Area-51

The pistons/barrels were not removed; just a decoke sufficient enough on this occasion. Wouldn't do a piston crown polish insitu; too much grit going into the ring lands.

Yes, sugar soap is alkaline, sodium carbonate. It rips the carbon deposits off pretty quick. Pulled the test piston out of the acid bucket this morning. It did not clean off the carbon as well as the sugar soap, and did not dull the metal. Below are the test pieces. Right to left, acid 24hr, sugar soap 1hr, sugar soap 2hr. And a couple of pics showing colouration between 24hr acid and 2hr sugar soap.

Today has been a day of discovery and success while cleaning piston crowns on the 914. After reading MSDS sheets on various you-beaut metal cleaning products off I went to the magic shed cupboard. Pistons from the scrap 912 80hp were used to test some science. One was thrown in a bucket of Selleys sugar soap (oven cleaner), the other in a bucket of nanoic acid (herbicide). After 15 minutes the sugar soap had softened the varnish which could be wiped off with a rag. After 30 minutes more varnish came off with a tooth brush; and after an hour most all varnish was vanquished, and the metal was just beginning to dull a bit. After two hours the piston was stripped fairly clean and the metal had not dulled that much in total. The second piston is still sitting in the nanoic acid at the end of the day without much change at all. Then it was time to clean piston crowns. First a plastic scraper was tried and was all but useless at scraping off carbon. Then a piece of ebony was used, and was all but useless. Then a brass brush was tried which left scratch marks. Then a piece of 1.75mm aluminium sheet was tried. It worked great and left no scratch marks! Then a piece of broken piston skirt was tried and it worked even better, and left no scratch marks because it was the same hardness and material as the piston crown... After nearly 50years I just discovered this today; amazing... With all the wonder of discovery the piston crowns on the 914 all got cleaned as well as they could in the afternoon by first scraping the carbon off with the bit of skirt followed by a 15 minute soak of sugar soap and a flush out with carbi clean and Rostoff, followed by roll over until no more gunk flowed out of the ring lands, then a finishing off of engine oil. The carbon on the top of the bores came off easy after a scrape with the piece of skirt and some light wiping with grey scotch brite soaked in sugar soap. Ready for reassembly...

Thanks, will do some research on that one... I think we are done here on this. thanks for everyone's input; some useful applied knowledge to refer to...

The turbo unit is in as new condition and free of compressor binding... If I knew these engines as well as I know others I would now use them without concern. But I don't have enough time on these things to know their practical limitations. Will still put set of standard valves in to tick the box; about $550 a valve. The engine is being built for reliability and distance work. Old ones can get polished and put into a lesser 80hp scavenger rebuild test pig unit.

After realising yesterday the valve head crazing was deposition, out of interest today I took to some old skills and decided to see if the deposition could be removed.

Rotax have been using sodium valves since 2018 in all their turbocharged engines, the 914, 915, and 916 all use the same part number. Besides an AD requiring replacement on one manufactured batch I have not seen any reports regarding either valve or valve guide failure with their sodium valves; and there are sure to be TBO'd engines running on condition by now in the field. The factory change to sodium was due to more extreme combustion environment in the turbo charged engines, i.e. heat affected deterioration. A 914 with an intercooler might negate this however the 915 and 916 probably not.

The valve stem is magnetic. The valve head is not magnetic.

Got the Nikon out tonight for a closer look at the rocket science; definitely corrosion right across the board... so no thermal shock as thought...image of outer valve head surface thought to be crazed but it does appear to be raised rather than pitted in this area; something bonded, something eroded... It's all just electrical plasmodium in the end!

I'm going to have to correct you on this. Contemporary high performance valves do come in a few different alloys these days along with coatings to mitigate a variety of combustion ed related badness... Maybe some water went back up the exhaust when the AC went into a ditch and caused thermal shock of the valve face (crazing) 🤷🏽‍♂️; which is puzzling to me.

Corrosion from acid is definitely plausible; there is no head gasket on the 9XX engines or water jacket in the cylinders. Other than a crack in the head itself, that leaves atmospheric vapour/humidity as the source of moisture to create sulphuric acid, or previous owner running an ethanol fuel. I found only one other similar question from 2013 regarding this valve head pitting on a 9XX; which received no responses. The engine had only 120hrs on it with a single exhaust valve displaying corrosion pitting and degradation of the face. Perhaps a valve coating issue at production? Have ordered two new standard valves. It will be good to see this engine go back together. Glad it got stripped down for inspection.

From experience another aspect of engines running water injection is the combustion chambers are clean and free of carbon deposits upon removal of the cylinder head. Maybe rust from sitting idle for extended period that burns off leaving an indentation as the hours go on?

Cheaper than a destroyed engine. Seats are good 👍

Thanks, all other aspects are within specification and condition. Will put a new set of exhaust valves in for insurance.

