Learn About Aircraft Engine Overhaul And More

Piston Overhaul

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Understanding Quotes and the Fine Print

The condition of your engine matters to overhaul shops and the two most important pieces they care about are your crank case and crank shaft. After they take apart the engine at the shop, clean it up, and inspect it, these parts will fit into 1 of 3 categories:

  1.  New limits – Basically the parts measure up to new standards. They don’t need any additional work, and can get reassembled as-is. This happens maybe 10-20% of the time and deserves a celebration dance. Hopefully luck is on your side.
  2.  Can be repaired to ‘new limits’ – Thankfully you don’t need to replace the parts because repairing them is usually a lot cheaper. But who pays for the repair? Is this included in your quote? Ah, this is the whole purpose of this section. Keep reading. 60-70% of cases/cranks fall in this category.
  3.  Needs to be replaced – Ouch! Your parts can’t be brought back to ‘new limits’ and you’ll need to buy a new or overhauled ‘new limit’ replacement. Around 10-20% of engines need to replace a case or crank. 99% of the time, the owner pays this bill, not the shop. Costs vary widely so I’m taking a real swing by saying a case or shaft could cost $3-7k for an overhauled replacement. This is when owners and shops discuss the merits of sending it to the factory for exchange.

Ok, let’s get back to our scenario of the case or crank needing to be repaired to ‘new limits’. What you want to see is language that says the price is contingent on parts (like cases, cylinders, cranks, cams, ect.) being ‘repairable’. You don’t want to see ‘serviceable’. What’s the difference?

Let’s learn about this through example. An engine is taken apart at an overhaul shop and on the crank case they find fretting (wear) on the bearing slots and along the metal where the two halves rub against each other. This is pretty common. But, the good news is it can be repaired to ‘new limits’ at a case shop (almost all shops outsource this). The overhaul shop is going to have to pay the case shop around $1,500 with round trip shipping depending on what needs to be done. Will they pass off this cost to you, or is this all included as part of your engine overhaul quote? The answer depends on whether they have a ‘repairable’ or ‘serviceable’ contingency in their quote.

If this happened with the shop who quoted a ‘serviceable’ contingency, you may be looking at extra charges. The shop with the ‘repairable’ contingency won’t charge extra. Make sense?

Ok, one other thing – if you weren’t aware of the difference between serviceable/repairable contingency, you might be able to negotiate with the ‘serviceable’ shop about covering the repair. Some shops look at this stuff on a case-by-case basis. Read that last sentence again if you missed the clever pun I threw in there. Someone needed to lighten the mood!

I want to start this post out with a service bulletin or ‘SB’. Stop rolling your eyes, this one is actually worth looking at!

If you’ve got a Lycoming, click here for SB240W. If you have a Continental click here for SB97-6B.

This is what all engine shops should follow when determining what parts to include in an engine overhaul and furthermore, which of those parts can be repaired vs replaced with new. Making sure that your shop follows these guidelines is a good idea.

So here are the major components that are typically included in a piston engine overhaul:

  • Cylinders
  • Camshaft
  • Crankcase
  • Crankshaft
  • Magnetos
  • Starter
  • Oil cooler and pump
  • Fuel injection system
  • Spark plugs
  • Ignition harness

You should ask your shop what components they quoted for overhaul vs new replacements as this can have a huge impact on price. But in the end, you get to decide whether most of these components should be overhauled or new replacement parts. Your shop can give you the best advice on that front.

There are 6 major expenses that may not be included in an engine overhaul quote. These costs range widely, but I’ll do my best to ballpark them so you have some idea. I meant the word ‘ballpark’ in that last sentence so don’t tell your shop “Well the website said it would cost X!” (insert serious face).

  1. Dismounting and Mounting the Engine – You need to find someone who can remove your engine and install the new one. Typically, this is someone who is local like an FBO, or your favorite mechanic or shop. This process takes a significant amount of time and can cost between $1-5k per engine. Your overhaul shop will probably give you the best price so they can have control of this process (they have an interest to know it’s done right).
  2. Shipping – The cost to ship an engine in the US is usually less than $1,000 round trip! This is paid outside of the Overhaul Bids website – often to the shop. Most shops don’t mark-up shipping and a few will include it in the quote. In 2014 I got a quote to ship a 500lb 6-cylinder engine from FL to CA for $350 one way. Sometimes the return trip costs more because you need to add more insurance for the added value.
  3. Replacement Parts – This is a big question mark on an overhaul. When most shops quote, they anticipate replacing all required components and overhauling the rest. Occasionally a shop will find unrepairable damage on components and have to replace them. The upshot is, you’ll be glad they found this damage so you’re not flying around with parts getting ready to fail. Here’s a few examples of components that our shops see from time to time:
    1. Crank case – An overhauled replacement for a Bonanza will be about $4,500. Your cost will depend on the exact model and the parts market. Around 10-20% have to be replaced
    2. Crank shaft – An overhauled replacement for a Bonanza will be about $4,500. Your cost will depend on the exact model and the parts market. Around 10-20% have to be replaced.
    3. Cylinders – Talk to your shop about cylinders because there’s two ways to look at cylinders. Sometimes owners prefer to get all new cylinders instead of overhauling their existing ones. New cylinders can cost $2-10k for a full set. If the plan is just to overhaul existing, sometimes a shop will find a cracked cylinder and need to replace just one. Again, talk to the shop here to work out the best plan of action for your situation.
    4. Camshaft – An overhauled Replacement will be around $650. This part has to be replaced around 60-70% of the time.
  4. Component Repair – This may or may not impact your engine overhaul cost. Some shops include major component repair, some don’t. See “Price contingencies” above so you know how to tell if a shop will charge extra for this. It’s important because there’s about a 60-70% chance your case or crank will have to be sent out in order to be restored to ‘new limits’. If you do get charged for Case or Crank repair, you’re looking at around $1,500.
  5. Sales Tax – Most shops quote overhauls without tax initially. They do this to see if you meet sales tax exemptions before adding that in. When you get down the details with a shop, talk to them about sales tax and if there are any ways to avoid it. Some states charge sales tax on parts and labor, others just parts, and some don’t charge at all. The percentage can range from 6-10%, so the tax could easily exceed $1,000. Sometimes there’s creative ways to avoid it. For example, one shop was able to save his client sales tax by selling to a broker in a neighboring state, and then have that broker sell it to the client. Again, talk to your shop about legit loopholes.
  6. Ancillary Parts – This stuff is considered outside the engine overhaul, but when you put the brand new engine back on your plane you might notice the hoses, baffles, fuel lines, and engine mounts are looking tired. The person doing removal and reinstallation will be the one to charge you for this. Also, some people decide to overhaul other components like the prop governor, alternator, vacuum pump, and electric fuel pumps. Costs vary on this stuff, so I’m not going to go there.

