Latest Jabiru 2200 - reliability

[Keith Page]

Keith, I don't think it is at all the position, at least for those enthusiastic about CAMit engines, that we maintain they won't / can't fail. However, what I do believe is that there are accepted areas for Jabiru engines where people have justifiable reservations about their propensity to fail under certain conditions and that any positive steps taken to improve their general 'robustness' cannot but be a good thing. I will bet that someone like Keith Rule, whose expertise with Jab. engines is well-respected, could produce a list of things he believes could be done better and it would be most interesting to have Keith Rule 'evaluate' a CAMit engine - when the final spec. to be used for the CAE engine for certifying is determined - to get his reaction to the various changes made.

Engine are a bit like a chain. The chain is only as strong as its weakest link.

An engine is old as strong as its weakest component.. Hence if the weakest component is modified then another component will take over, with engines there is another set of situations arise when there is a component modification other reliable parts start having turns of failing..

 

So quite often it is better to stay with the devil you know and manage it and be kind to it.

 

I have seen Cat D11Rs killed and they are boys proof, so there are people who can brake an anvil with only their hands.

 

Regards,

 

KP

 

 

[jetjr]

Sorry Keith, dont agree

 

You seem to be saying that product development shouldnt take place

 

If the weak component is upgraded and the next link in the chain is found later and less often then thats still a good advance. Continue upgrading components until reliable service lifes are achieved. Few can say that is the case with current offerrering from Jabiiru.

 

Many of the problems seen in Jabiru engines are somewhat understood. Someone is making improvements and seems to be making headway.

 

 

[Oscar]

Keith: yes, the 'weakest link' will always exist, and certainly understanding what breaks an engine and trying as best as possible to avoid that happening, is 'best practice'.

 

BUT: investigation of the cause/s and the nature of the breakage can - obviously - improve things. In a simplistic example: let us say one has a persistent problem with a bracket failing. Examination might show it is being fatigued along the bend line. So one doesn't just make it of heavier gauge material, but also looks at the way the fatiguing stress is being introduced: is it due to bending load being applied, due to flexing at a particular harmonic that is present in the assembly, due to a manufacturing error such as introducing a high-stress line by a too-tight bend radius? Then - before just changing over to a 'stronger' bracket, one might need to look at what that change will do by way of moving the problem 'along the line': e.g. instead of the bracket failing, the stronger bracket still with the same loading, now transfers the problem to the attachment fittings and the structure to which it is attached?

 

It's certainly fair enough to ask: 'well, what has CAMit done differently, and how does that improve things?', and I know that Ian Bent has catalogued at least many of those things as part of the information he has assembled as background to eventual certifying / certification of the CAE engines. Quite a bit of the technical stuff behind that is CIC and understandably not going to be widely publicly released, but it will be evaluated by experts operating in faith with the requirements for CIC, will of course be formally tested, and is currently being tested in real-life by the owners of CAE engines.

 

 

[Bruce Tuncks]

I reckon Keith has a point . When you have something working satisfactorily, you should only change it with great caution if at all.

 

When the carby on the Jabiru motor was increased from 32 to 40mm to get more power, I was unhappy because I didn't want more power, I wanted more reliability.

 

Not that the engine was at all unreliable, but reliability is one thing you can't have too much of.

 

There was a big Steiger tractor I worked, and the story was that it had the same engine as the main USA battle tank of the 1950's. The engine had a rated life of 10,000 hours in the tractor but in the battle tank it had an emergency power boost system which gave it about double the power with a rated life of 10 minutes.

 

Whether this story is strictly accurate I don't know, but I certainly think it is right in principle. With the Jabiru engine, the extra power of the 40mm carby would have to give extra cylinder head heating and extra loading on the through-bolts.

