Jabiru Letter #149 - through bolts

[Bryon]

Can you give a breakdown of how many had full suite of EGT and CHT sensors and what their temps were like in the lead up to the problems?If they had a full set of each and the temps were all good then it gives a different indicator of reliability (or lack thereof) compared to if they were just running in an unknown state or if they were known to be high.

Rod Stiff at Natfly said not to fit EGT and CHT guages as "they give you too much information"

 

 

[Guest DonC]

Typical of Stiffy!

 

 

[jetjr]

Yeah well thats Rod, he also wont admit openly theres any issue but will talk privately that the EGT spread has possibly been an issue since day one, albiet underestimated. Being fair this is a key issue for all carb engines just some use water or extra metal to overcome the problem. Jabiru engines are light and need to stay that way so its a VERY hard issue to solve.

 

Flying a Jab like a Cessna I believe is a core problem. They are a low volume production engine which is still being developed and sorted out. Through being part of a good value aircraft they have enterted the mainstream market where owners expect higher levels of refinement. Im not sure Jabiru are in the right mindset for this market although as they grow they will have to improve or slip back in market share. Lycoming and Rotax probably killed more engines in development than Jabiru have made yet.

 

Looking through the list of failed Jab engines there Ian theres a few with early hydraulic which were a known to have a lot of issues, others are in the right timeframe and models to be running the super lean jetting in the carb, and valve failures would link to that.

 

Another intersting point raised is the J200 - circa 2005? failing, these had thick finned heads, many had old cowls, and small oil cooler and ran hot even on a cool day, I fitted 6x EGT and CHT to mine and the spread was scarey, no doubt this engine was headed for an early grave, after playing with mixtures and cooling they were brought to much improved limits. This engine went to 800+ hours and was swapped due to low leakdowns but still ran fine. New heads knocks 40-50 deg C off the CHT and this was a good enough reason to change over for me.

 

In regards to the current overhaul of the same engine, only 400 hrs in ~ 10 years, this can be the possible cause, We have a 2005 Saratoga requiring rebuild as cylinders were corroded from lack of use ~ $20K in parts.

 

This could be part of the reason why training aircraft seem to get better run than privately flown.

 

I last week fitted cross vane in the exit to the aircleaner and it made a significant improvement to the EGT spread. I have now just one cylinder getting over ideal EGT limits.

 

 

[fly_tornado]

You wonder why Jabiru don't offer a dual carb option, that would fix a lot of the issues with the uneven mixtures... and oil cooling on the pistons and the exhaust valves would fix a lot of heat related issues as well.

 

 

[ianboag]

Flying a Jab like a Cessna I believe is a core problem.

Which page in the flight manual tells me that?

 

early hydraulic which were a known to have a lot of issues

Can't be - there were no SBs or other attempts by the factory to get owners to rectify them

 

others are in the right timeframe and models to be running the super lean jetting in the carb

the J200 got it after I bought it at 75 hrs TTIS - there was an SB that said it was a good idea so I bought the kit

 

the J200 - circa 2005? failing, these had thick finned heads, many had old cowls, and small oil cooler and ran hot even on a cool day

2003. What's this about "old" cowls? Yes the oil cooler was silly - it was the same as the 2200 cooler. I replaced it with a big one. Thick-finned heads were how it came.

Four wounded Jabs and five non-wounded 912's on our field. One of the wounded Jabs was fitted behind a relatively young dead one.

 

I can appreciate that you are a very tolerant test pilot sort of chap. You are willing to instrument things at your own expense beyond what the factory feels was necessary. You are also willing to muck about with configurations outside what the factory knows anything about.

 

I'm not like that. I just wanted to go flying and feel confident about the fan.

 

 

[jetjr]

The point Im making is that Jabiru have LET thier customers feel they are just like a Cessna etc etc, and its not true. They are a recreational Aircraft, built to differing standards, THAT is in the manual. Id say you also knew the AC you bought was homebuilt, and not certified. If you want the benefits of a old and proven US engine and aircraft, keep flying them, but they have down sides too. A Rotax is a good option too, but they arent problem free either.

 

Im not tolerant and certainly no test pilot, but the J200 is what I have and I have to make it work for me. I have very little to complain about apart from excess fiddling with engine which I agree shouldnt be needed.

 

By the way nothing Ive done is outside what the factory knows. I talk to them regularly.

 

I actually see this as a problem as youve outlined, unless you do this and trawl through web forums, how are you supposed to know what the issues are? This flows onto L2 and LAME's, how are they supposed to know what to look for?