Whoa! Are we scaring you? It’s worth pointing out again that we have zero tolerance for foul play. Shops know they’ll get booted from our network if they do anything unethical. The fact that the shops are still here shows you they’ve had an excellent history of being honest in reputable with many customers before you.

If this post has created more anxiety and questions, give us a call at (317) 550-0030. Or, we have an overhaul anxiety support group that meets Monday nights and you’re welcome to speak there.

The truth is factories are more likely to not charge you for bad parts than engine shops. After all, they can replace junk parts a lot cheaper than engine shops right? So they’ve turned this into an advantage to get more business when overhaul time comes. But, this doesn’t mean that the factory will accept an engine in any condition. They do have standards.

Continental could reduce your core value (the value they give to the engine you trade-in) if components aren’t ‘repairable’ which is the same verbiage as many overhaul shops. Lycoming has requirements for cores too. It’s also important to point out that if a part has to be replaced on your engine, the factory may charge ‘list’ price for it. By contrast, most overhaul shops will pass on a major replacement part at their cost. So, while buying a factory engine lowers your risk of added charges, it doesn’t completely eliminate it unless you get the factory to accept your engine in ‘as-is’ condition.

What if you change your mind and want a factory engine while your engine is already taken apart in an overhaul shop? Both Continental and Lycoming require that your engine is assembled so you must have the overhaul shop put it back together before shipping it to them. They do make exceptions to that rule for some shops who they trust. But what will the overhaul shop charge you? Overhaul shops vary with how they deal with this issue but most of them want to get paid for the work they’ve done. One shop I spoke to said they charge a flat $500 for reassembly in addition to the amount of labor they already had in the job.

Overhaul Basics

First of all, overhauling your engine is ‘recommended’ not ‘required’ for part 91 operators as long as an A&P said you’re airworthy in the last 12 months. Manufacturers set forth a recommended Time Before Overhaul (TBO) for every engine. Continental and Lycoming engines are 12 years and their flight hours vary from 1,200 to 2500 hours.

Continental TBO can be found here. Note: the majority of engine models manufactured after February 2012 have increased TBO’s by 200-400 hours depending on flying frequency. The 400 hour TBO extension is only earned on some models by flying 40+ hours per month.

Lycoming TBO can be found here.

Lastly, if you want to see TBO by popular aircraft, click here. This is a good resource if you’re in the market to buy a plane and you want to find something with a high TBO.

  1. Service Limit Overhaul – A service limit overhaul means that parts will be put back into your engine that are within ‘serviceable limits’. Basically, this means that if a part is allowed to measure + – .010” it can be put back if it is .009”. The big question here is how long does it take to wear an extra .001”? Don’t you want enough time to wear your parts out until the next TBO? If so, Service limit overhaul is out of the question. Shops only recommend these for lower-time prop strikes. In fact, many will refuse to do them. Note: Lycoming offers a service limit engine called a “Factory Overhaul”
  2. New Limit Overhaul – The engine and its parts must meet criteria for a new engine. For all practical purposes, your engine will be restored to ‘new’ limits. It will have margin for its parts to hopefully wear and stay within ‘service limits’ through its TBO (time before overhaul) life. As a personal note – I called every shop in the country for an engine overhaul and every single shop quoted a ‘new limit overhaul’. But after the engine is in the shop’s hands, how do you know they are actually putting ‘new limit’ parts in, and not ‘service limit’ parts? There’s certainly financial incentive to do the latter so read The Dark Side of Engine Overhaul so you don’t fall in this trap.
  3. Factory Rebuild and Factory New – Only the factory, or reseller thereof can give you a ‘factory rebuild’ or ‘factory new’. Factory rebuilds have some used parts that meet or are reconditioned to new limits. Factory new engines are comprised of completely new parts. About 10% of pilots buy factory rebuilds and 3% spring for the factory new engines.

Since practically no one gets a service limit overhaul at TBO, the real question that people face is to buy a new limit engine overhaul at a shop, or buy a factory engine. We know the factory is most expensive and recognized name of the two options. But does it carry added value? The next post answers that question.

I get asked this question a lot. The answer really depends on your situation and what you value in your overhaul. Sometimes the factory fits someone’s goals better and vice versa. So I recommend reading the article below and you’ll be able to determine which is a better fit for you.

But, before I can answer this question I have to define a couple of things mentioned in 3 Levels of Overhaul.

Overhaul – An overhaul can be done to two limits: 1. Service Limits and 2. New Limits as defined here. Note: a “Lycoming Factory Overhaul” is a service limit engine.

Factory Rebuild – An engine rebuilt by the factory using new and used parts to New Limits.

Factory New – An engine built by the factory out of 100% new parts to New Limits.

