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

[gandalph]

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

The Bong carb is used when you want to get really high

 

 

[acrofan]

After reading somewhere that HKS engines are air and oil cooled, I wondered if jabiru could use oil cooled exhaust valve guides? Perhaps some chanels cut in recess before guides are pressed in and joined to oil going to rocker gear?I've no idea of how it could be done except in my imagination but if it made a small temperature drop to the exhaust valve, could it improve possible detonation issues?

 

 

[turboplanner]

So what do the failed valves look like (because "Failed" is the description for most forced landings where they are listed as the cause.

 

Are they burned away and pitted or is it a stem failure.

 

 

[facthunter]

Since many of them do a fair amount of damage I assume it is stem failure. The burned badly seating ones might cause a secondary problem with higher temps. A momentarily stuck open inlet valve could impose catastrophic loads in another cylinder. (as happens with a gas system on some cars) when it backburns in the manifold.Nev

 

 

[jetjr]

I saw a pic somewhere where stem just above valve was eroded badly, next step would be end coming off and lots of rattley noises

 

Also anoher where valve itself had eroded on seat area, looked like a dad leak ans subsequent pitting, picked up n leakdown id guess

 

 

[facthunter]

Quite a few valves (exhaust) are subject to stem erosion. Continental 0-200 series as an example. It is very rare for exhaust valves to do a few thousand hours. They work in a terrible environment. Nev

 

 

[turboplanner]

Quite a few valves (exhaust) are subject to stem erosion. Continental 0-200 series as an example. It is very rare for exhaust valves to do a few thousand hours. They work in a terrible environment. Nev

I'm referring only to the Jab engines which have had problems FH - you've just about brought every aero engine that was ever made into the discussion.

 

 

[facthunter]

Only when it has some relevance.Turbs It's a common inspection for other engines so why wouldn't it apply to the Jabiru? Are we expecting it to be better than other "good" engines, in this respect? Nev

 

 

[turboplanner]

Facthunter: Continental 0-200 series as an example. It is very rare for exhaust valves to do a few thousand hours.

There are two major issues with the Jab engine as I see it.

 

1. Cost of repairs - which I see as a matter between the supplier and his customer

 

2. Forced landings due to exhaust valve failure - which I and it appears RAA and Casa see as a safety issue.

 

If the forced landings were occurring at "a few thousand hours", I suspect they would be classified as owner neglect rather than anything to do with the manufacturer.

 

If the forced landings were occurring at the same rate as Continental, there may be some merit in comparing Continental and RA in the same breath.

 

I was trying to get some facts on what is actually failing and where to try to find a cause in Jab engines.

 

 

[Keenaviator]

Has anyone seen a 912 hydraulic lifter? If so is it as big/heavy as those used in Jabs?

 

Laurie

 

 

[facthunter]

I haven't, but they are very expensive. Probably special to the engine. Auto sourced ones are extremely cheap due to large volumes being made. I know of one documented 912 failure of a hydraulic lifter, so it can happen. There would probably have been others. They sometimes come good but you run the risk of having a valve hit a [Piston or bending a push rod. I've personally had one in a Continental 0 -300, which just about halved the horsepower available. They can't fail IF they are not fitted, but people don't want to take the cowls off. Nev.

 

 

[jetboy]

TP the valve I saw most recently from a failure was bent/broken at the neck. It had a fairly straight break without obvious signs of necking, erosion, radialcracking or the like. the valvehead didnt look overheated. If it was my engine I'd say the valve probably stuck and got slammed by the piston, which broke and bent the conrod. Owner has a different theory.

 

Another engine nearby me was apparently sticking valves when I got asked to help out. It would start and run rough. Found #4 pushrod had slipped sideways from cup and got stuck under the rocker, leaving the valve permanently shut. (got to be better than permanently open) This happened for about 4 repairs 3 involving cleaning/reaming the guide etc. and he gave up and put Rotec water heads on

 

None of these had hydraulic lifters, and have not had any throughbolt issues

 

I've decided to replace exhaust valves around 250 hrs intervals - and will be getting the original type with the halfround collet grips not the squarecut cheaper sourced ones they run nowdays

 

 

[jetjr]

Found #4 pushrod had slipped sideways from cup and got stuck under the rocker

Ive had that once too, was running fine and noticed it in maintenance, no ideas how long it had been like that.