 

 

[facthunter]

Don't be too worried about the size of the butterfly of the CV carb. You can put oversize carbs on with CV's. They just won't bring the dashpot all the way up and the needle must be calibrated accordingly. Nev

 

 

[jetjr]

Theres work being done with twin carbs on 3300, single is borderline too small and may be related to uneven fuel distribution

 

Very little is being done to develop more power but make them run reliably to overhaul

 

A larger carb alone does very little to increase output

 

 

[Old Koreelah]

...When the carby on the Jabiru motor was increased from 32 to 40mm to get more power, I was unhappy because I didn't want more power, I wanted more reliability...

I have a similar story, Bruce. My baby was designed around a 27hp engine. It needed a bit more power and lots more reliability; the Jab 2.2 seemed ideal- but had way more power that what was needed.

I pestered the Jab factory about shimming the barrels to reduce compression and allow the use of crap fuel.

 

They talked me out of it, so I fitted a standard 85hp Jab and it transformed the little baby.

 

I would never go back in power.

 

 

[Oscar]

When the carby on the Jabiru motor was increased from 32 to 40mm to get more power, I was unhappy because I didn't want more power, I wanted more reliability.

With the Jabiru engine, the extra power of the 40mm carby would have to give extra cylinder head heating and extra loading on the through-bolts.

Whoa there, Nelly!

 

As JJ has indicated, there is not by a long chalk, a direct relationship between a larger carby throat and increased power.

 

The Rotax 912A - of about 1200 cc's, I think - has TWO 36mm Bing CV carbs, produces a rated 80 hp - line-ball with the 2200 Jab. Yet, 2 x 36mm carbies gives about 75% more intake area than a single 40 mm.

 

I used to race small cars with hotted Corolla engines, taken out to just under 1200 cc's - running twin 42 DCOE Webers. That's more than one 40 mm Bing PER POT - not feeding four. We got around 105 - 110 hp from them, at about 7800 rpm. At the end of a season of racing, we threw in a new set of big ends and mains, lightly honed the bores, a new set of rings and that was it for the next season.

 

My Honda VFR 750 runs four 36mm Kehin CV carbs, puts out 102 hp at 9,500, and they are legendary for reliability ( and NOBODY who rides a VFR just waddles along, they are too much fun for that). Honda HAD to build a reliable engine after the debacle of the Vf750R engine - and if you don't get 100,000 k's from a VFR 750 with no more than valve adjustment, you are having a bad time of it.

 

In the case of Jabs., there is way more to the question than just 'getting a bit more power'. Most aero engines have quite appallingly rudimentary inlet tracts; in part that is to keep weight down, in part that is a response to limited 'packaging size' to keep frontal area down, and in part that is to reduce fire risk from fuel leaks dripping onto hot exhausts ( though Rotax have foregone that last one; the 914 in particular has a carby positioned above the turbo housing.) The standard carburettor-fed Jab engine is certainly no better, but not ostensibly any worse, than comparable air-cooled aero engines.

 

So, let's look at some of the permutations of carby throat area vs. power output.

 

A larger throat area for a give engine capacity at the same rpm actually ( theoretically) reduces the atomisation of the fuel molecules, which lowers the fuel burn rate. PROVIDED that the inlet tract area will flow the necessary amount of fuel-air mixture to generate the power desired, higher airflow speed is generally desirable (packs more combustible mixture into the cylinder as the inlet valve closes, just for a start.)

 

BUT WAIT - THERE"S MORE!

 

If inlet tract airspeeds get towards supersonic, you get shock waves generated at changes of direction that reduce the inlet tract effectiveness to flow the fuel/air mixture. Effectively, the inlet tract chokes itself.

 

Then, there is, for a single carburettor in particular, being fed by an airbox that has to accommodate hot air intake as well, the question of swirl affecting the distribution of mixture from one large(ish) inlet feeding four small(ish) outlets via a very, very small plenum. The higher the airflow speed, (due to a small carby flowing the same airmass as a larger one), the more energy there will be in the airflow ( M V squared applies here) and hence the effects of swirl on individual cylinder distribution will be magnified.

