Jabiru Development, then........ Hydraulic Lifters........

[Keenaviator]

I believe that over the years, leading up to the hydraulic lifter version, Jabiru did a pretty amazing job of developing their own engine with basically just a few cluey blokes working together to produce a lightweight four stroke direct drive aero engine. Without the backing of a multi squillion multinational company. A big pat on the back for the Aussie spirit of having a crack!

 

The development included (amongst other things):

 

• flywheel screw failures - increase screw size from 1/4" to 5/16", dowells, 'spider'
   
   
  
• exhaust valve failures - redesign exhaust manifold to do away with gaskets
   
   
  
• cooling - ongoing
   
   
  
• induction distribution - several evolutions of manifolds
   
   
  
• hydraulic lifter development - change cam profile several times, fast bleed lifters, now roller followers
   
   
  
• through bolt failures (which appeared after hydraulic lifters introduced)
   
   
  

 

 

Does anyone actually know of a pre hydraulic lifter Jabiru engine suffering through bolt failure?

 

I know the Rotax 912 series of engines use hydraulic lifters.

 

Can anyone tell me what a Rotax hydraulic lifter weighs?

 

The reason I ask is that the hydraulic lifters used by Jabiru are a big, heavy lump of metal, something like 130 grams each (normally used in a Chevy V8). The original 'solid' lifters are very light, about 30 grams each.

 

Lifters are situated between the camshaft lobe, the push rod and rocker arm which is under spring compression load by the valve spring. As the engine operates the camshaft rotates, the lobe pushes the lifter which pushes the push rod which pushes the rocker arm against the valve spring. This all has to do this in unisen in addition to hydraulic lifters having to maintain correct clearances. When this is happening at operating speeds those heavy lumps of metal are expected to go backwards and forwards (stop and change direction) very quickly and the forces involved must be much higher than with the lightweight 'solid' lifters. A person with a better physics background than me would be able to calculate this in a flash using what I would think are common formulae.

 

It is my opinion that Jabiru are barking up the wrong tree persisting with trying to get the heavy hydaulic lifters to work (including now using roller followers to cope with the loads on the camshaft). Ian Bent is on the right track with retaining lightweight solid lifters (along with his other developments).

 

Why are Rotax are having a good run with hydraulic lifters (which operate at nearly double the speed). Are the ones they use much lighter than Jabiru's?

 

Laurie

 

 

[jetjr]

I have raised this question before, and someone said (without evidence) that yes they had seen a solid lifter break a bolt

 

My take is a different angle

 

Lifters are very sensitive to oil pressure, oil system is not that good, they can pump up/down, leaving valves not closed, burning valves and Im sure potential detonation

 

I was privately recommended NOT to do bolt upgrade on solid 3300 as Factory had never seen through bolt issue before hyd lifters introduced. I did anyway to comply but could have been a waste of money.

 

I think issues are related to mixture distribution and cooling BUT, this may have limits to getting any better so valvetrain and cylinders need work to toughen up.

 

 

[Old Koreelah]

A simple EFI might make a big difference. Is anyone working on this?

 

 

[jetjr]

Yep

 

SDS from Canada have a system. Kit from Edge performance in Norway??

 

http://www.avcom.co.za/phpBB3/viewtopic.php?f=59&t=137074&sid=926ae517c4ee47eae67830b78334a561

 

A good read here, finally has it going, numbers look really good

 

He has also done a full EFIS,EMS and electrical rework so bit more complex than just EFI update

 

Some guys in South Aus do sell and install more basic kit using same gear

 

 

[geoffreywh]

There is mention of EFI on the Jabchat page. According to Jabiru it is NOT going to happen.........Unless of course you do it yourself and go with E24- reg or 19- reg

 

 

[AVOCET]

SD

 

A simple EFI might make a big difference. Is anyone working on this?

SDS simple digital systems ( check website) doesnt get any simpler.

 

 

[Old Koreelah]

...everyone seems to have a "fix" for the Jab engine.

