Just a heads up!

[facthunter]

I would suggest there was surface rust and that is most likely the cause of the scuffing marks. Fine rust even can pug up the ring lands. Any motor I put into service I pressurise the oil system first and squirt some 2 stroke oil into the carb to make sure the bores aren't bone dry at initial fire up. 2 stroke oil won't cause carbon build up at all and doesn't reduce octane rating or affect plug insulators. If there's a bit of fine rust it will help to flush it out of the spaces between the rings, but dismantling if in doubt is the go. Nev

 

 

[Oscar]

Sorry Oscar, but there is no other way to put this. You are totally wrong. Others have seen, it appears, what you can not. Same as in your post#12 your post #46 may have been in haste. There was no Loctite used on the heads. Anywhere. Bolts or mateing surfaces.

Fine, then it is as it should be.

 

 

[Scotty 1]

Oscar - are you talking about the silver between 3 o'clock and 7 o'clock? It looks to me to be molten aluminium from the head. And my guess is the head was not properly tensioned to the cylinder face causing the hole and the burning across the face of the head cooling fin.

Have a close look at the first set of pics and you will see the cylinder has recessed into the head especially around the area of the blowout, would that not indicate that there was tension on the head bolts?

 

 

[01rmb]

Oscar - At home now and I can see what you were looking at. I would say that is just rust.

 

Scotty - It is possible there was tension at some stage but to me the molten metal over the cylinder-head sealing face would indicate to me it wasn't properly sealing and the head body and cooling fin just melted with the combustion. That is a lot of metal that has disappeared. Was the head tensioned prior to being run after the time in storage? How was compression on prop pull through prior to each of the flights?

 

I am not a mechanic and am only going off what I have seen with my engine and what I saw in Bundaberg when I did the Jabiru engine course.

 

 

[Scotty 1]

Would you agree that a pull through by a independent test pilot as well as the owner would show a soft cylinder? Does the manual say to re-tension the heads at between 5 and 10 hours? Would you suggest that as part of the pre-flight the heads should be re-tensioned before each flight?

 

If the head bolts loose tension that is a seperate problem. Remember this was the third test flight. Why is it so hard to believe that something caused a hot spot in the head which caused localised heat that has resulted in a warped head losing the seal between the head and cylinder in a very localised area and created the blowout. Remember how a oxy cutting torch works? Have a close look at the pics again and show me any signs off overheating other than very localised. To the people actually involved with this engine, the question is what caused that localised overheating. There has been some very informed responses that have probably held the answer, but I wonder if we will ever have a positive answer. A full strip down may provide further indication of the condition of the internals that may lead to assumptions but it does appear that it is not a common problem or it would have been seen before. Once again, thanks for all your thoughts. Any more news and I will post again.

 

 

[01rmb]

Apologies - you obviously feel that it is a manufacturing flaw. I only comment because I am learning too and keen to find out as much as possible.

 

I agree a pull through should pick up poor compression but maybe it isn't able to pick up a slight lack of sealing on the head but which is enough for the combustion gases to leak out.

 

The Jabiru manual does call for a 10 hour special maintenance check (5 hours for a solid lifter) which requires a re-torque of the cylinder head bolts so no, not between 5 and 10 hours. Although Jabiru emphasises - For a new aircraft or one equipped with a new or overhauled engine the first few hours of operation are critical. During this time the engine must be monitored carefully in operation and during maintenance.

 

This engine has been sitting around for several years and the Jabiru manual says an engine in storage needs to be reinhibited and inspected for corrosion every 90 days. The obvious signs of cylinder corrosion in this cylinder highlights an inherent problem prior to the test flights. Was the engine turned over to move the pistons during storage? What is the condition of the other cylinders?

 

Not eliminating the possibility of a hot spot and localised heating you could be right. Jabiru would be far more knowledgeable to advise.

 

 

[facthunter]

The discoloration near the leak area of the cylinder. which is the hottest part near the port is not as extensive as I've seen it in some engines that haven't failed. It's often more blue in colour. Some bolts may not have had sufficient torque and the sealing face failed causing erosion of the softer metal in the head. If there had been a flaw in the billet, I suggest it would be more localised and not fretted over a fair distance, as this is. Nev

 

 

[Scotty 1]

I agree Nev, I have seen a lot hotter. I don't believe the engine has been overheated which leaves the question as to the recessing of the head that would lead to loss of tension. A lot more pronounced around the area of the blowout, but still recessed on the opposite side. A lot more will be found with a tension wrench and a full strip down and inspection. That would also answer the question as to whether it has been inhibited correctly. Too many indicators in the bore for my liking but that may be from failure of that head. The condition of the other 5 pots will tell the story.