 

If you examine high-performance inlet plenums for say, Chevvy hi-po engines, the plenum volume is quite large and the good ones utilising the more sophisticated four-barrel carbies have complex airflow distribution ridges. The Jab. plenum is very small, and we KNOW that mixture changes with engine revs ( which means, mixture changes with the velocity of air through the carby), is one of the more intractable problems.

 

It just doesn't necessarily follow, that a larger carby makes for more power and therefore higher stresses for the engine concerned.

 

 

[facthunter]

Oscar I don't think you would ever get port velocities approaching supersonic. Take a bit of energy to do that but you will get pressure waves. You can usually feed 3 or 4 cylinders with a single carby only slightly larger than If you had one on each cylinder. Having carbys with floats in them is sheer stupidity near exhausts or superchargers. Should chuck them as far as you can and use injection, (even Mechanical) and you will NEVER get even mixtures from a single carb in multicylinder engines. The set up on the Continental 0-200. Updraft carb, clear of everything, with a cross shaped manifold fitting is close to as good as you will get. Nev

 

 

[Bruce Tuncks]

Thanks Oscar and Nev , you two sure know a lot about engines.

 

 

[Russ]

Carburettors................had their day, served us well. It's time......it's time to get onboard with EFI. Have now seen 2 injected jabs, owners just love it. Easy as to install.

 

 

[jetjr]

Whos supplying gear and doing install?

 

Should be much simpler second or third attempt

 

 

[facthunter]

I'm for injection not necessarilly E.. FI. An aero engine does not have the same environment to work in that cars do. I would like to have a system not dependent on a supply of electricity. Nev

 

 

[fly_tornado]

unlucky customer

 

 

 

[jetjr]

high quality parts are going to be hard to find and expensive.

 

Jabiru have been saying loosing CAE isnt a big deal........maybe this is what you get

 

 

[coljones]

unlucky customer[ATTACH=full]50211[/ATTACH]

can you cite the authoritative source?

 

 

[fly_tornado]

col RAA incidents

 

 

[gandalph]

I guess the only positive thing one could say about that string of bad luck is that the owner has FT advocating for him here.

 

 

[derekliston]

I am flying behind a Jabiru, I still firmly believe that improper maintenance is a large part of Jab problems. However, as has been pointed out in this thread, any engine can fail. Example 1, when I was working as a LAME at Archerfield I had a tomahawk return with a rough running engine. Cause turned out to be a cylinder which had cracked 360 degrees around the base. Only the fact that the crack spiralled and ended 25mm away from where it started prevented what could have been a total failure and that was a Lycoming O-235 Example 2, someone please correct me if I am wrong. Ross "Maj" Millard was frequently on this forum execrating Jabiru engines but I believe it was a Rotax which killed him. Fly always as though your engine may fail and as far as possible have somewhere to go if it does!

 

 

[Yenn]

They can all fail, but I love my Jab 2200, starts well, pulls well and sounds very sweet. Much preferable to those screaming Rotax, which sound as if they have just broken when you stop them.

 

 

[derekliston]

Can someone please tell me the meaning of a caution on my posts?

 

 

[turboplanner]

Can someone please tell me the meaning of a caution on my posts?

Yes, it's when there's BS

 

 

[derekliston]

Yes, it's when there's BS

Thanks turbo planner, please elucidate. Precisely where do you detect BS?

 

 

[turboplanner]

Thanks turbo planner, please elucidate. Precisely where do you detect BS?

"it was a Rotax which killed him"; There are several likely scenarios for his death, but none have been released by any of the responsible people.

If you have evidence that they don't, then you have an obligation to provide it to them.

 

 

[fly_tornado]

I guess the only positive thing one could say about that string of bad luck is that the owner has FT advocating for him here.

I just thought it was funny that Jabiru sanded a scratch out of a part and then I saw the other parts issues

 

Too good not to share, I'm sure you can see the humour in Jabiru's QA