Another engine failure

[Oscar]

01rmb: great post, and very useful in advancing the discussion, I believe. You've highlighted a very important factor: fuel and the correlation with the way the engine is operated. I reckon your point that: One thing is certain though - if the problem is not identified and fixed then the engine will fail should be inscribed on every aircraft operator's heart - gold award for expressing the bleedin' obvious that some of the trenchant critics of Jabiru engines seem to wish to ignore.

 

Can I make a couple of quick points?

 

Jaburi specifically advise against extended idle on the ground times, with good reason: the cooling airflow through the ram-air ducts is minimal at idle, and in crosswind conditions the downwind side (in particular) can actually experience negative airflow - i.e. no damn cooling of the pots on the downwind side at all! It's worse on the pax. side of the engine, with the prop 'retreating' across the cowl opening - and in a 3300, if only one cht is installed on pot 6, you have about the worst cht reporting situation you can have. Pot 6 tends to run the coolest of all on a 3300, so if holding across wind with the wind on your port side, you have the worst possible cooling situation for pots 1, 3 and 5. Then, one goes to full power for take-off at zero airspeed with one set of pots already very hot: you can see the potential for EFATO right up front! And that's no criticism of the operator: if you have to hold in a busy situation, who is going to feel comfortable about turning into wind to hold and then having to take-off without a clear picture of what's in the circuit? I'm buggered if I would, and if down at the pointy end of the runway I like to see what's incoming. So it's a juggling act at the best: managing engine temps vs. managing to fit into the traffic pattern. On that issue, it's also worth considering that proper management of the engine oil temp. situation requires some idling time, and an optimum oil cooler installation for operation in hot conditions will take some time at idle to come up to proper temps - a TOCA is very desirable to assist in getting the oil to operating temp quickly without extended idling.

 

Re using PULP: the aromatics in some PULPs have a known adverse affect on Jab. fuel tanks: check the 'Jabachat' http://www.jabiru.net.au/jaba-chat-a-news for June 2013 for more info. For older Jabs., using some PULPs can affect the fuel pump (the old 'Repco' pump can't handle ethanol, and very probably some of the PULPs as well), and as far as I know Jabiru haven't yet released a 'sloshing' compound that will protect the tanks against some of the more aggressive aromatics in some PULPs. I suspect (but others with more complete knowledge may be able to help) that 95 unleaded may be a safer bet than 98. The obvious corollary here is that the lower the RON, the more chance of detonation with very bad results - but as you suggest, full engine cht and egt monitoring is the first line of defence..

 

Nev: Valve guide wear is absolutely (as you said) affected by rocker geometry - including rocker bush wear - and also material, in terms of its ability to transfer heat. No doubt I'll be flamed as a CAMit tragic for this comment, but all of those elements are subjects of current CAMit developments. More information and results of current real-life testing will be forthcoming in the near future.

 

 

[Old Koreelah]

...until there is easy access to unleaded Avgas, I am going to be only running on premium unleaded mogas to prevent lead fouling problems and eliminate contamination of the sump oil.

Does this country still produce AvGas? I read somewhere that during the war the lead was supplied separately and added to the fuel before use. If so, perhaps the refiners might be persuaded to produce an occasional batch without lead. Sold in drums, there would surely be a market.

 

 

[Russ]

Champagne mix perhaps.....avgas 50/50 with 95pulp......yes ??

 

 

[Old Koreelah]

There was some discussion on a previous thread that the various additives may not be compatible. With so many exotic chemicals mixed into petrol, pure ethanol is starting to look attractive.

 

 

[facthunter]

It's done in Brazil 100% Ethanol. You wouldn't have as much range, the engine would get very cold in some places and burning ethanol is almost invisible as far as the flame is concerned. absorbs water. It's a fall back position and a possibility. Very high octane..Nev

 

 

[Old Koreelah]

Like Mark Twain said, rumours of the death of AvGas are exaggerated. The phasing in of a replacement is taking as long as the adoption of metric measurements.