According to a survey, about 10% go with the factory rebuild option and 3% buy factory new. But these numbers are probably much higher now because the price difference between overhaul and factory engines has reduced. Personally, I think closer to 15-20% go factory these days.

Service Limit build standards are inferior to New Limit overhauls. For most overhauls done near TBO, they aren’t even considered by pilots. In fact, most quality shops will actually refuse to do a service limit overhaul because they don’t want any liability or warranty issues down the road. Lycoming’s “Factory Overhaul” is a service limit engine but it comes with new cylinders.

Remember, New Limit Overhauls are done by overhaul shops/mechanics and Factory Engines are made in the factory or their designated facility and sold mainly by distributors like Air Power.

Build Standards

The build standards for a New Limit overhaul are the same as factory engines. In other words, they are both built to ‘New Limit’ standards. This puts New Limit Overhaul on the same level as a Factory Rebuild. But, are there differences in the parts that go inside?


Most overhaul shops will reassemble engines to New Limits with the engine parts you send in. A Factory Rebuild is assembled to New Limits from a pool of new and used parts. The used part pool is populated in part by engine cores that are sent in for exchange. So the crankcase that is used on your engine might have 200 hours on it, or it might have 5,000 provided it meets new limits. Luck of the draw.

I might be going into too much detail here, but it’s possible the factory could pull out a crank case that has been machined once or twice and brought up to New Limits, but doesn’t have enough material to be machined again to New Limits. In other words, this could be that part’s last run. On the other hand, the factory might not have a used case or crank on-hand when you order and you’ll get a brand new one.

There’s also the difference between factory genuine parts and non-factory genuine parts known as PMA Parts. Factories use all factory-genuine parts, and overhaul shops typically use a combination of factory genuine & PMA but there’s more financial incentive to use the less expensive PMA parts. Overhaul shops do vary on this matter so check with your shop.

‘Factory New’ engines have the best offering for parts – 100 % new. But they’re also the most expensive option.

Lastly, A overhaul shop might overhaul your existing cylinders if you want to save money, but the factory will always put new cylinders on all their engines.


Overhaul shops have more flexibility than factories have in terms of build processes and options. Here are some examples:

Build Process

An example of a build process is port and polish work where extra material is removed from the intake and exhaust ports so that gasses can flow more easily in and out of the cylinders to gain an extra 2.5-4 HP per cylinder. A process like this is not offered at the factory and would likely void the warranty. If you want custom processes like this, an overhaul shop is probably the way to go. But be careful – some build processes are for ‘experimental’ only.


Factories do not sell or provide STC’s with only 1 exception – the Lycoming IO-390 engine. So you have to purchase the STC separately. An example is an upgrade to a bigger engine. Factories do this all the time and the warranty is fully supported.

But there are some STC’s that may void the factory warranty (usually modifications to a certified condition). An STC to run automotive gasoline might be an STC that could hurt your warranty. You should check with the factory on the ones that you want.

You can look up STC options by aircraft here.

Financial Risk

There is more financial risk of sending your engine to get overhauled than buying a factory engine. Why?

The price you get from the engine shop assumes that your crankcase and crankshaft don’t have to be replaced. These are big ticket parts. A crankshaft or crankcase for a Bonanza might cost around $4,500 for a New Limit overhauled replacement.

Crankcase and Crankshafts have about a 10-20% probability of needing replacement. The factory won’t charge you extra for a bad case or crank as long as you meet their core return policy.

Also, some shops might charge extra if your crankcase or crankshaft need to be sent out for repair. In other words, at these shops, if these parts don’t wash off in ‘new limit’ condition you might have to spend around $1,500 to get them repaired. Around 60-70% of the time, this is necessary. The good news is, most big shops include this repair, if necessary, in your price. See price contingencies for more information.

Lastly, most pilots these days get new cylinders and a new camshaft. But, if you’re planning on saving a buck by getting them overhauled instead, you might bear the cost of replacement if they can’t be repaired.

Zero Time

I like to think of “Zero Time” as a trademark owned by the factory. We’ve established that a New Limit overhaul and a factory rebuilt engine have the same build standards, but only a factory can produce a Zero Time engine with a fresh logbook. Overhauled engines keep the same logbook but start counting ‘time since major overhaul’ starting at zero. There’s a great article by AvWeb that goes into further detail on this.

Despite this truth, every aircraft owner selling their aircraft will use a “Zero Time” engine as a marketing gimmick to get more money. Heck, I probably would too. Someone might take the bait.

Aircraft Value

Imagine you have two Identical Cessna 172’s except one has a Factory Engine and the other has an Overhauled Engine, which would you choose? The majority would choose the factory engine 172 so this could help your plane sell faster and for more money. But, if you spent $5,000 more on the factory engine, will you get $5,000 back out of it?

The answer to that last question really depends on who the buyer is and how they look at it. I think a good analogy for this question is the difference between Motrin Ibuprofen and Target’s generic Up & UP Ibuprofen. We know they have essentially the same ingredients, are built to the same specs, do exactly the same thing, but some people like to spend more money on Motrin because they recognize the brand.

It’s also worth pointing out here that some overhaul shops have more value than others. I have some amazing independent engine builders in my network that overhaul engines at or above par with major shops. But, if your buyer has never heard of them, are they going to assign the same value to that engine as you have? Probably not. Engine value will be proportional to shop reputation and recognition.

Lastly, as I’ll point out below, many overhaul shops have better warranties than the factory. So will a factory engine out of warranty carry more value than its overhauled counterpart that is still in warranty? This might be an important consideration if you have a plan to fly 2 years and sell it.

Turn Around Time

Out of the approximately 75 overhaul shops in the US that work on Lycoming and Continental, I’d estimate there are only 10 with a decent stock pile of engine cores and parts that are ready to be built up and sold as an exchange for your engine. These shops can compete and usually beat the factory on turnaround time.

