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Cylinder bore corrosion


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Some time back there was an article in a CASA publication (probably the Safety Digest) addressing the damaging effect of moisture on cylinder bores when engines are left idle for long periods without use.( This only applies to engines where the bores are steel or cast iron )


The article did not mention that the main source of moisture is actually from the combustion of the hydrocarbon fuel, the products being carbon dioxide ,water,some incompletely combusted carbon monoxide, and some oxides of nitrogen.


Just how much water is produced can be calculated using atomic weights for the elements concerned, and the result is in the order of 145/100 by weight ,water to fuel, so for each gallon of petrol you burn,you get about 1.15 gallons of water.


This fact is the reason why running your engine for short periods, where it does not get to operating temperature, can do a lot of damage & should be avoided. I have heard over the years, some owners mention bore rusting of Jabiru motors,as if it is a fault of the engine. This engine is no more prone to bore rusting than any other engine with steel cylinders & new or recently overhauled engines are more prone to it than when they have a few hours up.





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  • 2 weeks later...

Hi Facthunter,


Is it not also the case that certain synthetic oils are like magnets as far as moisture is concerned.


This was a real problem with model aero engines when a few years ago castor oil was a bit hard to acquire in bulk quantities.


I would also think that the climate where the aircraft is kept would play some part in it.


Wet or dry climate and cold or hot climate, condensation from temperature variations, do you agree?







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Corrosion/synthetic oils


rick-p, you are right there. Main bearing ( ballrace ) failure is common due to rust pitting in modern two-stroke motorcycles with modern synthetic oils .I believe some oils may have additives to correct this.


The mineral based oils are considered better in this respect. Running your oil temperature too cold allows moisture from blow by of the rings to condense in the oil, and in the cooler parts of the engine, causing sludge & corrosion. I like to see my oil temps about 95 degrees c. N....



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Corrosion /climate


I think climate has a lot to do with exhaust system corrosion (unless it is stainless ) but in the short term I doubt if it (moisture) would significantly enter the engine internals, from the outside air. A shot of WD40 up the exhaust pipe and a rubber plug in it wouldn't do any harm either to cover the situation where an exhaust valve is off it's seat. Long term storage is another matter& procedures are published to do that properly N...



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Facthunter, I think that it's not a bad idea for many reasons to plug the exhaust pipe particularily if you live in a rural region as you never know what may decide to take up residence in it if you leave the plane unattended for a few days.


Believe me from personal experiance I now never leave open any sort of opening on any of my aircraft that would allow the ingress of wildlife.


Corrosion is one thing but the little nasties that get into these openings can very easily bring down an aircraft through either mechanical failure or by way of a direct assault on the pilot.


Maybe we should start a thread on this specific topic as I really do believe that a number of aircraft in the past have been brought crashing to the ground by an unwanted stowaway.


Maybe some real life recounts in this area may just save a life.


How I got onto this topic I don't know but anyway as I said I myself have experianced such an incident and lucky for me I lived to talk about but the stowaway died, by hands.


A number of years ago when I was a very low time pilot I had a very close inflight encounter with a very nasty character.


The tale goes like this:-


It was a magic late Spring arvy, very balmy weather with little wind which was for all intents and purposes straight down the strip.


I decide that I would go for a fly and take in Callide dam and the lower reachs of Kroombit Tops.


After my very thorough pre flight of my Supa Pup Mk4, or so I thought, I primed the little beasty of a motor and then hand started it.


It immediately on the first flick swung into life.


I went through my further checks and run ups, lined her up to the North, gunned it, tail up within a few metres, stick forward, hold it hold it a little longer then easing back slightly on the stick, I was away, she leapt into the air, I stayed in ground effect for a little and then on having built up a goodly airspeed, back on the stick and she climbed like an homesick angel.


I then potted around for awhile mooching over and around the dam and the lower lying areas of Kroombit Tops as it is real tiger country high up and over the ranges there.


I decided after about an hour of doing this that I would return home and do a few circuits.