 

In regards to missing SB, what do you expect them to say regarding a non identified problem with major on line development in thier engine???? Most owners I know of with valve issues and lean carb kit had parts replaced cheaply or even free. Had EGT monitoring been pushed harder Id suggest much less problems would have eventuated.

 

The older cowls were fitted to J400 and some J200, they had smaller intakes sort of further on top of the cowl, and these also used older design airducts which didnt work too well. Being all homebuilts it isnt clear when changes were implemented.

 

 

[Guest Pioneer200]

So Ian, why did you buy another Jab if you were/are not comfatable with the engine??

 

 

[zodiac3813]

Hi All...

 

I had a broken through bolt (top, No. 1) on my reco 2200 engine about a year ago (at about 100 hours), and assisted a local L2 to replace all the through bolts. He had quite a few tools that he had adapted specially. Jabiru supplied new through bolts and nuts gratis (the least they could have done, considering the fact that they didn't replace them when they reconditioned the engine!). The job was complicated by the fact that the new O-rings supplied for the push rod tubes were too thick (to suit newer engine), and the ends of the tubes had to be chamfered to make them fit. Total cost to me was $900, and now I'll have to get it all redone at some stage in the not-too-distant-future... very disheartening! BTW, Don at Jabiru told me at the time (quote) "these through bolts are over-engineered, and won't ever be altered"..... Hmmmm.

 

Jim

 

 

[eightyknots]

has he kept the basic field maintainer in mind when it comes to basic maintenance.................Mmmm........NO !!..........................sorry not good enough IMOP...........................Maj....

That's an interesting point Maj!

 

One of the reasons why Rotaxes are so popular in Africa is that they can be serviced relatively easily and they are statistically reliable. Rotax in Austria has a sponsored training program for African service people and a number of additional service centres are being or have been established on that continent.

 

When flying over TRUE tiger country, African aviators talk of St. Rotax keeping them from danger.

 

 

[fly_tornado]

Would I be right in assuming that the through bolts are breaking because the block is deforming?

 

 

[Vev]

Would I be right in assuming that the through bolts are breaking because the block is deforming?

Almost but not quite ... I think it easiest to explain if you read the Jab's Advisory Notice, which explains in detail the cause and the fix.

 

JSB031-1 Jabiru Engine Through Bolts & JSD031-1 Service Directive

 

Cheers

 

Vev

 

 

[Relfy]

talking to Jamie at Jabiru last week, all indications were that the thread was pulling through the nuts. New nuts will help to fix this issue with greater contact area.

 

 

[frank marriott]

Ross (Maj) on this site

 

I know Ross - he is a friend but on this site his comments are not helpful - he is so far left

 

or whatever one likes to call it that the threads can be changed from helplful to basic bias - he is so biased to Rotax that I believe his comments should be put in General not in Jabiru specific forum.

 

 

 

 

 

 

 

 

 

Rotax promotion and Jab bashing does nothing for the Jariru specific site where those of us that own Jabs [or me particularly] are not interrested in Rotax promotion - but I have not done any Rotax bashing - nor will I.

 

 

 

 

 

 

 

 

 

If one wants to promote Rotax [or some other engine or aircraft] - great - but put it in some other forum - not in the Jabiru specific forum , I for one, am not interrested in some private agenda,

 

 

 

 

 

 

 

 

 

The brand specific forums are of great value to those who operate that particular aircraft - I don't even look at the other specific sites as I can not contibute anything of value.

 

 

 

 

 

 

 

 

 

I find this site very helpful but please if one has a view which is so far anty a perticular aircraft or engine then I would think it would be more helpful in the General Discussion area then in a type specific area. [i also read the General Discussion section and contribute only if I thing my comment can help].

 

 

 

 

 

 

 

 

 

Just my opinion as a somewhat new boy to this site [only two years but over 30 years of flying].

 

 

 

 

 

 

 

 

 

Too many times an interresting thread has been hijacked by a personal bias that I stop following the thread.

 

 

 

 

 

 

 

 

 

It it great to hear eveyone's opinion - but put it where it can be appreciatied.

 

 

 

 

 

 

 

 

 

Ross and an AAME mate [of both of us] have had toung in cheak conversations for a few years but to put some things in writing I don't think is helpful.

