Jabiru Letter #149 - through bolts

[slartibartfast]

I just received a PDF from Jabiru (via Garry Morgan) regarding the recent through-bolt failures.

 

They have advised that the nuts should be replaced with wider 12 point nuts and Loctite 620 used.

 

The buggers just sent me a new set of nuts a few weeks ago. You'd reckon they could have sent me the new ones.

 

Anyway - the PDF is in the downloads section here.

 

 

[old man emu]

I am chasing these nuts so I can supply them through QED Hardware. Keep an eye on my thread in teh Supplers Forum.

 

Old Man Emu

 

 

[Guest Maj Millard]

OK just read that. Two or three things come to mind.

 

1. It appears that by changing the nut type that they feel the nut is the problem. I feel they are wrong, and that the stud is the thing that fails.

 

2. They are recommending that no safety thread be left projecting from the nut (min 1 max 3). This is against normal aeronautical practise, as used throughout the industry, so they are out on there own with that. How does CASA let them get away with that ?. To rely on Locktite on such an important bolt is suspect thinking.

 

3. Why don't they spend some money, extend the length of the stud, and have safety on the nut.

 

4. Their reasons for stud failures is gibbley gook. All the factors they state are also experienced by other widley used engines. Blaming the failures on 'circut work' is way out in left field. Can we also assume that the engine is not then suitable, or safe for student training ?. Rotaxs don't experience stud failures, and they do just as many circuts.

 

 

[Thirsty]

1. I think they are saying the deeper nut spreads the load on the stud. They are not saying the nut fails just that the shallower nut stresses the stud more locally.

 

2. Yeah this doesn't sit very well with me either. Don't they mention in the bulletin that longer studs are available though? If so owners can change studs at the same time.

 

3. They have I think.

 

4. I agree. I want my engine to be able to just work without me having to worry that doing a couple of extra circuits is going to hurt my engine.

 

 

[gregv]

2. They are recommending that no safety thread be left projecting from the nut (min 1 max 3). This is against normal aeronautical practise, as used throughout the industry, so they are out on there own with that. How does CASA let them get away with that ?. To rely on Locktite on such an important bolt is suspect thinking.

I ordered a new set of throughbolts from the factory 4 weeks ago. They arrived with the new 12 point nuts (ARP) and throughbolts with slightly longer threads than the ones I am changing out that should give a 1-2 threads at each end.

 

The new overhaul manual does say that you can use the ARP nuts on the old throughbolts though.

 

Greg v

 

 

[jetjr]

Dont suppose you can swap through bolts without removing barrells?

 

Only have to remove ons side I guess?

 

 

[old man emu]

My attempts to locate a supplier for these nuts was stumped because Victoria hada public holiday today. I'll try later in the week.

 

OME

 

 

[deadstick]

I am a little perplexed at the approach as well, spreading the load over more threads does nothing to stop the through bolt failing and implying it gives more clamping force is just plain silly. If I read that correct then they are telling me they beleive the engines coming out of the factory are under torqued, dont get me wrong I am trying to like them, but with engines failing more often than they will admit and advice that goes against main stream aviation practices it bloody hard. beleive it or not I have just installed one of the latest build 2200's that is weeping around the cylinder bases due the new shim arangement (less than 200 hrs) and no fix, with this latest admission I have advised the owner to seek warranty on the repair. I am now seriously concidering selling my jab 230 before no one wants anything to do with them and I can't get a resale price. Prior to xmas I was advised that I would receive a replacement intake manifold (once available) due to the problems I was having with mixture distribution, now they want to charge me and after it has cost me a rebuild at 230 hrs. Give me a break! did they design this engine for australia? cause it is not up to the task me thinks! I have not seen one jab engine that does not require constant tinkering/ adjustment and I havent seen one make TBO yet! over.,... end rant!!!!

 

 

[Guest Maj Millard]

Ok, If the longer throughbolts are available then that's a step in the right direction. Are they the same stock, and diameter as the old ones that failed, and just longer ??

 

I have removed, refitted, and torqued many throughbolts on Lycomings and Continentals. I have never used Locktite on any. Generally they just either specify a clean oil-free thread or an oiled one. They don't give too many problems.

 

The throughbolts on any engine are a critical part, and I don't feel there should be any shortcutting done there. We are talking an Aircraft engine here afterall, not a lawnmower, so the standards need to be very high...Only time will tell.........................................................................................Maj...

