A diesel generator runs at max BMEP all the time, for decades
Yes but they are built like a Russian tank and are water cooled so CHT is not a problem.
I don't think BMEP alone is a problem. There is no stress failure mode in steel cranks and steel conrods so long as they are run well below their elastic limit (or whatever it is called). That is not true for aluminium, I think.
It is the stress on the thin cylinders which are made from aluminium, combined with a CHT which softens the aluminium. This is OK for a brief time (departing from some airport in say Greece in +35C, I can't avoid a 420F CHT for a minute or two, because obviously the CHT must track the OAT) but if you do it on every flight then ...
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.
If they can demo a 2000hr TBO they are welcome to it 
But they will never have to. The Lyco engines need to demonstrate a bench run of something like 150hrs, of which only some is at max power. One US engine shop which has done initial cert testing explained this to me when I was there, and I was amazed that so little dyno time is required to be demonstrated.
So it is only many years in widespread service that can actually prove a likely 2000hr TBO.
It is the stress on the thin cylinders which are made from aluminium, combined with a CHT which softens the aluminium.
The mindset has changed a bit. Cylinders are considered to be consumables and little to no work is done to cylinders these days. They get thrown away and replaced. There are multiple manufacturers of cylinders and they aren't that expensive.
For a P210 with a 325hp TSIO-520 in a super tight package, 850h is apparently a good number for a cylinder. I've watched the shop replace a bank of 3. Everything was accomplished in a single day.
departing from some airport in say Greece in +35C, I can't avoid a 420F CHT for a minute or two, because obviously the CHT must track the OAT
I was surprised how much influence OAT has. My limit is 380F (alert) and I take every measure short of CFIT to keep it under 400F. Usually this is no problem (huge cowl flaps) but these days it is remarkably difficult, no way I can climb at Vy and 75% BHP in cruise requires cowl flaps open.
If they can demo a 2000hr TBO they are welcome to it
It looks credible to me. The SMA engine is extremely sturdy. They got the 2000h TBO right away which probably means something. Also it's been around for a number of years now and most owners speak highly of it.
For a P210 with a 325hp TSIO-520 in a super tight package, 850h is apparently a good number for a cylinder. I've watched the shop replace a bank of 3. Everything was accomplished in a single day.
If you call that a "mindset change" then you should go into Marketing 
Obviously it depends on where you are when the, ahem, crack, appears... If you are say here that may not be so good.
Obviously it depends on where you are when the, ahem, crack, appear
The idea behind retiring the cylinders at 850h is to avoid these cracks. There are now good techniques to determine cylinder health and given that they are not that expensive or difficult to replace, many owners prefer to replace them rather sooner than later.
I think prices for cylinders have gone down in the last years which is why they are more considered to be consumables today. There were times where people installed oversize piston rings to improve compression on worn out cylinders but that's not necessary anymore.
They got the 2000h TBO right away which probably means something.
The way I heard it: The original SMA engine has been on the market since 2002 & apparently there's several flying in France with > 2000 hrs on the Hobbs (presumably on STC'd C182's). That's the main reason SMA got 2000 hr TBO straight away on the 2nd gen SMA...
The mindset has changed a bit. Cylinders are considered to be consumables and little to no work is done to cylinders these days. They get thrown away and replaced. There are multiple manufacturers of cylinders and they aren't that expensive. For a P210 with a 325hp TSIO-520 in a super tight package, 850h is apparently a good number for a cylinder. I've watched the shop replace a bank of 3. Everything was accomplished in a single day.
850 hrs TTIS might be a good operational life to avoid cracks on a TSIO-520 turbo Continental, but the average (say) Lycoming O-320, of which there are a whole lot more in the world, will probably never crack a cylinder head, full stop. Specific knowledge is required to assess whether cracks will ever occur on a given engine and installation. Cracking is not the driver for cylinder replacement with all engines.
It is perfectly reasonable practice to overhaul the cylinders on many engines, but the cost of new ones has come down dramatically, so now its field labor saving that's the driver, and time saving if its a quickie top overhaul with the rest of the engine still in the aircraft. On the other hand, if the owner has facilities to overhaul them, the cylinder can be bored oversize (if required) and valves, pistons, rings, guides, rockers etc can be replaced bringing the cylinder within new manufacture mechanical wear limits. The parts are usually not too expensive. In the old days cracks used to be welded up too, without particular issue, but that is not frequently done on common engines since cylinder prices have come down.
