Light Aircraft down Near Bundaberg

[facthunter]

No pin offset GOOD. There never should have been offset OR debate. If it's there, offset in the direction of rotation, and time your engine to accommodate it. Nev

 

 

[Oscar]

Now more info available: Investigation: AO-2017-063 - Engine failure and forced landing involving Jabiru J430, VH-OFR, 17 km S of Bundaberg, Queensland, on 18 June 2017

 

For those who wish to actually consider the evidence, rather than blaze into print with biased opinion, please look carefully at the picture of the 'modifications' done to the pistons - if you click on the photos in the ATSB report, they come up in detail.

 

I have built racing car engines - including modifying and balancing pistons. I have also rebuilt my Jab engine at CAMit, under the supervision of Ian Bent personally and all of his terrific people who were part of CAMit. I will state on pain of dismemberment, that the piston mods. shown did NOT come out of CAMit in that condition; Ian Bent would not have allowed it.

 

It is, frankly, bush-yard mechanic butchery. You don't have to be any sort of superior engine-builder to know that such rough work introduces stress-points / weaknesses, into pistons that are already very 'commercial' grade. You don't take a die-grinder and just blaze away with it, you polish all metal removal areas to ensure a safe transition of loads.

 

The level of workmanship shown on the photos in the ATSB report, would probably work on a lawn-mower engine, for a while.

 

 

[turboplanner]

Agree; that's an example of snatching defeat from the jaws of victory.

 

There are areas on a piston you can take to with a hack saw, but this is crazy!

 

 

[jetjr]

Some signs of overheating there, this is linked to plenty of problems.

 

Significant head recession, burnt oil under head and under piston

 

To get those oil stains after 150 hrs would be pretty hot

 

Some of the older piston had casting dags/lumps in these areas shown as ground

 

Jab direct pairing pistons, gives weight limits, and doesnt allow rebore of barrels, so did Camit.

 

Not sure how Jabiru claimed it was a Camit engine originally and not their fault?

 

 

[facthunter]

They ARE running too hot and from the scratching didn't have sufficient clearance for those temps. It was Probably seizing when the power loss occurred. Giving it more throttle was the final thing to finish it off. I've never liked that style of piston for an air cooled aero engine. Nev

 

 

[jetjr]

Increased clearances from Jab spec would be huge

 

Scoring could be from slap? Wonder what post build leakdowns were?

 

 

[Blueadventures]

Now more info available: Investigation: AO-2017-063 - Engine failure and forced landing involving Jabiru J430, VH-OFR, 17 km S of Bundaberg, Queensland, on 18 June 2017For those who wish to actually consider the evidence, rather than blaze into print with biased opinion, please look carefully at the picture of the 'modifications' done to the pistons - if you click on the photos in the ATSB report, they come up in detail.

 

I have built racing car engines - including modifying and balancing pistons. I have also rebuilt my Jab engine at CAMit, under the supervision of Ian Bent personally and all of his terrific people who were part of CAMit. I will state on pain of dismemberment, that the piston mods. shown did NOT come out of CAMit in that condition; Ian Bent would not have allowed it.

 

It is, frankly, bush-yard mechanic butchery. You don't have to be any sort of superior engine-builder to know that such rough work introduces stress-points / weaknesses, into pistons that are already very 'commercial' grade. You don't take a die-grinder and just blaze away with it, you polish all metal removal areas to ensure a safe transition of loads.

 

The level of workmanship shown on the photos in the ATSB report, would probably work on a lawn-mower engine, for a while.

I hope RAA investigate to ascertain if similar maintenance has been carried out on other engines by the engine builder?? and look into their condition. then take appropriate actions.

 

 

[turboplanner]

I hope RAA investigate to ascertain if similar maintenance has been carried out on other engines by the engine builder?? and look into their condition. then take appropriate actions.

This was a VH aircraft, investigated by ATSB.

You should write or email ATSB with your thoughts.

 

 

[Blueadventures]

This was a VH aircraft, investigated by ATSB.You should write or email ATSB with your thoughts.

Agree Turbs. I'm sure ASTB they are on to that. And I hope that RAA inquires in case this person has also worked on RAA aircraft engines. Would be good if this is the only engine to undergo this type of work; however as the person is described as experienced in the maintenance of this type of engine then he most likely has performed work on others. Interesting decisions and poor workmanship example and informative to all like other ATSB investigation reports about the reasons / causes of failures. Regards Mike

 

 

[fly_tornado]

very interesting, do we know why the owner had to rebuild the engine at 400 hours?

