A replacement automobile engine is an engine or a major part of one that is sold individually without any other parts required to make a functional car. These engines are produced either as aftermarket parts or as reproductions of an engine that has gone out of production.
Use
Replacement engines are used to replace classic car engines that are in poor condition or broken, or to install a more powerful or more fuel efficient engine in a vehicle. Replacement engines are often used to make old cars more reliable for daily driving. Classic car hobbyists may also install reproductions of a rare powerplant in a classic car. Aftermarket engines are used in many forms of motorsport. Some late model racecar series use "crate engines" many of which are made by independent firms. This ensures that drivers all have similarly powered racecars. Legends and Allison Legacy Series cars also use sealed crate motors.
Types of replacement engines
The four most common types of replacement engines are:
Long block - a short block, with mounted and gasketed cylinder head, valves and camshaft
Crate engine - a new or remanufactured engine, considered to be equivalent to a new engine. Parts include more than a long block, including intake manifold, and carburetor or fuel injection system, and perhaps an alternator
Short block
A short block is an engine sub-assembly comprising the portion of the cylinder block below the head gasket but above the oil pan. An in-block cam engine includes the camshaft, timing gear, and any balance shafts. Overhead cam engines don't include those parts. They appeared post-war when mass production of consistent engine models became widespread, rather than hand-building of varying engines. While they were common from the 1950s to the 1970s, but disappeared after this, as when overhead camshaft engines became the norm, the rational unit of replacement became the long block. A short block engine is a replacement component for use when a worn-out engine requires major servicing, usually beyond the capabilities of a local repair garage, and instead a machine shop is needed. The short block represents the major wear items of such an engine: piston rings, and potentially a rebore of the cylinder bores or replacement liners, together with reground bearings on the crankshaft. Although replacing the rings or bearing shells was at one time considered typical garage work, the need for a boring or crank grinding machine exceeded this. A short block represented the set of major parts needed, those beyond the garage capabilities, in one item. The third item sometimes requiring machining, the re-cutting of valve seats in the cylinder head, was less frequently needed. Grinding of valves to fit was a regular garage task, as was light re-cutting with hand tools, usually into a cast iron seat. Only once steel seat inserts came into use, either for unleaded petrol in the 1970s or fitted into aluminium heads, did machining of heads and the replacement of seats become equally commonly required. Aluminium cylinder heads could also be damaged by warping after overheating, often requiring machining to re-flatten them. A short block would have advantages over dismantling the engine and sending the crankshaft etc. away for rework. It would be quicker to obtain, requiring only a single shipping, rather than shipping twice and the time for machining. The short block would also have been built in a workshop hopefully cleaner and more organised for the specialism of engine building. Short blocks were OHV engines. Sidevalves were pre-eminent before the short block appeared as a common item, and they also offered little saving by omitting the head.
Long block
A long block is an engine sub-assembly that consists of the assembled short block, crankshaft, cylinder head, camshaft, and valve train. A long block does not include fuel system, electrical, intake, and exhaust components, as well as other components. A long block engine replacement typically requires swapping out parts from the original engine to the long block. These parts include the oil pan, timing cover, valve covers, intake manifold, emission-control parts, carburetor or fuel injection system, the exhaust manifold, alternator, starter, power steering pump, and air conditionercompressor.
Crate engine
A crate engine is a fully assembled automobile engine that is shipped to the installer, originally in a crate. Crate engines are manufactured by many different companies, but they all share the same characteristics of being complete engines ready to install once removed from the crate. Generally a crate engine only needs bolt-on accessories such as water pump, fuel system, and exhaust. This type of engine has various applications including general replacement, hot rod builds, and motorsports competition. Crate engines are often seen as an economical and more reliable solution as opposed to engine overhauls or custom builds. Such engines are built by specialist engine builders, working in clean and well-equipped workshops, rather than general purpose repair garages. Crate engines may be either brand new, or substantially rebuilt. If rebuilt, they will have been rebuilt to an extent such that they are considered to be of equal quality, reliability and expected lifetime as a new engine.
Applications
Crate engines are well suited in many different vehicle platforms. Engines are often used in the following applications:
Crate engines are often seen as an economical choice no matter what the application is. In general automobile engine replacement, a crate engine is often very competitively priced when compared to the cost of a full rebuild of a faulty engine. It is also quicker to ship from stock than to wait an equal time for parts, then to begin a rebuild. Installers often opt for the crate engine because of the cost and ease of replacement. Crate engines are typically a bolt-in replacement with no internal work being performed to the engine compared to a complete overhaul that requires internal part replacement by trained mechanics. Hot Rod and other custom street applications also often choose a crate engine because of the higher value when compared to a custom built engine. In motorsports, the crate engine option has become very popular for various reasons. Crate engines are often a more affordable option when compared to a purpose-built race engine so budget racers often go this route. The crate engine also has developed a large fan base in many different racing series because of the competitive racing. As all racers in the field have identical engines, the races are won by driver's talent and chassis setup, and not the amount of horsepower a team can afford to build into their engine.
EV crate engines
Most resto-mod EV conversions are achieved by repurposing drivetrains from an existing mass-produced EVs, such as Tesla. As of October 2019 there are no purpose-built crate engine EV kits available for commercial use, but such projects are in development.
New castings of some engines are sometimes produced by independent companies. These blocks commonly replace rare or popular designs for aftermarket rebuilding, especially when the original is no longer produced. They are sometimes available in aluminum instead of original iron, or in stronger alloys. Often they imitate the larger available displacements that were produced in small numbers or allow for displacements never available.