If you want your engine overhauled to New Limits it will take anywhere from 4-8 weeks. If you want a factory engine, the timeline to build it will really depend on your engine model and workload. There are so many engine models out there, it makes it hard for factories to have engines already built and sitting on a shelf waiting for a buyer. Most of the time, the factory will build up your engine after you order it. The build time for that is similar to an overhaul shop most of the time. But again, it depends on engine model.


When I quoted every piston engine overhaul shop in the country on a Continental IO-550-C, there were only 2 overhaul shops that exceeded the factory engine price. Everyone else was more than 20% cheaper than the factory rebuilt price. On average, I’ve noticed that factory engines are typically 20-30% more expensive than New Limit Overhauls from reputable overhaul shops.

We have to give the factory the advantage of reducing risk of paying for replacement parts like crankshaft or crankcase. So let’s do a quick math example of how to level the playing field.

Assume a New Limit overhaul costs $30k but there’s a 10-20% chance we have to replace a case or crank for $5k each. We should add $1,500 to the price of this overhaul because 15% of $10,000 is $1,500.

So to be fair to the factory when comparing price, adjust for the probability of a case or crank replacement. Most of the time, you’ll find that it’s still cheaper than the factory.

Lastly, it’s worth discussing the scenario of a case or crank replacement with the overhaul shop you’re considering. Sometimes you have a situation where both case and crank need replacement and the factory becomes the cheaper option (maybe 1 out of a 100). Ask the shop what you would owe them if you decided to send the engine to the factory after it was taken apart. Most shops only charge the labor they put into it and go to great lengths to make sure the customer is still happy with their service.

Liability Insurance

I hate addressing this one, but we all know the litigious propensities of our society and therefore it’s worth touching on. If something catastrophic happens in flight and the shop or factory is deemed negligent, their ‘product liability insurance’ will kick in. Most overhaul shops do not have product liability insurance because its cost is often six figures annually. Only a few of the biggest shops can pay this bill. The factories probably have this insurance but I have not confirmed this for sure.


Most people would agree that overhaul shops have an advantage over the factory for warranty. Many overhaul shops have warranties that exceed that of the factory. This is pretty important since roughly 30% of engines will have a warranty claim of some kind.

It’s also important to point out that many overhaul shops routinely cover more than the writing obligates them to. An example of this is shipping cost. Most warranties put shipping cost on the owner, but one of the shops in my network said that he covers shipping both ways 9/10 times.


In February 2012 Continental received a 200-400 hour TBO increase on most factory produced engine models. The 400 hour increase only applies to engines that fly 40+ hours per month. New Limit Overhauls done at overhaul shops keep the same TBO. So check to see if you can increase your TBO with a factory engine.

Continental vs Lycoming Differences

  • You can buy direct from Continental but not Lycoming
  • Lycoming offers a service limit engine called a “Factory Overhaul”. Continental does not
  • Lycoming will overhaul your engine or offer an exchange. Continental only does exchange

Aircraft Age

Newer and more valuable aircraft generally lean toward factory engines. Older and less valuable aircraft generally lean toward overhaul shops. It’s a lot like cars. New cars tend to use the dealer for maintenance and older cars go to the independent shops. Of course, this is a generalization and exceptions exist.

A few months ago I was shocked when a turbo normalized Cirrus owner decided to buy a factory engine for $22,000 more than what the overhaul shop would have cost him. Normally the difference between factory and overhaul shops is $2-5,000 and most aircraft owners go to an overhaul shop. So when I saw a difference of $22,000, I thought for sure this guy was going to buy from an overhaul shop. After all, he was not getting $22,000 of extra quality with the factory. But, he wanted to spare no expense and always buy premium with his aircraft since it was high value.


Deciding whether to buy a New Limit Overhaul or a Factory engine is a tough one. My advice to everyone getting an overhaul is to consider both and decide which best fits their goals and budget.


There are 3 levels of overhaul value. I rank them from highest value to lowest value.

  1. Name-Brand Shop Overhauled Engine – If you go to sell your airplane, odds are you’ll be asked where you got the engine overhauled. If you got it overhauled from a shop the buyer considers a trusted and reputable shop, this adds value. Examples of name-brand shops are Western Skyways (CO), Poplar Grove (IL), RAM Aircraft (TX), and Penn Yan Aero (NY).
  2. Unknown Shop Overhauled Engine – If your aircraft buyer has never heard of the shop who overhauled your engine, or is unsure of their reputation, this decreases value.
  3. Field Overhaul – A field overhaul is usually done by a local mechanic. Any FAA certified mechanic with a powerplant rating can sign off an overhaul. Engines with complex gear reduction systems and engines with integrated superchargers require an inspection authorization due to being considered major repairs (See 14CFR 43 appendix D). Anyway, They ‘ll have to send off most of your parts and components to shops who have the equipment to ability to overhaul them but the mechanic will be the one to inspect and reassemble them. While you may hold your local mechanic in high regard, the eventual buyer of your airplane might not. Some buyers will discount a field overhaul entirely and value your aircraft as if it’s hit TBO. Ouch! But, if you have a low value aircraft like a 150, 152, or ErCoupe, most buyers will probably be ok with a field overhaul. Don’t try it on a Columbia, Cirrus, or any other newer or high value aircraft.

Earlier I mentioned that I quoted a Continental IO-550-C with every engine shop in the country and the price varied from $23k to $60k for a ‘new limit’ overhaul. Well, 90% of shops were in the $29-32k range. My concern is the shops who say they can do it for under $25k because 75% of the engine overhaul cost is parts. The engine I’m talking about now will probably cost a shop around $24k in parts. So how can a shop offer a $23k new limit overhaul? Low overhead? Hmm…. I call BS!

