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Jabiru Bad experience

Old 20th Jan 2014, 12:21
  #61 (permalink)  
 
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JR

Hey hold on, I was up the front

There might have been a bit of rooting around but I got the most important question right
You did indeed. Nice to survive that test! Rutanaround was in the BN class though. More ratbags per sq M.....ohh hang on, no there were a lot from SA.

Merv, they do say they are OK on Premium Mogas, and they may well be. They approve them for 98RON, but I am not sure nor does it really matter about what they were certified with, but it would have been avgas at the time.

The engine itself doesn't care much, its all about getting it to the engine.
Old Akro The engine may not care much, but it does notice, but just like the STC's for many of the small HP carby engines, the engine will will see a change in the thetaPP no mater what. The fuel does not know the engine. It may well be fine on the PULP.

OA, think about this a bit more especially with hot heads.

The jab engine was designed around 100MON avgas. It may well be fine on BP/Caltex 98 and they do say in factory SB's that 95+ is OK, but lord only knows what was being run in it so far in this thread, hence my question.


PS : OA
Ignition timing might (come in Jaba).
The latency off the fuel affects the effective timing. In other words the sparks go off at 'X' DBTDC but the peak pressure and ThetaPP are directly affected. Longer latency of Avgas will mean lower ICP as a result of the later ThetaPP. As for heat and the energy produced, yep 100% agree.
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Old 20th Jan 2014, 12:23
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Sue has informed me that they will not be returning my heads
The heads are your property. They are not entitled to keep them. Period. I'd give them a solicitors letter and a deadline.

If you wanted an expert witness, there are a few guys from the engine labs of Toyota, Holden, Ford & Orbital that would be well qualified. I think you'll struggle to find an experienced engine calibration guy outside of Melb (or Perth for Orbital). For the purpose of preparing for a potential court appearance, I'd stick with a professional engineer.
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Old 20th Jan 2014, 12:31
  #63 (permalink)  
 
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OA, think about this a bit more especially with hot heads.
I thought the hot heads were on the Dick Smith thread???

I'd argue that the head temperature is a product of the power output (& cooling airflow) and largely independent of fuel. Indeed Mogas probably has a lower specific energy than Avgas, so might be a bit easier on the heads.

We must catch a beer. I'm in Brisbane in early Feb.
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Old 20th Jan 2014, 12:36
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I should add that I suspect part of Continental's problem is poor valve seat design which does not transfer heat from the valve to the head well. Thus the valve gets too hot and the seat wears causing valve recession. So, that's an area that might deserve investigation on the Jabiru engine.
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Old 20th Jan 2014, 12:36
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The engine we are talking about was run on 98 Mogas.
Was this what caused the valves to fail?
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Old 20th Jan 2014, 13:06
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Merv, not the valve failure needs to be determined as to how it failed. Valves generally fail due to poor machining of the head/valve seat and the guide. Valve guide wear through rocker geometry or through poor fit and then cargo or lead oxybromine ingress, then sloppy guides mean a rattly valve and then the head breaks off.

To make matters accelerate the CHT will not help if it is very high. There is no doubt the shorter latency of mogas Vs Avgas will have an impact but I doubt it has a serious impact if the cooling airflow is sufficient, but it does not help. There is a big difference from Avgas at about 110RON and 98RON that may well be a bit lower.

Getting back to the rapidly rising CHT, I am not saying it could not ever happen but a rapidly rising CHT is indicitive of a preignition event and not a valve failure.

Valve failure is not normally associated with a rapidly rising CHT. It can often be seen coming with the EGT races in the EMS. But even there not always. We had a C340 owner in a class once with a failed valve and no warning. That is a TSIO 520 Conti.

So was this failure a preignition event or not?

I wonder what the oil change interval was?

I think the valve geometry could be better, the guide material better. Are they post reamed and nice fit?

