Another Jab bites the dust.

[Bryon]

You guys have got it all wrong

 

Rod mentioned at Natfly that if we are having a problem with the engines (I am) it is because we are all operating them wrong.

 

He said that the reason we are having overheating problems with the 3000 engine is because they are tuned to operate in Bundaberg and we have different weather in Melbourne.

 

I wasnt sure whether he was recommending that all Jab drivers in Melbourne relocate to Bundy or that we get Jab to retune them for Melbourne weather

 

Any suggestions?

 

Cheers

 

Bryon

 

 

[Chook1964]

Well done to the instructor involved, I went through the exact same situation (failure of N0. 3 thru bolt on take-off) with only 6 hrs of solo time. Luckily, I still had 1000 mts of runway ahead of me.

 

 

[Kyle Communications]

Another member of the JEF club and not Motzarts one....at least this one wasn't airborne but very well could have been....A person on this forum just recently sold his aircraft and was about to deliver it 3 days ago when he was checking everything before trailering it to the new owner as he had replaced the through bolts and did 2 engine runs the last run when he stopped it... it made a weird noise so he started it again and a hell of a noise started...upon investigation he found the 2200 had dropped a valve seat so now he has to deal with Jab to get the engine repaired .TT on the engine I believe is 210 hours. just lucky the new owner wasn't flying it

 

Rotax are very reliable engines without the amount of failures as the Jab engines especially when you consider just how many are being used out there. Yes they do have failures but usually NOT broken mechanical parts...The accident at YCAB I believe the guy had some trouble with the engine and had it looked at over at Redcliffe and was taking the aircraft up to test the engine when it failed....no report on what it was yet but possibly electrical. Another guy on the weekend I witnessed a issue on his rotax 912ULS that had run ok but was really hard to start turns out to be both A and B electronic modules look like they have gone weak..so thats a $1600 bill for him the engine is about 6 years old but only 150 hours TT....

 

Every brand of engine can stop most are due to pilot/maint errors or lack of detailed inspection but the Jab failures are mainly broken engine parts. I am not a mechanic but I am a electronics guy and any electronics can fail especially when they are in close proximity to prolonged heat exposure. I read a lot of electronic issues on lots of engines and rotax is no different but I think the evidence is certainly there about Jab engines and they either need to redesign the engine or maybe get out of the engine market just too many failures

 

Mark

 

 

[Powerin]

You guys have got it all wrongRod mentioned at Natfly that if we are having a problem with the engines (I am) it is because we are all operating them wrong.

He said that the reason we are having overheating problems with the 3000 engine is because they are tuned to operate in Bundaberg and we have different weather in Melbourne.

 

I wasnt sure whether he was recommending that all Jab drivers in Melbourne relocate to Bundy or that we get Jab to retune them for Melbourne weather

 

Any suggestions?

 

Cheers

 

Bryon

Easy! Jab just needs to set up a retuning station at each airport so they can tune each Jab that passes through to local conditions. Problem solved!

 

 

[facthunter]

This retuning for local conditions would need a lot of explanation for me to wear it. Jabiru have been making excuses like that for ages. Incidently I' m not just a Jabiru basher. but the time has come for some serious assessment and answers.

 

I have always said the top end of the engine must be right. IF the exhaust valve guide is loose the valve head is more likely to become detached. Also the valve is more likely to overheat. This is one source of detonation.

 

I have never heard anyone mention the spark plug heat range or a suggestion for a colder plug to be fitted. This surprises me somewhat.

 

All you need is a bit of incandescent carbon in the combustion chamber ot on the plug and you could be unlucky.

 

IF you are getting detonation, bigger bolts will not save you. No engine can survive detonation. Do most of you really know what it is , or have seen the results of it?

 

It is probably the most common cause of failure in a high performance two stroke. Nev

 

 

[motzartmerv]

Nev. Can you explain the detonation thing please, I understand the principle an the factors but how is it manifest in flight. Is it short periods of rough running? Or is it more like a stutter or hesitatiOn? This engine never seemed to miss a beat as far as I could tell. Years ago when we first got it ( previous top end) it would occasionally hesitate and stutter for a millisecond occasiOnaly. It probaly happened 3 times in the 200 hundred odd hours I flew it.

