engine block and cylinder head

1    Engine block

The engine block is the basic frame of the engine. All other engine parts either fit inside it or fasten to it. It holds the cylinders, water jackets, and oil galleries. The engine block also holds the crankshaft, which fastens to the bottom of the block. The camshaft also fits inside the block, except on overhead-cam engines (OHC). 

In most cars, this block is made of gray iron, or an alloy (mixture)  of gray iron and other metals, such as nickel or chromium. Engine blocks are castings.

Some engine blocks, especially those in smaller cars, are made of cast aluminum. This metal is much lighter than iron. However, iron wears better than aluminum. Therefore, the cylinders in most aluminum engines are lined with iron or steel sleeves. These sleeves are called cylinder sleeves. Some engine blocks are made entirely of aluminum.

2 Cylinder sleeve:

Cylinder sleeves are used in engine blocks to provide a hard wearing material for pistons and piston rings. The block can be made of one kind of iron that is light and easy to cast while the sleeves uses another that is better able to stand up wear and tear. There are two main types of sleeves:  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 cannot easily be rebored. It's a pressed fit in its bore in the cylinder blocks.Its wall is about two millimeters 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.With  a  wet sleeve,the outer surface is part of the water jacket 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.

3  Cylinder head:

The  cylinder  head  fastens  to  the  top  of  the  block, just  as  a  roof  fits  over  a  house.  The underside  forms  the  combustion  chamber  with  the  top  of  the  piston.  In-line  engine  of  light vehicles have just one cylinder head for all cylinders; larger in-line engines can have two or more Just 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 when made of cast-iron.aluminum also conducts heat away  more  quickly  than  iron.in  petrol  engine,the  three  most  popular  types  of  combustion chamber are the hemi,wedge and semi-hemi. The cylinder head carries the valves, valve springs and  the  rockers  on  the  rocker  shaft,  this  part  of  valve  gear  being  worked  by  the  pushrods. Sometimes  the  camshaft  is  fitted  directly  into  the  cylinder  head  and  operates  on  the  valves without rockers. This is called an overhead camshaft arrangement.

4 Gasket

The cylinder head is attached to the block with high-tensile steel studs. The joint between the block and the head must be gas-tight so that none of the burning mixture can escape. This is achieved  by  using  cylinder  head  gasket.  This  is  a  sandwich  gasket,  i.e.  a  sheet  of  asbestos between   two   sheets   of   copper,  both   these   materials   being   able   to   withstand   the   high temperature and pressures within the engine.

5 Oil Pan or Sump

The oil pan is usually formed of pressed steel. The oil pan and the lower part of the cylinder block together are called the crankcase; they enclose, or encase, the crankshaft. The oil pump in the lubricating system draws oil from the oil pan and sends it to all working parts in the engine.The oil drains off and runs down into the pan. Thus, there is constant circulation of oil between the pan and the working parts of the engine.

This unit acts as a reservoir to store the oil that is reauired bv the engine lubrication .It further serves as a vessel in which any sludge,water and metal particles in the oil can settle out,and also provides an opportunity for any entrained air to escape from the oil.

Baffle plates are normally fitted in the sump to minimize both oil surging and agitation ,the former arising from the changing motion of the car and the latter from the oil flung from the crankshaft bearings ( Fig.2-9). A screwed plug is incorporated at the lowest point in the sump for draining the oil in service.