An engine block is a structure that contains the cylinders, and other parts, of an internal combustion engine. An early automotive engine’s engine block was made up solely of the cylinder block, to which a separate crankcase was attached. The crankcase and cylinder block are typically assembled as a single unit in modern engine blocks. Additionally, engine blocks frequently have components like coolant passages and oil galleries.

Functional Requirement For An Engine Block

One of the most crucial components of the engine is the engine block. Inside the engine block, where the combustion process takes place, high pressure and temperature environment must be maintained. Therefore, an engine block should be able to withstand vibrations in addition to being durable and resistant to wear.

Let’s examine a few of the functional prerequisites for an engine block, such as:

• High fatigue strength
• High modulus of elasticity (ease of machining)
• Corrosion resistant
• Low thermal expansion
• High thermal conductivity
• Low density

Material For Engine Block Casting

➢ Good thermal conductivity

➢ Manufacturability

➢ It should have less manufacturing cost

Based on the above features the most widely used material are cast iron and aluminum alloys to

manufacture the cylinder block.

In general, most of the industries also use cast iron for manufacturing the engine blocks because of the

following reasons:

➢ It is cheaper

➢ Excellent damping capacity

➢ Good wear and high temperature resistant

➢ Easily machinable

➢ Inexpensive to produce

➢ Can tolerate high pressure and RPM

But certain aluminum alloys contain most of the characteristics of cast iron but with low weight. And

also, aluminum alloy casted engine block gives a good surface finish and high machinability compared

with cast iron alloys. As the technology increases the engineers has found new materials such as

graphite cast iron which is lighter and stronger than the grey cast iron mentioned above.

➢ Grey cast iron alloys: Grey cast iron is the first and most material used for manufacturing of

engine blocks. Though the aluminum alloy also contains many similarities with low weight, it

is still used in the manufacturing of diesel engine blocks because their internal stresses are

higher. Grey cast iron contains 2.5 –4 % of carbon, 1 -3 % of silicon, 0.2 – 1% manganese,

0.02 – 0.25 % of sulfur, and 0.02 – 1 % of phosphorus. It has an excellent damping absorption,

good wear and thermal resistance, and it is easily machinable and less cost due to its

availability.

➢ Aluminum alloys: Aluminum alloys main feature for its popularity is its low weight, this

reduce the weight of the engine as well as in the vehicle. But the main disadvantage is their

cost compared with grey cast iron. Aluminum alloy has a good machinability property

compared with grey cast iron. There are two aluminum alloys that are mainly used in

manufacturing of engine blocks, they are 319 and A356.

319 aluminum alloy contains 85.8 – 91.5 % of aluminum, 5.5 – 6.5 % of silicon, 3 – 4 % of

copper, 0.35% of nickel, 0.25% of titanium, 0.5% of manganese, 1% of iron, 0.1% of

magnesium, and 1% of zinc. This alloy has good casting features, corrosion resistance, and

good thermal conductivity. Under the heat treatment of T5 process, it generates high strength

and rigidity for the engine block.

A356 aluminum alloy contains 91.1 – 93.3 % of aluminum, 6.5 – 7.5 % of silicon, 0.25 – 0.45

% of magnesium, 0.2% of copper, 0.2% of titanium, 0.2% of iron, and 0.1% of zinc. Although

the mechanical properties are similar to 319, when it is under the heat treatment process T6 it

gains higher strength than 319. But it has lower modulus of elasticity (72.4 GPa) than 319 with

modulus of elasticity of 74 GPa.

➢ Compacted graphite cast iron: Compacted graphite cast iron has a higher tensile strength and

modulus of elasticity compared with grey cast iron. It is due to the compact graphite found on

the microstructure of CGI. Similar to grey cast iron it has a good damping absorption and

thermal conduction, but its low machinability has limited its wide usage.

Tooling required for casting engine block

The main tool needed for sand casting is the mold, the mold is generated by a mixture of sand, clay,

and water. The pattern is the main tool required to form the mold, it is normally machined by wood or

aluminum which can be easily machined. The pattern is kept on the wood or metal frame and the sand

mixture is poured in to it, then vibrations are applied for the mixture to get free from air bubbles. After

the mold has being hardened it can be used for the casting process.