 

 

[Thirsty]

I've read all the threads on the Jab engine failures and the opinions on what causes the failures and just want to add something. Comparing the Jab to Lycoming and Conti engines is a bit unfair. Those engines are much larger capacity and are really understressed. If we could have higher weights we'd all be using them because of this - they rarely fail because they aren't stressed. The Jab engine is stressed quite a bit higher 'cause it weighs bugger all and produces a reasonable amount of HP. Maybe Jab should have gone the route of higher revs and a gearbox - to my mind this would have been a more reliable combination but heavier.

 

I don't have the answer but it seems to me they are trying to fix the issues - I hope they do it and soon 'cause I'd love to buy an all ozzie plane/engine combo!

 

 

[ianboag]

I am chasing these nuts so I can supply them through QED Hardware. Keep an eye on my thread in teh Supplers Forum.Old Man Emu

They are from ARP in the US - http://www.arp-bolts.com

 

 

[old man emu]

www.arp-bolts.com[/url]

I've tracked down an Australian supplier and am in discussions with him. If anyone wants to fit aviation certified hardware, then 12 pt nuts of the appropriate size for this job are NAS1804-6. I've made some enquiries about obtaining the NAS bolts, and the surest way is to follow a rocking horse with a shovel.

 

At work we deal with quite a few Jabirus, both privately owned and flying school hacks. From my observations I've formed the opinion that the Jabiru engine overall manufacture is very good. What I believe is letting the side down is that the Jabiru people are deficient in engine assembly knowledge. This is why they come out with some recommendations that make old timers scratch their heads in disbelief. They don't seem to have a good grasp of threaded fasterner behaviour. If they asked the old hands about the correct way to hold components together with threaded fasteners, then they could probably solve many of the current problems quickly and cheaply.

 

These problems aside, I think the Jabiru engine is worth supporting. Perhaps it is not really suitable for the harsh demands placed on it by hours of circuit work and multitudes of inexperienced pilots, but as a powerplant for a privately owned aircraft, it fills the bill.

 

OME

 

 

[David F]

There is an easy fix guys Paul Crowfoot did it dont think he has looked back.

 

Dave

 

 

[HEON]

I think Thirsty the Jab engines are being compared to Rotax engines and not the larger capacity US "iron".

 

On capacity the Rotax 80, 100, and 115hp are all under 1300cc. Jab's around 2200 and 3300cc!

 

On these figures the Rotax is more stressed and weight is very similar, yet all have a TBO of 2000hr, and seem to have a much better chance of reaching it.

 

I personally think there is more to it than a simple Ford/Holden arguement as I do not think they are similar for reliability.

 

I own all three Rotax engines...I will not own a Jab one until Forms such as this stop BECAUSE THERE IS NO NEED ANYMORE!!!

 

 

[deadstick]

OME, you have hit the nail on the head and I am thinking of sticking with them for the long haul, all the probs they recognise can be fixed and I think to a small degree they have done so. (almost there)

 

With a couple of small design inclusions and tighter quality control I think they will have a final outcome that is both cheap and reliable. I would like to see some support maybe in the form of a cost price on replacement parts for those affected to date.

 

I think they will save a dwindling customer base and allow those of us that Like to buy Australian a product worthy of our hard earned $'s.

 

HEON, what do you mean by this: ...I will not own a Jab one until Forms such as this stop BECAUSE THERE IS NO NEED ANYMORE!!! and I agree its not a holden v's ford thing its unbiased and constructive feedback/ critiscism, enabling a constant improvement loop and also information to others as thats what these forums are about.

 

Rotax and Jab are both chaseing the same thing reliability and cost effectiveness, where as rotax adapted the automotive style high RPM driving the prop through a reduction gerabox, Jab went for the high TQ low rpm direct drive in an effort to keep it simple with less moving parts. Cant wait for it to get sorted!

 

DK

 

 

[Guest Maj Millard]

Thirsty, I note your points. However most of my experience (but not all) with Lycomings and Continentals, is with engines installed in hard working ag planes. Most take-offs are fully loaded, and no ag-pilot worth his salt would agree with you, that those engines aren't stressed at take off. Generally one or more cylinders would be changed, and through-bolts checked at each 100 hourly during the working season...........................................................Maj...

