The engine overhaul I described will be good for TBO before it needs more work. The owner of the aircraft is an A&P and is the guy physically doing the overhaul. Everything internal was done to new limits... by an airboat machine shop :-) Interestingly enough, this shop does a lot more volume than aircraft machine shops also working on 540s and the like, has better equipment and is known to produce better quality results.
That said, the costs were also held down in this instance because the owner was lucky to get one of the discounted Lycoming crank replacement kits some time ago and held it until he was ready to overhaul the engine. He has many, many years of experience - his main business is designing, building and selling OEM parts and equipment for new production and kit aircraft. This was not a retail overhaul, it was how you do it when you know how to save money.
Peter - no, its not mandatory to replace cylinders at overhaul, only to overhaul them. Until about 15 years ago you couldn't buy new cylinders at reasonable cost and a cylinder overhaul shop was a lucrative business. That went away when everybody and their brother started selling relatively inexpensive new approved cylinders and now a lot of people can't be bothered overhauling them.
If you want to look at the legal angle as a separate issue, for an FAA regulated aircraft an operation described as an overhaul in the engine logbook must involve disassembly, inspection to ensure all components are within wear limits and thereby airworthy, and reassembly. Nothing more than that, or alternately it can be a lot more than that. All work can be done by any certificated A&P mechanic, and machine work can be done by anybody as long as the responsible A&P supervises and signs off on the work as airworthy. When its done in that fashion, its a 'field overhaul' but there is nothing that prevents a field overhaul from being completely to new limits or better.
Welcome to the world of US private aviation, as done by people with the skills, facilities and friends to do it that way ;-). Its not conceiving of such a thing that makes the business cases produced by diesel engine developers and their like fall flat on their face when exposed to the real world aviation business. The US customer base may not choose to take reducing costs as far as my friend, but OTOH they aren't basing their decisions on paying retail either.
Thielert had a very attractive model with fixed maintenance costs but they did not anticipate the kind of technical problems they would face in the field.
Thielert would have gone bust anyway, because no pricing model would have covered their technical issues so even if they managed to survive by shafting customers nobody would have bought anything from them afterwards - not least because most of their former customers would have no longer existed.
Their "laser printer sales invoices" childish-sophistication accounting fraud merely lubricated the process 
At the bottom of the crisis I saw a DA42 for £80k, and it would not have been a very old one... Anybody who bought that got a snip, but it was a bet on the engines getting sorted, because without an engine solution a DA42 is worth absolutely zero... maybe the avionics might be worth a few k.
I still like the idea of outlawing avgas, that would bring some innovation to the market.
You seriously think that? You would be happy to be grounded for say 10 years? If that happened, there would be no market existing to buy any engine, even if it ran on seawater.
The engine is a standard NA engine with reasonable overhaul costs and the turbo is separate
So, to OH your engine, you remove the turbo first and optionally OH it separately? That's interesting. That makes a huge case for aftermarket turbos.
I think most turbo-normalised engines don't make TBO (even though there is no extra power being generated) because people fly them "as they are supposed to fly them" i.e. full power all the way to top of climb. That is bound to hammer the engine more than the gradual loss of power in climb which you have in a NA engine, which is a hassle for the pilot but great for the engine
Years ago, I believe somebody asked Tornado Alley about a turbo for the TB20 and they wanted something like $200k for the STC, so it was a case of getting a lot of pilots to buy into it. It never happened, of course.
Yes but Thielert would have gone bust anyway, because no pricing model would have covered their technical issues so even if they managed to survive by shafting customers nobody would have bought anything from them afterwards.
Well, they made a bad judgement on the clutch/gearbox but they were not the first one. Porsche had to gift all customers a new lightweight 3-blade prop because the old props would beat the gearboxes to death. Apart from that, Thielert developed a good engine and the company has been profitable for several years now. In many ways, the Centurion 2.0S is superior to the Austro. Thielert's technical mistake was of the same category as Lyco's cheapo crankshafts that would break and which were paid for by customers.