The main way someone can cut costs on an overhaul is to use ‘service limit’ parts instead of ‘new limit’ parts (see ‘3 Levels of Overhaul’ to understand the difference). Worse yet, there’s actually been cases of ‘out of limit’ parts being used on overhauls.

Here’s a criminal case against a mechanic who used rusted, cracked, and wrong parts in his overhauls that resulted in two in flight failures.

Here’s another more recent criminal case of a mechanic who installed an out of limit crankcase that resulted in an in-flight failure.

There are more and more cases like this that continue to happen so buyer beware.

Before you can get your engine overhauled, you have to arrange the R&R (removal and reinstallation) which can range from $1-6k per engine. If you’re shipping your engine, your local FBO or shop will do this work or recommend someone who can. Otherwise, most overhaul shops perform R&R’s too. I recommend you ask the person doing work how many of R&R’s they do a year and if they have experience with your aircraft. There are as many horror stories of R&R’s as there are overhauls.

Overhaul shops have an interest to do the removal and reinstallation work so they know it’s done right. Because of this, they might give you a bargain price to entice you to use them.

Usually the person who does the removal and reinstallation will evaluate if you need replacement parts not included in the engine overhaul. These parts often include new baffles, engine mounts, and hoses.

The timeline for an overhaul (once at the shop) varies from 3-8 weeks or sooner if your shop has an engine ready to exchange for yours. In most cases the timeline is so long because there’s only a few shops in the country that overhaul cranks and cases and it’s their timeline that primarily sets the schedule.

You’ll also have some down time removing and reinstalling the engine and possibly a few extra days for shipping too. There are sometimes unforeseen circumstances that can delay your engines. The two most common delays outside the shops control are: 1) Delay getting new parts – most of the time this is cylinders. and 2) Delays at the case and crank shops. They get backed up during random surges of work and at the end of the year. Sometimes these situations can delay you as much as a month or so.

One last note – Double check your timeline with the shop right before shipping. Things change so quickly and within a few days time, the shop could have received a pile of work. Don’t assume that his estimate from 90 days ago will still hold up.

If downtime is a major issue for you, contact me at (317) 550-0030 and I’ll find a shop that can prepare an exchange engine for you ahead of time. This way, your new engine can be sitting next to your airplane when it’s time to pull the old off.


About 70% of overhauls buy new cylinders instead of overhauling their existing.

If you decide to overhaul your cylinders, you may want to ask your shop if it’s your cylinders getting overhauled or someone else’s. If they are not your cylinders, you should insist on them being first-run cylinders (meaning it’s their first time being overhauled). But since there’s never any real ‘proof’ that cylinders are first run, request the following:

  1. Standard barrels
  2. Non destructive tested heads
  3. Valves, guides, springs, keepers, piston, rings, and piston pin are replaced NEW (don’t reuse this stuff)
  4. Verify there’s no weld repairs on the cylinders

If you go with new cylinders, you’ll have 3 options depending on the exact type of cylinder:

  1. Factory (Continental, Lycoming, Etc.)
  2. ECI (Purchased by Continental in 2015)
  3. Superior

ECI no longer produces Continental parts. Only Lycoming and experimental.

Aviation consumer did a survey on new cylinder reliability and satisfaction back in 2008.

The survey results are pretty dim. Only 13% of Continental cylinders made it to TBO, 63% of Lycoming, 72% of ECI, and 68% of superior. Keep in mind the survey is pretty old and only had 277 respondents. But it’s the best third party source I can give you at this time. Aviation Consumer Magazine came out with a new survey in November of 2015 but you have to be a subscriber to view it.

Most of the shops I’ve spoken to still report Continental cylinder troubles though a few have said they’ve improved. The main complaint I hear is that the choke wears out within 350-750 hours which forms a gap between the rings and the cylinder wall. Oil blows by the rings and you lose compression. Second to that were comments about valve guides wearing out prematurely. The flipside of this argument is that it’s either a result of the operation (excessive leaning and downtime) or that it’s an old opinion that has been circulated longer than the problems have existed.

But, here’s some perspective. Factories have pushed down pricing to compete with overhaul shops for business – especially Continental. This has put downward pressure on overhaul shop pricing and profits. Consequently, shops may have a bit of bias in their opinions about the factories. But, I think shops care more about making sure the customer is satisfied than they do about this possible bias. And remember, they’re the ones that are going to warranty it so they have an interest to steer you in the most reliable direction. You can’t argue that that self-interest.

Accessory overhaul is typically not included in an overhaul quote, but can be added as an option. Some accessories to consider overhauling or replacing are:

  • Alternator or generator
  • Exhaust manifolds
  • Electrical Fuel pump (engine driven fuel pump should be taken care of in overhaul)
  • Hydraulic pump
  • Propeller
  • Propeller governor
  • Turbos
  • Vacuum pump
  • Engine baffles

An overhaul is a great opportunity to replace or upgrade accessories since everything is already off the engine and your airplane is out of service.