Cylinders are of course not aluminum, they are steel, but they are screwed into the aluminum cylinder heads at manufacture and never in general ever disassembled again.
but the cost of new ones has come down dramatically, so now its field labor saving that's the driver, and time saving if its a quickie top overhaul with the rest of the engine still in the aircraft
Until, the owner realises he needs to fly at 75% + power, well ROP, for the first 50 hrs or whatever it takes for oil consumption to stabilise, burning maybe 30%-50% more juice than he should be burning...
The cost of that procedure is a few k in extra avgas, which is not insignificant.
I did that in 2008, following the crank swap job.
It actually took closer to 100hrs for all six cylinders to bed in properly.
In a non-turbo engine one also cannot do any high altitude IFR flights during that time, because one cannot achieve enough power at altitude. Basically you write off all IFR for maybe 50hrs, while you go boring around the local burger runs at a few k feet, burning as much juice as you can.
So I am not keen on a cylinder life of 850hrs - even if the cylinders were £10 each.
850 hrs TTIS might be a good operational life to avoid cracks on a TSIO-520 turbo Continental, but the average (say) Lycoming O-320, of which there are a whole lot more in the world, will probably never crack a cylinder head, full stop
I bet they do. We had a Continental C-85 crack a cylinder head (it was discovered after sending the cylinder off to get a new spark plug hole put in after the original brass one stripped, the shop did a dye penetrant test before doing anything more and found it).
I have both an O-320 and an A-65 Continental - you're right that the little Continentals crack heads. The 4 cylinder Lycomings don't crack heads with anywhere near the same frequency.
Looking at it from another perspective, the world is seemingly filled with uncracked, used A-65, C-85, and O-200 cylinders. A friend of mine has about 25 he's collected. People replace them in sets when one is cracked... and if you're a cheapskate (as he is :-) you can overhaul the others and use them when needed, which is fine for a piddle-dinking around airplane like the one he's been regularly flying since 1976 without engine failure. He's probably got enough to last him the rest of his lifetime, and an A&P certificate to replace them when needed.
This thread is actually very useful in drawing out background to describe the 'hill' that diesel engine manufacturers face when introducing new engines. Putting aside the product's complexity, they also have to compete with 60 years of business development, with competitive engine parts and services available from many vendors, supporting every owner's philosophy and situation. That saves people money and they aren't dumb, they understand it. Its been my observation that European manufacturers aren't so likely to understand that value in their competitors products, instead starting out with the view of themselves as a (self-pronounced) monopoly. That POV doesn't sell well to the aircraft market, but I think that might actually be the biggest problem they face.
Peter - if you have any Lycoming cylinder problems prior to major overhaul, I think you might rework only the cylinder that has the problem. Then replace them all at overhaul someday.
That saves people money and they aren't dumb, they understand it. Its been my observation that European manufacturers aren't so likely to understand that value in their competitors products, instead starting out with the view of themselves as a (self-pronounced) monopoly.
I am certain that the aspect in which Europe differs from the USA is that there is FAR (no pun intended) less expertise over here.
This applies to every aspect but especially mechanical parts, where a certain amount of skills and experience is needed, whereas avionics is easier because the design process is much simpler and the installation is a load of hole cutting, wiring and connector crimping...
I know a TIO-540 owner whose plane was grounded for 6 months because the main dealer didn't know how to adjust the turbo wastegate.
Most people who have serious money and buy nice hardware just drop it off at their dealer for each service. Of the SEP population, SR22 owners are perhaps the best example of this way of "maintenance management", and the dealers have a nice captive market which some, shall we say, make the best of, and the owners don't mind, or don't notice. Diamond owners, perhaps a bit less so.
But basically the big money in light GA is mostly found where the punters don't want to get too involved.
And if you (the owner) doesn't want to get too involved, the industry will never have any incentive to evolve solutions for people who do give a damn.
There are far more tech anoraks in America, and with the internet, and warts-and-all mags like Aviation Consumer it is very hard to pull wool over peoples' eyes.
We have very far proper tech anoraks in Europe... most of them are on EuroGA
But I don't think this is the biggest issue, which is that an engine going for say €90k is just too pricey - unless your mission profile is a 500hr/year FTO, or you spend your life flying between Greek islands excluding Crete, Corfu, or Samos.
Peter - if you have any Lycoming cylinder problems prior to major overhaul, I think you might rework only the cylinder that has the problem. Then replace them all at overhaul someday.
Sure, but you still have to bed the piston rings in the same way - whether you have to bed in rings on 1 cylinder, or all 6. Otherwise, you end up with a glazed pot, crap compression, and a 1 litre/hr oil consumption...
