Wednesday, September 4, 2013

Engine Overhauls

At some point in every airplane's life an engine overhaul has to be performed.  To many owners it's an expensive and black-box-like process; some people avoid it altogether by buying an engine with low times and then selling when it nears TBO.

I was lucky enough to have a conversation with Charlie Melot of Zephyr Aircraft Engines.  They are a very reputable engine shop in Florida known for their overhauls and amazing customer service. Charlie is a regular on many popular general aviation forums and is always giving out great advice to pilots with maintenance problems.  For our example pricing, we'll be taking a look at what I consider one of the staples of the general aviation fleet: the Lycoming IO-360.

Let's first start by looking at the popular types of options for any pilot seeking an overhaul:

The priciest of options is the Factory Rebuilt. What you get back is a zero-time engine that is, for all intents and purposes: new.  The biggest benefit from a rebuilt engine is the impact it has on your aircraft's value. This is effectively the same as any other part you have that gets sent in for an overhaul-exchange. When they receive your engine, it will become someone else's overhaul. All pieces which meet the minimum standards for a factory-new part are re-used, and those which don't are replaced with actual new parts.

Everything you receive will meet or exceed new tolerances, and this will run you a flat rate of $30,000 at the time of my writing this.

A Factory Overhaul is exactly what it sounds like. You send your engine off to the factor that made it, Lycoming or Continental for most planes, and they perform an Overhaul. Going with the Factory Overhaul instead of Factory Rebuild on this engine costs about $27,000.

There are some shops out there that are Overhaul Specialists like Charlie's Zephyr Aircraft Engines. They're mechanics who focus almost exclusively on engine overhauls and not too much else.  There are many big names out there with great reputations such as Zephyr, Penn Yan Aero, and G&N Aircraft. All three of these locations overhaul your engine, but the pricing isn't as flat: you have a lot more options than the Factory option, which impacts the cost.  The base rate for a 180HP IO-360 at Zephyr is $21,000.
An old 6-cylinder on a stand and ready to be disassembled

Technically any A&P/IA can perform an overhaul on an aircraft engine. This is commonly referred to as a Field Overhaul. If you have a trusted A&P this is a perfectly viable option, but it's also a perfectly wonderful way to get fleeced. Removing all of the cylinders, splitting the case, then putting it all back together afterwards is labor intensive. An A&P that's a friend willing to a Field Overhaul with all new cylinders, crank, and cam for little or no labor cost can be an amazing savings, but it should be a huge red flag to have a back-of-the-truck mechanic offer to do an overhaul for close to cost.

In his experience, Charlie says these are commonly people lowballing the price to not include new parts and reusing items which are questionable as to whether they meet overhaul requirements.

As with all things run by the bureaucracy, there are specific standards, rules, regulations, paperwork, red tape, and definitions to all words which have legal meaning.

According to FAR 43.2"No person may describe in any required maintenance entry or form an ... aircraft engine ... as being overhauled unless [using] methods, techniques, and practices acceptable to the Administrator, it has been disassembled, cleaned, inspected, repaired as necessary, and reassembled; and  It has been tested in accordance with approved standards and technical data, or in accordance with current standards and technical data acceptable to the Administrator ... No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions."

So anyone who performs an overhaul on an aircraft engine must conform to these same standards set by the engine manufacturer, but getting a crank shaft ground and polished to the passable bare minimums versus a shop that'll tell you early on that the crank will need to be replaced soon. It should be noted that some people refer to rebuilds as Factory Remanufacture, but this isn't a term recognized by the FAA; these engines are officially rebuilds. 

Properly done, an overhaul is the inspection of every single little piece of the engine. It really is a complete disassembly and reassembly of the engine with any parts showing significant wear being replaced.
During the overhaul every single bolt, hose, wire, clamp, and seal will be inspected and repaired to like-new standards or replaced. This isn't even getting to the inside of the engine yet.
The inside of a crank case. This is something you want handled with care; any problems which cannot be repaired can lead to a very expensive replacement cost. Another reason to go with a specialty shop.

And here, down in the very core of your engine, is the crankshaft. Every inch of that has to be tested for tolerances and parts either replaced or repaired. Overhauls are expensive, but unlike avionics, instruments, interior, or even fresh paint: this is what helps keep your plane in the sky.