 

 

 

 

[facthunter]

Lines from top to bottom are not from piston slap. That just can't happen from that cause. Who knows what clearances were used. No comment on them in the undamaged cylinders. The piston disintegrated, which is pretty uncommon. A bit more careful; inspection of the broken parts might give more clues. For instance if the ring grooves weren't deep enough the scoring would result when the piston overheated and it's possible for the top to lift off the piston. The scoring is in the ring travel area. I don't think they know what to look for. I doubt the lightening of the piston had anything to do with it. Nev

 

 

[planesmaker]

Photo of scoring from cylinder 2. Possibly stuck valve resulting in piston disintegration or overheat seizure. Interesting it had done about the same number of hours as the factory new engine had done when for some unstated reason it was "rebuilt"

 

 

[facthunter]

Later pistons have relief to allow stuck valve to clear. Perhaps in this instance, not quite enough but the valve head did not detach and there's no sign of continuous heavy impacting. The cylinder under those conditions would not run hot at all but would lose power. An exhaust valve stuck doesn't affect the engine as much as an inlet does, but is more common. Perhaps metal from the cylinder helped to cause it to stick? It has to go somewhere. Nev

 

 

[Yenn]

Could the piston falling apart be due to machining marks left by the work, causing stress risers.

 

It seems an unusual way for a piston to break up. Could the valve have been the full cause of the problem?

 

 

[fly_tornado]

I did some googling on YouTube and people are drilling pistons to match weights.

 

 

[turboplanner]

I did some googling on YouTube and people are drilling pistons to match weights.

That's a very broad statement; the same as people are blowing pistons; where are they drilling them.

 

 

[onetrack]

In my experience, nearly every engine I have had suffer from total piston destruction, has suffered from piston overheating.

 

The remainder were destroyed via heads falling off valves, or ingestion of turbocharger metal after compressor turbine failure.

 

The scores in the bore of the Jab engine indicate to me, piston scuffing, caused by the piston overheating, and associated ring jamming, caused by the overheating.

 

The authoritative advice from engine components manufacturers is that you should never, ever remove weight from pistons via drilling. This only causes stress risers where the drill hole is.

 

Weight should only ever be removed from pistons via machining.

 

One must always be aware, also, that many pistons (even cast ones) are heat-treated to improve their life and performance, and using the likes of a belt sander to remove material from pistons is highly likely to affect any heat-treatment, as the use of a belt sander creates intense hot-spots very quickly.

 

 

[Keenaviator]

In my experience, nearly every engine I have had suffer from total piston destruction, has suffered from piston overheating.The remainder were destroyed via heads falling off valves, or ingestion of turbocharger metal after compressor turbine failure.

The scores in the bore of the Jab engine indicate to me, piston scuffing, caused by the piston overheating, and associated ring jamming, caused by the overheating.

 

The authoritative advice from engine components manufacturers is that you should never, ever remove weight from pistons via drilling. This only causes stress risers where the drill hole is.

 

Weight should only ever be removed from pistons via machining.

 

One must always be aware, also, that many pistons (even cast ones) are heat-treated to improve their life and performance, and using the likes of a belt sander to remove material from pistons is highly likely to affect any heat-treatment, as the use of a belt sander creates intense hot-spots very quickly.

And the common thread for failure, OverHeating!

 

 

[facthunter]

They usually drill into the thicker part of the crown from underneath. Pistons often have lumps of metal below the pin boss where you can mill some metal off if you wish to make weights equal. This is done at manufacture to get within a batch tolerance of probably 3 grammes.

 

In the skirt area where the lightening was done there are often lines where the dies do not quite match. Levelling them off wouldn't hurt anything as long as there were no areas of excessive thinning or sudden changes of thickness or you removed part of a web or strut. You will notice a web around the base of the skirt. that is untouched...The highest concentration of stresses is usually at each end of the machined slot in the oil ring groove. The casting is usually thicker in a that area.. Because of that feature( the groove) the top of this type of piston often separates if the rings get damaged, seize or don't have enough end gap clearance. It's designed to limit heat travelling from the crown to the skirt in such a way the skirt distorts and becomes less oval as the piston crown heats up and takes the bosses with it. That's why "W"slot pistons were put in water cooled CARS. To stop piston noise when cold..Nev

 

 

[Csjhay]

It's interesting noting the report does not give a cause for the piston failure.

 

Looking at the cylinder scouring, that piston was definitely picking up before the failure.

