Jabiru Engine 2200 Mechanical Problem Reporting

[Vev]

Hi Bob,

 

 

Sorry to hear about your engine failure but thank you for taking the time to share this info.

 

 

At what stage in the flight (climb/cruise/final?) did the engine fail and how long had it been in the air? I’m also interested to know if you have had high/low ground and flight temperatures and if/when this happens.

 

 

I think that Walter’s point re “uneven thermal expansion” is quite plausible when you consider the different coefficient of expansion and different thermal conductivity of the engine materials… I wouldn’t be surprised if this is part of the failure mechanism.

 

 

However for all our speculation here, it will be interesting to hear Jabiru’s thoughts on the reasons for the failure and what is their recommendation is in terms rectification and prevention.

 

 

Cheers

 

Jack

 

 

[RKW]

Hi Tomo,

 

It was the lower bolts between cylinders 2 & 3 and between 3 & 4 which broke. When the motor is in situ it is hard to see the ends of the bolts. (Especially when they are not there!)Both had broken where the thread ends. This means that number 3 pot was attached by only the two upper bolts. It uses 100LL avgas exclusively, so you would't expect detonation to be the culprit but I'm starting to think it may be. Regards, Bob

 

 

[RKW]

Hello Jack,

 

It was on a training flight at the time and climing with the intention to practice turns when the motor started to vibrate and lose power. It had travelled about 12nm at the time. I think the temperature on the ground was in the low 30's.

 

I shall keep you informed as the saga unfolds. Regards, Bob

 

 

[facthunter]

Thru-Studs.

 

There is no doubt that there is a different rate of thermal expansion/ contraction of the stud and the aluminium case. The effect of this dimensional change can be reduced by designing the stud to have large sections of the plain part of the shank dia. reduced to something just smaller than the thread minor diameter. Has this been done? Nev

 

 

[RKW]

Hi Nev,

 

The through-bolt is 10mm in the centre and is tapered down each end, to a smaller diameter where it is threaded. Both bolts broke where the thread ends. They are not high tensile bolts with a rolled thread. From what I can gather, they are machined from crome molly rod and not heat treated. Regards, Bob

 

 

[facthunter]

Design of Stud

 

Doing it that way would concentrate all the stress in the threads below the nut and quite easily take that small length beyond the elastic limit, or cause fatigue over a period of time. Jabiru have suggested that detonation could be a contributing factor and you could not rule that out. Quite possibly the exhaust valve could be overheated and cause premature ignition, if things are not right with mixture and timing.

 

I'll stick my neck out and suggest the stud should be redesigned to distribute the strain along more of it's length. Nev.

 

 

[RKW]

Hi to all on the forum,

 

I got the engine back from Jabiru today and read the damage report. The report indicates that number 3 cylinder had a leak between the head and the cylinder. They do not have a head gasket so they rely on good machining and evenly torqued head bolts. The report suggests that the number three cylinder was detonating as a result of the leak and /or the use of poor quality mogas. ( It has always been run on 100 LL) The leak was caused by uneven tension on head bolts. Apparently the checking of head bolt torque should be done at service intervals. Now the engine is back together complete with new cylinder (No 3 was cracked around base) new exhaust valve in no 3 head and new rings all round. And new through-bolts. Should be good for another 300 hours! I wish I could express confidence that the cause of the problem had been resolved. Confidence is a valuable asset when you're at cruising altitude. Best Regards, Bob

 

 

[BigPete]

Make sure you tension all SIX studs - one is hidden under a plug, and if my memory serves me right this is quite often the only stud that will require more tension. Always done every 50 hours after initial run in.

 

 

[RKW]

Thanks Peter, I will make sure the head bolts are torqued correctly. Regards, Bob

 

 

[facthunter]

Head bolt tensioning.

 

Since it is a hot area,(near the exhaust port), the bolts tend to bind and it is a good idea to remove, clean, and apply an antisieze and retension. Other wise you will not get an accurate tension established, or at least back-off a few degrees, (crack the thread) and tension with the torque wrench after the bolt has freed up. Nev

 

 

[Vev]

If ever I find a loose head bolt its always the bottom one (as per Big Pete's post) ... to access it you need to remove the rocker cover and then the grub screw, which requires a long allan key socket to reach the bolt head.