 

Those yanks sure don't like change.

 

.

 

 

[Keenaviator]

[ and as far as I know Jabiru haven't yet released a 'sloshing' compound that will protect the tanks against some of the more aggressive aromatics in some PULPs. /QUOTE]

 

Jabiru recommended I use Kreem sloshing compound, bought from a local motorbike shop - I did my 65 litre tank form the UL 450. Laurie

 

 

[Oscar]

Very true - but it looks as if all the Avgas production on the East Coast has / will likely cease, so we may be reliant on imported - and if that happens, my guess is that increasingly it won't be available at locations other than major G.A.-centric sites, which are off-limits to most RAA aircraft. One of the attractions of RAA-class aircraft is - to me at least - the relatively low-cost ability to go adventuring 'off the beaten track' in terms of airfields, and the availability of Avgas is likely to constrict very much to 'on the beaten track'. If we want to have geographical freedom, we're going to have to be able to use other than Avgas at times, so setting up our aircraft to have tolerance of, at a minimum, 95 ULP is very likely to be of practical benefit.

 

On that point: in more remote locations, the actual RON that comes out of the pump nozzle is less likely to be 98 than what the bowser says, because of the rate of evaporation of the aromatics that are needed to get to 98 RON with both time and elevation. As we've discussed many times - getting your cooling right and having decent cht and egt monitoring will become even more essential if you want to venture beyond the area of supply of Avgas.

 

 

[Oscar]

[ and as far as I know Jabiru haven't yet released a 'sloshing' compound that will protect the tanks against some of the more aggressive aromatics in some PULPs. /QUOTE]Jabiru recommended I use Kreem sloshing compound, bought from a local motorbike shop - I did my 65 litre tank form the UL 450. Laurie

Laurie - that's a damn good start - have Jabiru 'officially' released it as a SB? I'm very keen to find out, as I also have a 65-litre tank that I am concerned about. Sloshing compounds have somewhat of a chequered history, the ideal would be, I reckon, an aromatic-resistant-resin based tank replacement, but so far I've only found one that claims decent performance. However, a decent sloshing compound and a good gascolator ought to be a reasonable half-way house answer - if you keep an eye on what drains out of the gascolator!

 

 

[facthunter]

Avtur sales would dwarf Avgas. I'm surprised it is still available. I don't agree with the situation but you are not served well when you are a small market.

 

 

[Keenaviator]

I just spoke to someone who was pretty helpful and happy to advise, Mark I think it was. My tank was new and never had fuel in it. It had been sloshed with the brown stuff from years ago but this is not resistant to ethanol. The Kreem is pretty expensive, about $65 for 500 ml but with patience I was able to make it coat the entire inside of the tank. I'm using a mixture of avgas and 95, about 30/70 ratio. Laurie

 

 

[2tonne]

lillydale had a engine fail after leaving here one day never found out what happened

The failure at Lilydale happened in a J160 I had been having lessons in. My instructor, Bob, was taking a 16 yr old girl on a TIF when engine ran rough long enough to make pan call. He landed dead stick on the runway without incident. Engine had over 800 hours and I heard that it was a valve that gave out (might have been speculation).

 

Needless to say every lesson after that had simulated EFATO at various positions in the circuit. Was drummed into me not to consider turn back unless on crosswind, so at least 500 ft gal. I enjoyed the glide approaches as they introduced a couple of new skills and thought processes.

 

Best thing though was that the girl who was onboard returned a few weeks later for another go. Tony

 

 

[jeffd]

i t

 

I'm happy to just quote your post Aldo; I'm not quite sure what an HSE person is.

i think he is upset with u turbo

 

 

[Powerin]

I find it all a bit odd. As a potential aircraft buyer at some stage, who would quite like to buy Australian, what am I to think of a company (Jabiru) who continues to manufacture engines to a specification that is clearly coming up short? So much so that the very company that manufactures the engine (CAMit) is making their own improvements?