 

I'm also wondering what caused the half moon shaped indent in the combustion chamber ?? Given it hasn't dropped a valve, very symmetrical and to small a radius to be the edge of the piston skirt, it can't be seen in the photos if the gudgeon broke up ,or the conrod.

 

While the die grinding on the piston is hardly neat ,would it cause a stress fracture ,given the very sharp radius on the inside of the piston skirt would be a much more susceptible spot for a crack to start. ( which they all have )

 

If piston to cylinder clearance was the cause you would imagine failure would have occurred much sooner in hours after the rebuild ??

 

While it sounds bad that a non genuine piston was used and I can't comment on a time frame outside of 2000-2005, the pistons were a well known brand of automotive piston at that stage.

 

 

[facthunter]

The rings have made the marks rather than the piston skirt. It's in the ring travel area on the bore surface. . This is probably caused by not having enough ring groove depth and the engine getting too hot as it had run hours before this happened. It's possible the ring end gap was not enough but again, since it ran a while before this happened, it's less likely to relate to that source. I'd like to have the top section of the piston to examine. If it has happened the ring grooves will clearly show the effect of the rings bottoming in the grooves. Nev

 

 

[turboplanner]

When you reduce the piston/ring clearances and you lean the engine, you generate heat.

 

How do I know that? I bought a few dozen pistons to replace the ones I broke.

 

Before anyone jumps to conclusions, this heat is in the combustion chamber area, and is separated from the fin area where the wind blows, by about a thousand degrees, and that thousand degrees can pulsate faster that you can back off the throttle at times, and cannot be measured in the exhaust.

 

 

[bexrbetter]

Without seeing the entire piston, rod, valves etc, then it's impossible to determine possible reasons for the failure. Very convenient that the owner's mods are shown and nothing else.

 

And what a load of crap giving the engine to Jabiru for analysis, like they haven't got a vested interest and never had a valve seizure before ....

 

The exhaust valve is bent, with Jab's history of it, someone want to tell me why the scenerio isn't a valve seizure followed by the piston slamming into it. Maybe the official report should be reading that the aftermarket piston wasn't strong enough to withstand whacking the stuck open exhaust valve ...

 

Looking at the cylinder scouring, that piston was definitely picking up before the failure.

As Nev said, too tight, that's ring land scouring. Clearly the wrong clearance for this aircooled engine. But that happened a long time ago and resolved itself through wear.

 

I'm also wondering what caused the half moon shaped indent in the combustion chamber ?? Given it hasn't dropped a valve, very symmetrical and to small a radius to be the edge of the piston skirt, it can't be seen in the photos if the gudgeon broke up ,or the conrod.

It's a very strange mark, leads to another question, did something enter the engine? I've seen rods bent and the gudgeon near 90 degrees, but still wouldn't get to that position. Possibly a part of the piston pin boss, but we can't see that area of the damaged piston.

 

While the die grinding on the piston is hardly neat ,would it cause a stress fracture ,given the very sharp radius on the inside of the piston skirt would be a much more susceptible spot for a crack to start.

.

While not beautiful, and not certainly reccommended, it's a convenient scapegoat. I've seen all sorts of mods done to piston skirts and done quite a bit with them myself, especially with 2 strokes.

 

Removing metal from the bottom of the gudgeon bosses of a piston is a standard practice for balancing.

 

While it sounds bad that a non genuine piston was used

Piston is inanimate, doesn't care what engine it's in, only the parameters it's offered.

 

My summary is there's a clear lack of evidence to determine the failure without seeing that damaged piston as a whole, the exhaust valve and it's guide, the backside of the intake valve, the conrod etc.

 

Too many questions, and very poor form that the engine wasn't independently evaluated, but I strongly suspect exhaust valve strike.

 

 

[scsirob]

My €0.02 : The big red flag is the valve sticking out. That doesn't happen unless a piece of piston is found wedged under the valve, or it was stuck to start with.

 

Stuck valves have happened before due to lead build-up, insufficient clearance, or burned oil residue from overheating. I'd put my money on overheating. Valve sticks, piston hits valve and shatters on first impact due to being weakened, valve bends. The investigation reveals the die grinder and sander marks, which are bad, but these are only secondary to the damage.

 

 

[gibby]

Investigation: AO-2017-063 - Engine failure and forced landing involving Jabiru J430, VH-OFR, 17 km S of Bundaberg, Queensland, on 18 June 2017

 

Atsb report