Editing Automobile engine replacement (section)

==Short block==
[[File:Stripped Rover V8 engine.JPG|thumb|right|Short block 3.5L [[Rover V8 engine]]]]
A '''short block''' is an [[engine]] sub-assembly comprising the portion of the [[cylinder block]] below the [[head gasket]] but above the oil pan,<ref name="Erjavec2005">{{cite book|author=Jack Erjavec|title=Automotive Technology: A Systems Approach|url=https://books.google.com/books?id=U4TBoJB2zgsC&pg=PA227|year=2005|publisher=Cengage Learning|isbn=1-4018-4831-1|pages=227–}}</ref> which usually includes the assembled engine block, crankshaft, connecting rods, and pistons with piston rings properly installed.<ref name=MT-2020>{{cite web |url=https://www.motortrend.com/how-to/difference-between-long-and-short-blocks/ |title=What's the Difference Between Long and Short blocks? |author=Rupp, Steven |date=March 23, 2020 |work=Motor Trend |access-date=7 October 2022}}</ref> An in-block cam engine short block includes the [[camshaft]], [[timing gear]], and any [[balance shaft]]s. [[Overhead cam]] engines don't include those parts. Short block engines became popular after World War II, when mass production led to great consistency between individual engines; before then, most engines were hand-built and had idiosyncratic variations. Short blocks became less popular after the 1970s when [[overhead camshaft]] (OHC) engines became the norm, as the rational unit of replacement was the long block, which includes the head, camshaft and valve gear.

A short block is the preferred replacement component for a worn-out engine that requires major servicing beyond the capabilities of a local repair garage, when instead a machine shop may be needed. The short block represents the major wear items of an engine: piston rings, and potentially a rebore of the cylinder bores or replacement [[cylinder liner|liner]]s, together with reground bearings on the crankshaft. Although replacing the rings or [[bearing shell]]s was at one time considered typical garage work, the need for a boring or crank grinding machine now exceed the capabilities of a standard automotive repair garage. A short block includes the preassembled set of major parts needed that generally exceed the capability of the garage, 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 once a regular garage task, as was light re-cutting with hand tools, when cast iron seats were common. Once steel seat inserts came into use, either as a result of the switch to [[unleaded petrol]] in the 1970s or fitted into high-performance aluminium heads, machining of heads and the replacement of seats became equally commonly required. Aluminium cylinder heads could also be damaged by warping after overheating, often requiring machining to re-flatten them.

A short block has advantages over dismantling the engine and sending the crankshaft and other related automotive parts away for rework. It is usually quicker to obtain, requiring only a single shipment, rather than having to ship parts to and from the machine shop and the interim time spent at the shop to re-machine those parts. The short block would also have been built in a workshop that was hopefully cleaner and more organised for the specialism of engine building.

Short blocks were [[Overhead valve engine|OHV]] engines. Sidevalves were pre-eminent before the short block appeared as a common item, and they also offered little saving by omitting the (simple) head.