So many variables and the same is said for the maintenance of them. Don't get me wrong, my IO540 is my preference but many a jab engine does not get the life it should from external factors. But on the other side of the coin the cir clip events showed how easy things come undone too.
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Old 20th Jan 2014, 13:11
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1.
We had a C340 owner in a class once with a failed valve and no warning.
2.
That is a ...... Conti.
3.
QED
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Old 20th Jan 2014, 13:21
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Jaba. There are two separate engines being discussed here.
The J230 was a CHT overheat event. I highly;y doubt it was pre ignition or detonation as the engine gave no rough running sympotm at all, The only indication was the flashing light warning me the CHT was over 180 deg's. That was late upwind, about to turn xwind on a normal 80 kt climbout on a 28 deg day. By the time the turn was completed the CHT was 210 deg's, then 220. That was when I levelled out, reduced power and returned to the strip.Where it subsequently stopped.
My questions relate to the valve failure at 300 hours in the 2200 with an engine that has logged history in 4 channels on CHT and EGT. None of which show anomalies. no overheat issues indicated. jab quote that valve seats start dropping out at 250 degs (see engine inspection report).
When we have one engine that fails at 220 degs, and jab saying 250 is where the seats let go. Why, has this 2200 engine dropped a seat with NO over tempt issues.
Thats the 64000 dollar question
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Old 20th Jan 2014, 13:56
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Notes inserted below in RED

Jaba. There are two separate engines being discussed here. Take it easy on me
The J230 was a CHT overheat event. I highly;y doubt it was pre ignition or detonation as the engine gave no rough running sympotm at all, With all respect, it is apparent you do not clearly understand what either of these events actually are, and no you will not notice rough running at all in either case, until preignition kills the cylinder The only indication was the flashing light warning me the CHT was over 180 deg's. That was late upwind, about to turn xwind on a normal 80 kt climbout on a 28 deg day. By the time the turn was completed the CHT was 210 deg's, then 220. Could have been a lot of heat build up from some unintended machining going on, but this is pretty much how preignition goes That was when I levelled out, reduced power and returned to the strip.Where it subsequently stopped. Yep that too. But it may have been a circlip problem (refer SB) and subsequent chewing up metal.

My questions relate to the valve failure at 300 hours in the 2200 with an engine that has logged history in 4 channels on CHT and EGT. None of which show anomalies. no overheat issues indicated. jab quote that valve seats start dropping out at 250 degs (see engine inspection report).
When we have one engine that fails at 220 degs, and jab saying 250 is where the seats let go. Why, has this 2200 engine dropped a seat with NO over tempt issues.
Thats the 64000 dollar question Add some more zero's on the end So the 220d failure, was this a valve too? How did the 300 hour one fail? What were the guides like? I am not at all defending the Jab engine build, just trying to help in the understanding. 250dC is too hot to run the engine at but should not have seats falling out of the head
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Old 20th Jan 2014, 20:59
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Another question. How do other aircraft engines that allow both types of fuel handle the issue? Im assuming the engine manufacturers have similar or dare I say it, better knowledge about these problems?
Generally the engines approved for lower octane fuels have relatively low compression and were originally designed for low octane fuel. Apart from lead polution higher octane 100LL does no harm as the slightly slower combustion event finishes a few degrees later safely after top dead centre. Peak pressure is well after TDC making it lower and easy on the valves and cylinder heads. As peak pressure occurs in a good place mechanically very little power is lost.

When lower octane UL fuel is used in engines designed for high octane fuel bad things happen.The spark occurs where the factory set it. The time from spark to completed combustion is shorter with UL so peak pressure occurs earlier in the cycle sometimes before the piston reaches TDC. This is very hard on the engine and it's a credit they hang together as well as they do.

One way to help the PP to occur later is to use higher revs. Now this is all very well for Jabba with his fire breathing monster engine fitted with a constant speed prop but for us mere mortals the only option is to lower the nose. It's unfortunate that engines fitted with fixed pitch props reduce revs just when they are working hardest ie in climb.The cooling air decreases and the PP occurs in the worst place creating more heat. The combination creates excellent conditions for detonation but by using low octane fuel detonation is not very well resisted and can quickly get out of hand.
Automobile engines get round the problem by having knock sensors which retard the spark in the above scenario.
Don't ask me past this point as the rest of the seminar was after the long liquid lunch and Jabba's dulcet tones put me to sleep.
Cheers RA
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Old 20th Jan 2014, 22:34
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Detonation doesnt cause rough running?
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Old 20th Jan 2014, 22:45
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not normally, might create an unusual sound as it get to heavier detonation, but mild detonation usually goes un-noticed.
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Old 20th Jan 2014, 22:51
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the 2200 (J160 ) Failed on startup. ran rough and spluttered. pulling ther prop through by hand we found a cyliner to have zero compression.
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Old 20th Jan 2014, 22:55
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Not till it gets out of hand. Some big bore turbo'd engines live with mild detonation for a lot of their operation. The high octane fuel prevents it running away (generally)
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Old 20th Jan 2014, 23:01
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from my understanding, the 2200 was the failed valve seat? the failure of the valve seat is irrelevent to EGT, or fuel type burned. and most lilely a manufaturing defect, even though Jabiru claim its valve seats fail at 250degC, which the 2200 never reached.
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Old 20th Jan 2014, 23:06
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merv

as pointed out above detonation is unlikely to be noticed in an aircraft engine. I doubt the Jab engine will detonate anyway, although given the right circumstances with low octane, hot temps etc you might be able to. But not easily.