Thanks for the technical information there. I did not factor in the water aspect regarding pitting. Would this not display across all four cylinders though? The deposits do not scrape off; at least not with light pressure. They are resembling crows foot aspects which I would associate with thermal shock. The more I get into this engine the less I am confident it has only run for the 147hrs logged. The valve throats are consistent with normal oil ingestion from the turbo shaft seals to induction side; nothing too extreme but not what would be expected at 150hrs TT. And then there is the lifter face condition previously found to consider as well. But the exhaust system appearance is consistent with 150hrs usage. Maybe some rascal got to it and swapped out a couple of the heads at some stage; who knows. At least its getting a thorough scrutiny and attention before spinning up again.

Interested on what people may think of these two exhaust valve images? Is this possibly lead fusion from running avgas? Combustion chambers and piston crowns all present well.

Failure is not the end result; its just the pathway. Started about 25 years ago with a program called Vellum, on an old macintosh classic, and a tutorial book drawing a 2D square. The shapes progressively became more frustratingly complex. After a month the square became a 3D cube. After a year an engineering professor let me use their lab after hours to learn Catia and model an airframe. Have not stopped since. Probably have more time than a senior qantas check captain and now design complex without any limitations other than time... Modern software makes the game very accessible and intuitive now days. Players still need to put in at least 50-100hrs to start jogging a little. After about six years you might play a little Bach or Dire Straights... try SketchUp or Fusion and just do the tutorials over and over until you start making your own shapes.

After several iterations and failures the 3D printed 9XX valve compressor gizmo works great 👍

Yeah, can also just get a 6" x 2" china pneumatic machined AL ready made you beaut wheel and tube tyre for $16 off ebay. Bought two three years ago; still on the first one and the new spare sits in the stow locker. Weighs about 300g. Never had an issue with it.

A manufactured tailwheel assembly

What would you consider a fair price in AUD, and what features would you require?

Welcome to "Aviation"

Wombats are prime suspects year on year in AEE's (ASIC evasion event). Its rare for echidna to be involved in an AEE, and are generally not prosecuted due to genetical poor eyesight and nationwide standards regarding social equality and equity for those suffering from hidden disability.

Can we assume the ground staff actions were driven toward orange boy not having a current ASIC ?

The local aviation mob sat down with both CASA OAR and Air Services last week to discuss the development in more detail over several face to face meetings with individual airfield groups/clubs of the area. Hopefully information gathered from these these discussions assist in a greater enhancement of "Equity" for all users; Commercial to Recreational. As it stands the current air space design for Ballina is fairly mature; and yes, for all the reasons documented, much needed and overdue. ATC will be managed remotely, probably from Brisbane. The most recent proposal update released by CASA last week provides IFR APPROACH/STAR/SID data, Evans Head Active and Non Active; which gives the proposed air space foot print logic. And any way you look at it Commercial Op's will always take priority over GA and Recreational. A coastal VFR transit was discussed. This is still being worked out and will likely be a unique solution for GA and Recreational. Again it is being worked out; how RaAus will actually affect transit through Delta is not yet known. For Lismore flight schools its a great bonus due to proximity to Controlled Airspace training. For Murwillumbah and Ballina; waiting to hear their thoughts. For the Tyagarah CTAF area the main issues of concern are the lowering of the CLL6500 over land to CLL4500. There is a genuine safety concern mutually shared by both flying clubs at Tyagarah on several levels for VFR aircraft operating OCTA. First concern is loosing 2000' G airspace and having the same amount of traffic compressed into a thinner layer; more opportunity for mid air collision or loss of separation, and busting through the step with a higher probability of incursions occurring. Secondly terrain to the west of Tyagarah over Mt Jerusalem is 2800'. A CLL4500' leaves inadequate clearance or height to affect an emergency landing reaching a suitable field in an engine failure situation. Heading in any direction the flight will end with the aircraft landing in the trees. Not a good day. Thirdly the area of concern is a training area used by Tyagarah, Goldcoast, Murwillumbah, Archerfield. CLL4500 means flights are at 4000' max. Not enough height for a novice solo student to hopefully recover successfully from an unintentional spin. Not a good day. (please do not use this point to railroad the post into yet another endless discussion about do's and don't's about spins). The decision to affect a CLL4500 over Tyagarah is an arbitrary one. It is driven by the precept for a "standardisation of airspace between Goldcoast and Ballina". The is no ATPL or Commercial operational driver other than ATC being provided a single flat space to manage. As mentioned to CASA and Air Services during the face to face, the CLL4500 is not required and should therefore remain at its current CLL6500 for previously mentioned reasons of safety; they were previously unaware of the level of training that actually occurs within the Tyagarah CTAF area. In very simple and short terms a 2000' step reduction in the area of concern increases the chances of a fatality occurring for VFR flights OCTA. Nothing further to add.