Poplar Grove Airmotive outlines two types of overhauls, and clarifies what constitutes a rebuilt engine.
Although the terms “overhaul” and “rebuild” are sometimes used interchangeably, there really is a difference—and it’s a codified difference.
Engine overhauls can legally be done at the factory or by many service facilities in the field. Overhauls can include used parts, as long as they fall within approved limits and your engine time continues on from where you left off in your logbooks. Each engine manufacturer (with approval from the FAA) sets the minimum standards that will comply with engine overhaul requirements.
Service Limit Overhaul
In a service limit overhaul, the engine is disassembled, parts are checked and any part that falls within the service limits set by the manufacturer is reinstalled. If a given part has an allowable wear tolerance of .010 inches before being out of service limits and it measures .009 inches during inspection, it can be reinstalled in the engine as part of the overhaul.
An engine overhauled using service limits may not reach TBO without additional maintenance.
New Limit Overhaul
Each manufacturer also establishes the limits allowed for parts used to build a new engine. In a new limit overhaul engine, parts are reworked or replaced as necessary to meet theses more stringent requirements.
Only the engine manufacturer can legally create a rebuilt engine; no field service facility has the authority to rebuild your engine. That’s because a rebuilt engine is manufactured using strict processes and specifications that bring the engine back to new-engine standards. Even if used parts are included, they must meet new part standards. As a result, every rebuilt engine gets a zero-time logbook, as if it was a brand-new engine.