Another Jab bites the dust.

[motzartmerv]

Havnt vw been doing gasketless engines for years??

 

 

[turboplanner]

in the bike business there is yamaha bond #5 which is this ultra fine silicon adhesive. its designed for sealing machined surfaces.

It still has to pass through the caress of the digit, and fine as it might be, if "Grubby" leaves a dollop of it on the surface, or lets it cure there will be a failure.

 

 

[fly_tornado]

nothing is idiot proof.

 

 

[old man emu]

Let's stop talking about silicone for a moment and take time to look at aero and automotive engines.

 

The first thing to note is that, in general, aero engines have individual cylinders. Auto engines, with the exception of air-cooled horizontally opposed ones, have a block which contains the cylinders. While you can pull an individual cylinder from the crankcase of an aero engine, you can't do that with an auto engine.

 

How are aero engine cylinders attached to the crankcase? By bolts from the crankcase, through a flange at the base of the cylinder.

 

How many bolts hold each cylinder to the crankcase? The Jabiru has four.

 

What do these four bolts do? They stop the cylinder, and its attached head, from pulling away from the crankcase.

 

Since the cylinders of an auto engine are integral to the block, we only need to bolt down the head, which in most cases is a block of metal with a combustion chamber for each cylinder cut out of the block (plus holes for lubrication, water cooling etc.)

 

How many bolts hold down the cylinder head? Probably still four per cylinder, but every bolt helps the rest of the bolts keep the head on the block.

 

So the difference between an aero engine and an auto engine is that there are more bolts per cylinder in an auto engine working to keep things from being blasted off the block than there are in an aero engine.

 

As soon as you start interfering with achieving the proper torque on the bolts, you open yourself up to the cylinders being able to move minutely back and forth against the cylinder base bolts with each combustion phase of the cycle. This movement stops then the cylinder base flange hits the nut on the bolt. It is like a blacksmith continually hitting the cylinder flange with a hammer. In most cases, the metal in the bolt is much stronger than the metal in the cylinder, so eventually, the cylinder fails, and those circumferential cracks form and enlarge until the base of the cylinder fails.

 

There is a trade-off here. If you use silicone on the crankcase/cylinder base interface, it is unlikely that oil will seep out of the joint, BUT your cylinder with fail at its base. On the other hand, if you don't use silicone, oil might seep out of the joint, BUT your cylinder won't fail at the base. You can always wipe seeping oil (which is not there under pressure) with a rag.

 

I know I'd prefer to keep flying on the smell of an oily rag,

 

OME

 

 

[damkia]

Why not use an "O" ring (of silicone?) in a groove around the base of the barrel where it "plugs in" to the crankcase, allowing the flush mating surfaces under pressure to come together sans silicone, and using the inner part of the crankcase hole and outer barrel as the oil sealing surface? Seems to be a far more elegant way of doing it...

 

 

 

[XAIRVTW]

Havnt vw been doing gasketless engines for years??

Motz does this engine have less than 500 hours TTIS or more than 200 hours TSO. Did it have the newer style nuts fitted?

Good to hear all are ok

 

 

[Vev]

Why not use an "O" ring (of silicone?) in a groove around the base of the barrel where it "plugs in" to the crankcase, allowing the flush mating surfaces under pressure to come together sans silicone, and using the inner part of the crankcase hole and outer barrel as the oil sealing surface? Seems to be a far more elegant way of doing it...

The Jab engine does use an o-ring between the barrel and crankcase. Silicon is used when the spacer have been added to lower the compression on early barrels by raising the barrels 0.5mm, which was an interim fix (during 2010) while the new barrels where being designed and put into production. When you raise the barrel with shims the o-ring no longer has the same interference fit to squish it into the machined grove in the crankcase... it seals ok but its not as good without the shims.

 

The current engine has 0.5mm longer barrels and therefore doesn't have spacers and relies entirely on the o-ring to seal between the barrel and crankcase.... Essentially Jab have addressed this issue.

 

Cheers

 

Vev

 

 

[biggles]

The Jab engine does use an o-ring between the barrel and crankcase. Silicon is used when the spacer have been added to lower the compression on early barrels by raising the barrels 0.5mm, which was an interim fix (during 2010) while the new barrels where being designed and put into production. When you raise the barrel with shims the o-ring no longer has the same interference fit to squish it into the machined grove in the crankcase... it seals ok but its not as good without the shims.The current engine has 0.5mm longer barrels and therefore doesn't have spacers and relies entirely on the o-ring to seal between the barrel and crankcase.... Essentially Jab have addressed this issue.

 

Cheers

 

Vev

Thanks Vev . I wondered how long it would be before someone mentioned this.

 

Bob

 

 

[motzartmerv]

I don't know much about it's history ( maintenance) . It had 220 hours since overhaul. And it was the model with the spacer shim.

 

 

[Vev]

Motz does this engine have less than 500 hours TTIS or more than 200 hours TSO. Did it have the newer style nuts fitted?

From what Dead-stick has already said from his preliminary inspection ... the engine had done 1370 hrs, 3 topends and was supplied before the thru-bolt upgrade was put into production.

 

Several people here have tried to ask the question in a subtle way .... forgive me for being direct but I can only draw from DS statement that this engine was not compliant with the Manufactures Safety Direction and was still running parts that are known to fail.

