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Glossary Of Engine Internal Parts

Modern internal combustion engines are complex. In this glossary, we help you understand major internal engine components that rotate, move up/down, pump, seal, or stay fixed.

Terminology Of Engine Components

Internal combustion engines are extremely complex and feature a wide array of components that rotate, move up and down, pump, seal, or remain stationary. When repairing or rebuilding your engine, you will come across many different terms when referencing repair manuals and ordering parts. We know it can be confusing, especially when the repair is complex. Even if you are paying a professional to do the work, it's good to be conversant with the topic. In order to help you understand the terminology of engine components, we've created the following glossary, listed in alphabetical order.

Engine Components Variety

Note that this glossary is limited to definitions of “internal” engine components. These are parts contained within the engine block, cylinder head, and crankcase. In contrast, external engine parts are bolted on to the outside of the block (see our related Glossary Of Engine External Parts for definitions regarding such components).

Balance Shaft

Balance shaft – a counterweighted engine shaft that offsets unwanted crankshaft vibrations by rotating in the opposite direction. In our Balance Shafts & Components section, we also offer related hardware such as shaft seals, individual counterweights, replacement sleeves, and more.

Balance Shaft

Bearing

Bearing – A curved metal piece that allows motion between components with minimum wear and friction. A bearing that surrounds a shaft may be circular in shape (camshaft bearing), or semi-circular (connecting rods, crankshaft), in which case it is also known as a bearing shell. Also see Main bearings and Rod bearings. In our section for Bearings & Components, we’ve got camshaft bearings, crankshaft main bearings, connecting rod bearings, balance shaft bearings, auxiliary shaft bearings, and much more.

Bearings

Bearing Cap

Bearing cap – A retainer, held in place by nuts and bolts, which secures bearing shells in place.

Bearing Cap

Camshaft

Camshaft – A shaft in the engine connected to the crankshaft via gears, belts, or a chain, which contains a series of cams to open and close intake and exhaust valves. We also stock related camshaft hardware such as sleeves, bolt lock plates, end caps, dowel pins, o-rings, seals, oil line fittings, oiler control valves, retainer clips, thrust buttons & plates, and much more.

Camshafts

Camshaft Follower

Camshaft follower – See valve lifter.

Camshaft Plug

Camshaft plug – A cup-shaped seal that’s pressed into the back of the engine block where the rear of the camshaft is located. This prevents external oil leaks from a camshaft.

Camshaft Plugs

Compression Ring

Compression ring – The piston ring which forms a seal with the cylinder wall to prevent compression loss or gas blow-by (also see piston rings).

Compression Ring

Connecting Rod

Connecting rod – The piece which forms the mechanical link between the piston and crankshaft, converting the piston's up-and-down motion into the crankshaft's rotary motion. Related hardware pieces include connecting rod nuts and bolts.

Connecting Rod

Crankcase

Crankcase – The lower portion of the engine block that encloses and supports the crankshaft, including an oil pan in most cases.

Crankcase

Crankshaft

Crankshaft – The engine's main shaft that rotates after being driven by up-and-down piston motion. At the rear of the crankshaft is an external flywheel, which transfers power to the transmission. On our crankshaft & components main page, we offer related hardware pieces such as lock keys, seals, seal retainers, spacers, thrust washers, and more.

Crankshaft

Crankshaft Hub

Crankshaft hub – a specially-shaped metal piece that fits onto the front of the crankshaft. Mounted externally, the hub serves as the mounting point for a harmonic balancer.

Crankshaft Hub

Cylinder

Cylinder – The hollow tubular space inside an engine block where piston travel occurs.

Cylinder

Cylinder Head

Cylinder head – The upper engine section that provides a top to enclose the cylinders, and which houses the valves, spark plugs, and overhead camshafts. In our Cylinder Heads & Components section, we’ve got related parts such as studs, dowel pins, fitted nuts, plugs, seals, washers, and more.

Cylinder Head

Cylinder Head Bolts

Cylinder head bolts – Bolts used to secure a cylinder head and gasket to the engine block underneath (also known as head bolts).

Cylinder Head Bolts

Cylinder Head Gasket

Cylinder head gasket – A flat gasket typically made of layers of steel, rubber, and other materials, placed between the cylinder head and engine block to maintain a seal as oil and coolant move through the engine, and as both components expand and contract. Also known as a head gasket.

Cylinder Head Gasket

Cylinder Head Shim

Cylinder head shim – Positioned above or below the cylinder head gasket, these are wafer-flat spacer pieces that move cylinder heads slightly higher – restoring valve clearance, valve train geometry, engine compression, and timing to proper specs if cylinder head and/or block surfaces have been resurfaced below factory limits.

Cylinder Head Shim

Cylinder Liner

Cylinder liner – A replaceable, hollow tube that fits into the cylinder bore or sits within the crankcase, inside which the piston moves up and down (also known as a cylinder sleeve).