 

I also agree with Nev's comments, you do need to ensure you use some anti-sieze or crack back and then torque.... the engine needs to be cold too. The guys at jab have told me over the phone to tension to 24 ftlbs which is higher then the manual, which is what I do every 50hrs.

 

Just one issue for me out of the report is the leaking head causing detonation ... whilst this possible it does sound a little out of the ordinary? Does anyone have a real experiance with detonation via a head/cyclinder leak? What do you think Nev?

 

Cheers

 

Jack

 

 

[facthunter]

Head leak/ detonaton.

 

Inso much as it could cause local overheating, I suppose so, but it would never reach the temps that the exhaust valve head or spark plug electrodes run at. A bit of incandescant carbon build up is always a possibility too, as a cause.

 

I am of the view and I believe that the jabiru people say (or used to say), that attend to the top end if and as soon as the compressions deteriorate. "tickle it up" and keep the compressions crisp. Top end work was often required on a lot of the "older" aircraft ( gypsy Majors etc) motors to keep them running well and it is not such a big job really, where the heads are detachable, without removing the barrells. Very few aircooled motors run to TBO without attention to the valve seating. Nev

 

 

[Ballpoint 246niner]

Just had 50hrly(TT) done by Jab on new 2200B(hydraulic) in my J120. All OK - Ts & Ps always in mid green. Normal early oil usage on run in oil but now very minimal (normal). I flew one of the A/C in Q in this thread with no problems and was surprised to hear of stud through bolt failure. I ALWAYS pull through on daily and I understand 15W/50 will be the advised std oil for hydraulic lifter engines( new cowl stickers are being printed.

 

Oil and filter will be changed every 25 hrs with head tensions checked at same interval.

 

This same servicing was performed by LAME on the 120 that was just ferried to NZ in recent JabaChat( I looked at buying it before deciding on new).

 

 

[Ballpoint 246niner]

I watched Mark at Jabiru do mine on Monday and noticed the one little sneaker behind the grub screw. Mark also did a full leak down as well. For me at YCAB it's a no brainer to fly up and have 50hrly's done by the experts. I know this is possible only for a few of the thousand + in service. The bill was reasonable as well- cheaper than a lot of bikes I get serviced! There is clearly a lot of highly experienced but dispersed knowledge within this thread on Jabiru engines and history- and we can all learn lots from it. For my two dollars the guys at the factory see and hear just about all of it and when their spanners are on my engine I fly more relaxed!

 

I copped a lot of friendly jibbing from fellow flying friends and acquaintances before I bought my Jab- and in these early days I can't yet say they are catagorically wrong- but I'm damn sure I'm going to be right on top of professional maintenance with mine, as many (not all) engine problems can be explained by variations to schedule, either inadvertantly or through lack of education/knowledge.

 

On AVGAS, I'm sure everyone has read the bulletin- read between the lines- you fly an aircraft- put aviation fuel in it. I know of 5 people in the last month who have had water contamination with MOGAS in their cars/bikes, some were premium as well! (use Mr Funnel if in a/c). There is also at least one case of an a/c with ethanol damage to wing tanks as well...

 

Now that might stimulate some discussion....

 

 

[RKW]

Hi Neil, Before startup, I always turn the prop thru at least four compressions and its not just cylinder pressure that I check for. I have had the crank bind on a j170 last year, and this was also considered (by the good folk at Bundy) to be caused by detonation. I'm still at a loss as to why they are so prone to detonation. What maintenance procedures can we adopt to eliminate this problem? Regards, Bob

 

 

[Ballpoint 246niner]

Hey Bob, I hear what you're saying-and many owners/operators /pilots who have had EFATO would throw their hands in the air asking the same question. I don't know either. So why do you think the Jabiru engineers put the failure down to pre- detonation. From what you stated in the report it's not that they said the detonation was the root cause- it sounded like thet stated that "incorrect head tension", causing a leak on No3 cylinder causing detonation was the actual cause. The question that needs to be asked then is everyone doing and getting their head tensions right within the required service intervals?

