How to improve the reliability of the 6 Cylinder Jab

[JabSP6]

Hi all. I am currently in the process of rebuilding my Jabiru SP6 motor after experiencing No2 exhaust value deciding it would rather travel thru the top of the piston several times instead of closing on the exhaust seat. It separated from the exhaust value stem at the base of the head and at 2800 RPM as you can imagine caused a fair bit of damage. luckily i was 10mile out of the airfield and at 4000feet AGL so manged to perform a glide approach and land safely. luckily the motor continued to spin over although obviously running extremely rough so i reduced to just above idle and it somehow continued to run untill i shut it off after taxiing from the runway.Total time on the Motor and plane is 750hrs and it was fully overhauled by a LAME at 320hrs after finding metal in the oil filter. At 550hrs the leakdowns were quite bad and oil usage was extremely bad so a top end was again performed which revieled bad piston carbon deposits and rings siezed in the grooves.I would welcome the chance to talk to you all about anything you might have done to try to improve the reliability of these motors as i use the plane for transport to work and have flown 240 hours in the past 9 months. Has anyone looked into the option of running one piece stainless values to eliminate the chance of the 2 piece std version separating again? Also has anyone looked into running a nickasil coating on the bore and running a better quality ring to reduce the chance of the std 4140 barrell devloping rust deposits if left sit for lengths of time and then the initial start up prematurely wearing the cast rings resulting in poor leakdown results in relitively short hours. Also what about applying a ceramic coating to the combustion chamber and top of the cylinder to stop as much combustion heat transfering into the air cooled engine components? Just some ideas that are comonly used in other forms of transport which don't require anywhere near the amount of maintenance repairs. Don't get me wrong - I love my Jab. i just want to try to make the 1000hr claimed TBOLooking forward to utilising your knowledge and experience.Andrew

 

 

[Guest Walter Buschor]

Hi Jabsp6

 

You are one of many with these problems. If I was in your shoes I would sell / junk the Jab donk and install a 912 ULS. That way you WILL go to 2000hrs plus and on to perhaps 4000 - 5000 hours as some engines have achived without engine problems. As a bonus you can count on arriving at your destination without the ever looming threat of the fan stopping any time. It's about peace of mind.

 

As for the suggested engine mods they might solve some / all your problems but you enter new ground as far as these units are concerned . Since the motor was never done with these coatings etc Jabiru would most likely point the finger at you should you have any future engine problems of any kind.

 

You like the SP6 and I'm shure it is a great plane. - give it the engine it deserves.

 

fly safe

 

Walter

 

 

[JabSP6]

Thanks Blackrod and Walter.As you are all quite aware the Manufacturer believes that there is nothing wrong with their motor design and when operated within their strict operating guidelines the motor is extremely reliable and will make the 1000hrs TBO.I, on the other hand believe in the concept a motor should be 100% reliable, especially in a plane and should be able to withstand a variables that often are thrown at us from time to time. My plane is not a factory build so the concern about entering new ground is exactly what i think we need to do and won't change anything with reference to the manufacturer pointing the finger. They do it now with a completely standard configuration. I am a firm believer of sticking with what you've got and if necessary use the wealth of knowledge and experience that is available to improve things. The engine design is quite simplistic and with a few improvements should easily be able to out perform the trusty 912. I was just curious to see if anyone else had tried some of the suggestions. I have seen photo's of a gentleman's motor in NSW that has fited multi point (& single point as a back up) fuel injection with great results. These are the sort of ideas i am looking for.Thanks again for your input. Andrew

 

 

[Tomo]

Like you said, they are an extremely simple motor, it seems funny they have so much trouble.

 

Dropping a valve is something that happens on anything, but like you said the bores could possibly be made a little more bullet proof, and fairly easily. Wonder if anyone has tried a sleeve/liner?

 

 

[quentas]

My J230D had leaky exhaust valves at 350 hours. When my Lame pulled the heads off his recommendation was to replace the exhaust valves as they appeared heat affected and pitted. Now it has strong compressions all round so I guess the best option to keep your Jab running reliably and safely would be to change exhaust valves and freshen the top end every 3-400 hours. Lucky the bits are reaaly cheap and the engines are easy to work on. Having said that I love flying the 230! I go everywhere in it.