Usually, people with a constant speed propeller will have the governor overhauled or at least flushed. If not, all of its accumulated dirt and junk will flow around into your oil system and through your freshly overhauled engine. The same is true for a turbo.  It’s like taking a shower after working out at the gym and then put on your sweaty clothes. Just don’t…

Some shops offer special processes with their engine overhaul to enhance performance or reliability

  • Dynamic Balancing – Balancing a rotating part like a crankshaft (different from ‘static balancing’). Click here for a video explaining this option at 5:35. It’s kind of like getting your tires balanced after they shake your car on the highway.
  • Nickel Plated Cylinders – It’s a corrosion/rust resistant treatment. Great for airplanes that sit for a month or more at times. Click here for some info.
  • Porting Click here for info on porting. Basically, it promises improved airflow in the intake and exhaust ports by removing some material and polishing the channels so you develop more power. There’s speculation whether this is safe and effective. Shops that do this include Ly-con Rebuilding (CA), Johnson (CA), Victor (CA), Performance Aircraft Powerplants (AR), and a few others. To my knowledge, this is not FAA approved so there may be some limitations on using this for certified aircraft.
  • Cryogenic – Dunking your parts in liquid nitrogen may improve their reliability (yes I’m serious). Only three shops have this ability: Performance Aircraft Power Plants (AR), Ly-con Rebuilding (CA) and Victor Aviation (CA). PAP was the first to use it and has reported improved reliability on cylinders, camshafts, and crank cases. You might think of it as a cheap insurance policy for your cylinders for about $120 each (depending on weight). Racing pilots swear by it. Oh, and it’s not FAA approved so there may be some limitations on using this for certified aircraft.

There’s some discussion about whether these extras carry any benefit. You’ll also hear chatter from other shops disregarding some of these as ‘gimmicks’, not upgrades. It’s up to you to figure it out. Before spending extra cash, you might want to ask for a recent customer that got the extra you’re considering and see if they can tell the difference. And like I said above, if it’s not an FAA approved process, it might not be a good idea to do it to a certified aircraft. Also, if you plan on selling your airplane it might cut down on the potential buyers.

STC’s are Supplemental Type Certificates. Basically, these are FAA approved modifications. Sometimes there are hundreds of STC’s available for one type of aircraft. Overhaul time is a perfect opportunity to see what your options are. Click here to lookup STC’s by make and model on the FAA’s Website.

Here’s a few popular examples of STC’s:

  • Rubber gasket to seal the case halves – Ly-con Rebuilding in CA offers this for some Lycoming cases. Ordinarily, shops are stuck using silk thread. I’m not kidding.
  • Turbo Normalizing – Maintain sea-level power at altitude. Western Skyways in Colorado offers this for Bonanzas and 200 series Cessna aircraft.
  • Bigger engines – Put a 300hp engine in your Cessna 182 for example. Many shops have STC’s like this. RAM Aircraft has the largest selection in TX
  • Looking for something specific? Email alan@overhaulbids.com and I’ll find it for you. There’s a mountain of STC’s out there.


First, it’s good to know the industry standard warranty is 6 months and 240 hours plus a pro-rated period. Around 30% will have a warranty issue of some kind so understanding the fine-print is important.

Normally warranties are split up in two portions – 1. The initial portion where the engine is covered 100% or nearly 100%. 2. The prorated period where coverage declines to your engine’s TBO at actual flight hours used or a specified number of hours per month whichever is greater (40 hrs/mo is common). If your TBO is 2,000 hours and warranty declines at 40 hours per month, you’ll run out of benefit a little after 4 years right? Hah, is anything with overhaul that simple? Here’s the catch!

Simple math says if a warranty is prorated to a 2,000 hour TBO, it will pay half of an eligible repair at 1,000 hours right? Not necessarily. Most warranties say that you’re liable to pay your share at the ‘retail cost’ (which is like list-price, or MSRP) and they cover the rest. In this same example, let’s say you work with a shop that invoices you for $1,000 for a warranty repair. But, the retail cost of that repair is $2,000. In this case, you’ll be paying the entire bill because your warranty says you have to pay half the ‘retail’ repair cost before the shop or factory contributes. To summarize, pro-rata warranties with ‘retail cost’ in the wording may only useful for about half their life because it’s not uncommon for a shop to discount work by 50% of the ‘retail cost’.

Before I leave you with that dim picture of the prorated period, it’s important to point out again that most good shops will extend themselves beyond the writing in their warranty. If you ask nicely, you might be able to get a shop to cover half of the actual cost of the repair and not hold you to the ‘retail cost’ sharing program.

I heard a not-so-funny story about an independent mechanic who put a lifetime warranty on a part that broke 7 years later. The aircraft owner calls him up and the mechanic says his wife came down with cancer. Well, the warranty was null and void right there.

I’m not saying that an independent’s warranty is less reliable than a big shop. I remember buying a $250 3 year warranty on a laptop I bought from Circuit City in 2007. We all know how that story ended. Anyway, the point is obvious – you should evaluate the likelihood of the warrantor to cover costs throughout the length of the warranty.

Here are some things to consider with that:

  • Does the shop have a good history of covering warranty problems?
  • If the shop owner is retiring soon, what is the succession plan?
  • Does the shop carry product liability insurance to protect themselves against lawsuit?
  • Does the business appear to be flourishing, or really slow?

This benefit is kind of a half-truth, but worth pointing out. If you do your overhaul with a shop close to where you’re based, they will most likely end up doing most of the warranty work themselves. They can be more flexible and cover more when they don’t have to pay another shop to do it. Shops cringe when they have to pay another mechanic or shop book rate for services they can do in house. They’d probably rather send a mechanic to your field to handle your issue if you’re a reasonable distance away.

But why is it a half truth? A couple of reasons:

  • I’d take a quality shop over an average local shop because the point is not have warranty issues to begin with.
  • Whether shops like it or not, they may be contractually obligated to pay another shop to do eligible warranty repairs.
  • If your engine is having trouble, are you going to fly it to the local shop, or get it repaired where it sits? Sure, you might be able to get a ferry permit from the FSDO to take it to your local guy, but do you feel comfortable flying it? Is he going to drive to you if he’s busy?

To summarize, the local shop benefit might apply to the small percentage of eligible repairs that occur during the warranty period and can take advantage of proximity. So, the local warranty advantage is not larger than the advantage of getting a quality overhaul.

PS: Here’s some advice on making the most of your warranty. Always try to talk to your shop about any problems you’re having and get their guidance on how to handle it first. They are more likely to pay for something they advised to be done rather than find out after the fact from another mechanic when a bill is already on the table.