On about the 3rd touch and go, on finals, without any warning a four foot thats right a four foot long very aggresive brown snake lobbed in my lap having exited the wing through a hole in the wing root 'rib'.


I could hear this bloody great serpent hissing in anger even though I had on a headset and the 447 was making it's usual noise.


Somehow I managed to get the snake out of my lap and onto the floor of the plane.


At the same time my attention once again became focused outside and it was then that I realised that the planes attitude was dangerously steep, relevant to terra firma, I was in a steep dive towards the ground.


The fast approaching ground had now got my attention over the snake.


Stick back and throttle full on and feet on the edge of the seat. Yes you heard right I had pulled my feet of the pedals to avoid the snake.


I looked down but couldn't see the snake, though I did think that I could hear it thrashing around under the seat.


I looked up and out again just in time to see the top branches of a Black Wattle tree pass under the Supa Pup and at the same time feeling a slight bump from underneath.


A thought passed through my mind, like a bullet and that was that unless I composed myself I could die today.


I pulled myself together and got back to the job at hand, flying the aircraft. The snake wasn't in sight and I reminded myself that I wasn't in ordinary circumstances frightened of snakes.


I eventually composed my self, completed the circuit and landed the Pup without a further appearance of the snake.


I only returned my feet to the pedals moments before touchdown, which just goes to show that you can fly without rudder if you have to.


Anyway, back to the tale at hand.


As soon as the Pup stopped rolling, no brakes fitted, I bolted from the aircraft as I had shut down the engine and I could hear the snake still hissing in a very angry fashion under the seat.


I stood back for awhile thinking as to how I would get it out of there without getting myself bitten.


I very gingerly peered under the seat to see to my suprise the snake wrapped around the right hand rudder cable along with one of those sticky pad mouse traps I had previously placed in the Pup to stop the little vermin, in their tracks.


The snake had it's head well and truly stuck to one of these pads which in turn was stuck to the rudder cable.


I reached in grabbing the snake just behind the head and pulled but it wouldn't shift so I gave a very hard tug which worked and i pulled the snake out thrashing, but minus it's head as the rudder cable severed it from it's body on my giving it that last mighty yank.


I was amazed at the snake's size, it was quite big, about four feet in length.


I assume that the snake must have been chasing mice and it got up into the wing through the wing root rib, fell asleep but then was eventually woken up by the noise of the engine and movement of the aircraft.


I was extremely lucky on a number of counts that day such as not impacting the ground or the tree and not suffering multiple snake bites.


Lesson here to be learnt, expect the unexpected and ensure that the wildlife in your area can't make those recess' in your aircraft their home or resting place by either the use by you of temporary means or permanent if such won't interfere with the safe operation of the aircraft.


I know of a number of other life threatening incidents that have happend to other pilots in similar circumstances so particularly you pilots in the bush stay alert at all time and always be aware that there may be on board an unwelcome stowaway.:devil:


True story,





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Good greif Rick


That is exactly what nightmares are made of.


We had a close encounter with a very large brown in our hanger which is on a bush strip like yours. The snake appeared from behind a cupboard as we were havinging a cup of tea after a mornings flying after a quick flee outside and a long wait the snake eventually moved outside the hanger.


Then a sickening thought came into my head as a looked at my Sapphire with its tail boom open and sitting just off the ground. What would have happened if the snake had gone up the boom ,which by the way leads directly to the cockpit in the Sapphire, and appeared during flight? No room to lift your legs in a Sapphire.


I have made a plug for the boom and install it after every flight now.


I pray I never have to have your experience







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It was Factfinder and it took me a long time to get over it as you just can't pull over and jump out.


But think about what prompted my story telling, how many good men have come to grief through a similar incident whilst flying their aircraft? No one can explain what happend as the snake, spider or wasps just to name a few nasties, has, after the crash decamped the scene leaving no trace as to the reason for the pilot and his aircraft's demise.


I remember some time ago reading, I think in AOPA, a pilot's story about a green ant that had got on or in his cap that he had placed on the ground when he landed with his family to have a picnic and when they returned to the air the ant entered his ear and stung him.