 

 

[JabSP6]

Quentas.This is my point exactly. It is stated that they should be able to go 1000hrs so why should you settle for replacing valves every 400hrs. By replacing the valve with a stronger better wearing one piece Stainless Steel valve and reducing the temps of the components with Ceramic coating wouldn't this help to achieve the reliabilty we are all after. I have looked into the cost of these valves and the ceramis coating and you would be surprised at who little the cost actually is to help achieve the result s i am after.Any thoughts out there on this?

 

 

[jetjr]

A few points and ideas.

 

Theres mixed info as some failures are in 4 cyl and can be due to different issues. Also theres old and new versions. Problems get dumped on Jabiru engines as a whole. By spending a few bucks on simple replacement early could save engine failure and big damage you are seeing

 

Leakdowns can pickup many of these problems early too.

 

Id expect you have an early model and there have been some improvements.

 

I feel many of Jabs 6cyl issues are because of poor mixture distribution and overheating of heads. With individual EGT and CHT probes this is seen regularly. Really sorting out air cooling helps a lot but mixture is tough.

 

Poor or inexperienced maintenence is another big problem Id expect.

 

Two fairly fundamental issues but there are fixes.

 

EFI looks good - look up Simple Digital Systems in US, they sell the hard bits required for the upgrade to Jabiru 6. there are people here in AUS who have done a couple. Much of the complex redundancy gear isnt required if you use a carb as throttle body.

 

Liquid cooled heads - not sure if they are real yet but they are coming. They will reduce and even out head temps, they will also be made from more suitable material than originals. Similar cost and weight as original heads.

 

Its possible they might incorperate injector port for EFI but not sure.

 

 

[facthunter]

Cyl Mods.

 

You use Nikasil on aluminium cylinders. Not appropriate for 4130 but maybe use Porous chrome. Beware of hydrogen embrittlement with any plating. The article has to be heat treated immediately following the plating process.

 

Sleeving would not be the way I'd go either. Rusting of bores is common with ALL steel aero cylinders. Shut the engine down hot and don't leave it sitting idle for extended periods without some inhibiting process.

 

Valve life, Keep them seated and don't run lean, or have loose guides. replace valves if any doubt as to their condition or age. (particularly exhaust).

 

Pistons- ring carboning. Probably caused by overheating. I do not particularly like the type of piston used in the Jab but maybe the later ones are better. The full slots in the oil ring groove reduce the amount of heat getting away from the crown. Nev..

 

 

[JabSP6]

Jetjr.My motor is the early Solid lifter engine and i agree Jabiru have done some R&D to try to improve a few things in this area. I have purchased 6 EGT and CHT sensors and gauge that will be fitted when the engine goes back in as i believe my motor has suffered from inconsistant mixtures between cylinders as you mentioned. To combat the overheating of the heads i have purchased a set of the latest fine finned heads. Thanks for the tip on the EFI site. I will look into this as i believe, like you, this is a real problem. The performance and efficiency gains are quite remarkable and will solve this issue. The water cooled heads for a Jab are now available from around $3500. Not sure if i would have room for the radiator in my SP6 engine bay although i was seriously thinking about them before i settled on the fine finned heads. This is why i was thinking about what else we can do to these engines to make them go the distance so we don't have to constantly be told how bad our motors are every time you go to a fly in etc. Eg a friend of mine had fitted a Subaru 2lt EFI automotive engine to his gyro and has achieved 7000 hours and is still on the same set of pistons, rings and valves for that matter. I'm not suggesting we can achieve this from our motor but surely we should be aiming higher than 400hrs. I don't believe this is too much to expect.

 

 

[jetboy]

Hi Andrew, Quite a few topics here I'll start from my experiences with the O-200 over a 12 year period where the maintenance manual expects it to be flown daily if not weekly, any longer than about 4 weeks is considered requiring storage treatment, of course we all can't meet those desires and I frequently felt and heard the rust scrape off the bores on first pullthrough, after as little as 3 weeks tiedown, this also happens to my 2200 and is just one of those indications that I'm not flying enough to make taxicab mileage out of the engine.

