Engine Basics: Parts and Function

Engine Basics: Parts and Function

• An engine's basic parts and their functions are explained.
• The engine shown is a 1.8-liter Honda engine from a 1990 Acura Integra.
• Motor is an electrical component, while engine is short for ingenious device.

Valve Cover and Camshafts

• Under the valve cover are the camshafts, controlling valve functions.
• This engine has a dual overhead cam (DOHC) design.
• A water pump is connected to the DOHC system.
• DOHC engines have two camshafts, one for exhaust and one for intake.
• The exhaust camshaft controls exhaust valves, the intake camshaft controls intake valves.
• The intake manifold is on the intake side, the exhaust manifold on the exhaust side.

Camshafts and Valve Operation

• Camshafts, or "bump sticks," determine engine breathing.
• Cam lobes dictate when and how far valves open, impacting horsepower, torque, and fuel economy.
• The camshaft is mechanically timed with timing gears.
• The camshaft can be considered a mechanical computer program for the engine.
• Cam lobes push followers to open valves.
• This engine has two valves per cylinder, totaling 16 valves for a four-cylinder engine.

Valve Train Variations

• Pushrod engines use lifters to open valves.
• Hydraulic lifters filled with oil allow for quieter operation.
• Solid valve trains offer more accurate timing but require periodic adjustment.
• A push rod sits inside a cup on the lifter and is pushed by the cam to open the valve.
• Overhead cam engines are designed to activate the valves.

Timing and Distribution

• The back of the intake camshaft has a slot that drives a distributor.
• The distributor is mechanically connected to the camshaft and may be connected to the oil pump.
• The distributor transfers spark to each cylinder as it comes up on its compression stroke.

Oil Pump and Exhaust Manifold

• An old-school oil pump is driven by a long shaft connected to the distributor.
• Oil pumps and distributors are often tied together.
• The exhaust manifold has runners from each cylinder that collect into the manifold.
• Equal length runners ensure each cylinder produces equal power.

Crankshaft and Timing Belt

• The camshafts keep the top part of the engine in time, while the crankshaft keeps the bottom in time.
• A timing belt connects the crankshaft and camshafts.
• The water pump, driven by the timing belt, circulates water throughout the engine.
• A tensioner maintains tension on the timing belt.

Timing Chain and Gears

• Older V8 engines use a timing chain to connect the camshaft and crankshaft.
• The camshaft gear is larger, rotating once for every two crankshaft revolutions.
• Double roller timing chains are stronger.
• Gear-driven setups are more accurate but noisier, diesels are often designed this way from the start.

Intake Manifold

• The intake manifold has runners to each cylinder of the same length.
• Long, narrow intake manifold runners are good for low-end torque.
• Short, wide runners are made for higher RPM horsepower.
• Long and narrow runners increase air velocity into the cylinder.
• Big open areas allow the engine to draw in more air at higher RPMs.

Fuel Injection

• Fuel injectors spray fuel into individual cylinders at the correct time.
• A fuel rail supplies pressurized fuel behind the injectors.
• The engine computer uses sensors to determine when to inject fuel.
• In fuel-injected engines, air flows to the cylinder, and fuel is added at the last second.
• Carbureted engines have air and fuel mixed in the runners leading to the cylinders.

Cylinder Head and Combustion Chamber

• The cylinder head is connected to the block with a head gasket guided by dowels.
• The combustion chamber's shape and size vary, affecting engine performance.
• Hemi engines have hemispherical combustion chambers.
• "Penta roof" combustion chambers have a sharp angled design.
• The design and angle of valves all influence engine performance.
• Engineers balance fuel economy and power when designing the engine.

Valve Components and Function

• Valve components include the valve, valve spring, and keepers.
• Keepers sit in a groove and are tapered to wedge and hold the valve.
• The valve spring closes the valve after the camshaft compresses it.
• Valve springs must combat the forces opposing them and rapidly re-expand to close the valve.

Valve Float and Valve Springs

• Valve float occurs when the spring cannot close the valve fast enough.
• Valve springs affect high RPM engines and the ability to close the valves in milliseconds.
• Stronger valve springs can put more stress on the cam and valve train.
• If valve springs are too weak, valves will stay open, leading to compression loss, power loss, and engine issues.

Valve Seals

• Valve seals, positive type seals, lock onto the valve guide.
• Bad valve seals can lead to oil being sucked into the cylinder.
• Umbrella seals sit inside the valve to keep oil out.
• Worn valve guides can increase oil consumption.

Flywheel and Flex Plate

• A flywheel is a weighted component used with manual transmissions.
• A flex plate, thinner, and lighter, is used with automatic transmissions.
• Automatic transmissions utilize flex plates.

Piston Movement and Firing Order

• In a four-cylinder engine, pistons fire every 180 degrees.
• Sister cylinders refer to pistons that move up at the same time due to crankshaft design.

Oil Pan and Oil Pickup

• An oil pickup in oil pan sucks oil into the oil pump and the engine.
• The oil pump, driven by the crankshaft, circulates oil.
• A windage tray in the pan scrapes oil off the crankshaft to improve efficiency.
• A screen on the oil pickup prevents large particles from entering the pump.

Crankshaft and Pistons

• The crankshaft turns chemical energy into mechanical energy.
• Counterweights help balance four-cylinder engines.
• Connecting rods link pistons to the crankshaft.
• Harmonic balancers dampen pulses created by piston movement and rotation that is transferred to the crankshaft.

Harmonic Balancer

• Harmonic balancers dampen accelerating and decelerating forces within the crankshaft.
• Dampening prevents the engine from shattering due to force.

Power at the Flywheel

• Power at the flywheel refers to the twisting force (torque) at the back of the engine.
• Torque indicates an engine's ability to push down bigger cylinders.
• Connecting rods transfer power to the crankshaft.

Pistons and Cylinders

• Pistons move within cylinders, creating displacement.
• Displacement is volume between cylinders and pistons.

Piston Rings

• Shiny spot is called the skirt
• Pistons have an oil control ring and two compression rings.
• Piston rings seal against the cylinder walls.
• The wrist pin allows the connecting rod to pivot as the piston moves.

Valve Grooves

• Grooves on top of the piston allow clearance for valves. The valves may be close when the piston rises to the top.

Oil Holes

• Small holes in the piston lubricate the area and cool the piston.

Internal Combustion

• Internal combustion engines convert chemical energy to mechanical energy, only 20% efficient.
• 80% of the heat generated is lost through friction and other factors.
• Moving a piston up and down is inefficient.
• The internal combustion engine is not very efficient. However, the process has been refined significantly.