 

The attached Service Bulletin... it says it all ... I hope all Jab owners have read this and make sure they have implemented these Safety Directions

 

http://www.jabiru.net.au/Service%20Bulletins/Engine%20files/JSB031-1_JSD031-1_Engine_Through_Bolts.pdf

 

 

[Sunrayisa Flyer]

Yet again let down by a Jabiru, well done to your instructor I know exactly what he went through, only having the same thing happen to me a few weeks ago. I'm ready to start a class action on this mob at Jabiru, something needs to be done, before more people are seriously hurt. And the insurance companies aren't concerned, Jabiru blame everyone but themselves for the failures, so it's only the airframe that the insurance companies have to pay for, not the engines.

 

 

[planesmaker]

Sunrayisa Flyer, was it a thru bolt that failed on you too? Same type of engine, ie hydraulic lifter with the spacers under the barrels? how many hours since new or o/h? was the cylinder base cracked as well? just want to see if there is a pattern to these failures. Good you got it down safely. Tom

 

 

[planesmaker]

SF, no worries I just read your other post, seems a rare occurrence having a gudgeon circlip dislodge. how many hours? Tom

 

 

[johnm]

sunrayisa says 'people are seriously hurt. And the insurance companies aren't concerned, Jabiru blame everyone '

 

sunrayisa also raises an interresting point - if there is a percieved danger and insurance companies reacted - things could get ....................... uncomfortable

 

I magine there is no impost by any insurance company re this subject so insurance is not an issue ? ............................... which is good

 

jm

 

 

[damkia]

The Jab engine does use an o-ring between the barrel and crankcase. Silicon is used when the spacer have been added to lower the compression on early barrels by raising the barrels 0.5mm, which was an interim fix (during 2010) while the new barrels where being designed and put into production. When you raise the barrel with shims the o-ring no longer has the same interference fit to squish it into the machined grove in the crankcase... it seals ok but its not as good without the shims.The current engine has 0.5mm longer barrels and therefore doesn't have spacers and relies entirely on the o-ring to seal between the barrel and crankcase.... Essentially Jab have addressed this issue.

 

Cheers

 

Vev

Thank you for the full explanation.

 

 

[Gnarly Gnu]

I'm ready to start a class action on this mob at Jabiru

Well I can understand the frustration but think that through first please as this sort of thing does not boost the aviation industry or help keep our costs down; the only winners are lawyers.

 

 

[fly_tornado]

Its a lot quicker and cheaper just to avoid Jabirus.

 

 

[Bandit12]

Its a lot quicker and cheaper just to avoid Jabirus.

That is a little disappointing. As far as I am aware, Jabiru is about the only meaningful contribution that Australia has made to the international aircraft market for a long time; Jabiru equals money and jobs for Australians (okay, not a huge industry). Better to try and encourage a fix than just abandon them. I know that many people have tried, and provided plenty of feedback, but walking away isn't going to win us a reliable, locally produced aircraft at what really is an affordable cost compared to most.

 

It's a lot quicker and cheaper to not treat cancer too.

 

 

[fly_tornado]

There are plenty of punters prepared to take risks to save a buck, so no chance that Jabiru will go broke.

 

 

[motzartmerv]

Plenty of rotax 2 strokes have failed FT.. Pull your head in.

 

 

[fly_tornado]

This is the standard Jabiru answer isn't. Basically, accept that a high level of engine failure is normal and move on, problem fixed.

 

 

[facthunter]

You sail close to the wind ft. I have never thought anything like what you say is the situation, was ever expressed by anyone connected with Jabiru. Can't you be a little more constructive? There are flying schools and individuals out there who want jabiru to be around. I really don't know where you are coming from. Just what would you like to be done. Let's imagine you are in a position where YOU have to make the big decision here. What would YOU do. More than one line please. Nev

 

 

[motzartmerv]

Gee I'd love to see a contributing post from you FT. Your like a catfish in the salmon tank, there for one reason, to keep stirring. You seem happy to take the risk of flying a 2 strOke, so what's your rationale?? What makes you all warm and fuzzy when your flying your drifter???

 

 

[Guest Andys@coffs]

You sail close to the wind ft. I have never thought anything like what you say is the situation, was ever expressed by anyone connected with Jabiru. Can't you be a little more constructive? There are flying schools and individuals out there who want jabiru to be around. I really don't know where you are coming from. Just what would you like to be done. Let's imagine you are in a position where YOU have to make the big decision here. What would YOU do. More than one line please. Nev

Nev, its never going to happen so dont bother waiting for it. When its clear that he's P'd off everyone to the point that they may well band together and ask that he be removed, he'll shut up for a day or two and then go back to the one liners.....Sad really.....theres probably a fix for it if our mental health systems were funded a little better.......

 

Andy

 

 

[facthunter]

I hope some of it is productive Andy, and safety ( how boring) is my thing. Making a plane fly like you are part of it. The thing that gets me real bad is when people come unstuck when it was preventable by a bit more knowledge training , application and care. With a two stroke I don't fly over what I can't land on, but your average two stroke today wouldn't be in as good nick as the average used to be because they are not as new or popular, so the knowledge is harder to get.

 

We are on jabs though at the moment.. There is enough there. Cheers Nev