Cylinder Liner

Dual Overhead Camshaft (DOHC)

Dual overhead camshaft (DOHC) – An engine with two camshafts in each cylinder head, with one camshaft operating the intake valves and the other camshaft operating the exhaust valves. Also see Single overhead camshaft (SOHC).

Dual Overhead Camshaft (DOHC)

Engine Block

Engine block – The lower section of the engine, cast out of metal, which houses the cylinders, pistons, crankshaft, and other internal engine components.

Engine Block

Engine Displacement

Engine displacement – a measurement of engine size based on volume inside all of the cylinders. The volume of a cylinder is the cylinder bore (distance across the center) multiplied by the length of the piston’s stroke. This number is then multiplied by the total number of cylinders to arrive at the total engine displacement figure – a number that’s expressed in liters, cubic centimeters, or cubic inches.

Engine Displacement

Exhaust Valve

Exhaust valve – A camshaft-driven valve in the cylinder head that opens to allow burned exhaust gases out of the cylinder after combustion.

Exhaust Valve

Expansion Plug

Expansion plug – A steel plug that fits snugly into an engine block opening to provide pressure relief if engine coolant expands and freezes (also known as freeze plug).

Expansion Plug

Flat Engine

Flat engine – an engine design with pistons that move horizontally rather than vertically. This type of engine will contain two separate sets of cylinder banks, both of which are laid out in a horizontal plane. This arrangement creates a flat-shaped block – giving the engine its descriptive name. As both sets of pistons share a crankshaft, they move in opposite directions. For this reason, flat engines are also described as “horizontally opposed” or “boxer” engines.

Flat Engine

Four-Bolt Main

Four-bolt main – A crankshaft main bearing cap held in place by four bolts instead of the usual two to provide extra strength in high performance and racing applications.

Four-Bolt Main

Four-Valve Cylinder Head

Four-valve cylinder head – An engine with two intake and two exhaust valves for each cylinder instead of one each.

Four-Valve Cylinder Head

Head Bolts

Head bolts – see cylinder head bolts.

Hydraulic Valve Lifter

Hydraulic valve lifter – A valve lifter that uses hydraulic oil pressure to maintain zero valve clearance, reducing valve noise and eliminating the need for valve adjustments.

Hydraulic Valve Lifter

Intake Valve

Intake valve – A camshaft-driven valve in the cylinder head that opens only to allow the unburned fuel-air mixture into a cylinder before combustion.

Intake Valve

Inline Engine Block

Inline Engine Block - If all cylinders are positioned in a row, one behind the other, you’ve got an inline engine. Most modern 4-cylinder engines and some 6-cylinder engines are laid out this way. Inline engines have one single cylinder head.

Inline Engine Block

Integral Valve Seat

Integral valve seat – A valve seat that is machined into the cylinder head instead of a separate piece being inserted (also see valve seat).

Integral Valve Seat

Long Block

Long block – An engine block that’s fully assembled with internal components such as pistons, crankshaft, valvetrain, cylinder heads, and more. Long blocks do not include any fuel system connections (fuel injectors, fuel rails), electrical system components (spark plugs, coils, wires, distributor), or externally-mounted intake/exhaust system parts. “Long” does not refer to actual size or length of the engine block. See also short block.

Long Block

Main Bearings

Main bearings – The bearings which are located between the crankshaft and the machined surfaces of the block. The crankshaft rotates on its main bearings.

Main Bearings

Main Bearing Caps

Main bearing caps – Removable, semicircular caps which bolt to the engine block to secure main bearings and the crankshaft in place.

Main Bearing Caps

Oil Control Ring

Oil control ring – A piston ring designed to control oil consumption within the cylinder (also see Piston rings).

Oil Control Rings

Oil Galley Plug

Oil galley plug - A metal plug that’s threaded into a hole in the engine block casting.

Oil Galley Plug

Oil Pan

Oil pan – Bolted to the underside of the block, the oil pan encloses the crankshaft and serves as the engine's oil reservoir (also known as a sump).

Oil Pan

Oil Pump

Oil pump – A pump that delivers oil to all moving internal parts of an engine.

Oil Pump

Overhead Cam Engine

Overhead cam engine– An engine with a camshaft or camshafts located in the cylinder head(s) and above the valves.

Overhead Cam Engine

Overhead Valve Engine

Overhead valve engine – An engine with its camshaft located in the engine block, activating the valves in the cylinder head(s) through mechanical linkages.

Overhead Valve Engine

Piston

Piston – A cylindrically-shaped metal piece that moves up and down within a cylinder of the engine block, and is attached to a connecting rod on its bottom side.

Piston

Piston Wrist Pin

Piston wrist pin – A cylindrical or tubular metal shaft that attaches a piston to a connecting rod.

