Free Auto Repair Resources
Understanding the terminology used in engine and transmission repair can be confusing. This glossary explains common industry terms in simple language to help you understand the repair process and make confident purchasing decisions. For a more detailed explanation, please see our Complete Buyer's Guide.
An old engine that has been completely disassembled, cleaned, inspected, and rebuilt to factory (or better) specifications in a production environment. All wear parts are replaced regardless of condition. This is the most reliable and highest-quality option after a brand new engine.
An engine that has been repaired, often in a local shop, by replacing only the specific parts that failed. The overall quality, longevity, and warranty can vary greatly depending on the skill of the builder.
An engine taken directly from another vehicle, typically from a salvage or junk yard. Its internal condition, maintenance history, and true mileage are largely unknown. It is the most affordable but highest-risk option.
The core of the engine. It includes the engine block, crankshaft, pistons, and fully assembled cylinder head(s). You must transfer over all external parts (intake/exhaust manifolds, accessories, tinware) from your old engine.
A step below a long block. It's the engine block with the internal rotating assembly (crankshaft, pistons, connecting rods) already installed, but it does *not* include the cylinder head(s).
The most complete option. It's a long block that also comes with most external parts pre-installed, like the intake manifold, valve covers, oil pan, and water pump. It's the closest to a "turn-key" or "plug-and-play" installation.
Forced induction is any process that actively compresses air and forces it into an engine's cylinders, rather than letting the engine draw it in naturally. By packing more air molecules into the cylinder, the engine can burn more fuel, resulting in a more powerful explosion and significantly more horsepower. There are two primary types: the Supercharger, which is belt-driven by the engine for instant power, and the Turbocharger, which is spun by waste exhaust gas for greater efficiency. This technology allows smaller, more fuel-efficient engines (like Ford's "EcoBoost") to produce the power of much larger ones. While older turbos had a "lag" or delay in power, modern technology has made this nearly imperceptible in new cars. ...show more
The stamped sheet metal parts that are typically transferred from your old engine onto a new long block, such as the oil pan, valve covers, and timing cover.
The collection of parts in the cylinder head that control the flow of air and exhaust: valves, springs, rockers, lifters, and the camshaft(s).
Serial numbers stamped or cast directly into the engine block and cylinder head. These are essential for precisely identifying the engine model to ensure a perfect fit.
The company that originally built the parts for the car manufacturer. "OEM parts" are the same quality and specification as what the car came with from the factory.
The "core" is your old, failed engine or transmission. You pay a refundable deposit called a "core charge" and get that money back when you send your old part back to the supplier for remanufacturing.
The fluid coupling that connects an automatic transmission to the engine. It acts like the "clutch" of an automatic, allowing the car to be stopped in gear while the engine is still running.
The complex hydraulic "brain" of an automatic transmission. It directs fluid pressure through a maze of channels to engage clutch packs and shift gears. It is a major component replaced or updated in quality remanufactured units.
A type of automatic transmission that uses a system of belts and pulleys instead of fixed gears, allowing for seamless acceleration without traditional shift points. Common in many modern sedans and SUVs for fuel efficiency.
A deep, hammering or knocking sound from the engine that gets faster with RPM. It's caused by excessive space between the connecting rod and the crankshaft, a sign of severe internal damage requiring engine replacement.
The seal between the engine block and the cylinder head has failed. This allows coolant to leak into the cylinders (causing white exhaust smoke) or oil to mix with coolant (creating a milky, sludge-like substance in the oil cap).
A common failure symptom where the engine RPMs rise, but the car doesn't accelerate accordingly. It feels like the transmission is struggling to "catch" the gear, often due to worn internal clutch packs.
The engine's cylinders can no longer hold the pressure needed for proper combustion. This causes a loss of power, rough running, and hard starting. It can be due to worn piston rings, valves, or a bad head gasket.
A critical engine bearing has seized and rotated in its housing, cutting off oil supply. This quickly leads to catastrophic engine failure and is often the cause of rod knock.
This occurs when an integrated transmission cooler (inside the radiator) fails, allowing transmission fluid and engine coolant to mix. This creates a destructive, pink, milky fluid that can quickly ruin the transmission.
The gearbox located on the axle that allows the left and right wheels to spin at different speeds when turning a corner. Essential for smooth handling, it can be "Open," "Limited-Slip (LSD)," or "Locking" for off-road use.
The gearbox in a 4WD or AWD vehicle that takes power from the transmission and splits it between the front and rear axles, allowing for all-wheel traction.
A small, radiator-like device designed to cool a specific fluid, such as engine oil or transmission fluid, to prevent it from overheating and breaking down under heavy load like towing.