HowAutoWorks.com
Cylinder block
Let us look at cylinder blocks. The cylinder block is 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 form gray arm or it can be alloyed with other metals like nickel or chromium.
The iron casting process begins by making up the shapes of what would become water jackets on the cylinders as sand cores which is fitted into mounts. This stops these paths becoming solid iron. Molten-iron is poured into sand moulds that are formed by patterns in the shape of the block.
Arte 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 Welch plugs. The casting is then machined, cylinders are bored and finished, surfaces smoothed, holes drilled and threads capped. All cylinder blocks are made with ribs, webs and fillets to provide rigidity but also to keep weight to a minimum.
As more manufactures try to make vehicles lighter and more fuel efficient, more and more engine blocks are being cast from aluminum. A block made of aluminum 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.
Aluminum alloy blocks are made by various casting processes including pressure casting. Another method is gravity casting with the molten metal is poured into molds. Cast-iron liners are usually used in the cylinders of aluminum 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 the surface area to assist heat transfer from the sleeve to the block. Some blocks do not 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 mono-block construction. This is called a horizontally opposed block, it 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 a separate paths then bolted into the same crankcase. Each cylinder has cooling fence, they are often machined to give uniform fitness under low free flow of air.
Transcription by:
Scribe4you Transcription Services