 

What do you reckon?

 

 

[RKW]

Hi Neil, I think it very likely is detonation and to suggest (as per damage report) that it was caused by a leaking cylinder head is a bit fanciful. The engine has no auto spark advance. Instead, it is set at a fixed 25deg btdc, which is a substantial amount of advance. I believe a car engine would ping its head off with that amount of advance, and wide open throttle applied. The J160 is also used for training and some students and others who hire it, will instantly "firewall" the throttle on takeoff and during endless t&g sessions. This puts an enormous strain on the motor and this is when I believe most of the damage occurs. I have observed this on numerous occassions and whilst I bring it to the attention of the instructors, the message does not seem to filter through. I advocate the progressive advance of throttle over 3 or four seconds to at least let the revs build up. I would like to thank you and the other posters for your interest is this saga.

 

Best Regards, Bob

 

 

[jetjr]

Maybe this particular bolt is the problem, being relatively hard to access.

 

With Hydraulic lifters theres even no need to take the rocker covers off maybe gets forgotten

 

I believe theres people out there who overestimate thier mantenence capabilities.

 

 

[RKW]

While on the subject of head bolts, and the obvious need to tension them at service intervals, do they undo themselves, or do they stretch? I believe they stretch, rather than undo themselves, maybe there is a limit to the number of times they can be retorqued before they break. Regards, Bob

 

 

[facthunter]

Few points.

 

The head bolts that need the most retensioning are in the hot area near the exhaust port. If the threads are not clean they will bind and give an appearance or feel of being at the correct tension.. The loosening is either due to stretching of the bolt which would occurr when the aluminium expands or distortion of the aluminium, or a combination of both.

 

Re the ignition timing. 25 degrees of advance is NOT a high figure. Most aero engines that do not rev as high as the Jabiru use more. (28 degrees is common). The fact that the plugs are close together in the Jab would normally need more advance to compensate, so I don't think the problem lies with the advance figure. The engine could probably do with more, but that might cause a starting problem.

 

If detonation is a problem, I would be considering the build-up of combustion deposits. (lead, dust and carbon), to be a possible factor. These deposits can incandesce and cause the charge to ignite before the spark plug does it's job (pre-ignition) and that can lead to detonation, and make the engine get even hotter, which creates a vicious circle of events. Detonation will destroy the strongest of engines. Plugs that have a heat range too hot for the engine can be a factor also. Nev

 

 

[Vev]

Just after reading the Jan Jab Chat (on line now) about their star rating on fuels, it makes one wonder if one should be using a blend of Mogas 98 and LL Avgas. The LL Avags to keep the octane up and the mogas additives system to clean up the depositions ... combined both would stop posible detonation form low octane and incandescent ignition sources at the same time.

 

Cheers

 

Jack

 

 

[Guest Topend]

This thread has been an interesting read for someone thinking about building a Jabiru. I do have one question, why did Jabiru come up with the Economy Tuning Kit? This term conjures up an impression of "lean burn", which would raise CHT.

 

Cheers,

 

Dave.

 

 

[facthunter]

Lean Burn Concept.

 

Since no response so far, I believe it had something to do with installation in UAV's where more economy was required by the purchaser. Nev..

 

 

[Guest Flygirl]

I have brough 7 new 2.2 and 3.3 ltr motors and never had a problem. touch wood! having had VW and other motors, I would only use Rotax or Jabiru. as they are the only ones i havent had to work at getting them to run right.

 

 

[Guest Flygirl]

I only get to about 400hrs and i am on to the next project.with the 2.2 I had the eco. jetting and it looked lean 14ltrs an hr but the new jet the fuel burn was more like 20lph and the colour was better, it also was a model no. with the lifter problem but i didnt get any problem, but i never filled the oil over 1/2 way.The last 3.3 is wasnt running CHT in the bottom of the green through it was a falty gauge but it wasnt.