Preignition you will likely not hear or feel much there either until you have a trashed piston.

Your description of what you found is not very diagnostic at this level so maybe none of our collective somments are of any use.

The likely issues are valve guide wear then damage to the valve as a result. High temperatures will not help either.

Complete lack of data along with so many experts having their opinion along the ay mean finding the truth is almost impossible.
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Old 20th Jan 2014, 23:12
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Recap gents,
the 230 suffered a cylinder head overheat on number 4 only no valve seat movement or valve failure, the subsequent bulk strip at the factory, revealed the bottom end was destroyed by the original inadequate thru bolt design.


The 160, dropped a valve seat whilst sitting at idle after the pre take-off mag checks. Upon inspection the cracks in the heads were discovered.


"The word from the engine section regarding the heads is that there is evidence of overheating of the exhaust port areas probably from leaking exhaust pipes. This overheating has resulted in the valve seats dislodging and valve stem damage."


The heads show cylinder creep (ridging) only around the exhaust port.


Fuel used primarily is Caltex 98, but when away, fuelling at other strips they use avgas.


Jabba, My experience on these engines and I have opened up a few, is that Avgas leaves deposits everywhere, the common issue I have noticed caused by it is ring sticking.


I have tried to post pics but cant figure it out, drop me your email and I'll send you some.


Request: can we keep it civil? accusations that the standard operating advice from Jab has not been followed are unfounded and completely wrong. It has been maintained and operate within the guidance and documented requirements set down by the manufacturer.


I get accused of this by Jabiru, always when asking for some kind of warranty or an explanation why their product isn't performing as it should.


But for the life of me can't understand why others have to belittle or be suspicious even after multiple denials, I have nothing to hide I have done everything that the factory has asked.
(My next step will to have a monk bless the bloody thing in hopes of 1000 trouble free hours).
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Old 20th Jan 2014, 23:14
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Jabba,
"Complete lack of data along with so many experts having their opinion along the ay mean finding the truth is almost impossible"


This is why I want them back, and that's why they won't give them back!
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Old 20th Jan 2014, 23:15
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Ok thanks. I thought Deadstick gave a pretty detailed explanation about both failures, with an engine report aswel. I was just relaying what happened from the cockpit. Not being an engineer I am relying on the lames technical description of the post failure inspections.

Your right about the experts. But even the factory experts (small engine mechanics) have not been able to explain why either of these failures occurred.
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Old 20th Jan 2014, 23:35
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It would seem DeadStick that based on the information from your previous post that your warranty is void unless there is a subsequent SB after JSL007-4 from December 6th 2011.

http://www.jabiru.net.au/Service%20B...l_Guidance.pdf

DeadStick1 Fuel used primarily is Caltex 98, but when away, fuelling at other strips they use avgas.
(Not my boldings)


3.3 Shandies

A "shandy" is a mix - for the purposes of this letter it is a mix of any 2 or more different fuels.

 In some areas it has become popular to operate Jabiru engines on a shandy of AVGAS and MOGAS. This might be done to reduce the cost of fuel, to reduce lead buildup in the combustion chamber, to "beef up" the octane rating of a sub-standard fuel or other reasons.

This practice is unsafe. Jabiru Aircraft do not endorse it and may void any warranty of an engine or aircraft which has been operated using such a fuel.


In terms of chemical composition AVGAS is totally different to MOGAS. A petroleum company representative described mixing the two as similar to "mixing Gin with Beer".



Hardcore cocktail fans aside, mixing these drinks is a bad idea it tastes bad and the after affects can be messy & expensive. There is potential for elements in the fuels to react to each other and the finished blend would have unknown knock resistance because the fuels are so complex you cannot assume that mixing 110 RON AVGAS with 91 RON MOGAS at almost any mixing proportion will result in a fuel with acceptable knock resistance for a Jabiru aero engine.
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