 

Hows the best way to early diagnose a sticky guide?

 

 

[geoffreywh]

bad idle with a cold engine, getting better as it warms up. my experience anyway....

 

 

[Keenaviator]

I haven't, but they are very expensive. Probably special to the engine. Auto sourced ones are extremely cheap due to large volumes being made. I know of one documented 912 failure of a hydraulic lifter, so it can happen. There would probably have been others. They sometimes come good but you run the risk of having a valve hit a [Piston or bending a push rod. I've personally had one in a Continental 0 -300, which just about halved the horsepower available. They can't fail IF they are not fitted, but people don't want to take the cowls off. Nev.

I was talking to a LAME mate this afternoon and he described Contintal and Lycoming hydraulic lifters to me- sounds like they are about half the size and probably quarter the weight of Jab hydraulic lifters.

Laurie

 

 

[facthunter]

They have to be a big enough diameter at the cam contacting face to prevent the cam digging in at the edge of the lifter. This problem is eliminated by having roller ended followers .

 

A "clean" break of the valve stem could be the result of a loose guide allowing the valve to rock and hit the seat unevenly over time. I have always suggested checking the stems for play. This can be done in situ with some engines but it is a bit of a fiddle and is not as good as dismantling the head(s), but at least you get some indication.

 

IF valves are sticking to any extent you DO have a problem. If it was an inlet it COULD be the cause of most of the other serious issues the engine has. If it is the exhaust (most likely) it will probably pop the pushrod out and maybe have the valve tap the piston crown or bend the pushrod. You can design the set-up to keep the pushrod where it can't fall far out of alignment and won't force the valve down.

 

Regarding injection, Throttle body is little different from a carburetter as far as mixture distribution is concerned. Individual port injection would solve the distribution issues.

 

DIRECT Very high pressure. BEST I suppose but I can't see it happening.. Nev

 

 

[jetjr]

There is a bolt on mechanical injector for experimentals, any ideas why this might not work too well

 

 

[Old Koreelah]

There is a bolt on mechanical injector for experimentals, any ideas why this might not work too well

You have my attention...

[jetjr]

http://www.precisionairmotive.com

 

Beyond my knowledge, expensive i recall

 

 

[facthunter]

I go for a mechanical(with manual leaning) individual port injecting system. They can be tuned to individual cylinders, so that will even up the mixtures and temps. You should also gain some economy as now you have to tune to the leanest cylinder. With the other set up they ate pretty even. Nev

 

 

[jetjr]

Asking a lot, but how do these mech systems work?

 

Aircraft spruce says they are $3K, no idea what model ec thats to suit really, thats just the unit.

 

 

[Downunder]

Do the electronic injection systems have individually adjustable injectors (fuel amount)? It should be possible......

 

 

[facthunter]

The system is extremely simple using diaphragms to regulate the position of a needle that controls fuel flow flow. Starting the engine is a bit of tweeking with the primer, but there is no reason to not use the fall back simple throttle block idle system, and progress to the other above fast idle. Nev

 

 

[turboplanner]

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

You have to get the sonic waves right first. No point injecting a precise amount of mixture if it's going to be set on fire just as it's forced out the exhaust.

 

 

[jetjr]

Do the electronic injection systems have individually adjustable injectors (fuel amount)? It should be possible......

Not the ones available, im told it isnt necessary as distribution is even and engine should use it evenly.

 

The piezo injectors actually operate all the time not per stroke, tiny pulses of fuel constantly i think

 

With current carbs it appears we need to have differential injection

 

Theres some EFIS pictures on Avcom illustrating Egt spread after SDS injection fitted, pretty nice.