Engines: Engine Components

Cylinder blocks	Cylinder block	The cylinder block is the largest part of the engine. Its upper section carries the cylinders and pistons. Normally, the lower section forms the crankcase, and supports the crankshaft.
	Cylinder block construction	Cylinder blocks made of aluminium are lighter than cast-iron blocks of the same size. They usually have cast-iron liners which provide a hard-wearing surface for pistons and piston rings.
	Engine blocks & pistons	The cylinder block is the largest part of the engine. Its upper section carries the cylinders and pistons.
	Cylinder sleeves	A dry sleeve can be cast or pressed into a new block or used to recondition cylinders. A flanged, dry sleeve has a flange to fit a recess in the block. A wet sleeve has an outer surface directly exposed to coolant.
	Grey iron	Grey iron is a cast iron that contains carbon in the form of graphite, plus silicon, manganese and phosphorus.

Cylinder heads	Cylinder head	The cylinder head bolts onto the top of the cylinder block where it forms the top of the combustion chamber. It carries the valves and in many cases the camshafts.
	Cylinder head design	Cylinder head’s combustion chambers are designed to help improve the swirl or turbulence of the air-fuel mixture, and prevent fuel droplets settling on the surfaces of the combustion chamber or cylinder walls.
	Diesel combustion chambers	Direct-injection diesels inject into the combustion chamber formed in the top of the piston. For indirect injection, the combustion chamber is a separate chamber formed in the head.
	Intake & exhaust passages	Smaller intake and exhaust passages and ports allow more torque at low engine speeds. At high speeds, smaller passages restrict airflow. Larger passages produce greater power at high engine speeds.
	Gaskets	Gaskets form a seal by being compressed between stationary parts where liquid or gas could pass. Gaskets around a rotating part would quickly wear out. Oil seals are used to seal these parts.
	Gaskets and oil seals	Gaskets form a seal by being compressed between stationary parts where liquid or gas could pass.
	Head gaskets	Head gaskets seal and contain the pressures of combustion within the engine, between the cylinder head and the block.
	Turbulence	Turbulence refers to the swirling motion of a liquid or a gas.

Valves & valve trains	Valves	Engine valves control the intake and exhaust flow to and from the combustion chamber.
	Valve seats	A narrow valve seat is desirable because a thin circular contact with the valve face forms an efficient seal. But a wider seat transfers heat better from the valve to the cylinder head.
	Valve seats in cylinder heads	In some cast-iron cylinder heads, valve seats are cut directly into the edge of the valve port. Valve seat inserts are metal rings that match the shape of the valve.
	Valve rotation	An operating valve tends to rotate and keep seating in a new place. This helps keep its face and seat free of carbon, and reduce sticking in the valve guide. It also spreads heat around the valve seat.
	Valve stem oil seals	Coil springs normally hold valves on their seats. Their coils are usually closer at the bottom than the top. Oil seals on valve stems or guides prevent too much oil passing into the combustion chamber.
	Intake valves	Intake valves are usually larger than exhaust valves because pressure forcing charge into the cylinder is much lower than that forcing the exhaust gases out. Different engines use different valve combinations.
	Valve trains	An overhead valve or pushrod system has the valves in the cylinder head and the camshaft in the block near the crankshaft. Many engines use hydraulic valve lifters to quieten the engine and eliminate valve clearance adjustments.
	Valve-timing diagram	The time valves in a 4-stroke engine cycle actually open and close can be measured by angles. These angles can be easily read using a valve-timing diagram.
	Variable valve timing	Valve overlap is the amount of time the intake and exhaust valves are both open at once. Less overlap produces a smooth idle and more slow speed torque. More valve overlap allows better engine breathing at high speeds.

Camshafts & drives	Camshafts & drives	The camshaft can be cast or machined. It drives the valves and the distributor. It has a cam for each valve. Some also have a cam known as an eccentric to drive the fuel pump.
	Overhead camshaft	The overhead camshaft is located in the cylinder head. Double overhead cam systems often use a bucket tappet. Some overhead cam engines use a hydraulic lash adjuster to eliminate need for valve clearance adjustment.
	Cam lobes	The cam lobe opens a valve at the proper time and gives it proper lift. It lets it stay open for a sufficient time, then lets it close at the proper time. Accurate valve timing is crucial.
	Timing belts & chains	Timing belts and chains are used on overhead camshaft engines, because the camshaft is further from the crankshaft. Timing belts are quieter than chains but usually require regular tensioning and replacement.
	Timing belts & tensioners	The toothed, or synchronous timing belt is used for driving camshafts, balance shafts, water pumps and diesel injection pumps.

Pistons	Pistons	The piston assembly transfers the force from the power stroke to the crankshaft. Its design depends on the type of engine, its speed and compression ratio.
	Piston rings	Piston rings keep a tight seal within the cylinder to stop the heat and pressure in there from escaping. They also stop oil passing up into the combustion chamber.
	Connecting rod	The connecting rod joins the piston to the crankshaft. It is fastened to the piston at its little-end by a piston pin, or gudgeon. It must be very strong, rigid, and as light as possible.
	Compression ratio	An engine’s compression ratio can be a guide to the power it can generate, the higher the engine's compression ratio and the more powerful the engine.

Crankshaft assemblies	Crankshaft	The crankshaft rotates in the main bearings in the crankcase. Connecting rods are attached to offset areas called throws where the reciprocating motion of the piston is changed into rotary motion.
	Engine bearings	Bearings support and protect rotating parts and let them turn freely. Bearings can be either plain, usually called bushes, slippers or shells - or they can be anti-friction with rolling balls or rollers.
	Flywheel	The flywheel is mounted on the rear of the crankshaft. It links the crankshaft to the transmission, through the clutch. With manual transmission, the flywheel is very heavy, and its momentum helps smooth out engine operation.
	Reciprocating action	Reciprocating action is used to make rotary action and has many applications.
	Crankshaft & bearings	The crankshaft turns because of the forces transmitted through the connecting rods. At the same time, it must be held in place.
	Valve train overview	In the 4-stroke gasoline engine, the inlet and exhaust ports are opened and closed by valves. These valves need a system to control how they work.

Engines procedures	Testing cylinder compression	Before performing a compression test, disable the ignition system to prevent electrical shock.
	Checking idle speed	Checking the idle speed can only be done with a tachometer, which measures the engine revolutions per minute (rpm).
	Obtaining & interpreting scan tool data	The standard procedure for diagnosing an OBD II vehicle is different as it requires that the codes should NOT be cleared until the vehicle is repaired.
	Removing & replacing a cam belt	Cam belts should be kept in their packaging until required. They should be stored in an environment that has minimal humidity, consistent temperatures and is free from dust and oil contamination.
	Inspecting & adjusting an engine drive belt	A belt that has been soaked in oil will not grip properly on the pulleys and will slip. If the oil contamination is severe enough for this to happen, replace the belt.
	Replacing an engine drive belt	If you don't have a tension gauge, you can estimate the tension by pushing the belt inwards with your hand.