 

We nurse these engines like you wouldn't believe . We decend with power from altitude, warm the engine every 1000 feet religiously, after periods at idle ( pfl) we smoothly apply 50% throttle and get the cht back up before going to full power. We baby them all the time. And run them hard in the cruise at 2800-2900 and never stooge them around at low rpm.

 

It's always been run on avgas with very occasional 98 octane vortex fuel.

 

 

[turboplanner]

These statistics come from 48 RAA/Sport Pilot magazines between May 07 and March 12, so they represent a random period of 48 months.

 

It appears that not all forced landings make it to Pilot Notes, so the numbers may be under representing what's actually going on.

 

Only aircraft with Jabiru engines are listed.

 

There were 35 mechanical failures (Unbelievably there were about 3 more where the cause was no oil in the sump)

 

Of these, there were:

 

28 forced landings

 

6 found "on the ground" - which if the pilot had been alert should have been forced landings (one case, not included, was where a crankshaft broken in half and the pilot flew home on the front half cylinders and crank)

 

1 "landed", which probably should have been a forced landing

 

26 were 2200 models and 7 were 3300

 

Of the 35 incidents only one injury was reported, a serious one

 

Of the 35 incidents there were:

 

16 thru bolt failures

 

6 valve failures

 

6 exhaust valve failures

 

3 seized

 

1 conrod failure

 

1 catastrophic engine failure

 

1 cylinder crack

 

1 misfire and shudder

 

The standard of reporting in Pilot Notes (which comes from RAA reports) leaves a lot to be desired and itself tends to mask what the problems exactly are - for example, conrod failure, seizure, catastrophic engine failure, cylinder crack are results rather than failures, and misfire and shudder is a sympton, not a cause.

 

Of the 35 total time in service (TTIS) was:

 

0 - 200 hrs - 3

 

201 - 300 hrs - 4

 

301 - 400 hrs - 5

 

401 - 500 hrs - 6

 

501 - 600 hrs - 1

 

601 - 700 hrs - 3

 

701 - 800 hrs - 2

 

801 - 900 hrs - 3

 

901 - 1000 hrs - 4

 

1001 -1900 hrs - 1

 

Not specified - 2

 

In looking at these statistics we have to be mindful of the fact that we know because of open discussions on this forum and others that:

 

A percentage of owners do not use specified oils and do not change oil at correct periods

 

A percentage of owners do not understand filter technology

 

A percentage of owners are not mechanics, and so settings on some engines will be permanently incorrect

 

A percentage of pilots do not monitor operating temperature as they should

 

...and so on

 

Conclusions

 

28 forced landings in 48 months represents about 7 per year, and we could maybe double that if we include forced landings not reported in Pilot Notes

 

46% of these are due to thru bolts

 

34% are due to valves

 

 

[fly_tornado]

nursing your engine wont make any difference, this is a great article on detonation. http://www.eaa.org/experimenter/articles/2012-01_detonation.asp

 

 

[turboplanner]

Nev, from my experience with two strokes, detonation is when you light the fuse and the engine blows to pieces.

 

 

[fly_tornado]

Normally detonation manifests itself as a hole in the piston, I have never heard of a Jabiru with a hole in the piston.

 

 

[facthunter]

It takes no time really to demolish the engine. It is most likely to occur when the engine has been on load for a while. When I say "for a while" it could be as short as as a few minutes, but it is most likely to happen at full throttle at lower altitudes, when the engine has maximum load.

 

The motor loses power and develops an extreme harshness, this is more so if the engine is doing it on all cylinders. I think this is unlikely in an aero engine unless it was overboosted ( supercharged).

 

In the Jabiru it will most likely be on one cylinder only, so the other 3 will still be driving it. You won't have much time to notice the symptoms because failure of components is almost instantaneous, such is the overload.