Cost of an Overhaul by Zephyr
They were able to give me a basic cost breakdown of an overhaul for our IO-360 (180hp).
The base rate is $21,000 and includes:

  • Overhauls on the mags
  • New Engine Harness
  • New spark plugs
  • Overhaul on the entire Fuel Injection System
  • Overhauling the Cylinders
  • Regrinding the Cam and Crank

If you want brand new cylinders from Lycoming tack on another $1,600.
A new Cam adds $700 to the cost.
If a whole new crankshaft is desired (or required) you can expect to add another $5,000!

So at a price of $26,300, although the engine isn't officially a zero-time engine, you have all new parts (minus the crankcase itself).
The "Cylinder Room" at Zephyr. It is kept immaculate because every single particle of dirt that's in the engine when reassembled will shorten the life of it. This is another reason I'd go with an overhaul shop instead of doing it in the field.

When to Overhaul
This is perhaps one of the most controversial items to discuss, but really these engines run long and well. The advice from Zephyr is to look for the obvious big problems: metal in the oil, multiple cylinders failing at the same time, and oil leaks from the crank and other places where you're likely to spend the money to split the case anyways.

They've seen first hand a Lycoming O-320 come to their shop with 4,500 hours since overhaul without any problems, and the only reason it went into the shop was that the owner's primary passenger found out about the engine times and refused to ride until it was "fixed" up!

I personally know someone whose O-540 made it to 3,400 hours before the oil consumption reached the point warranting an overhaul.

Sadly, anecdotes aren't evidence. I've been able to find a plethora of stories of engines making it well beyond TBO as well as those where the owners felt it was time to overhaul early.  In many cases the common theme seems to be oil leaking from the bottom components or metal in the oil filter/screen. All but one of the engine failure related NTSB reports I've read while researching for this posting were due to top-end components failing.  I strongly recommend all pilots read the NTSB aviation accident database regularly. It can be a downer, but it's an amazing resource from which to learn.

The Real Cost of Engine Overhauls
The base cost of all of these overhauls has some contingency built in. Assuming nothing is majorly wrong with your engine the bottom line of the overhaul will cost Zephyr roughly 65% of their base rate in parts alone.  It's only when the parts cost gets ugly that their price will go up, but often their base rate works out just fine.

There's one special consideration when it comes to field overhauls: accidents do happen. I don't view warranties as "we stand by our work" so much as "we're all human, and mistakes happen."  Without any warranty, a mistake by your A&P leading to a bad crank can cost you thousands of dollars; or worse, any mistakes during a field overhaul that damage the case could cost $12,000 by itself, let alone collateral damage to other parts from high-speed metal banging around in the case.  Mistakes are expensive!

Once you've taken that first flight since the overhaul, the mechanic that was your friend who performed the overhaul can claim that it was caused by improper break-in by the pilot, etc., etc. Without a paper warranty your mechanic's mistakes become your financial responsibility.  To me, for something so important to the safety and monetary impact of your flight, a specialty shop or factory overhaul is one spot I wouldn't recommend flying on the cheap.
A freshly cleaned and overhauled crank case and camshaft.

My next few posts are in the works. I've received some great feedback from individuals offering their details for this series of articles.  It looks like in the near future we'll have the Real Cost of:

Bell Helicopter Ownership
Seaplane ownership
Light Sport versus Part 23 aircraft
Starting Up and Running a Part 135 Operation (I'll be giving an especially big thanks to my FBO on this one)
and some standard real-cost reviews of popular General Aviation aircraft.


  1. Could you explain this line a bit more (specifically what top-end components are failing)?

    "All but one of the engine failure related NTSB reports I've read while researching for this posting were due to top-end components failing."

    Thanks so much for blogging about all of this. It is EXTREMELY informative, and I appreciate all the hard work you're putting into it.

  2. I believe top end is valvetrain; valves, cams, seals, etc. All of that is essential to an engine as it controls the amount of air/fuel going into the piston, and most importantly, seals the combustion chamber to generate the pressure required for the pistons to keep rotating that fly-wheel and prop!

  3. Do these costs include getting the engine in and out? Shipping it to from the manufacturer or other overhaul shop?

    If not how much dless that add?

    How different would these coats be for a o-320?

  4. Do these costs include getting the engine in and out? Shipping it to from the manufacturer or other overhaul shop?

    If not how much dless that add?

    How different would these coats be for a o-320?

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