What Is Engine Block?- Definition, Function and Uses

What is an Engine block?

An engine block is a structure that contains the cylinders, and other parts, of an internal combustion engine. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attached.

The purpose of the engine block is to support the components of the engine. Additionally, the engine block transfers heat from friction to the atmosphere and engine coolant. The material selected for the engine block is either gray cast iron or aluminum alloy.

Modern engine blocks typically have the crankcase integrated with the cylinder block as a single component. Engine blocks often also include elements such as coolant passages and oil galleries.

The term “cylinder block” is often used interchangeably with the engine block, although technically the block of a modern engine (i.e., multiple cylinders in a single component) would be classified as a monobloc. Another common term for an engine block is simply “block”.

Importance of Engine Block

The engine block is also known as a cylinder block, which contains all of the major components that make up the bottom end of a motor. This is where the crankshaft spins, and the pistons move up and down in the cylinder bores, fired by the fuel combusting. On some engine designs, it also holds the camshaft.

Related: What is a Crankshaft?

Usually made from an aluminum alloy on modern cars, older vehicles, and trucks it was commonly cast iron. Its metal construction gives it strength and the ability to transmit heat from the combustion processes to the integral cooling system in an efficient manner. Aluminum blocks typically have an iron sleeve pressed into them for the piston bores, or a special hard plating applied to the bores after machining.

The block was originally just a block of metal holding the cylinder bores, the water-cooling jacket, oil passages, and the crankcase. This water jacket, as it’s sometimes known, is an empty system of passages, circulating coolant in the engine block. The water jacket surrounds the engine’s cylinders, of which there are usually four, six, or eight, and which contain the pistons.

When the cylinder head is in place secured to the top of the engine block, the pistons move up and down within the cylinders and turn the crankshaft, which ultimately drives the wheels. The oil pan sits at the base of the engine block, providing a reservoir of oil for the oil pump to pull from and supply the oil passages and moving parts.

Air-cooled motors, like the old VW flat-four, and the original Porsche 911 sports car motor, don’t really have an engine block. Much like a motorcycle motor, the crankshaft spins in engine cases, bolted together. Bolted to these are separate finned cylinder “jugs”, in which the pistons go up and down.

Related: What is Engine Piston?

engine block

Components of an Engine Block

The main structure of an engine typically consists of cylinders, coolant passages, oil galleries, crankcase, and cylinder head(s).

1. Cylinder blocks

A cylinder block is a structure that contains the cylinder, plus any cylinder sleeves and coolant passages. In the earliest decades of internal combustion engine development, cylinders were usually cast individually. Cylinder blocks were usually produced individually for each cylinder.

Following that, engines began to combine two or three cylinders into a single-cylinder block, with an engine combining several of these cylinder blocks combined.

In early engines with multiple cylinder banks such as a V6, V8, or flat-6 engine each bank was typically a separate cylinder block (or multiple blocks per bank). Since the 1930s, mass production methods have developed to allow both banks of cylinders to be integrated into the same cylinder block.

Related: What is Internal Combustion Engine?

2. Cylinder liners

Wet liner cylinder blocks use cylinder walls that are entirely removable, which fit into the block by means of special gaskets. They are referred to as “wet liners” because their outer sides come in direct contact with the engine’s coolant. In other words, the liner is the entire wall, rather than being merely a sleeve.

Advantages of wet liners are a lower mass, a reduced space requirement, and that the coolant liquid is heated faster from a cold start, which reduces start-up fuel consumption and provides heating for the car cabin sooner.

Dry liner cylinder blocks use either the block’s material or a discrete liner inserted into the block to form the backbone of the cylinder wall. Additional sleeves are inserted within, which remain “dry” on their outside, surrounded by the block’s material.

For either wet or dry liner designs, the liners (or sleeves) can be replaced, potentially allowing overhaul or rebuild without replacement of the block itself, although that is often not a practical repair option.

3. Cylinders.

These are the spaces where pistons travel. They are large in size and have precisely formed holes to create a seal with the piston. The size and number of cylinders measure the power and size of an engine.

4. Oil Passages or Galleries.

These allow oil to reach the cylinder head and the crankshaft.

5. Deck.

This is the top surface of the block where the head of the cylinder sits.

6. Crankcase.

This houses the crankshaft and is found at the bottom of modern engine blocks. Other components include engine mounts, core plugs, coolant, ancillary mountings, and faults.

Common problems with engine blocks

Being a big, precision machined, a hunk of metal, the engine block is designed to last the lifetime of the car. But sometimes things do go wrong. These are the most common engine block failures:

1. External engine coolant leak

Puddle of water/antifreeze under the engine? It might be caused by a leak from the water pump, radiator, heater core, or a loose hose, but sometimes it’s the engine block itself.

The block can crack and begin leaking, or a freeze-out plug could work its way loose or rust out. Freeze-out plugs can be easily replaced, but cracks are usually terminal.

2. Worn/cracked cylinder

Eventually, after hundreds of thousands of miles, the smooth machined walls of the cylinders. It will wear to a point where the piston rings can’t seal against them well. On rare occasions, the cylinder wall can develop a crack, which will quickly result in a motor needing a rebuild.

Worn cylinders can be bored larger, for oversized pistons, and in extreme cases (or in aluminum blocks) iron sleeves can be inserted to make the cylinder walls perfect once again.

3. Porous engine block

Caused by impurities that got into the metal during the manufacturing process. Blowholes in the casting often do not cause any problems at all for a long time. Eventually, a poorly cast block can start to seep and leak, either oil or coolant, from the area where the imperfections are.

There’s nothing you can do about a porous engine block. Because it’ll have been faulty from the day it was molded. Having said that, any leaks that may arise from a porous block should be minor. If they surface within the manufacturer’s warranty period the engine should be replaced free of charge.

5 Symptoms of Engine Block Failure

A cracked engine block can cause a range of problems. Ultimately, since the circulation system that cools the engine is comparatively fragile, a cracked engine block will lead to coolant leaking out of the area it is needed and leaving the engine to overheat. If left untreated, this will lead to engine failure and may result in the vehicle having to be written off. A cracked engine block can result in:

  • Oil and antifreeze mixing
  • Engine overheating
  • Low engine compression
  • Excessive engine smoke
  • Visible crack in block

How Much Will Engine Block Repair Cost at a Garage?

A failure in the engine block will leave you stranded and more often than not facing a huge repair bill (at least $1,200, probably more).

The cost of repairing a cracked engine block can vary considerably depending on the garage you visit, the severity of the crack, and the car you drive.

The technique used to repair the crack can also affect the total and you may have to weigh up the sense in repairing it when it may be more cost-effective to buy a new engine or even a new car.