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Scotty 1

Just a heads up!

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image.jpeg.cd0b7ee5efc0d23f65859334468fb58c.jpeg I have just been shown this head this morning and post the pictures for your comments. The motor has less than 5 hours on it as the plane is in the test flying period and all 6 cylinder temperatures were reading within limits. Temp probes have all been checked and found to be reading correctly.

 

Any ideas?

 

Cheers Scotty.

 

image.jpeg.679e95e8f6d4bee9de2013c8fe85e308.jpeg

 

image.jpeg.66db71baefc7a1ec311f65231352eb04.jpeg

 

image.jpeg.7cd7fc992fa99d01e0d693ed0b98bf78.jpeg

 

 

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What engine? - casting failure, head not down square, not torqued on side? What dose the piston look like. New engine I assume with 5 hours, full warranty job.

 

 

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Head may have a striped stud or broken not tighten down correctly will cause that type of blow out only needs a small compression leak too destroy the head like that !

 

 

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6 cylinder Jab. There is an indication the cylinder has recessed into the head so I would assume it has been torqued at some stage. Less than 5 hours.

 

 

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Piston and cylinder all look good. You might be on the money with "casting issue" Mike or more likely material issue.

 

 

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Nev, no indication of any other problem, no broken bolts so it is starting to look like poor or faulty material. That is our guess without any further testing too Lyle.

 

 

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Looks like a high pressure leak, escaping air can erode very quickly, havent seen on an engine before though.

 

Should have felt and heard on hand prop or in early inspections

 

Ill bet something preventing head pulling down properly at assembly

 

Looks like leaks and burnt oil around other side too

 

What were EGT and CHT running at?

 

 

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That is quite an old Jabiru head - thick fins. I can't see from the piccies whether it is the Mk.1 heads or the Mk. 2 heads. So that engine, with only 5 hours on it, has been sitting around since at least before about 2008, I think.

 

It looks to me like mechanical damage from a broken push-rod; and I'd be looking at corrosion causing binding of either the lifter or the valve gear from growth of the rocker bushing causing the push-rod to break, thrash out the push-rod tube, and finally impact the head fins.

 

 

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That is quite an old Jabiru head - thick fins. I can't see from the piccies whether it is the Mk.1 heads or the Mk. 2 heads. So that engine, with only 5 hours on it, has been sitting around since at least before about 2008, I think.

It looks to me like mechanical damage from a broken push-rod; and I'd be looking at corrosion causing binding of either the lifter or the valve gear from growth of the rocker bushing causing the push-rod to break, thrash out the push-rod tube, and finally impact the head fins.

You are right in what you say about the early model motor Oscar, but it is definately not from mechanical failure of any part of the valve gear.

 

 

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Then, it a massive inclusion of crap in the billet - and needs to be reported to RAA as a defect, so that all heads from that batch of material can be withdrawn.

 

 

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I have heard of the material used in Jab heads is of improper grade because of whatever the reason but if it was that alone I believe we would have seen many more pics like this. There is definately recessing of the head at the portion of the blowout especially, and the grade of the material may not have helped. After the plane landed following this problem during it's third only flight of the test flying period the head studs were loose on that head only. Nothing was found in the preflight checks. As I have said only less than 5 hours total on a new motor even though as Oscar has stated it is an older model motor. The test pilot stated the temps were all good. The sender units were then checked to see if they were reading correctly and they tested ok. I believe there may have been a fault in the billet material that has started the problem with maybe a hot spot which has caused the blowout. The grade of material and the fact it is billet may have contributed to the problem. The plane has been run on avgas but for only less than 5 hours and again no signs of improper combustion or lead buildup. Your thoughts?

 

 

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Then, it a massive inclusion of crap in the billet - and needs to be reported to RAA as a defect, so that all heads from that batch of material can be withdrawn.

It is VH rego and has been reported to CASA.

 

 

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It is VH rego and has been reported to CASA.

They'll be so excited, tripping over themselves to claim it as a potential problem on all current models.

 

 

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I have done enough work on everything to assure everybody that casting and forging flaws occur in every manufacturer in the world from Lada to Rolls Royce - ask me about the nightshift work I did changing Honda VFR 750 porous casings on the sly ...

 

This one I would put down to simply an unfortunate flaw and doubt it's anything more.

 

 

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I'm curious to where the engine has lived for 8 or so years with only 5 hours of use. Actually I think it's older than that. My first engine was a 2007 engine (I think) and it was definitely a thin fin one.

 

Tropical humid or salty climate? Plenty of scope for corrosion to spread from a single point like a scratch or pit.

 

If it's been in a clean dry climate etc then maybe more chance it's manufacturing fault.

 

 

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I'm curious to where the engine has lived for 8 or so years with only 5 hours of use.Tropical humid or salty climate? Plenty of scope for corrosion to spread from a single point like a scratch or pit.

 

If it's been in a clean dry climate etc then maybe more chance it's manufacturing fault.

Taree. No sign of corrosion. No sticking valve. No indication. Look at the photos. After a 10 year build you may be able to understand how the owner of the plane feels.

 

 

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I think the fact the head studs (bolts) were loose on that particular head, shows where the problem originated. Any substantial leakage will gouge out a part of the mating face and once it starts it will progress quickly. As to comment around about "wrong" type of aluminium billett, less than optimum grade might be a better definition. There is always a compromise with choice of materials. Ease of machining would come into it, and cost. It's got the material in common with all the motors made around that time. The damage would have been obvious by the noise from the gases escaping, I would have thought. Having engines sitting around for lengthy periods requires some repeating of the inhibiting effort. Nev

 

 

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They'll be so excited, tripping over themselves to claim it as a potential problem on all current models.

I'll buy shares in Aussie tissues then 092_idea.gif.47940f0a63d4c3c507771e6510e944e5.gif

 

 

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I think the fact the head studs (bolts) were loose on that particular head, shows where the problem originated. Any substantial leakage will gouge out a part of the mating face and once it starts it will progress quickly. As to comment around about "wrong" type of aluminium billett, less than optimum grade might be a better definition. There is always a compromise with choice of materials. Ease of machining would come into it, and cost. It's got the material in common with all the motors made around that time. The damage would have been obvious by the noise from the gases escaping, I would have thought. Having engines sitting around for lengthy periods requires some repeating of the inhibiting effort. Nev

Just had a look at the last image in the OP at 500%, and yes, it's pretty obvious that the two head bolts either side of the damage must have been under-tensioned ( for whatever reason) and the head has warped and lifted enough to allow the gases to escape. That greyed area, you can see what looks very much like flame scouring, and there is what looks like a trace of burnt oil in the very bottom of the flame-gouged track through the fins. Also, the burnt oil around several of the other head bolts suggest that most of the head bolts were not at correct tension. WHY that was so, deserves close attention.

 

 

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Even without the 500% you can see what looks to be chattering marks on the head/barrel fit between the 11 o'clock and 3 o'clock position.

 

 

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