It took all his willpower to stay with it and fly and land the plane, the thought of his family going down with him kept him from passing out from the severe pain of the ant sting on his eardrum.


Another story I know of involved a friend of mine who had multiple engine failures on a return trip to his home in central Queensland as a reult of a mud mason in a very short period time blocking the breather tube to his fuel tank.


The insect had some how got it's doings up inside the breather tube where it couldn't be seen and this act of sabotage took place in a matter of about twenty minutes whilst my friend was attending to some business a short distance away from his aircraft, not thinking that in such a short time something like that could happen.


From the account of his girlfriend who was with him my friend had to do 3 emergency outlandings before he discovered the cause of the engine stopping.


Once the plane was on the ground the pressure equalised and the engine ran ok until he got altitude again.


As I previously said maybe we should start a thread in these forums titled Believe It Or Not (Fact at times can be stranger than fiction).







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Fact ?


rick-p, I think you have trumped us most likely. Perhaps you fella's in central Queensland have all the excitement with God's little creatures.


I've only had wasps blocking the pitot (at West Maitland, took about 5 minutes). We got good at flying without airspeed indication. & one time at Mudgee, before flying an Auster, noticed a bit of powder on the ground, on opening an inspection panel under the wing, found the wingspar half eaten through by what was presumeably, a rat. Cheers..N...



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Facthunter, yes I have heard some horror stories about rats chewing into wing spars on Moth's and Auster's and that is one very thorough check I give my Auster J1N regularly, all panels open and it's then done with mirrors.


A wing departing your aircraft will most certainly spoil the rest of your day.


Stay safe, fly safe.





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I believe most of the moisture in a cylinder gets in when the engine is cooling down and the pressure dropping, so it is a good idea to plug the exhaust but it will only slow down the ingress. Most of my flying is done in the morning so the air is probably fairly dry when I stop, but the relative humidity might be high.


I never had a trace of trouble with my 2 stroke 503 Rotax using Penrite Green Slime, it had a lovely coating inside the motor.


I see that rick-p is in the Callide Valley, are you a member of the Callide Valley group. I am not current with them as I was away for the Smokey Creek weekend and havn.t paid up yet.


barandbrew, your strip at Jim Crow is not much better than a brown snake. When I land there I cannot see the strip as it is narrow and behind the nose. People complain about the house in the middle of the strip at Rodds Bay but the mountain in the circuit and power lines on final put me off your place.



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Yes Yen I am a member of Callide Valley Flyin Group.


I don't think that too much has been happening lately, I have been away myself before and over Christmas for better than 2 months.


As to the green slime I think you are right to use it. I used it myself in the Supa Pup engine (447) and it ran without a hitch. In fact the chap that bought it a few years back flew it from Biloela to Gove without a problem.





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Hi Ian


Yes our strip is not for the weak hearted. Total length is 600 mtrs with power lines at both ends and a large volcanic plug just to the north that produces some very scary wind sheer at times.


Having said that after we were thrown off our old airfield ,Hedlow, our options were our strip at Jim Crow or Lawn Bowls. We chose the tight airstrip.


I must admit that I have no problems flying in and out of our strip in most conditions and find when we fly to places like Smokey Creek I don't know what to do with all that extra strip.







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  • 8 years later...

After reading many posts IRT Jabiru engines bores corroding if not ran every week or two. I am guessing a lot of Jabs are not started for months. That would seem to me to be a possible cause of a lot of the engine problems. What do you guys reckon?


Ps- sorry for the old thread revival.



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Obviously Ian Bent at CAMit sees the effect of it enough to incorporate an oil injector system for use on shutdown. I've been carping on about it for years but I thought I must be using some of Turbs "invisible ink" when I post on the matter.


Don't be sorry Dazza. Im glad you revisited it.


Air can't really flow through a four stroke motor to any real extent. You have to have a cylinder stop where both valves are open together, and even if you have a large number of cylinders this won't happen on more than one as the overlap is about 60 degrees. The valves are not far open either at that stage.