 

 

 

 

 

 

 

 

 

Frank

 

 

 

 

 

 

 

 

[bushpilot]

Ross (Maj) on this siteI know Ross - he is a friend but on this site his comments are not helpful - he is so far left or whatever one likes to call it that the threads can be changed from helplful to basic bias - he is so biased to Rotax that I believe his comments should be put in General not in Jabiru specific forum. Rotax promotion and Jab bashing does nothing for the Jariru specific site where those of us that own Jabs [or me particularly] are not interrested in Rotax promotion - but I have not done any Rotax bashing - nor will I. If one wants to promote Rotax [or some other engine or aircraft] - great - but put it in some other forum - not in the Jabiru specific forum , I for one, am not interrested in some private agenda....

 

Frank

 

 

I agree 100%. We want to see constructive contributions in these specific-subject topic forums.

 

Some may think that being defensive about a particular brand/type relates directly to what the defender owns; indeed this is a natural reaction. But as Frank says, such bias (for or against) is not necessarily helpful.

 

In my case we have just ordered our 4th Jabiru. We gain nothing from doing so other than some fleet efficiency. But if we did see obvious commercial advantage in going another way - buying another type of a/c, then we would. In fact each time that we get to the point of needing an additional a/c we do re-visit the options. We got close to ordering a Cessna Skycatcher recently, but decided that there are too few of them out there at this stage for them to have any in-service history. We also looked at some of the Euro brands, but in talking with owners became concerned about the availability of parts.

 

In a school environment we need all of our a/c servicable for 99% of the flying days - save for regular servicing; and Jabiru gives us this operational capacity..

 

Whilst not related to this thread, there is also the issue of 'eye appeal', particularly from the point of view of newbies to aviation or recreational aviation; Jabiru's basic design/s meets the expectations of what a 'normal' a/c should look like - and makes the 'looker' more likely to sign on..

 

 

[Guest Maj Millard]

Post editied by Moderator in relation to Frank and Chris's response. This thread will only be available for Jabiru specific issues. All other discussions should be placed in new threads outside this one.

 

- Moderator

 

 

[Thruster87]

About bloody time Cheers T87

 

 

[fly_tornado]

is anyone really stopping you starting your own jabiru thread?

 

after reading that service advisory, yes the engine blocks are twisting! thats a bit of a worry, another limitation of air cooled engines. At least they have recognised the issue and are putting bigger threaded bolts in.

 

 

[Jaba-who]

Which service advisory is that?

 

So far I have read all that have come my way but maybe haven't seen them all.

 

So far all that has been mentioned in the ones I saw are fretting (which is due to movement (often micromovement) and happens usually without any change in shape of the parent structure) and thread failures on either the bolts or the nuts (I'm not sure which but the assumption seems to be the thread on bolts rather than the nuts.)

 

I'd be keen to see an official statement showing the engine blocks have actually twisted.

 

 

[Bruce Robbins]

after reading that service advisory, yes the engine blocks are twisting! thats a bit of a worry, another limitation of air cooled engines. At least they have recognised the issue and are putting bigger threaded bolts in.

fly_tornado,

 

The SB does not say the block is twisting, but may sometimes be fretting along the joint between the crankcase halves.

 

I am relatively new to Jab engines, but have flown behind them now for five years. Initially an hour or two a week, then weekend instructing and finally full time instructing. For the first four years I saw no issues with through bolts in five heavily used aircraft. In the last twelve months however I have had three different engines in three different aircraft break a through bolt or stud. Engine times since new or since overhaul ranging from 850 down to just 200. Two were four cylinder, one was a six cylinder. I have shown or discussed the broken bolts with a number of mechanical engineers and L2's. All said the same thing - " .....looks like a fatigue break. The likely cause is loss of tension in the bolts, leading to movement, fatigue, and then breakage."

 

I had another engine reconditioned by the factory that was showing signs of possible impending failure after just 80 hours in service. Fretting and oil leaks from the cylinder bases, and what looked like the start of fretting between the crankcase halves. Investigation discovered a loose base nut. We replaced the nuts with the new 12 point nuts and all the signs dissapeared. The engine even seemed to run smoother. That engine did another 150 hours before moving on to another school with no further problems.

 

There are many things that can cause a loss of tension in the bolt, but I am convinced in my mind (although I have no actual stats or evidence) that the reason for losing tension was cylinder base nuts that were not up to spec with regards to material, dimensions or thread pitch angle. The nuts mentioned in the SB, and the newly designed ones on our latest spec six cylinder motor seem to have solved the problem, provided they are installed and tensioned correctly.