Their "laser printer sales invoices" childish-sophistication accounting fraud merely lubricated the process
You keep coming back to those allegations but you can't substantiate them. There have been no criminal proceedings against Thielert or its principals. Therefore one has to assume that there was no fraud or anything like that. Today, Thielert is in business with the US military and others and as I said, the company has been profitable for several years (they are under insolvency administration which makes it impossible to accrue losses).
So, to OH your engine, you remove the turbo first and optionally OH it separately? That's interesting. That makes a huge case for aftermarket turbos.
Yes, exactly. The turbo typically does not make the 2000h TBO but it is not that expensive to overhaul. Good shops will know how to maintain it for maximum life, e.g. scrape off deposits with a knife every 50h, spray mouse-milk on the wastegate, etc.
About the market for aftermarket turbos. Well, it is hard to add to an airframe that wasn't designed for it because it needs space and a completely different exhaust system as well as modifications to the fuel system (a big difference if you can make 75% bhp at FL200 vs 40% bhp at FL180). Then you need to be able to show that the engine works fine with it. That is probably too much for an aftermarket 3rd party.
I think most turbo-normalised engines don't make TBO
Do you have examples? Turbo normalization is rare in GA. One drawback is that turbo engines usually have some improvements to handle the higher-than-ambient pressure in the intake and the back-pressure in the exhaust whereas the aftermarket turbos don't have that. In my example, the exhaust pipes are attached to the cylinders with two bolts whereas the turbo Lycos use 3 bolts. This is a weakness and requires replacing the gaskets every now and then (but they are cheap and it's an easy job).
My theory about why turbo normalization is so rare is that airplane makers always need as much power they can get to sell their aircraft. Extra HP through turbo charging is much easier to sell than no extra power through turbo normalization even though the customer might be better off with TN. Cirrus developed the SR22TN because Conti did not offer a turbo engine, Cessna did the TR182 because they didn't have time to adjust the airframe to fuel injection (took until 1996).
Looking at the TB20, in my view the TB21 is a rather bad airplane. If Socata had come up with a TB20TN, this would have been a killer. My draggy airframe makes 175KTAS at FL200, the TB20TN could do at least 185KTAS with lower fuel flow. They might still be in the SEP business because the TB20TN could actually compete with the Cirrus...
Rumors on the DiamondAviators board say that Thielert/Centurion has been sold to a major US aircraft engine manufacturer and the sale will be made public sometime this week.
May be just a rumor, but interesting nevertheless. I'm guessing Lycoming.
Without getting too specific, I know that a different US company looked seriously at buying Thielert as an engine supplier and did not do so. That would not be the same deal as is now rumored, but substantiates in my mind that the company has been very much for sale.
I understand Frank Thielert was jailed in June.
I understand Frank Thielert was jailed in June.
Right, I missed that. Took them a long time to build a case and from what I could find evidence is not that clear. It's the typical stock market thing: fake revenue to make the company look better. I was in the middle of the dotcom bubble as a software entrepreneur and I have seen first hand that faking revenue was more the rule than the exception. There are barely legal ways to do it, outright illegal ways and a lot of in between where the courts have a hard time coming to a conclusion.
Keep in mind that Frank Thielert has won his first lawsuit against his investor and the bank.
That would not be the same deal as is now rumored, but substantiates in my mind that the company has been very much for sale.
Hehe, of course, that is the job of an insolvency administrator. The reason it is taking so long is because the company is profitable to there is no limit to insolvency administration. The moment it loses money, it has to be closed down or sold off to whoever makes a bid. The administrator is committed to closing a good deal so he keeps on running the company. What makes it harder is that Thielert is an important supplier to the military so there are strings attached.
The TB21 is turbo normalised to 250HP.
Apart from some fiddly adjustments and an apparent near-total lack of turbo expertise in the UK, owners have reported that turbo to be generally trouble free.