Alternatives to Overhaul and Factory Engines

If you’re on a tight budget, buying a used engine might be a good way to save money. Most of them come with engine logbooks so you know their history. Some of these used engines are prop strikes that are only a few hours old. Many used engine sellers will put a 30 day warranty on them. But remember, removal and reinstallation is a big expense (up to $6k) so a good deal on a half-timed engine might not be as good of a deal if you add in that cost.

Buying a used engine after yours runs out is more common with turbines than piston engines.

This is a real hot topic and there’s two schools of thought on it. You understand I’m biased in the matter for obvious reasons but here’s my best shot at giving you unadulterated info to make a decision.

Flying past TBO is considered safe by many. According to engine shops, some engines are more likely to last longer than others with some flying 4,000 hours without major repair. There’s a lot of discussion about whether TBO recommendations are necessary or arbitrary.  Some pilots have received advice from mechanics to continue flying until they experience excessive oil consumption or metal fragments after an oil change. If you’re not checking for metal fragments, you better start – especially if you subscribe to this school of thought.

If you want to join the crowd flying past TBO, consider the following:

  1. You are intentionally going against your recommended maintenance schedule. If you have an incident or accident, any prosecuting attorney will capitalize on this as ‘negligence’. It’s potentially a huge liability. Here’s an example of the NTSB faulting an aircraft owner for not complying with his recommended overhaul schedule. If this pilot had hurt anything other than marsh land, he would have been toast in court. Which brings me to the next point.
  2. Will your insurance policy cover an operation that doesn’t follow recommended maintenance procedures? You may not want to ask your agent…
  3. Are you going to find a shop to sign off your annual inspection if your engine is past TBO? There’s a lot of shops that won’t for liability reasons.
  4. How would you feel if something happened? Was you decision based on money, or did you really feel it was safe?

I see a lot of people who subscribe to the Mike Busch point of view that engines should be overhauled on condition, not on time. There might be some validity to this, but we have to consider Mike’s bias in the matter the same way we considered mine. He owns Savvy Aircraft Maintenance which collects $500-1000/year from aircraft owners and then offsets that cost mainly by deferring maintenance. So if there was evidence out there which proved that it wasn’t safe to fly past TBO, he’d be the last to find it. I’ve seen other expert opinions that contradict his points of view, but Mike’s are by far more popular. After all, your wallet is motivated to believe him.

There’s no evidence to prove definitively that flying past TBO is safe or unsafe. But we know a couple of things for sure:

  1. The liability is a real risk
  2. Some insurance policies don’t cover operation past TBO
  3. Some mechanics won’t sign an annual past TBO
  4. Engines don’t last forever and the longer you fly, the less likely you’ll be able to reuse expensive parts like a crankcase. This could eat any savings
  5. Overhauling your engine adds value to the plane and can be financed in many cases
  6. Some engines are more likely than others to run longer past TBO


It is possible to get your engine overhaul or factory engine financed. The biggest stipulation is that your aircraft is either owned outright or can be refinanced with a favorable debt to equity ratio. No finance company in aviation will be in 2nd position on the loan.

There are four main companies that do financing:

  1. NAFCO
  2. Van Bortel
  3. Dorr Aviation
  4. Air Fleet Capital

The last I checked in early 2015, interest rates were between 5-8%. But we know those can fluctuate daily.

About the Shop

Is the shop an FAA Certified Repair Station? FAA certification increases cost and requires checks and balances. Some non-certified shops still comply with standards but don’t want the hassle or the liability. Generally, FAA certified shops have better record keeping and are more likely to comply with SB’s than non-certified shops.

Are all employees A&P’s? Most shops don’t have all certified mechanics.

How many employees does the shop have? 3-5 is a typical size of a piston overhaul shop. But it ranges from 1 to 50+

What’s the average experience level of the employees? Ask them about their most senior and junior employees. The best shops have most employees with 15+ years experience and very low turnover.

Are the employees subject to random drug testing?

Does the shop carry product liability insurance? This is not ‘hangar-keepers’ insurance. It’s worse case scenario liability coverage. Only big shops can afford these policies which often top 6 figures annually.

How many engines do they do a year? 60 engines per year is what an average piston overhaul shop puts out. Only a handful do more than 200/yr

What goes into the engine?

Do they use all factory genuine parts or do they save money with PMA (non-factory) parts? Most shops will use some PMA parts. You might be able to specify what you want.

Does the overhaul NOT include anything that the shop would recommend you have done? Discuss these components with this question: Prop Governor, Oil Cooler, Alternator, New Camshaft, and Turbocharger.

Do they comply with all AD’s and SB’s? Quality shops will tell you they comply with both. Some shops only comply with AD’s to save money.

Shop Processes

What processes does the shop outsource? Most shops do all engine processes in-house except crank and case repair. Accessories are often sent out.

How does the shop test the engine? Most put the engine on a dyno. Some have million dollar machines and a few will test fly them. Ask them if they put a ‘thrust load’ on the bearings during testing.

Does the shop offer any special processes, STC’s, or upgrades? Are there any that they would recommend considering for your specific model?

Do they balance the engine? Dynamic, Static, or both? Continental and Lycoming don’t balance either way. They consider 20 gram spreads statically balanced. Quality shops take their parts and improve them with balancing.


Is the overhaul subject to sales tax? On parts, labor, or BOTH?

What makes the shop different from other engine shops? This is my favorite question.


See “Hidden Costs” above – #5.

Turbine Overhaul

The Process


Once you decide on a turbine overhaul shop for your engine, it’s time to arrange delivery of the engine. A lot of overhaul shops like to have you fly the aircraft to them so they can do the removal and reinstallation on site. This way the shop knows that it’s going to done correctly and won’t have to worry about problems that sometimes come up when an outside vendor does the reinstall job and the engine doesn’t perform because of something they did or didn’t do on site. Shops hate those headaches.

