When should I overhaul my engine?
Updated · Wingman AeroCare, KFNL
Short answer: Overhaul your engine when its condition calls for it, not only when the clock says so. The manufacturer's time between overhaul (TBO), in hours or calendar years, is a recommendation; for most privately operated Part 91 aircraft it is not mandatory. Clear signs it is time include metal in the oil filter, cam or lifter damage, rising oil consumption that cylinder work does not fix, significant internal corrosion, a prop strike that requires teardown, or an engine well past TBO showing multiple trends heading the wrong way.
What is TBO, and is it mandatory?
TBO is the engine manufacturer's recommended interval between overhauls. Lycoming publishes TBOs in Service Instruction SI 1009, and Continental publishes them in SIL98-9. Both also specify a calendar limit, commonly 12 years, because engines that sit deteriorate even without hours.
For aircraft operated under Part 91 that are not used for hire, TBO is generally not a regulatory requirement. 14 CFR 91.409 requires inspections, not overhauls at a set time. Commercial operators under Part 135 typically must follow TBO or an approved extension under their operating specifications.
That means a private owner can legally operate an engine past TBO if it remains airworthy. Whether that is wise depends on the evidence.
What signs say it is time?
| Sign | Why it matters |
|---|---|
| Metal in the oil filter or screens | Indicates internal wear or failure; type and amount determine urgency |
| Cam lobe or lifter spalling | A bottom-end problem that cylinder work cannot fix |
| Rising oil consumption across multiple cylinders | Often ring and cylinder wear that has become engine-wide |
| Oil analysis trends rising sharply | Especially iron, chromium, or bearing metals trending upward |
| Multiple cylinders with persistent low compression | May be more economical to overhaul than replace cylinders one at a time |
| Internal corrosion from inactivity | Rust on the cam and crank surfaces does not reverse |
| Crankcase cracks | Can require major work |
| Prop strike or sudden stoppage | Manufacturer guidance (Lycoming SB 533, Continental SB96-11) calls for complete engine disassembly and inspection after a propeller strike as each bulletin defines it |
What signs say it can keep flying?
An engine past TBO may be a reasonable candidate to keep running "on condition" when:
- It flies regularly, at least several times a month.
- Oil consumption is stable and reasonable.
- Compression readings and borescope images look good.
- Oil analysis and filter inspections show stable trends with no new metal.
- Engine monitor data shows no unusual temperatures.
- The bottom end has no history of corrosion or cam problems.
Owners who run on condition should monitor more often, not less: oil analysis at every oil change, filter inspection, and a borescope look at each annual.
Overhaul, rebuilt, or new: what is the difference?
- Overhauled: disassembled, inspected, repaired as needed, reassembled, and tested to approved standards (14 CFR 43.2(a)). It keeps its total time; time since major overhaul resets.
- Rebuilt (zero time): returned to service by the manufacturer or its approved agency to new-part limits (14 CFR 43.2(b)). It may be issued a new logbook with zero time in service (14 CFR 91.421).
- New: a factory new engine.
Owners also choose between overhauling their own engine (field overhaul, which keeps the core but means longer downtime) and an exchange engine (faster, with a core charge).
What does an overhaul cost?
Overhaul costs vary widely by engine model, overhaul type, and what the teardown finds. As a rough industry range, overhauls for common four- and six-cylinder Lycoming and Continental engines often run from the mid-tens of thousands of dollars to well above that for large six-cylinder engines, plus removal and installation labor and accessories. Get specific quotes for your engine.
Should I overhaul early or run it out?
Many owners plan financially for overhaul long before TBO by setting aside a reserve per flight hour. If the engine is healthy, running past TBO on condition can be reasonable for a well-maintained, frequently flown engine. If the engine is near TBO and needs significant cylinder work, spending heavily on a top end may make less sense than an overhaul. See cylinder replacement vs. top overhaul.
How Wingman handles it
Wingman AeroCare works on Lycoming and Continental engines and does inspections, cylinder and top-end work, and troubleshooting in-house, so we can help you read the evidence before you commit. When an overhaul is the right call, it goes to a vetted partner shop and Wingman manages the process for you. Our Managed Maintenance Program includes oil analysis on every oil change, which builds the trend data that makes this decision clearer. See piston engine maintenance or contact us.