Another Jabiru engine bites the dust

[Oscar]

For the less educated amongst us, what is the thermal expansion rate of the cylinder heads, compared with the crank case?

Um, Merv, the cylinder heads aren't held on by the through bolts.... different system..

 

 

[deadstick]

Two weeks! wow I'm impressed! explains a lot mate.... back to the books I expect! leave the certified engines to the professionals, you can't insult me! I have no respect for who you portray yourself to be! However you are a dangerous individual , purely because some poor unsuspecting person looking for advice on this site may believe your drivel and pay the consequence.

 

Motz: I'm cool, however I seem to have broken my rule not to argue with idiots! ( they will drag you down to their level then beat you with experience) lol

 

Indeed, I have rebuilt one. Under the watchful eyes, the instruction and with the help of the guys who build them all, not only showing/checking what was done but explaining all the things that matter about what was being done. With the guy who manufacturers them telling me what to do and teaching me how to do the machining and inspecting my work (and even hand-making some tools just to do my old engine to the new specifications). With the guy who measures each and every engine for production checking my work every step of the way, in a laser-measuring-equipped, temp. controlled measurement room. In the build room that every new Jabiru engine comes out of, using the tools, the benches, all the gear that every new Jabiru engine is assembled with. Following the assembly procedure from dedicated bench to dedicated bench, starting with the crankshaft and down to the electrics.Got a 'tick' from those guys. Would I suggest I can do it for a living? - NO. I learned so much from the experience of being there, I know how precise and experienced one needs to be, and I certainly know that I don't have that level of experience, nor do I have the very specialised tools for doing certain procedures correctly..

 

Not from books, little Noddy, but from DOING IT. Spent two weeks learning and doing it, making mistakes, learning from them, fixing them.

 

So suck it up, princess, and get off your own high horse.

[Oscar]

I see I have received a 'last warning'.

 

Fair enough - I don't respond well to snarky criticism that is completely incorrect in fact. I'm out of here.

 

 

[motzartmerv]

I see I have received a 'last warning'.I don't respond well to snarky criticism.

Oscar, please. You can put your views forward without insulting people.

 

 

[motzartmerv]

Um, Merv, the cylinder heads aren't held on by the through bolts.... different system..

Yes I know. Was just wondering, seeing as they are all connected, if theres a disparity in the thermal expansion qualities for the different materials.

 

I know from operating a lot of these engines how quickly the heads cool compared to the rest of the engine. Was more a question more for your relatives than it was for you. :)

 

 

[deadstick]

Motz,

 

Jabiru at one stage a long time ago advised of differing expansion rates between the heads the cylinder barrels and the Case, and mandated an extended warm up period.

 

 

[motzartmerv]

Yes I recall that.

 

 

[Dafydd Llewellyn]

Yes I know. Was just wondering, seeing as they are all connected, if theres a disparity in the thermal expansion qualities for the different materials.I know from operating a lot of these engines how quickly the heads cool compared to the rest of the engine. Was more a question more for your relatives than it was for you. :)

As you can see from my earlier post, the data for 5083 (which was the material in Jabiru heads for a long time) do not go above 90 degrees farenheit. The data for 6061 go to 600 degrees farenheit, which is well above the maximum permissible head temperature. These data are from MIL-Handbook-5 ("Metallic materials for aerospace vehicle structures" which is jointly published by the FAA and the U.S. Dept of defense; it can be downloaded from the net, and is the definitive document for aircraft materials). So whilst I do not fully understand your question, the data in my previous post are all I have available. Lycoming & Continental cylinder heads are a quite different alloy, BTW.

I do know that Rod Stiff started out with cast crankcases, but the rejection rate due to porosity was such that he had to abandon them; the Australian aluminium casting industry is not, it appears, capable of casting something like a Lycoming cylinder head.

 

 

[AVOCET]

I made the original patterns for the head & crankcase , and the problem wasn't the Australian ally foundries, it was, at the time cheaper to have them cast at the local aluminium balustrade place around the corner ,( at my vocalised disapproval ) .