 

Incidently your engine has been severly stressed. It needs a complete dismantle, inspection and rebuild.. I wouldn't mind talking to your instructor if he would like to. I think you have the number. Nev

 

 

[Louis Moore]

Merv, the biggest problem with detonation is the fact that it is nearly impossible to pick up in an aircraft when it is occurring. The images you see in the PPL and BAK theory books, with the hand pushing on top of the piston to demonstrate normal combustion and the harmer smashing a piston down to give an idea of detonation, in fact even the very name gives the misleading impression that it would be accompanied by rough running, loud noises, shaking etc... While in extreme cases this can be the case, if the detonation is so bad you can feel it shaking your plane about, your engine is mere seconds away from self destruction!!

 

When I was big into sports cars I used to tune them right on the edge of detonation, which is fairly common and when you had your foot down hard in top gear or were lugging the engine up a steep hill you could here the detonation occurring in the chambers. It is nothing more than a deep metallic sounding knock in the engine, hence it being called engine "pinging". Sounds like someone is tapping a 20c piece on the inside of the cylinder walls I guess and the engine note drops a couple of octavies when it starts also. It is actually not a big problem if it is only occurring on occasion, if it is prolonged thats when you start to get issues!

 

In an aircraft, wind, prop, headsets (Especially now most of us use ANR) really aid in drowning the sound out!

 

Again just to be specific, detonation will necessarily cause fast/instantaneous destruction of your engine (this seems to be the general opinion of most people, that detonation will only happen briefly before your engine goes BOOM!). It can occur on a mild basis for a long time, I would run my vanguard engine for MILES with mild "pining" drumming away without severe side effects (Like when I was climbing up the big hill on the bypass near Wollongong). Eventually it will ruin your engine, melt a piston, snap rings or maybe even brake a through bolt! But it can be occurring every time the engine is under heavy load etc... for a number of hours before finally causing failure!

 

Mr Fix it has a fairly detailed page about knocking so I will add the link.

 

. We baby them all the time. And run them hard in the cruise at 2800-2900 and never stooge them around at low rpm.

As a note about knocking it will usually not occur at low RPM, normally it is when the engine is "working" or "lugging" that it begins to start.

 

http://www.misterfixit.com/deton.htm Mr. Fixit

 

http://en.wikipedia.org/wiki/Engine_knocking Wiki Page

 

 

[damkia]

Nev, from my experience with two strokes, detonation is when you light the fuse and the engine blows to pieces.

Don't confuse detonation with satisfaction...

Seriously though, detonation is also caused by the incorrect RON fuel being used. Any chance these people were using automotive 91 RON ULP instead of the 95 RON or higher that is recommended?

 

 

[old man emu]

Detonation is NOT the cause of the throughbolt failures. Never was, never will be.

 

The cause of all these throughbolt failures is Jabiru's insistence in putting silastic on the cylinder bases. It is impossible to torque down correctly where there is a compressible material between the surfaces that should mate together and the joint fastened with a bolt.

 

Lycoming, Continental and Rotax would have a heart attack if they found out that someone had used silastic on these joints in their engines.

 

Old Man Emu

 

This post was made at the request of my boss who has over 40 years' experience as a LAME.

 

 

[facthunter]

We had better be careful here. The "pinging pinking" or preignition is usually survivable but can lead to detonation if it is prolonged. It can occur at low revs. When you leave your car in top gear at too low a speed and open the throttle. It's a fairly heavy metallic rattle not inlike the diesel knock those engines exhibit when idling. I suppose you could regard Detonation as severe pinging. It is an uncontrolled rapid (explosive) burn happening far too early. The peak pressures go off the scale.

 

Detonation can take the side out of pistons, push the valves into a new shape shorten conrods break blocks, smash the top out of pistons. Break Jabiru crankcase bolts? ( The holes in two stroke pistons are often a melting process which can result from detonation, or lean mixture, as a lot of heat results from it also).

