Peter wrote:
With 78-79/80 compressions, the valves will be fine.
That just one indicator and not very meaningful. The valve guide will be worn and so will the valve stems after 800h. The valves will be weaker than new due to heat. It’s not very expensive and once the pot is off the case and a good number of hours have accumulated, it makes an awful lot of sense to replace.
No. If I was going to do stuff like that, which is not necessary (on present evidence) I would stick the engine in a box and DHL it to Barrett Precision in Oklahoma, like in 2008. I would not use any European shop.
IO540 engines routinely make TBO. It is the turbo 540 ones which usually get shagged before TBO.
Also, the logistics of hanging around in Germany for a while (it will take longer than a day or two) make it unattractive. There is no way to travel home from these places. Plus the need to bed-in newly honed bores means no IFR for a long time so I could not fly it back home IAW the correct procedures unless the weather was very good.
Peter wrote:
I would stick the engine in a box and DHL it to Barrett Precision in Oklahoma, like in 2008. I would not use any European shop.
You mean a “most reputable shop” where the engine starts to use more oil than avgas after 800h? 
I think your impression on engine shops in Europe is a bit overly negative and I have no idea where you got it from. I don’t think there is any reason a good workshop in Europe would deliver any lesser work than a good shop in the US. I’m sure the UK has at least one shop that can easily match the quality found in the US. Let’s face it: these engines have not changed in over 50 years and no single step in the whole process requires any skills that could be remotely called “high precision workmanship”.
Peter wrote:
Why would new rings require a re-hone (assuming there is no glazing)?
Very simple. After some time (definitely 800h), the barrel becomes slightly oval. If you insert new, 100% round rings, they won’t work for long, you get a lot of metal and then bad compression. The aim of the honing process is to make the barrel round again (and to remove potential scratching). You would not replace pistons and/or rings without honing the cylinder. And you would change the valves as well while at it… 
spirit49 wrote:
Why would these Conti cylinders be so tired, if most of the time its only the valves that are the culprit?
Fix the valves, and hone/new rings, and they should be as new. Or?
Well, Conti cylinders do have a history of metallurgic fatigue and fatal cylinder head / barrel separation. Much more than Lycoming. In the 300hp class they have an average lifespan of 600-800h. Therefore I would not think it’s very wise to do that type of work at a certain age of the cylinder. Get a new one with factory warranty (from Continental or a PMA manufacturer) and you can rule out fatigue.
I have no idea where you got it from.
The copious response to my Q on reputable engine shops in the southern UK (which one can fly to) might be one indicator
I am sure there are some. It’s just that, as per usual UK practice, almost everybody who has used any of them has had both types of experiences.
But my A&P has found a politics-free hangar we can work in which I can fly to and he can drive to, and we can do it there. The various gaskets need to be pre-ordered, etc.
But I will do more test flights. The oil burn is coming down; 35% drop between last two flights but still way too high. One more flight was done today so I should have another data point tomorrow. But, hey, tomorrow is Justine’s birthday, so that will have to wait
BTW, I phoned up Röder and the guy told me they communicate only in German, which makes it difficult for me. He basically made it clear they don’t want non-German business.
achimha wrote:
The aim of the honing process is to make the barrel round again (and to remove potential scratching). You would not replace pistons and/or rings without honing the cylinder.
@Achim – Please do not take this personally , but the above is technically in-correct.
Honing does not actually machine the cylinder to over-size.
Honing simply scratches the surface. It is highly recommended whenever you put new rings in to enable them to “bed-in” to the cylinders.
edit: here’s the Wiki def: Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive stone against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but may also improve the surface texture.
Peter wrote:
BTW, I phoned up Röder and the guy told me they communicate only in German, which makes it difficult for me. He basically made it clear they don’t want non-German business.
That’s strange ‘cause I’ve been on the phone with them (in English, don’t speak a word of German) almost every day for the last 2 weeks trying to sort out a serious problem on a TB21 engine with just 30 hours since they majored it …
It is actually correct that if one changes the ring(s) one has to re-hone the cylinder, otherwise the new ring(s) won’t seal properly.
However I am now investigating another possibility, to do with the breather pipe… will report in due course.
Honing is primarily used to improve the geometric form of a surface, but may also improve the surface texture
Exactly what I said, no? I guess there is agreement that installing new piston rings without honing would be wrong. Therefore I don’t see much good from the proposed jig removal with an A&P unless there’s a cylinder workshop involved.
Röder have a huge percentage of non German speaking customers. Even my Bavarian boondocks shop has at least 50% non German clientele.
I still stand by my very first recommended course of action: collect breather output to see if that’s where the oil goes. The oil seal ring as the culprit is still a very premature conclusion.
Wouldn’t a crankcase pressure test now be appropriate to decide if the oil goes out the breather?!
That would require a spare oil filler cap modified with a pitot/static fitting, with lines to a old Airspeed indicator.
Checking the AS indication on the ground vs in the air would determine if there is cylinder blow by or prop oil seal ring leakage.
I know Mike Busch wrote an article on this, and what kind of AS indication would be normal to determine the blow-by/leak. Need to search for it.
The problem on my P210 is to have access to the AS in flight without penetrating the pressure vessel……
Maybe a go pro recording the AS in flight.
Honing should have no effect on the circularity of the bore. If it was oval before it will be oval afterwards, as a newly honed surface takes up the (average) form of the original surface. That is the difference between honing and grinding/machining.
I’m not sure what this means in practice if you have a new (circular) ring running in an old (honed but still oval) bore. Presumably you still end up with a badly sealing ring. But if the cylinder is oval beyond tolerance you would replace it anyway, not hone it?