 

I'd like Nikasil bores, CAMit valve train etc, EFI and maybe even Rotec liquid-cooled heads.

 

Now for the airframe: a J170 taildragger adapted for STOL. Now that's an aeroplane for this continent.

 

 

[DGL Fox]

I would have thought water cooling the engine or cooling in general would have been the main number one issue that needs to be addressed before EFI systems?

 

David

 

 

[Russ]

Chap my way is currently fitting EFI into his 3.3 Camit. I don't have the details, but easy as to do, and PROVEN.

 

 

[Old Koreelah]

I would have thought water cooling the engine or cooling in general would have been the main number one issue that needs to be addressed before EFI systems?David

Keep it simple. Can't beat the simplicity of air cooling. Feeding each pot equally might prevent most problems.

 

 

[Old Koreelah]

Has anyone researched the likely cost of repairs for possible Jab engine failures?

 

Those of us with low-time, but so far reliable engines might want to weigh up the certain cost of upgrades vs the possible costs of repairing failures. Detonation-induced thru-bolt? Exhaust valves. Flywheel studs?

 

How much cheaper is the upgrade than repairing a failure (assuming a safe out landing)?

 

...or maybe we should await the results of the current negotiations.

 

 

[Yenn]

How will failure of hydraulic valve lifters cause the valve to not seat. The valve is seated by spring pressure, with gas pressure assisting. A failure of the hydraulic lifter is going to cause the valve to not open correctly. Low oil pressure is also going to stop the valve opening.

 

 

[facthunter]

There is a hydraulic lock in the valve lifter and it takes a while to lose all of the oil and have it bottom out Unless it is faulty a small amount of oil should keep it working. High pressure could cause the lifter to pump up and cause poor valve seating, which would overheat the valve since a lot of its heat is dissipated through the valve seat. You also lose power. Nev

 

 

[jetjr]

Dunno Yenn, well beoynd my knowlege

 

Theres an interesting video on valve clearance and push rods by Rotec. Very fine tolerance and wouldnt take much lifter or oil press problems to stuff things up.

 

Through bolts problem only came with hydraulic lifters and in my mind is detonation based.

 

The failures are too random to be a pure design flaw

 

With cooling, its correct cht are critically important, but good numbers can be achieved without liquid cooling.

 

CAE with SDS would be near perfect.

 

 

[Old Koreelah]

...CAE with SDS would be near perfect.

CAE = CAMit? SDS=?

 

 

[skeptic36]

CAE = CAMit? SDS=?

Fuel injection

 

 

[Downunder]

http://webshop.edgeperformance.no/index.php?id_product=74&controller=product

 

 

 

[jetjr]

CAE = Camit Aero Engines

 

 

[jetjr]

The kit pictured is the whole deal, inc requiring dual pumps, new TBody and probably backup battery setup

 

It can be done using Bong carb and single fuel pump

 

Cheaper and inc full mechanical backup

 

 

[facthunter]

BONG carb.. That doesn't ring a bell. Nev

 

 

[Downunder]

He just missed the comma after Bong.

 

"It can be done using Bong, carb and single fuel pump"

 

 

[Guest Andys@coffs]

He just missed the comma after Bong."It can be done using Bong, carb and single fuel pump"

However your results, if bong lit, may be no less predictable that the solution your trying to better....

 

 

[Yenn]

Why go to the expense of the full fuel injection. You can get an aeroinjector for a few $100, put CHT and EGT on all pots and solve any fuelling problems. Personally I don't trust the Bing carby, I seem to be always running too rich.

 

 

[Downunder]

Isn't "direct" injection far better than "manifold" injection with regard to mixtures?(even mixtures to all cylinders)

 

I see manifold injection as a bit half arsed. If your going to do it, do it right........

 

 

[jetjr]

yep, few stories aero injector not working that well, Rotec make one which would be nice throttle body but they are really just different carb's, Better no doubt.

 

Lots of changes needed to cables etc too.

 

Issues with uneven distribution still exist with TBI like these, port injection is the way to fix issue