Warbird Information Exchange

In the US you follow FAA Regulations. It can be repaired or Overhauled depending on the amount of damage.
In either case it needs to meet appropriate FAA approved conditions to be considered AIrworthy.
Basically you replace worn or damaged parts with New, overhauled or repaired parts.
Typically there is FAA approved data that shows the dimensions and condition the parts need to be.
As an example, the Rolls Royce Griffon in the Spitfire I maintain has limits of wear.
The new or overhaul limits for a Rocker Arm Shaft in the Cam Racks are .654 - .655. It must be repaired or replaced when worn to .65025.
The Rocker Arm has bushings where it pivots on the shaft.
The new or overhaul Dimension Limits on those are .65625 - .65725. They must be replaced at .661.
The fit of these parts together has Clearances of .00125 - .00325 New or Overhaul and the Max allowable Clearance is .006.
If you collect the Cam Rack parts and after the required inspection and cleaning as specified in the Rolls Royce/Military Manuals they meet the dimension requirements above you can call the Cam Rack Overhauled.
If you use some parts that have enough wear that they no longer fit the New/Overhaul Specs, but are less than the size stated to be considered worn out, the Cam Rack would be considered Repaired.
The FAA doesn't recognize the term "Rebuilt". It is either Overhauled or Repaired and must be considered Airworthy.
You have to be careful as you could end up with an Engine that has had everything done in accordance with the work required to Overhaul but had many parts used that were a hair away from being considered Worn Out Beyond Limits. The Engine would be considered Repaired, it might be represented as Overhauled and some of those parts would end up being worn out after a short time of usage.

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Rich Palmer

Remember an Injured Youth
benstear.org
#64- Stay Strong and Keep the Faith

BOOM BOOM, ROUND ROUND, PROPELLER GO

Don't Be A Dilbert!

To clarify further, the manufacturer usually has a list of mandatory replacement parts that must be observed to qualify as an "overhaul" rather than a repair. As an example, say you have an engine that has a catastrophic failure 3/4 of the way to TBO. Let say als,o that you had replaced the carb and mags 10 hours before that failure. The carb and mags would have to be replaced or overhauled as well to qualify the engine as "overhauled", even though they may only have one flight on them. If they (or whatever listed components required) aren't overhauled then the engine is only "repaired" - even if everything else was new. And you'd still have an engine 3/4 of the way to TBO

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Lest Hero-worship raise it's head and cloud our vision, remember that World War II was fought and won by the same sort of twenty-something punks we wouldn't let our daughters date.

Thank you 51 fixer !
How do you deal with massive damage ,change the complete part,even if it is a crankcase ?
Apparently in WWII Merlin cases were soldered if need be,can it still be done,would you think it's safe to do that ?
Also,when a motor has a shock,everything shoud be checked,from bearings to tolerances to (residual) quality of the metal,how is it done in real life ?
Thanks.

Thank You,shrike.

There are typically several sources of info. All maint, rebuilding and overhaul has to be done in accordance with some FAA Approved data.
With Aircraft you can't just do whatever you feel needs to be done or not done. There are requirements by the FAA to be Airworthy. The Airworthiness of a part is determined using some guidelines, usually from a Manufacturer or whatever Engine, Prop, Airframe or Component bolted onto the airframe. Sometimes someone figures out a way to improve something or make a part that is no longer made by the original manufacturer. These have a process where you prove to the FAA your parts are equal or better in strength and performance as the original parts and the FAA will issue a Supplemental Type Certificate (STC) or you might get a Parts Manufacturing Approval (PMA) for that part. This allows you to legally install a part that isn't original on the aircraft or made by the manufacturer and also will give some guidelines on maintaining or overhauling that part.
Airlines, military and operators can also come up with repair procedures that become accepted for Overhauling or repairing parts.
These approved methods, parts and procedures are what give you what can be done to repair the engine or part. There has to be something in a manual somewhere that tells you what something should be in condition and dimensions, it should be identifiable by some type of part number, it should be listed in a parts manual and there should be a maint manual that tells you how it should be maintained and possibly installed. In addition there needs to be a logbook of some kind in which any maint performed is recorded or a record of maint on file with a repair station.

I've seen a R-2800 that had been used by an Airline and had 20,000+ hours in the logbook. There were very few major parts left on the engine that were original to when it left the factory.

The engine in the P-51 I maintain was overhauled by Roush Aviation. In addition to the official manuals for the Merlin they have developed hundreds of repairs, have many parts they make and incorporate various mods that were introduced on later models of the engine. They are an FAA approved repair station and everything done that isn't a part of the original manual or design has been engineered, tested and gone through an approval process to makes it FAA approved to be used.
Included in this is some advanced welding procedures for cracks and even areas that are missing chunks or severely corroded areas of these parts. Stuff that never was considered when the engines were built.

_________________
Rich Palmer

Remember an Injured Youth
benstear.org
#64- Stay Strong and Keep the Faith

BOOM BOOM, ROUND ROUND, PROPELLER GO

Don't Be A Dilbert!

I'm not at work, so I'm not speaking Ex Cathedra. Silliness may ensue.

As 51fixer pointer out there are usually procedures the manufacturer has called out in the manual for dealing with most eventualities. In the GA world, Lycoming and Continental both have detailed service bulletins that cover the process and any mandatory replacement parts. Packard, RR, P&W and everyone else has theirs too.

Real world for all of them is roughly as follows.
1 Engine is completely disassembled. At this point any truly mangled parts are identified, and gawked at with expressions of disbelief, low whistles and occasionally cursing.
2 All the parts are cleaned, paint removed etc.
3 Detailed visual inspection and measurement of all parts. Here it will be determined if any major components will need to be, or can be overhauled. Close attention paid to geartrains. Cases may be repairable through welding and machining.
4 Steel parts magnafluxed, and non-ferrous parts zyglowed (or magnetic particle and liquid penetrant inspection respectively for the trademark conscious). In some cases 3&4 can be mixed up in order. Continental cranks for example are know to have a bad habit of cracking under shock, so they get magnafluxed first so as not to waste effort on a high dollar humpty dumpty.
5 Put everything back together with new seals, bearing and whatever else needed replacing and make sure it works.

_________________
Lest Hero-worship raise it's head and cloud our vision, remember that World War II was fought and won by the same sort of twenty-something punks we wouldn't let our daughters date.

Leaning out an R2800 to the point that a valve seat falls out of the head... Yes, I have pictures & the cylinder in question is sat in my garage.

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Those who possess real knowledge are rare.

Those who can set that knowledge into motion in the physical world are rarer still.

The few who possess real knowledge and can set it into motion of their own hands are the rarest of all.

Thank You !