 

Looking at the 4 logbooks of the O-200 showed those 1800 hr cylinders typically pack up in 6-700 hrs although some did go longer. The ones that got repaired the most got repaired again the most. My new cylinder kits had to be reworked twice in 200 hrs possibly because the LAMEs neglected to use the correct oil - nothings perfect.

 

My 2200 did 300 hrs in 6 years when I replaced the exhaust valves because of minor leakage - very small pitting on the seats and valves - it appears the problem here was insufficient regular running. I thought, in reading up on the website, Jaba Chat etc. that the valves are one piece construction, certainly my new ones look to be, and all the AAIB recent investigations point to lean mixture causing valve stem failures in UK, very lean low octane fuels in my opinion, as I know my engine did 50 hrs at the leanest and meanest tuning kit and a further 200 hrs without anything like the look of problems to the stems. I really don't think theres anything worth spending time on changing, once you have the revised cylinder - piston clearances, revised basenuts, cooling and oilflows & valveguides OK the factors affecting its longevity are more in the way its operated. I have since only done the basenuts mod - if I had known about the honing and ring work that would have been done at the time too. It was worth 200rpm more in flight which is a substantial increase.

 

There is nowdays a huge amount of info in the manuals, Jaba Chat, etc. that needs consideration before 'making it better', especially the facts that they've gone thru 2 or 3 valve suppliers and seat types in the search for the holy grail....and still searching.

 

Half my friend's 912s have delivered heaps more failures, so I don't see them as better, just different. Yes I'd put a 912 in my plane, except I can buy 2 new 2200s for the same cost of changing over, so in my case it would be a nicer to fit a UlPower, if they ever get a track record, because of the mounting arrangements. For cost and reliability I'd go with their carb option, or consider the aussie TBI.

 

I'm really hoping my 2200 will just wear out slowly, say over the next 6 years, with the normal maintenance work, and plan to replace it because overall it will be marginal to refurbish some areas. A case of "the whole amounting to less than the sum of its parts", to misquote an old Greek saying.

 

Ralph

 

 

[Gnarly Gnu]

Wouldn't stainless steel be a poor choice for valves? Just asking because I believe it is much softer than most high carbon steels etc....

 

 

[jetjr]

Just remembered too - someone was using FLashube in fuel at very low rates has a significant decrease in cylinder rust forming when not used much

 

Regular use is a key too, its often commented that regularly mistreated school AC engine reach TBO yet pampered personal AC have more problems

 

 

[JabSP6]

Jetjr.that is a good point about the flashlube. When i bought the plane the previous owner suggested i use upper cylinder lubricant in the fuel which i have done. i use around 50mls in every tank.Gnarly.There is a company in brisbane that can make 1 piece valves from stainless. titanium etc. They also use a nitriting process to harden them. I don't know exactly what takes place here but they use these in all types of Drag motors which are subjected to much higher RPM's than 3300.Jetboy.Thanks for sharing with us your experiences. These types of stories are all too common which is exactly why i posted this forum. I just want to make it clear that i am not here to run down Jabiru. I live in Bundy and have a good mate that works there and has been extremely help ever since i bought the plane. He has helped ensure the Maintenance is done by the book but still the problems occur. When this motor goes back together it will have all the latest mods done to it including a full set of new nuts, bolts, seals, oil pump mods, dowled crankshaft, latest fine finned heads, barrels, pistons, rings and the list goes on. As i said earlier i will be fitting a set of CHT & EGT sensor to try to see what is happening also. What i am trying to achieve hear is to put together a motor that i won't have to think every time i go to work, is it going to make it. Unfortunately at the end of the day the feedback I have recieved, and i won't mention any names, is that even with all these changes i still probably won't make the TBO. This is why i am asking if anyone has tried thinking outside the square like some of the things i have suggested and had any success with these ideas.