 

they stuffed the head pattern , and their quality and ability to melt aluminium , well , that's it really ,

 

and at about the same time CNCwas coming to a place near you .

 

so ian bent got involved .

 

also at the time rod wanted to keep all the work & contracts local .

 

and at that time ,for casting heads & crank cases , you needed aluminium patterns and shell moulding technique

 

all of which were available in Melbourne , at a price$$$$$.00

 

cheers mike

 

 

[pmccarthy]

My brother has an aluminium casting business using the tilt moulding technique. He is disparaging of the quality of his Aussie competitors and imported products. But the lowest prices win contracts.

 

 

[Dafydd Llewellyn]

Interesting - has he ever tried casting 242 alloy? I suspect it needs some sort of "impact moulding" technique to be sufficiently free of porosity in an air-cooled cylinder head; the fins on a Lycoming head are pretty formidable to cast. Most Australian foundries seem to use mainly silicon eutectic alloy, which runs like water and is barely stronger than Kraft cheese, or the occasional one that can manage 601 alloy, for wheels. I had some peripheral contact with a "difficult" casting for the Laser Airborne Depth Sounder, and the best anybody could do for that was 401, which is still well short of what is needed for a cylinder head that works at Lycoming-type temperatures.

 

The wrought alloys are generally completely free from porosity, so they lend themselves well to billet machining - but that puts considerable constraint on the form of the cylinder fins. Take a good look at the finning on a Pratt & Whitney R1830, and ask your brother how one could do that.

 

However, that's not the point of this thread; the point is that it is NOT the choice of crankcase material that is the issue with the Jabiru through-bolts. There are about six contributory factors, as far as I can see, and Ian Bent has done extensive research into all of them. The Devil is in the detail, and there are a whole bunch of relevant details. Ian can explain them better than I can.

 

 

[Dafydd Llewellyn]

They're water-cooled - so an entirely different ball game to a closely-finned air-cooled head. Has ROTEC obtained a supplemental type certificate for those heads?

 

 

[facthunter]

They claim superior metal to the Jabiru heads I went to a night where a talk was given and they had piles of stuff to look at Nev

 

 

[Dafydd Llewellyn]

Nev, they could be made of unobtanium, but it cuts no ice unless they STC the engine for them.

 

 

[facthunter]

I get involved with some castings related to non aviation engine items so I'm not into the aviation matters, but I do recall some gypsy major heads being made somewhere (Albury?) Apart from Dee HAV's carrying on, I don't know how they went. I'm sure they ended up on aircraft .

 

Porosity is a problem with watercooled heads more so than aircooled heads which have a requirement for strength when hot, where they may fail outright, or undo the heat treatment process they had undergone.. Reliability is difficult with some casting situations.. That is why Jabiru used billet CNC process. Some Lycomings are forged which is exotic. You get what you pay for (if you are lucky) but you won't get GOOD stuff for peanuts. It can't be done, especially on low volume runs. Nev

 

 

[Dafydd Llewellyn]

I get involved with some castings related to non aviation engine items so I'm not into the aviation matters, but I do recall some gypsy major heads being made somewhere (Albury?) Apart from Dee HAV's carrying on, I don't know how they went. I'm sure they ended up on aircraft .Porosity is a problem with watercooled heads more so than aircooled heads which have a requirement for strength when hot, where they may fail outright, or undo the heat treatment process they had undergone.. Reliability is difficult with some casting situations.. That is why Jabiru used billet CNC process. Some Lycomings are forged which is exotic. You get what you pay for (if you are lucky) but you won't get GOOD stuff for peanuts. It can't be done, especially on low volume runs. Nev

Were they aluminium or bronze? GMH built Gipsies for the Tiger Moths used for the Empire Pilot's Training Scheme; they were early Mk 1s, I think, with bronze heads - I had one, in my Auster Mk III.

You're dead right about small production runs; CNC is much easier from a QA standpoint. Porosity is a major problem for any kind of cylinder head.