 

The thing about aero engines is the steady, continuous high load and that means things get bad real quick. Nev

 

 

[Louis Moore]

We had better be careful here. The "pinging pinking" or preignition is usually survivable but can lead to detonation if it is prolonged. It can occur at low revs. When you leave your car in top gear at too low a speed and open the throttle. It's a fairly heavy metallic rattle not inlike the diesel knock those engines exhibit when idling. I suppose you could regard Detonation as severe pinging. It is an uncontrolled rapid (explosive) burn happening far too early. The peak pressures go off the scale.Detonation can take the side out of pistons, push the valves into a new shape shorten conrods break blocks, smash the top out of pistons. Break Jabiru crankcase bolts? ( The holes in two stroke pistons are often a melting process which can result from detonation, or lean mixture, as a lot of heat results from it also).

The thing about aero engines is the steady, continuous high load and that means things get bad real quick. Nev

Nev, Preignition is not pinging. Preignition is the fuel being ignited by means other than the spark plug earlier than it is supposed to, usually by carbon deposits, hot spots etc... Pinging is just a non technical term for detonation. We simply assume detonation is more severe because it has a more destructive name Severe detonation, severe pinging same thing.

 

The point I was making is we should not assume our engine will get detonation for a brief period before destruction occurs. If it is severe it will end quickly, if it less severe it can take a lot longer. There are cases of people putting Jet A1 into piston engines and flying for a number of hours before the mild detonation occurring finally made the fan stop.

 

 

[facthunter]

Louis I think we are saying the same thing. I can't agree with jet A1 in avgas taking a while to kill the engine. It's usually on the first takeoff.

 

damkia, it could be bad fuel ( in some cases) Mogas can go stale, and is not a product that can be guaranteed to be consistent. ( at point of delivery)

 

OME You know I will have to disagree with you. I don't suggest that silastic or such under the cylinders is a good idea especially if it hardens before you tension it, but aren't all (conventional) crankcases put together that way. ( Between the two halves at least).

 

Nev

 

 

[Louis Moore]

OME You know I will have to disagree with you. I don't suggest that silastic or such under the cylinders is a good idea especially if it hardens before you tension it.

OME I have to agree with Nev. While I am not a supporter of the approach I fail to see how a side effect of it is going to be something as drastic as broken through bolts. Even though it can prove to be impossible to torque down correctly with the compressible liquid there if this was huge issue wouldn't you expect it to result in cylinders coming loose?

 

There is story that yanks had all sorts of issue when they first started playing with Merlin rebuilds, so they sent a bunch of brit engine fitters out to give them a hand. Apprantly the issue was the brits rarely used a torque gauge and assembled the engine all by hand and feel.

 

 

[i_like_planes]

Hi guys. Here's a flight path mock-up. Props to Motz, he's taught me everything I know. I hope you all have as good an instructor as I do.

 

Cory.

 

 

 

[farri]

Our J160 suffered an engine failure on takeoff yesterday afternoon. It gave no indication it was about to pack it in. My junior Instructor (I_Like_planes) was doing circuits with a student.At about 200 feet it started running ruoughly and vibrating, then over the next 4 or 5 seconds it lost power and started misfiring badly with a heavy knocking noise. He did a hell of a job to get it down safely, using what power that was left to clear a row of trees and a power line before dumping all the flap and sideslipping into the paddock. The ground was very soft and the nose wheel dug in tipping it up onto a wing. Both he and the student escaped with nil injuries.cheers

Motz, that`s an excellent outcome! We all know,aircraft can be repaired or replaced!

 

Over the years, I`ve experienced 3 failures under 150` AGL on take-off and each one with a student on board! One before we ran out of strip so I was able to get back down on the strip. The other two just off the end of the strip and I had to put down on the paddock, so I understand what it`s all about.

 

Positive end result with each and no damage to the Drifter or ourselves

 

Frank.

 

Ps, Sorry to you, i_like_planes! I forgot to mention that you did well.

 

 

[Guest ozzie]

Anyone running those water cooled heads? If it was possible to have pressure cast cylinders instead of the machined billet type then good chance the dropped valve seat problem would go away. Another thing i would look at is dropping the compression ratio way down and fit a turbo charger and waste gate. This would help keep detonation down and give a more even distribution to the cylinders. That 3300 fitted to the Storch had two instances where the valves locked up in the guides after shutdown. I put that down as poor cooling to the rear cylinders. Don't really swallow the tuned for Bundy and not Melbourne bit.