But, the truth is, most engines get shipped to turbine overhaul shops mounted inside specially designed crates. Many shops will ship the crate to aircraft where you’ll need to find someone who can remove the engine. This is a very labor-intensive process and will costs thousands so your local FBO or shop will be happy to quote it. J

When the engine is finally ready to go, the logbook is sent also. But before you hand UPS or Fed Ex your logbook, be sure to make photo or electronic copies of it just in case it gets lost. My recommendation is to put an electronic copy in cloud storage like Dropbox. You do not want missing logbook problems – trust me. Also, make sure that everything is insured in transit.


Once the shop receives the engine, they will crack open the crate and lift the engine onto a wheeled engine mount. Then the shop will insert your engine’s documentation into a clear plastic sleeve attached to the engine mount. So exciting ‘arrival’ deserves its own section right? Stay with me…

Preliminary Inspection

Before any disassembly takes place, an inspector will take a look at the engine and accessories for any obvious problems such as fluid leaks, corrosion, or damage from Ace Ventura delivering the engine. After the inspection is done, the engine will be drained of all its fluids while on the rack.


At this stage the engine gets taken apart piece by piece and put onto a wheeled multi-level cart. While removing each piece the technician will once again check for any obvious anomalies.


Practically every part on turbine will need some sort of cleaning to get inspected. For this, shops have variety of methods like dunking parts into an agitated chemical soak (looks like a deep fryer), ultrasonic cleaning, and blasting the parts with grit which can be sand, glass, or plastic. Many of the blasting machines look like those chambers scientists use where you insert your hands inside the gloves which dangle inside the glass chamber.

Once everything is clean, and back on the multi-leveled cart, it’s ready for inspection.


The inspection station of any shop is always the cleanest and it’s where you find employees with the most experience, often a gray haired guy 20+ years of knowledge. In this section you’ll find an array of measuring instruments like precision calipers and computerized equipment that the tech will use to see if it matches up to the tolerances in the overhaul manual.

The spinning blades are the most critical part of the inspection. They are precision parts that have to spin in the housing within a hair’s width and be perfectly balanced. The tech will check these for any deformation, corrosion, pitting, or deterioration.

Another area of interest is the dye penetrant section. This is a darkened room where techs sprinkle powder over a part and then use a UV light to see if the glowing powder highlights any cracks or anomalies that would otherwise be missed by the naked eye.

My favorite machine in the compressor inspection process. Each of the compressors will be mounted to this machine and the computer will test the efficiency of the blades by driving a prescribed amount of air through them at a specified velocity. The computer will let the tech know if there are any air handling issues like blade deformation.

Lastly, there’s a fuel flow machine that checks for proper regulation, volume, and spray patterns.

Firming Up the Quote

At the end of the inspection, the shop will have a list of what parts can be reused, reworked, and which ones need to be replaced. The shop will send list of these parts and their recommended course of action. At this point, the customer will have a firm quote that should not change after it’s approved.  Yes, finally you get to know what it costs.

Some shops can get to this point in a few days. Others take weeks.


There will be parts that don’t meet tolerances but can be machined, grinded, plated, etc. to get back into tolerances. Shops are going to call this ‘rework’ and often it’s cheaper than going after replacement parts. Some rework can be done at the shop, and other components have to be sent out to specialty shops with plasma sprayers, lasers, and computer assisted grinding and drilling machines. Many small shops just can’t justify the extreme costs of these machines. So the shop has to do a bit of coordinating to make sure everything gets shipped back in time.

Replacement parts

I’m not going elaborate too much on replacement parts here because this is so significant it deserves a section of its own. But the customer and the shop will have decided on one of 3 options for each replacement part:

  1. Factory New
  2. PMA (non-factory, generic)
  3. Overhauled

These parts will be ordered after the quote is finalized and they will join the cart of engine parts when they arrive. It’s also worth noting that overhaul manuals will specify that some parts have to be replaced new like gaskets. So the owners choice will be limited in their choice to just Factory or PMA.


At this stage, the shop has all of the parts on a cart and will put it all back together piece by piece on the rolling engine mount we talked about earlier. This is another area of the shop with the most experienced techs. Everything must be assembled in order and torqued to factory specs. Usually there’s a two part process where one person does a task and then another checks that the task was done and notates it on the paperwork to prevent missing anything.

Once assembled, the engine gets wheeled over to the test cell assuming the shop has one in house. You’d be surprised how many shops don’t have their own test cell. For example, I quoted 7 PT6T independent overhaul shops and only 3 had their own test cell. The others ship the engine to one of those 3. That doesn’t necessarily mean a shop without a test cell doesn’t know what they are doing. It’s solely a matter of cost justification.


In the test cell, the engine is mounted and hooked up to a variety of engine monitors, fuel and oil lines. There’s usually some kind of metal surrounding to protect the tech from a worst case scenario of parts flying off the engine.

The tech here will run the engine through a variety of RPM’s and loads to make sure all parameters meet specs. If it doesn’t, the engine is wheeled back to remedy whatever didn’t pass. If everything checks out, the engine is moved to a holding area where everything will be reviewed by quality assurance personnel.

If quality assurance signs off on everything, it’s ready to be put back in the crate and shipped back.


Most shops won’t ship the engine back until the remaining balance is paid. Only big shops can afford to do this and usually it’s only with other big companies. So after the invoice is settled or a PO generated, the engine is mounted back in the crate with enough lubricant to protect parts from corrosion and it’s shipped out. It might not be a surprise to you that the return shipping is typically more expensive than sending it in. Why? You’ll need to insure a higher value.