Editing Engine tuning (section)

===Overhaul===
An overhauled engine is one that has been removed, disassembled, cleaned, inspected, repaired as necessary and tested using [[factory service manual]] approved procedures. The procedure generally involves [[Honing (metalworking)|honing]], new [[piston ring]]s, [[Bearing (mechanical)|bearings]], [[gasket]]s and oil seals. The engine may be overhauled to 'new limits' or 'service limits', or a combination of the two using used parts, new [[original equipment manufacturer]] (OEM) parts, or new [[Aftermarket (automotive)|aftermarket]] parts. The engine's previous operating history is maintained and it is returned with zero hours since major overhaul.

Aftermarket part manufacturers are often the OEM part-suppliers to major engine manufacturers.<ref name="mattituck1">{{cite web|last=MR|first=MR|title=Engine Overhaul Terminology and Standards|url=http://www.mattituck.com/articles/ohterms.htm|publisher=Mattituck Services, Inc|access-date=20 August 2011}}</ref>

A "top overhaul" is composed of the replacement of components inside the cylinder head without removing the engine from the vehicle, such as valve and rocker arm replacement. It may include a "[[valve job]]". A "major overhaul" is composed of the whole engine assembly, which requires the engine to be removed from the vehicle and transferred to an engine stand. A major overhaul costs more than a top overhaul.

"New limits" are the factory service manual's approved fits and tolerances to which a new engine is manufactured. This may be accomplished by using "standard" or approved "undersized" and "oversized" tolerances. "Service limits" are the factory service manual's allowable wear fits and tolerances that a new-limits part may deteriorate to and still be a usable component. This may also be accomplished using "standard" and approved "undersized" and "oversized" tolerances.<ref name="mattituck1"/>