 

 

[gandalph]

I get involved with some castings related to non aviation engine items so I'm not into the aviation matters, but I do recall some gypsy major heads being made somewhere (Albury?) Apart from Dee HAV's carrying on, I don't know how they went. I'm sure they ended up on aircraft .Porosity is a problem with watercooled heads more so than aircooled heads which have a requirement for strength when hot, where they may fail outright, or undo the heat treatment process they had undergone.. Reliability is difficult with some casting situations.. That is why Jabiru used billet CNC process. Some Lycomings are forged which is exotic. You get what you pay for (if you are lucky) but you won't get GOOD stuff for peanuts. It can't be done, especially on low volume runs. Nev

 

The LCH heads on display at Natfly this year had many pits showing on some of the machined surfaces. Whether that's indicative of porosity or inclusions in the casting process is beyond my level of expertise. I'll see if I can upload a photo when I get home tonight so those with more expertise can give their opinion.

 

 

[AVOCET]

Fr

 

The LCH heads on display at Natfly this year had many pits showing on some of the machined surfaces. Whether that's indicative of porosity or inclusions in the casting process is beyond my level of expertise. I'll see if I can upload a photo when I get home tonight so those with more expertise can give their opinion.

from memory :

Inclusions form from

 

sand or mould particles breaking loose when metal is pored in , porosity is caused buy gases formed by impurities in the base metal or additives .

 

Mike

 

 

[Gnarly Gnu]

the Australian aluminium casting industry is not, it appears, capable of casting something like a Lycoming cylinder head.

Actually quite the opposite Dave, surprising to you but the best quality and most complex aluminium pressure castings are made right here by an old South Australian company.

 

 

[Dafydd Llewellyn]

Well, not so surprising, because the LADS project (which I mentioned earlier) was done in Salisbury, SA - the best they could do for the LADS project was 401 alloy, which ain't good enough for cylinder heads. That's almost twenty years ago - but unless people are demanding something akin to cylinder head castings, how are they going to become familiar with those alloys, and the problems of casting deep cooling fins? - Go look at a Lycoming head. You're looking at closely-spaced fins of around 30:1 depth to thickness ratio. You want to see GOOD foundry technique? Go to France.

 

 

[AVOCET]

With the sort of casting techniques and where they could be done is irrelevant .

 

At the end of the day no Aussie engine manufacture is going to foot the bill for tooling that's only viable if your order begins with the number of units In

 

the thousands .( unless it's made in China )

 

Mike

 

 

[rankamateur]

3D printing?

 

 

[motzartmerv]

Just to shed a little light. The aeroplane that stars in this thread was an RAA rego'd 160

 

Had approx 400 hours on its engine, and almost 2000 on the airframe.

 

Not sure of which engine this one was, i am aware of 2 engine replacements in this aeroplane, but have been out of touch with it for a couple of years.

 

The cylinder was indeed cracked at the base and the through bolt has sheared at the flange.

 

The through bolts and nuts were latest spec. Thats all I have for now.

 

 

[AVOCET]

3D printing?

Ours is on it way .

Great for prototyping , rapidly

 

When I think of how long it used to take to make an air cooled head pattern

 

This is a Magic wand

 

 

[facthunter]

Some of the best drag twin cyl nitro.engines in the world are built in Australia and exported to the USA. They are purpose built from the ground up and there is nothing Harley in them.. Here and there you may well find pockets of excellence. New Zealand makes camshaft Velocette heads. Irving Vincents are produced here.

 

Porosity is usually from gas in the metal. Inclusions will be foreign matter, or oxidation . Some alloys will stratify and be uneven in composition. Silicon is hard to keep even throughout the casting.

 

I can get alloy steel parts cast that are motorcycle quality, and the pouring temperature is way above most other substances. That tends to burn the sand.

 

Re the gypsy heads. as you say the early ones were bronze and the 10Mk2 was alloy. The bronze heads ran no inserts for the valve seats originally so didn't like lead tetraethyl in the fuel. They are outrageously heavy too for their size, when done in bronze. Die castings are the most accurate and costly and often the shape is to allow it to be cast and not necessarily the best shape for the functionality of the product, or a good appearance. Once you have the dies, you can make a lot for close to materials cost alone. if you make thousands of them. Nev