After the casting process is over the casted engine block is passed through few machines to get the

surface finish and correct dimensions. Computerized milling machines and boring machines are used

in this operation

How An Engine Block Is Made

Sand casting is the method that produces engine blocks the most frequently and widely. Die casting is also employed occasionally with aluminum.

Sand molds, which are used in sand casting to maintain the mold cavities, are made from a mix of sand and binders. Sand molds are simpler to make but can only be used once per casting.

The mold is segmented so that patterns can be inserted to create cavities. Typically, the pattern is made of wood, metal, or polymeric material. As the metal will contract after solidification, extra care is taken when creating patterns to maintain dimension tolerance.

The mold cavity is filled with molten metal after the pattern has been removed, and then it is left to cool. The sand mold is dismantled to prepare the cast product or engine block for machining after the metal has solidified.

Machining

To get rid of extra sand, the engine block that was cast is vibrated. Following casting, the block is machined to produce the desired dimensions and to smooth out the surfaces.

Possible Casting Defects

Casting can have problems during the production of engine blocks if proper precautions are not taken. Examine some potential casting flaws to determine the cause if the engine block was cast with undesirable flaws or irregularities:

• Blowholes –due to entrapped gasses during solidification
• Shrinkage cavity – due to contraction of metal on solidification in an uncontrolled environment
• Mismatched – due to misalignment of sand mold sections (upper and lower)
• Metal penetration – due to the large sand grain size as metal fuses into the sand and solidifies

These are just a few of the numerous flaws that can be eliminated by using proper casting and molding techniques. For instance, having enough ventilation in the mold will help you avoid blowholes, whereas using sand with small grains will help you avoid metal penetration.

What Material Is Used To Make Engine Blocks

Typically, grey cast iron or alloys of aluminum are used to make engine blocks. Both substances have excellent molten-state flowability for casting and thermal conductivity for resistance to thermal shock damage. While aluminum alloys can significantly reduce the weight by up to 50%, cast iron is preferred because of its strength and low production costs.

Engine block casting calls for accuracy, study, and engineering. For successful casting, quality control makes sure the right mix of raw materials is used and the right production process is followed. NDT techniques are frequently used to look for internal flaws in products.

To stop engine blocks from cracking, proper maintenance is necessary. Some of the main reasons for engine damage include overheating brought on by a lack of coolant, driving on a blown head gasket, and oil leakage. Repairing an engine block that has cracked typically costs a lot of money and is occasionally even impossible. Consequently, replacing an engine block will put an excessive strain on your finances.

Common Problems With Engine Blocks

The engine block is built to last for the entire life of the vehicle because it is a sizable, precisely machined piece of metal. But mistakes do happen occasionally. The following are the most typical reasons for engine blocks to fail:

External engine coolant leak
Under the engine, is there a pool of antifreeze or water? Sometimes the engine block itself is to blame, but it can also be a leak from the water pump, radiator, heater core, or a loose hose. The block could split and start to leak, or a freeze-out plug could become loose or start to rust. Cracks are typically terminal, but frozen-out plugs are easily replaced.

Worn/cracked cylinder
The cylinders’ smooth machined walls will eventually deteriorate over time and hundreds of thousands of miles to the point where the piston rings will no longer be able to effectively seal against them. Rarely, the cylinder wall may crack, in which case a motor will need to be rebuilt right away. For oversized pistons, worn cylinders can be bored out larger, and in extreme circumstances (or in aluminum blocks), iron sleeves can be inserted to restore the cylinder walls to their original perfection.

Porous engine block
Voules in the casting are frequently not noticed for a very long time because they were brought on by impurities that entered the metal during the manufacturing process. A poorly cast block may eventually begin to seep and leak coolant or oil from the flaws. Porous engine blocks are defective from the moment they were molded, so there is nothing you can do to fix them. Having said that, any leaks from a porous block should be minor, and if they manifest during the manufacturer’s warranty period, the engine should be replaced at no cost.