 

 

[facthunter]

ALL aero engines are stressed. They don't carry surplus metal anywhere if they are designed properly or they would be too heavy. Rpm does not imply more stress by itself as the stroke is shorter (for one thing) reducing inertia/dynamic loads. Nev

 

 

[HEON]

I am sorry Deadstick I thought what I said was quite clear.

 

Trust this is now clear. I will never own a Jab engine while so many post negative comments on this, other forms, and by word of mouth, about the reliability of Jab engines. Unlike some I feel that so much comment by so many is not just the feelings of Jab engine haters trying to "cut down" the "Tall Australian". Within the comments is the fact that although they are getting better, they do not have the reliability of a Rotax at this point of time.

 

Have said before that in my opinion the Jab 170 is the most cost effective two person Australian touring aircraft...when fitted with a Rotax 100hp engine.

 

When I did my training (in Jab LSA and 160) the school where I did it had both Jab and Rotax powered aircraft. I asked about engine problems as I was going to buy an aircraft and had heard about some Jab problems. The reply was every Jab they had owned had had a major engine problem, while none of the Rotax had.

 

Made up my mind for me, and I have yet to see the evidence to change it. In other words the negative comments stop in Forms because they do not break as they still seem to be doing.

 

 

[deadstick]

Heon, I do agree with you my friend just wasn't sure what you were saying forms? or forums? our network here helps to spread the word on what is happening and also avail us all of the experience gained by all. quote ...I will not own a Jab one until Forms such as this stop BECAUSE THERE IS NO NEED ANYMORE!!! this was not clear to me perhaps you meant I will not own a Jab engine until forums such as this stop reporting failures and problems. sorry but didn't make gramatical sence to me.

 

 

[old man emu]

I think that the reason Rotax engines are performing so well is that they are past their development stage. Jabs are still undergoing development, and it is just a matter of numbers in service that gives the number of reported defects.

 

I still say that these problems seem to stem from the Jab people not having a good grasp of how components shoud be joined with threaded fasteners. I think that in most cases, the specifications of the materials used to make the engines are comparable with other aero engine manufacturers, but I would like to see more data about the materials being made available.

 

OME

 

 

[Guest Maj Millard]

Old Man Emu, Can you tell me how long Jabs development period is ??...it's been going now for close to 20 years !!!.......................Maj...

 

 

[old man emu]

Old Man Emu, Can you tell me how long Jabs development period is ??...it's been going now for close to 20 years !!!.......................Maj...

Well, if we don't learn something new every day, we must be dead.

 

The engine may have been first designed 20 years ago, but I wonder how the numbers of engines in service have increased over time. I suspect that the rate of introduction to service per annum has increased in the past 10 years, and with more units in service, it stands to reason that there will be an increase in the number of problems. The question is: Have the number of problems increased proportionally to the rate of increase in introduction to service?

 

Anyway, we have a flying school Jab in for a 100 hourly and it has failed the leak down test in one cylinder. We decided that while we have the aircraft U/S, we will replace teh through bolts as per the letter. I ordered a set on the new spec bolts and a set of 12pt nuts today. Hopefully I'll have some more information for you on Thursday.

 

OME

 

 

[Guest Maj Millard]

Engine leakdown checks have to be done with the engine at operating temps (warmed up). Doing them cold is a waste of time. Make sure you have some anti-sieze on the plugs to be removed hot, so that they can be removed without damage...................

 

As far as numbers of engines produced supporting a higher number of failures, then yes, that figures. However there are many thousands of Rotax 912 engines produced worldwide, in the past 20 years also. Their failure rate per thousand would not be anywhere as high as the Jab engines.........................................................................................................Maj...

 

 

[ianboag]

Engine leakdown checks have to be done with the engine at operating temps (warmed up). Doing them cold is a waste of time. Make sure you have some anti-sieze on the plugs to be removed hot, so that they can be removed without damage...................

If you fish around on the Net about this one, opinion seems divided. I have heard opinions that hot leakdowns are likely to give better numbers than cold ones (expansion and all that). On that basis, if cold numbers are OK, hot ones are likely to be better .....

 

 

[facthunter]

If cold ones are good the hot ones are most likely to be good. Hot tests will give the most CONSISTENT results. Engines that have been sitting for a while, can give some bad readings that will markedly improve with a few hours running. This should not be done where there is suspected damage like valve guides/stems rusted or extensive cylinder surface rust. (Internal). The engine should be part dismantled and the fault rectified. It's an aeroplane motor and it's YOUR life. Nev