Handout Activity: HA181

Transcription

1 Cylinder block Handout Activity: HA181 HA181-2 Cylinder block The cylinder block is the largest part of the engine. Its upper section carries the cylinders and pistons. Normally, the lower section forms the crankcase, and supports the crankshaft. The cylinder block is the largest part of the engine. Its upper section carries the cylinders and pistons. Normally, the lower section forms the crankcase, and supports the crankshaft. It can be cast in one piece from grey iron. Or it can be alloyed with other metals like nickel or chromium. The iron casting process begins by making up the shapes of what will become waterjackets and cylinders as sand cores which are fitted into moulds. This stops these parts becoming solid iron during casting. Molten iron is poured into sand moulds that are formed by patterns in the shape of the block. After casting, core sand is removed through holes in the sides and ends, leaving spaces for the cooling and lubricant passages. These holes are sealed with core or welsh plugs. The casting is then machined. Cylinders are bored and finished, surfaces smoothed, holes drilled and threads cut. All cylinder blocks are made with ribs, webs and fillets to provide rigidity but also keep weight to a minimum. 1. All cylinder blocks are made with ribs, webs and fillets to provide rigidity but also keep weight to a. 2. It can be cast in one piece from grey iron, or it can be alloyed with other metals like nickel or. 3. Its upper section carries the cylinders and. Score / Page 1

2 Cylinder block construction Handout Activity: HA182 HA182-2 Cylinder block construction Cylinder blocks made of aluminum are lighter than cast-iron blocks of the same size. They usually have cast-iron liners which provide a hard-wearing surface for pistons and piston rings. As more manufacturers try to make vehicles lighter and more fuel efficient, more and more engine blocks are being cast from aluminium. A block made of aluminium alloy is lighter than if it were made of cast iron. So if two engines are generating the same power, the alloy version would have a better weight-to-power ratio than the cast iron version. Aluminium alloy blocks are made by various casting processes, including pressure casting. Another method is gravity casting, where the molten metal is poured into molds. Cast iron liners are usually used in the cylinders of aluminium blocks, and sometimes in cast-iron blocks. Some sleeves are cast into the block. Grooves on the outside form a key that stops any movement in the cylinder. They also increase surface area to assist heat transfer from the sleeve to the block. Some blocks don t need liners. They can be made of wear resistant material that makes a hard-wearing surface for the pistons and piston rings. Or the cylinder bore may have some sort of surface treatment to make it hard-wearing. When the cylinders, block and crankcase are all cast together, it is called a monoblock construction. A horizontally-opposed block has a split crankcase. The two engine blocks are joined together by the flanges of the crankcase. In air-cooled engines, the cylinders are usually made as separate parts, then bolted to the same crankcase. Each cylinder has cooling fins. They re often machined to give uniform thickness and allow free flow of air Page 1

3 Cylinder block construction HA They also increase surface to assist heat transfer from the sleeve to the block. 2. In air-cooled engines, the cylinders are usually made as separate parts, then bolted to the same.. 3. As more manufacturers try to make vehicles lighter and more fuel efficient, more and more engine blocks are being cast from. 4. A horizontally-opposed block has a split crankcase. The two engine blocks are joined together by the of the crankcase. 5. When the cylinders, block and crankcase are all cast together, it is called a construction. Score / Page 2

4 Engine blocks & pistons HA981-2 Handout Activity: HA981 Engine blocks & pistons The major engine components include the cylinder block, cylinder head, pistons, connecting rods and crankshaft. The cylinder block is the largest part of the engine. Its upper section carries the cylinders and pistons. Normally, the lower section forms the crankcase, and supports the crankshaft. All cylinder blocks are made with ribs, webs and fillets to provide rigidity but also keep weight to a minimum. The cylinder head bolts onto the top of the cylinder block where it forms the top of the combustion chamber. In-line engines of light vehicles have just one cylinder head for all the cylinders. Larger inline engines can have 2 or more. V-type and horizontally opposed engines have a separate cylinder head for each bank of cylinders. As with engine blocks, cylinder heads can be made of cast iron, or aluminum alloy. A head made of aluminum alloy is lighter than if it were made of cast iron. The piston, with its connecting rod and bearing, transfers the force of the combustion and expansion of the power stroke to the crankshaft. The piston itself, its rings, and the piston pin, also known as the gudgeon pin, are together called the piston assembly. The cutaway shape on this piston allows it to clear the counterweights on this rotating crankshaft. The connecting rod connects the piston to the crankshaft. It is fastened to the piston at its little end, by a piston or gudgeon pin. The big end of the connecting rod has a detachable cap, and carries 2 halves of the big end bearing. The big end is attached to the crankshaft at the crankpin journal Page 1