 

 

[Steve Donald]

Yea. I love the aircraft . It's a good solid trainer. I have major issues with the quality control and the service provided by the factory. I have had 3 online for a number of years and have dealt with every conceivable problem that could be imagined. I've given up dealing with them directly. We just get the problem sorted without their help. I could write a long list of QC issues we have had over the years. My favorite was a brand new propellor that let go of it's leading edge after a 5 min ground run.

great Job guys, those bloody bolts, Andrew JP6 has the fix for that 3 x stronger rolled thread with the 12 point nuts that fit correctly, he is trying to get Rod's attention the supplied bolts are useless as is the AD, ROLLED THREADS STRONGER MATERIAL SIMPLE, the test on standard bolts can fail at the required tension, scary huh 30ft ibs the grade 8 rolled thread hang on to 60 ft ibs go figure, ALL PROVEN DATA.

 

 

[cscotthendry]

I've pretty much had a gutfull of jabiru. We are all taking bets at the moment as to what blame jabiru are going to put on us for the failure. Good luck, my engineer is a navy mechanic and does evrything by the book. Strictly by the manual. He doesn't know any other way.Anyone got any rota powered acft they want to put online with a good school?

I spoke with one of the Jab reps at Avalon last year and he ASSURED me that they had conqured all these engine issues. That's why I fly Rotax.

 

 

[Vev]

In terms of the thru-bolt failure, is there any evidence that the new longer bolts and nuts are failing? In my mind this is the real acid test, everything before this upgrade is past events and falls into the history bucket and already known. There was an AD out to upgrade the bolts and/or nuts which had timed out for mandatory completion on the 14th April 2012... this AD also included crankcase dowels in some prescribed circumstances.

 

We know Jab have added 0.5mm to lengthen the barrels or have fitted 0.5mm of spacers on earlier barrels to lower the compression to help manage the detonation .... to the best of my knowledge this has not been mandated to owners but has been a standard process during factory rebuilds since 2010 inclusive of new production engines.

 

On the current production engine they have increased the thru-bolt dia as well as the longer 12 point nuts, along with a higher interference fit on the crankcase dowels ..... this is a significant improvement but it can't be preformed on old engines easily.

 

In terms of retrospective upgrades today ... is there any evidence of the new longer thru-bolts with 12 point nuts failing????

 

Cheers

 

Vev

 

 

[RKW]

In terms of the thru-bolt failure, is there any evidence that the new longer bolts and nuts are failing? In my mind this is the real acid test, everything before this upgrade is past events and falls into the history bucket and already known. There was an AD out to upgrade the bolts and/or nuts which had timed out for mandatory completion on the 14th April 2012... this AD also included crankcase dowels in some prescribed circumstances.We know Jab have added 0.5mm to lengthen the barrels or have fitted 0.5mm of spacers on earlier barrels to lower the compression to help manage the detonation .... to the best of my knowledge this has not been mandated to owners but has been a standard process during factory rebuilds since 2010 inclusive of new production engines.

 

On the current production engine they have increased the thru-bolt dia as well as the longer 12 point nuts, along with a higher interference fit on the crankcase dowels ..... this is a significant improvement but it can't be preformed on old engines easily.

 

In terms of retrospective upgrades today ... is there any evidence of the new longer thru-bolts with 12 point nuts failing????

 

Cheers

 

Vev

Hi Vev, the new 7/16 thru bolts do not use the 12 point nut. It's a rather unusual nut. Approx half the height of the nut is round and the top half is hex. I have them on my J160. While the bigger thru-bolt is stronger, if detonation is the problem, this will make little difference, as Nev pointed out. We don't have sufficient hours on it to draw any conclusions so far. BTW I cannot see what difference it would make changing the standard hex nut to the multihex nuts on the 3/8 thru-bolts. Regards, Bob