 

An inspection by fully qualified people, not people on a forum looking at pics, is what will be undertaken. I merely put up some pics and asked some questions to see if it is a common problem. It doesn't appear to be that common with these engines. I hope we can all get some positive answers especially for the owner.

 

 

[Downunder]

The brown ring inside the top of the bore.

 

Could that be accumulated rust, pushed up by the rings?

 

 

[jetjr]

Or the entire bore was like this and the rest is polished off.

 

I believe you should feel and/or hear that leak with a pull through. Even a cylinder on limits can be clearly felt and this is far bigger leak.

 

Solid lifters have tappet check at 5 hrs, this requires head bolt tension.

 

Head recession would not occur in 5hrs, its incremental often caused by running hot and tensioning down heads. If it is recessed its likely the engine or head has time on it.

 

 

[facthunter]

The pistons rest in different positions so not all bores will show the same pattern of rust. It's also may not be even .It may be only in a particular area. The motor should have been visually checked re the condition of the bores with something like a boroscope when it had been unused for that long. Probably retorque the heads also. Nev

 

 

[01rmb]

...Does the manual say to re-tension the heads at between 5 and 10 hours? Would you suggest that as part of the pre-flight the heads should be re-tensioned before each flight?...

I have just been going through the Jabiru engine maintenance manual checking for something else and found as part of the engine installation section 9.27 step 26, following the initial test flight, to "Check Head bolt tensions torqued per Table 10". Additionally, as per Special Maintenance sections 8.11 and 8.12 the head bolt tensions should be re-torqued at the 10 and 25 hour inspections.

 

So the answer to your question is the engine head tensions should be checked after the first flight, 5 hours if solid lifter, 10 hours and 25 hours and then at each 50 hour inspection - not wait until 5 hours for the initial check. My experience is that the bottom bolts (where the failure occurred) need tensioning as the engine is run in. If head bolt tensions had not been checked since the engine has been shipped several years ago or after the initial flight then you can not eliminate a poor seal on the heads having led to the failure even if there is a recess on the sealing face.

 

 

[jetboy]

The head bolt check after first engine run is done by Jabiru in the factory. If it was an overhauled engine and test flown on the plane, then the clause about head bolt checks after first flight would apply. The next check is called for after 5 hours run by the customer, which the engine has not got to yet.

 

 

[Oscar]

For new Jab. engines, that first engine run is done by CAMit on its dyno and the head bolt check is part of the 'build sheet' documentation supplied to Jabiru. However, as you say, if it was a 'rebuild' done by Jabiru, I am not aware if they do a test run.

 

 

[jetjr]

a new engine in the box, as its upside down, is a easy place to pinch a new head of required on a hurry.

 

Could have happened before of after sold

 

 

[Scotty 1]

I have just been going through the Jabiru engine maintenance manual checking for something else and found as part of the engine installation section 9.27 step 26, following the initial test flight, to "Check Head bolt tensions torqued per Table 10". Additionally, as per Special Maintenance sections 8.11 and 8.12 the head bolt tensions should be re-torqued at the 10 and 25 hour inspections.So the answer to your question is the engine head tensions should be checked after the first flight, 5 hours if solid lifter, 10 hours and 25 hours and then at each 50 hour inspection - not wait until 5 hours for the initial check. My experience is that the bottom bolts (where the failure occurred) need tensioning as the engine is run in. If head bolt tensions had not been checked since the engine has been shipped several years ago or after the initial flight then you can not eliminate a poor seal on the heads having led to the failure even if there is a recess on the sealing face.

Just had a count of the engines I have around the farm, from 2stroke leaf blowers and chain saws to diesel tractors, 17 in total. No 18 with the plane, guess I had best spend next week checking the head bolt tension on them if that is what is needed. If it's to be an on going requirement I guess it will be a couple of days a month from now on.

 

Thanks for letting me know the accepted standards 01rmb. Now can you tell me why the head bolt tension needs to be checked so often, and not just because it said so in the manual?

 

 

[jetjr]

Because the head tension is varied by material changes due to heat. In this engine the valve clearances and more damaging things can go wrong as you have exhibited, if case movement or head tension isnt monitored.

 

Some research would show plenty on head recession and overheating problems with earlier Jabirus. this along with constant valve clearance adjustmnet. Its the reason they produced new cooler heads and hydraulic lifter changes. This has brought its own string of problems.

 

Other than cooling, the older solid lifter engine is a good thing, its where Camit restarted their development. Look into replacing heads with new versions and id reclommend moving oil line.

 

Not sure how many of your 18 air cooled motors have as serious consequences if or when they stop.