Engine Block, Cylinders and Lubrication: Fundamentals of Engine Components

Engine Block Manufacturing

1. Engine block and cylinder liners: The engine block is generally made of cast iron or aluminum alloy with silicon. The molten metal is poured into the mold, and special care must be taken with the process to obtain a laminar graphite structure, which gives resistance and stability. Cylinder liners are made of resistant materials, and the block is generally cast with the same materials.

Types of Cylinders

2. Types of cylinders:

• Integral block: The cylinders are directly machined into the block, so care must be taken with the block without liner.
• Dry liner: The thin-walled cylinders are mounted into the block, fitted around the orifice of the block interference fit.
• Wet liner: The coolant comes into direct contact with the outer surface of the cylinder. These liners are removable and the thick flanges protrude over the block.

Cylinder Wear

3. Cylinder wear

Causes: Cold start-ups, not changing the oil and filters at the recommended intervals, engine operation in dusty atmospheric environments, and using the engine at high revolutions cause wear. This wear produces an oval and tapered shape in the cylinder, which leads to leakage of compression gases, lowers engine performance and increases oil and fuel consumption.

4. Cylinder wear: The upper part of the cylinder suffers more wear because the forces acting on the piston are greatest there, and in that area the temperatures are high and lubrication is poor.

Engine Components

5. Piston: Its mission is to transmit the force produced by the combustion gases to the connecting rod through the piston pin. It prevents the oil from passing into the combustion chamber, maintains the gas tightness so that gases do not pass into the crankcase, and transmits heat from combustion to the cooling system.

6. Piston expansion: Pockets are placed in some parts of the piston, where expansion is needed.

7. Lateral forces: Holistic balancing efforts: when the crank-rod mechanism is off-center, the longitudinal axis of the piston does not coincide with the axis of the crankshaft, so the cylinder wears equally on both sides.

8. Piston rings: Their mission is to ensure gas tightness, and to evacuate heat from the piston to the cylinder, preventing oil from passing into the combustion chamber. Compression rings close the cylinder almost completely and evacuate most of the heat; the first ring is the one exposed to fire. Scraper rings are placed in the lower part of the piston; they remove excess oil from the cylinder wall so it does not reach the combustion chamber, where it would form carbon deposits, and they also help lubricate the upper part of the cylinder.

Balance

Static and dynamic balance: Balance is achieved when all the parts are arranged to rotate around the axis, so the rotor remains in position for any angle it adopts. When it does not turn freely and is not well balanced, it will come to rest in a fixed position. Rotors are balanced when the crankshaft turns and the moving masses produce centrifugal forces around the axis that compensate each other, so that the sum of the forces is zero.

11. Piston pin bushings: Resistance to seizing, good thermal conductivity, easy adaptation to a stump, and easy embedding of solid particles.

Flywheel

12. Flywheel inertia: The flywheel is made of cast iron, with a high-mass disk capable of storing the kinetic energy of the impulses and returning it, so that no energy is wasted. It softens the motor's operation and reduces the large holistic efforts that would twist the crankshaft, and it opposes rapid changes in speed.

Vibration Dampers

13. Dampers: They serve to avoid vibrations between the crankshaft and the flywheel. This prevents vibrations from being transmitted to the chassis. The flywheel distributes the mass in two parts that are joined by a flexible system and cushioning, and it only acts at low-revolution vibration regimes.

Counter-Rotating Shafts

14. Counter-rotating shafts: They serve to compensate for the vibration forces that appear when the crankshaft is not in good balance. The shafts are located on either side of the block and rotate in opposite directions at double the crankshaft speed. They produce equal-magnitude forces in opposite directions, so the imbalance vanishes.

Oil Functions in the Engine

Functions of oil in the engine: Oil reduces friction and mechanical losses between the surfaces in contact, lubricating them. It cools the areas where heat is generated: the oil absorbs the heat and transfers it to the place where it is cooled. It increases compression by improving the seal between piston and cylinder. It dampens efforts and cleans the bearings of friction particles.

Types of Lubricating Oils

Types of lubricating oils:

• Mineral: Compounds of hydrocarbons of mineral origin.
• Synthetic: Obtained by synthesis, a process in which the molecular structure is changed.
• Semi-synthetic: Compounds of part mineral and part synthetic oil.

Characteristics of lubricants: They must hold back water contamination, resist corrosion from fuel leakage, and tolerate high temperatures.

Oil Viscosity Classification

Determining the viscosity of commercial oils: The SAE classification system relates viscosity to the temperature at which the oil is used. The number indicates nothing about quality or cost. Grades from 0 to 25 are used with the letter W (winter), and grades from 20 to 50 indicate the viscosity of hot oil.

Multigrade oil: Multigrade oils carry two different grades that identify the viscosity at cold and hot temperatures. The cold-viscosity fluid maintains the necessary flow during start-up and avoids dry friction, while the hot-viscosity fluid keeps its film at operating temperature.

W: Winter.

Lubricant Property Classification

Lubricant property classification: For Otto engines, each new category is above the previous one. For diesel engines, each responds to the first operation characteristics of the different types of engines.

Lubrication Systems

Current lubrication system: oil pressure: The oil is stored in the crankcase. A pump draws it in through a filter and sends it under pressure through the main oil channel, from which it reaches the points that need to be pressure lubricated, and also lubricates the cylinder walls and some other parts.

Splash lubrication: The oil is mixed with fuel in a 2% ratio. Only two-stroke engines use this method: the oil mixed with the fuel enters the crankcase and goes to the cylinder, lubricating the parts it passes over (cylinder, crankshaft, connecting rod), and part of it passes into the combustion chamber where it burns together with the fuel.

Oil Pump Types

Types of oil pumps:

• Gear pumps: Formed by two meshing gears. The driver gear sets the driven gear in motion, transmitting movement between them.
• Rotor pumps: The inner rotor and the outer rotor turn in the same direction.
• Internal gear pumps: One end is set in motion by the crankshaft, which drives the inner gear, and the rotor engages directly with the outer gear.

Relief valve: Its mission is to limit the maximum pressure of lubrication. If the pressure is too high, the valve opens and the oil returns to the crankcase; if the pressure is high, it opens and goes back to the crankcase.

Oil Filters

Necessary oil filter: It keeps the oil clean and prevents impurities and wear particles from circulating. There are two types:

• Series filter: The full oil flow passes through the filter, so all the oil requires the filter in series.
• Bypass filter: Part of the filtering system of the oil circuit is separate from the lubrication circuit; it is efficient because it filters more thoroughly.