5 Engine blocks & pistons HA The big end is attached to the crankshaft at the journal. 2. The cylinder block is the part of the engine. 3. All cylinder blocks are made with ribs, webs and fillets to provide but also keep weight to a minimum. 4. The piston itself, its rings, and the piston pin, also known as the pin, are together called the piston assembly. Score / Page 2

6 Cylinder sleeves Handout Activity: HA183 HA183-2 Cylinder sleeves A dry sleeve can be cast or pressed into a new block or used to recondition cylinders. A flanged, dry sleeve has a flange to fit a recess in the block. A wet sleeve has an outer surface directly exposed to coolant. Cylinder sleeves are used in engine blocks to provide a hardwearing material for pistons and piston rings. The block can be made of one kind of iron that s light and easy to cast, while the sleeve uses another kind that is better able to stand up to wear and tear. There are three main types of sleeves - dry, flanged dry, and wet. The dry sleeve can be cast in or pressed into a new block, or used to recondition badly-worn or damaged cylinders that can t easily be re-bored. It s a pressed fit in its bore in the cylinder blocks. Its wall is about 2mm thick. Its outer surface is in contact with the block for its full length. Its top finishes flush with the top of the block and can hardly be seen. Once in place, dry sleeves become a permanent part of the cylinder block. A flanged, dry sleeve is like a normal dry sleeve, but a flange at the top fits into a recess in the surface of the engine block. It s not a tight fit and it can be replaced if it s worn. With a wet sleeve, the outer surface is part of the waterjacket around the cylinder. It s called wet because it has coolant against its outer surface. This helps speed up heat transfer between the sleeve and coolant. The sleeve is sealed at the top to prevent coolant leaks. This stops coolant entering the combustion chamber, and the bottom of the crankcase. A flange at the top of the sleeve fits into a recess in the block. The lower end has 1 or 2 neoprene sealing rings. With coolant in direct contact with the cylinder sleeve, corrosion can be a problem. It can even insulate the sleeve from the coolant, which reduces the main advantage of having a wet sleeve at all. The walls on wet sleeves are thicker than on dry sleeves. They don t have the same support from the block as dry sleeves so they depend on their wall thickness to stop distortion. In diesel engines, vibration caused by combustion can cause cavitation. This damage appears similar to corrosion and it can eventually destroy the cylinder Page 1

7 Cylinder sleeves HA It s a pressed fit in its bore in the cylinder. 2. With a wet sleeve, the outer surface is part of the around the cylinder. 3. There are three main types of sleeves - dry, flanged dry, and. Score / Page 2

8 Grey iron Handout Activity: HA184 HA184-2 Grey iron Grey iron is a cast iron that contains carbon in the form of graphite, plus silicon, manganese and phosphorus. Grey iron is a form of cast iron. There are many different kinds of cast iron, depending on the particular materials they contain. Grey iron is a cast iron that contains carbon in the form of graphite, plus silicon, manganese and phosphorus. The fractured surface of a cast iron with graphite appears grey, hence the name. It is brittle and cannot absorb shocks. It resists heat and corrosion, and can be cast into many different shapes. It is used for many components. 1. The fractured surface of a cast iron with graphite appears, hence the name. 2. Grey iron is a cast iron that contains in the form of graphite, plus silicon, manganese and phosphorus. Score / Page 1