 

I'm not sure what an HSE person is either, but if that's a person who does due diligence and researchs facts and evidence then I'm happy to be labelled as such. It is incorrect to say that there are many more Jabiru engines in Australia than other types. The RAAus register shows there are not. So therefore the apparent higher failure rate of Jab engines is real. A look at CASA and ATSB records show this to be the case. Exhaust valves may not know they are in a Jabiru engine, but the stats show something is causing them to fail on a regular basis.

 

By all means defend Jabiru as having a great aircraft; as having to be one of the best value aircraft out there; as being a great Aussie success story against the odds. You can certainly defend the engine as being affordable, but there seems to be a downside to this affordability. You cannot defend the engine reliabilty on the evidence compared to many other common 4 stroke aero engines. CAMit has obviously realised this, the sooner Jab does the better for what is left of Australian manufacturing.

 

 

[dazza 38]

For people who don't know. HSE stands for Health Safety and Enviroment. All resource companies have HSE advisors.

 

 

[01rmb]

As discussed earlier in post

 

Is there something wrong with the way the Jabiru engines are being operated which is exasperating the premature failure of the engines?

After 300 hours - running mostly Avgas the pressure leak test was down in the 40's on 2 cylinders but worse it was picked up that there was leakage past the exhaust valves on at least one of the cylinders necessitating removing the heads for inspection.

 

I have attached a photo showing the level of buildup from the lead fouling that was found before being cleaned up.

 

 

The lead buildup had started to affect the exhaust valve sealing (small valve) and then the valve started to get burnt which you can see at the point closest to the spark plug. What you can't see is that on the underside of the valve there is a small hole being burnt through leading to low cylinder pressure and combustion into the exhaust. Eventually the leak will lead to the valve stem being burnt through and the valve head falling into the engine. Fall flat, the engine may at least run, fall at an angle and the piston impacts the valve head and leaves pieces of piston in the sump along with a pretzel of a piston connecting rod and more loose pieces of metal in the engine. But basically, if it happened when you were in the air, you will be landing rather quicker than intended. Following inspection of my engine the LAME advised that it would not have lasted the next 20 hours.

 

The LAME removed all heads, gave them a thorough cleanup and replaced all valves and springs (cheap parts so not worth mucking around). Good as new and will easily last until the scheduled overhaul time.

 

The consensus is that the problem is totally related to running avgas and the resulting lead fouling. Some running conditions (with longer idle times resulting in cooler combustion temperatures) will expedite the level of buildup and decrease the time to problems occurring. Two aircraft I know that are doing 20-25 hours per week each in typical ad initio training were having all sorts of problems with the engines including 2 near forced landings when running on avgas - After switching to premium mogas there have been no problems.

 

Good enough evidence that following my own problem that I will only run premium mogas.

 

Importantly - Do your preflight checks and at any sign of poor compression, leaking gas into the exhaust or rough running have a mechanic check the engine before the wheels leave the ground. If running avgas maybe it is worth inspecting the exhaust valves much earlier than scheduled maintenance advises if your running conditions may lead to greater lead fouling potential.

 

 

[frank marriott]

O1rmb

 

I run avgas (all the time) but do a leakdown each 50hr service and pop the head and reseat the valves on any head that is down i.e. if not better then 60/80. (500hrs)

 

 

[01rmb]

O1rmbI run avgas (all the time) but do a leakdown each 50hr service and pop the head and reseat the valves on any head that is down i.e. if not better then 60/80. (500hrs)

And 50 hours ago the worse cylinder was 72/80... So good advice but worth caution because this engine was not going to do another 20 hours!