 

After starting to lose confidence in the Jabiru engines, I am comfortable to once again fly behind them and hire them out to customers. I believe the problem was in the base nuts, and appears to have been addressed.

 

Regards,

 

Bruce

 

 

[ianboag]

.....looks like a fatigue break. The likely cause is loss of tension in the bolts, leading to movement, fatigue, and then breakage.

Yep. Movement. Not enough clamp. But the studs were prone to strip if reefed up. If one stud breaks from fatigue, the others are all moving down the same road. Arguably if one breaks, the right thing is to replace all of them.

 

Fretting and oil leaks from the cylinder bases, and what looked like the start of fretting between the crankcase halves.

Not enough clamp. Movement. Fatigue .......

 

the newly designed ones on our latest spec six cylinder motor

Nuts are not "specially designed". They are an off the shelf item from ARP.

 

 

[Bruce Robbins]

G'Day Ian,

 

Looks like we agree on the end result (loss of tension in the bolts) but not the cause.

 

.....looks like a fatigue break. The likely cause is loss of tension in the bolts, leading to movement, fatigue, and then breakage.

 

Yep. Movement. Not enough clamp. But the studs were prone to strip if reefed up.

 

(..and I still believe the problem is with sub standard nuts, not the bolts themselves. Have a good look at some fairly recent used base nuts, and see how little of the thread area is actually load bearing)

 

If one stud breaks from fatigue, the others are all moving down the same road. Arguably if one breaks, the right thing is to replace all of them.

 

(agree, or at least all the bolts and studs on the affected cylinders)

 

Fretting and oil leaks from the cylinder bases, and what looked like the start of fretting between the crankcase halves.

 

Not enough clamp. Movement. Fatigue ......

 

(due to a base nut that had loosened slightly after less than 80 hours on a rebuilt engine, leading to loss of tension and clamping. We replaced the nuts only. Problems dissapeared and the engine is still running strongly).

 

the newly designed ones on our latest spec six cylinder motor

 

Nuts are not "specially designed". They are an off the shelf item from ARP.

 

(Our latest motor is a brand new unit. The nuts are a different design, NOT the 12 point ARP nuts as per the SB which we have fitted to all oour 2200 motors. They are a hexagon nut with a deep flange under the hex. Look like they could be CNC made by Jabiru themselves, though that is just my speculation, considering the cost of the ARP nuts)

 

Bruce

 

 

[jetjr]

(Our latest motor is a brand new unit. The nuts are a different design, NOT the 12 point ARP nuts as per the SB which we have fitted to all oour 2200 motors.

The brand new 3300 being fitted here right now has come with old nuts - after SB went out.

 

 

[Modest Pilot]

To replace the barrel nuts the Heads and the pushrods and their tubes have to come off to reach the lower nuts.

 

 

[Jaba-who]

I'm not sure of your terminology. If by barrel nuts you mean the nuts on the through-bolts you're right....partly. It's even more complex than that.

 

To get to the rear upper nuts you also have to remove the starter motor. To get to the lower ones you also have to remove the exhaust and inlet pipes.

 

I started doing mine (actually two of us planned to do two 3300s) and decided I could better spend my time doing other stuff and have booked both in at the factory at the same time as the Wide Bay Air Show. SO we'll go to the show, hang around an extra day and get the two done by jabiru for free.

 

One Jabiru service guy near here has said he just pulls the whole engine out and puts the engine on a swivel bench mount. Jabiru factory allocates a full day and two blokes for them to do one engine.

 

So all in all it is not a simple job.

 

 

[Modest Pilot]

That's it Jaba. Took me all day, it's hardly worth removing the engine, as the time works out greater. The factory have it down to about 3 hours with two guys on the aircraft. Hint: a stud clamp would be handy, saves having to double lock stop nuts to stop the stud turning when you put( or take off) the first nut. I was probably over cautious and did one nut at a time, which meant that you have to wait 10 minutes or so to let the Locktite set up and not let the first nut turn, so that's 2 hours gone. You might be able to set up a sequence that's faster and not risk distortion of the case. I spent the time cleaning the lead build up off the heads! It's worth doing an oil change as the cowls are off, taking off the oil filter and adapter, gives a better swing for the Torque Wrench on the lower forward nut. Also the new ratchet torque wrench's are hopeless for this job; you need to keep the crows foot adapter at the same angle for the correct torque. I would not do this job with a non certified wrench either. Having said all this I must add that this is one of the nicest and easiest engines I have worked on.