minimum leakages and less bore deformation. Bolt elongation is estimated by using classical method, FEA method using Hypermesh software and compared with experiments using Vernier height gauge. Cylinder head bolt preload estimation methodology is validated by FEA and experimental work.