 

 

[facthunter]

It is more common to have this effect with the Rotax 912's as they run too cool for 100LL. They usually recover after a few tanks of mogas but you cannot be sure some valve or seat damage won't be done in the meantime. There is a fair amount of lead in 100LL so a shandy might be preferred. You need higher octane with the aircooled motors because of the higher temps as a general rule. Jabiru recommend avgas, but a lot of taxiing and being s bit rich at low revs may cause extra problems. Nev

 

 

[Oscar]

Jab. exhaust valves will start to corrode on the stem just below the head quite markedly if run at cht's above about 215, which is very likely to cause fracturing of the head in reasonably short order. Little run time at this sort of cht is required for damage to start to happen, and extended idling in a crosswind can raise some head temps very quickly; if only one cht is fitted to No. 6, the operator may well not realise that the even-side pots (in particular) are running considerably hotter than the single cht instrument is suggesting. That can't fairly be classed as an 'operator fault' but neither is is particularly an 'engine fault' - if the engine is going (unobserved) out of limits on some pots, it ought to be considered a 'consequence' of running out-of-limits.

 

I believe that the occurrence of cases of in-flight stoppages of Jab engines could be markedly reduced if operators had - and correctly interpreted - full recording of cht and egt performance, on the 'forewarned is forearmed' principle. Being able to read the actual cooling performance of the specific installation and possibly also patterns of use is a pretty damn useful tool for predicting problems that are arising.

 

 

[Oscar]

The J120 POH states absolute max. 200C (for 5 minutes max time), max. continuous 180C. Since they're all the same heads, I assume (but admit I don't know for sure) that this is the same across all (fine-finned head, anyway) engines.

 

 

[Keenaviator]

Hope my CHT's remain close to these in summer. By then I should have 2 x new MGL guages for 4 x CHT and 4 x EGT. Laurie

 

 

[Bruce Tuncks]

Hi Thirsty, I thought from your home of Adelaide and other posts mentioning the Adelaide Soaring Club that this had happened at Gawler, but after calling some people I don't think it did, and you didn't really say it was Gawler.

 

Where was this engine failure and when? I guess it could have been Murray Bridge.

 

regards, Bruce

 

 

[Thirsty]

Yep Murray Bridge.

 

 

[AVOCET]

w

 

As discussed earlier in post

 

After 300 hours - running mostly Avgas the pressure leak test was down in the 40's on 2 cylinders but worse it was picked up that there was leakage past the exhaust valves on at least one of the cylinders necessitating removing the heads for inspection.

 

I have attached a photo showing the level of buildup from the lead fouling that was found before being cleaned up.

 

[ATTACH]29303[/ATTACH]

 

The lead buildup had started to affect the exhaust valve sealing (small valve) and then the valve started to get burnt which you can see at the point closest to the spark plug. What you can't see is that on the underside of the valve there is a small hole being burnt through leading to low cylinder pressure and combustion into the exhaust. Eventually the leak will lead to the valve stem being burnt through and the valve head falling into the engine. Fall flat, the engine may at least run, fall at an angle and the piston impacts the valve head and leaves pieces of piston in the sump along with a pretzel of a piston connecting rod and more loose pieces of metal in the engine. But basically, if it happened when you were in the air, you will be landing rather quicker than intended. Following inspection of my engine the LAME advised that it would not have lasted the next 20 hours.

 

The LAME removed all heads, gave them a thorough cleanup and replaced all valves and springs (cheap parts so not worth mucking around). Good as new and will easily last until the scheduled overhaul time.

 

The consensus is that the problem is totally related to running avgas and the resulting lead fouling. Some running conditions (with longer idle times resulting in cooler combustion temperatures) will expedite the level of buildup and decrease the time to problems occurring. Two aircraft I know that are doing 20-25 hours per week each in typical ad initio training were having all sorts of problems with the engines including 2 near forced landings when running on avgas - After switching to premium mogas there have been no problems.

 

Good enough evidence that following my own problem that I will only run premium mogas.

 

Importantly - Do your preflight checks and at any sign of poor compression, leaking gas into the exhaust or rough running have a mechanic check the engine before the wheels leave the ground. If running avgas maybe it is worth inspecting the exhaust valves much earlier than scheduled maintenance advises if your running conditions may lead to greater lead fouling potential.

what sort of Mogas are you using ?

98 or 95 ? as I'm running LCH , so cooler heads .

 

I've had issues with mogas 98 softening fuel lines because of aromatics .

 

mike.