Piston Wrist Pin

Piston Pin Bushing

Piston pin bushing – A removable bushing that serves as a bearing surface for the piston pin.

Piston Pin Bushings

Piston Pin Clip

Piston pin clip – A circular clip used at each end of a piston pin to secure it in place.

Piston Pin Clips

Piston Rings

Piston rings – Thin metal rings installed around the top of a piston that form a seal between the piston and the cylinder wall.

Piston Rings

Push Rod

Push rod – A connecting link found in overhead valve engines that transfers motion of the camshaft in the engine block to the valve-actuating components in the cylinder head.

Push Rod

Push Rod Guide Plate

Push rod guide plate – Found on some older push rod engines, these are bolted in place and serve to keep the push rods moving in a straight path without wobbling. Some newer pushrod engines featured guides that are cast in place, and do not need bolt-on guide plates.

Push Rod Guide Plates

Push Rod Tubes

Push rod tubes – Found on older air-cooled engines, these are long hollow tubes that surround the push rods and serve as guide pieces.

Push Rod Tube

Rocker Arm

Rocker arm – A lever driven by a pushrod or camshaft lobe which transfers motion to open and close the intake and exhaust valves. For various engines, we stock numerous rocker arm hardware pieces such as adjusting screws, balls & ball studs, nuts & bolts, bridges, oil baffles, pivot pieces, retainers, rocker arm shafts & hardware, and studs.

Rocker Arm

Rod Bearings

Rod bearings – The bearings which are located between the crankshaft and the connecting rods.

Rod Bearings

Short Block

Short block – An engine block that contains only basic internal moving parts, but not cylinder heads or oil pan. An older engine with camshafts inside the engine block will include said camshaft(s), timing gear, and balance shafts (if so equipped). Compared to a long block engine which is well-equipped, a short block is a bare-bones assembly. “Short” does not refer to actual length or size of the engine block.

Short Block

Single Overhead Camshaft (SOHC)

Single overhead camshaft (SOHC) – An engine with one camshaft per cylinder head, with that camshaft operating both the intake and exhaust valves. Also see Dual overhead camshaft (DOHC).

Sleeve

Sleeve – see cylinder liner.

Sodium Cooled Valve

Sodium cooled valve – An exhaust valve with a hollow stem filled with sodium. When heated, the sodium melts and helps carry away heat, allowing the valve to operate at lower temperatures.

Sodium Cooled Valve

Sprocket

Sprocket – The set of teeth found around the outer circumferences of rotating wheels used to drive items such as a timing belt or chain.

Sprocket

Sump

Sump – see oil pan.

Tappet

Tappet – see valve lifter.

Timing Belt

Timing belt – A toothed belt made of reinforced rubber and riding on sprockets, which synchronizes the rotation of the crankshaft with the rotation of the camshaft(s) so that the valves open at the appropriate time.

Timing Belt

Timing Chain

Timing chain – A chain riding on sprockets, which synchronizes the rotation of the crankshaft with the rotation of the camshaft(s) so that the valves open at the appropriate time.

Timing Chain

Timing Gears

Timing gears – A set of gear wheels in direct mesh with each other, which synchronizes the rotation of the crankshaft with the rotation of the camshaft(s) so that the valves open at the appropriate time.

Timing Gears

V Engine

V engine - Most modern engines of 6 or more cylinders are laid out in a V configuration with 2 banks of cylinders. Half of the cylinders will be in the first bank, and half will be in the second bank. Because each bank of cylinders features its own cylinder head, a V engine is equipped with two separate cylinder heads.

V Engine

Valve

Valve – In an internal combustion engine, a device which opens to allow the passage of intake or exhaust gases, and closes in order to seal the combustion chamber.

Valve

Valve Cover

Valve cover – The piece which bolts on the top of a cylinder head, effectively serving as a protective lid.

Valve Cover

Valve Cover Gasket

Valve cover gasket - A seal, typically made of rubber or cork, placed between a valve cover and cylinder head to prevent oil leakage.

Valve Cover Gasket

Valve Guide

Valve guide – A cylindrically shaped opening in the cylinder head which serves as the channel for the valve stem as it moves up and down.

Valve Guide

Valve Lifter

Valve lifter - A cylindrical piece, actuated by the camshaft, which transfers its motion to open an intake or exhaust valve (also known as cam follower or tappet).

Valve Lifter

Valve Seat

Valve seat – A surface, either machined into the cylinder head or pressed into place, against which the valve sits when it is closed.

Valve Seat

Valve Spring

Valve spring – A spring that keeps a valve closed, and against which the valvetrain must exert pressure when opening a valve.

Valve Spring

Valve Stem

Valve stem – The long cylindrical portion of a valve which moves up and down in the valve guide.

Valve Stem

Valve Stem Seal

Valve stem seal – A round seal located between the valve stem and cylinder head to prevent oil in the cylinder head from leaking into the cylinder.

Valve Stem Seal
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