Air does contain moisture. (Water) but it's a pretty small% in absolute terms. At the poles or in a desert is is nearly zero.


Far more damaging is the residue of combustion of the hydrocarbon fuel (and it's impurities)


Fuel is Carbon plus Hydrogen giving CO2 some small amount of CO and H2 O (water.)


If you look up the atomic weights you can calculate the equivalent amount of water for an amount of fuel. That will give you a ratio one to the other. The last time it did it I think there was more water made than the weight of hydrocarbon.


Paraffinic hydrocarbons are C (n) H (2n+1) long chain. I think carbon is around 6. (Vev will know)


Cyclic (Benzine) C6 H 6. Why so much water?. Oxygen is from the atmosphere and you don't pay for that but it has a fair weight which contributes to the mass of the formed water. Hydrogen is the lightest of all atoms. Nev



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Do you think this corrosion is aiding to bind rings?


Even in engines that dont fail, premature high leak is a common cause for top end rebuild


Camits inhibitor looks nice, will be an onclusion on my next engine for sure


He promoted 2 pumps, 6cc on shutdown, if possible another pump after cooling and brief restart


From the data it seems regular running Jabs have more big problems,, schools,


maybe others suffer from this more and relates to early engine swap outs



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It can completely "pug up" rings. I've seen that term used. The engine would be lucky to survive as most likely ring overheating scuffing and warping and bore scratching would result and /or broken ring lands. Rod has always advocated early rectification of any compression problem. I agree with that. All these situations have a rapid deterioration pattern. If there was an indicator of blowby available it would predict a lot of failure modes


Note SOME schools haven't had a problem. My personal opinion on top overhauls is that you shouldn't expect to go high hours without head removal. IF a motor is overheated (even once) above a certain temp the Al is permanently softened An overheated valve stem will show tiny cracks.. These happenings are going to affect the motor later in it''s life. It's only a matter of time.. They used to make paints that changed colour at a certain temperature. They did this when developing the Wright J5 whirlwind. Probably one of the best engines of the time in the late 20's. If you had this on some engine parts you would know the temp has been exceeded and the part is scrap no matter how good it looks. It won't work for exhaust valves. They don't cost much in a Jab If in doubt chuck them out..Nev



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Might account for some of the random nature of failures


I did comment once in jest that the biggest common issue in Jabiru failures was hangering east of great divide


Maybe more humid air does contribute?



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Not convinced it's a big factor in cylinder corrosion(internal). If the motor is up to temp before shutting down that helps. If you leave your pride and joy in front of the clubhouse till nearly dark and then taxi it for a couple of minutes and shut it down you are courting disaster. especially if you leave it for a week or two. There will be obvious rust on the surface within that time.. Nev



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Fair enough, as you say the water comes from onside engine not outside


Im seeing low leaks after 200 hrs on 4 out of 6 cyl


Other 2 are like new


Has been sitting around for months at a time (unplanned) over last 12 months



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Every three days I turn my Jab 2200 prop over 10 blades to disturb the piston positions and (I hope) defray the onset of corrosion in the bores etc.



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The exhaust valve seats can corrode too. You can also get lead deposits on them. (more of a problem with the Rotax and avgas as it runs cooler.


You could remove a plug from each cylinder and squirt some thinned out outboard oil in. Better if it mists. Not too much .


The CASA site usually has details of the prescribed way of inhibiting an engine but that is a bit complex if you aren't sure you may leave it idle for an extended period. This doesn't have to be months. The oil rings don't leave much oil on the cylinder surface and even a week may see visible corrosion. The impurities in the fuel when burned help the corrosion to occur..


Note this applies to steel or cast iron (rare) VW and Franklin motors.. cast iron is probably better than steel (more porous) but still corrodes. Nev



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I reckon the best way to inhibit a motor for say up to a year would be to inject two stroke oil into the carbie air intake, than turn off ignition. Having seen the insides of two stroke engines, that would coat the cylinders nicely.


Turning over a Jab engine without running it will scrape all the lubricant off the camshaft and cam followers. Not a nice thing to do.



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