Most TB21 owners I know have not reached 2000hrs without cylinder changes. Whether you call that "not making TBO" is a matter of opinion I vaguely recall that was one of the (many) things which led to me getting kicked out of the Socata owners' site, back in 2008 
Technically, anything that is not an "overhaul" is not an "overhaul", of course
The reason for the TB20+turbo enquiry was that there is no Socata-sponsored modification for adding the TB21 engine to a TB20. Why not? Completely stupid; it would be trivial. The two planes are identical except for the engine etc, and some trivia in the cockpit e.g. the EDM700 is no longer allowed to be the primary (only) CHT gauge. But maybe there is a big paperwork reason, and obviously Socata wanted to sell the TB21 at, at the time, some €80k extra.
@Silvaire .. What your friend did is not considered an overhaul that leads to a new 0 hrs. At best you can call it a top overhaul.. offcourse this can prolong the life of the engine but it is not a full overhaul.
@peter The main reason for tio540 not reaching tbo is offcourse enginemanagement. A turbo engine runs a lot hotter. Especially with lousy cooling designs like on the commander tc.working with old and usually useless enginemonitors certainly does not help. running lop is generally advised as a very bad idea + most pilots do not know how to manage their engine properly..
I do think that we should stop comparing Thielert with SMA. thielert went out there and made everybody enthusiastic with a modified car engine with gearbox. when their commercial model failed it was seen as A "I told you"".
Sma is designed as a true aiviation engine. It is their second gen .. The problem is weight, price and performance. Converting will only make sense on the more powerfull aircraft .. And at tbo.
50k for a TIO overhaul or a bit more (and offcourse not the artificial 90k price) and it suddenly makes a hell of a lot of sense. second hand value will also increase!
Can the SMA engine be considered fully working and problem-free?
I have not followed it so I don't know. There seems to be very little field feedback on it.
running lop is generally advised as a very bad idea
You just knew you were going to start a whole new thread there
most pilots do not know how to manage their engine properly..
I am sure that is true statistically, and definitely historically, once one gets away from pilots who participate in internet forums.
It is used by PA46 owners to dismiss the appalling engine "problem rate" (most were not sudden and total stoppages but nevertheless stuff that required some urgent action) reported in the pilot communities - of the order of 10% suffering failures.
But even pilots I know who have an EDM700 etc don't usually reach TBO without at least cylinder work, on TIO engines. This forum is read by about 500 people daily and I know many TIO owners read it, so they can say if they make 2000hrs.
An IO540 runs at max BMEP and max CHT for only tens of seconds. A climb to FL150 might take 30 mins (can be done quicker but there isn't any point) and the BMEP decays linearly to c. 50% of the takeoff maximum. The CHT also drops rapidly away from the c. 400F value considered to be the safe maximum.
But a TIO540 runs at max BMEP and max CHT for say 15 mins (a climb to FL150) which places it at max stress for (of the order of) 10x longer.
These engines are not exactly over-engineered so on the basis of the IO540 supposedly making only 2000hrs plus a bit extra, something has got to give when you push things that far.
I guess if you climbed the TIO540 at +500fpm instead of +1000fpm (say, an IAS of 130kt rather than 110kt) it would be a lot cooler, but very few pilots are going to do that if they paid all that money for the capability - notwithstanding the fact that the fuel burn to cover a given distance is going to be very similar.
But a TIO540 runs at max BMEP and max CHT for say 15 mins (a climb to FL150) which places it at max stress for (of the order of) 10x longer.
The question is whether max BMEP means a lot of stress to the engine or not. A diesel generator runs at max BMEP all the time, for decades. A motorcycle engine is toast in no time if you get near max BMEP for more than a few minutes...
I think the reason is that airframe makers tend to put the engine with the maximum BHP they can get so they can show good numbers. This tends to favor over-stressed engines.
The turbocharged O-540 in the TR182 is flatrated to 235hp (31"MP and a lowly 2400RPM) which I think is why it is generally considered to last 2000h and beyond. Cessna did this because the goal of the project was to replace the lower camshaft Conti O-470 with a top camshaft Lyco model so they gain space for the nose gear. Later they just added a turbocharger to the existing design, had to be quick and simple. If they had had more time for this design, they would have probably chosen a different engine setup so they get more BHP for the size/weight. Luckily they didn't do it...
The SMA engine is designed to operate at 100% BMEP all the time. They recommend setting full power for takeoff and leaving that until top of descent.