 

 

[jetjr]

Have you weighed up value in an exchange Zero time engine from Jabiru? ~$10K and it includes all the upgrades you listed inc new heads etc

 

Thats probably the direction Im going to go

 

Regarding the valves, Air and water cooled heads act very differently. Most automotives types are liquid cooled and temps are even and apparantly the heat moves out of heads near exhaust valves faster. Anything running methanol shouldnt have temp issues anyway

 

There can be localised VERY hot spots in air cooled heads esecially near ex valves

 

This is the basis for liquid cooled upgrade increasing reliability. Couldnt the radiator somehow fit in top air intakes? They wont be needed much anymore.

 

These "replace with 912" comments show what I said before, confusing 4 cyl with 6 cyl problem. There isnt a solid option for 120hp aero engine other than Jabiru

 

Even if you reduce TBO to 750hrs Id be suprised if Jab3300 int still a good value option.

 

By the way mines just done 750hrs with no major issues, runs great, leakdowns on limits but OK.

 

 

[deadstick]

Have you weighed up value in an exchange Zero time engine from Jabiru? ~$10K and it includes all the upgrades you listed inc new heads etcThats probably the direction Im going to go

Regarding the valves, Air and water cooled heads act very differently. Most automotives types are liquid cooled and temps are even and apparantly the heat moves out of heads near exhaust valves faster. Anything running methanol shouldnt have temp issues anyway

 

There can be localised VERY hot spots in air cooled heads esecially near ex valves

 

This is the basis for liquid cooled upgrade increasing reliability. Couldnt the radiator somehow fit in top air intakes? They wont be needed much anymore.

 

These "replace with 912" comments show what I said before, confusing 4 cyl with 6 cyl problem. There isnt a solid option for 120hp aero engine other than Jabiru

 

Even if you reduce TBO to 750hrs Id be suprised if Jab3300 int still a good value option.

 

By the way mines just done 750hrs with no major issues, runs great, leakdowns on limits but OK.

 

Hey JETJR gotta say the 914 would kick the 3300's ****, the 3300 is rated at 120hp at 3300rpm, static you see 2800-2900 and in flight you can get 3300 but not without reaching the VNE or exceeding penetration speed and with alt you lose what you have, the 914 being forced does not suffer from the humidity, altitude and temp power drains as much so at 115hp rated I think you are more likely to get what you are quoted power wise I would love to have a certified In flight adjustable prop so I can utilise the full potential of my 3300 but that another dream I suppose i_dunno

 

 

[jetjr]

DStick thats probably true but now we are talking 914 and much more complex and Im not sure it carried reliability rep of 912

 

Are there many around?

 

Whats a 914 cost?

 

What are extra servicing needed for turbo engine?

 

 

[deadstick]

DStick thats probably true but now we are talking 914 and much more complex and Im not sure it carried reliability rep of 912Are there many around?

Whats a 914 cost?

 

What are extra servicing needed for turbo engine?

Yep your right I beleive it has slightly less reliability than the 912 and is dearer and more maintenance intensive. Interesting it may be but a NZ chap was telling me the other day that Jabiru engine owners over there are using forged pistons and a coating in the bore as well as fuel injection and seeing solid increases in power, efficiency and reliability, one thing I noticed and rectified in mine when I rebuilt it at 200 hours was the inlet and exhaust runners were poorly machined and missmatched in diameter from head to head, a quick clean up with the die grinder and some blueprinting on volume (cc) and I have noticed the engine responds better to power changes than others I have flown.

 

 

[jetjr]

Interesting regarding port matching.

 

Reports Ive heard from older injected 6 are extremely good

 

More power (heaps), easy start, way lower fuel burn and obviously way more even EGT

 

These newer type should be easier to fit and have better redundancy

 

 

[Dieselten]

I have just done the 600-hourly on my 2200 engine which had the heads overhauled (new glacier-bushes, rocker-rods and exhaust-valves) at 500 hours. I also wrapped the exhaust headers all the way from the head to the muffler in glass-fibre exhaust heat-wrap (about $8/m from vehicle exhaust system specialists). The idea is to keep the exhaust gases hotter so they are less dense and flow out of the head more efficiently. Potentially this can result in slightly cooler exhaust-valves and valve-seats.

 

We observed no visible discolouration in the head inside the rocker area in the vicinity of the exhaust-valve. Previously there was a notable change in clour indicating localised heating. Cylinder-head bolts were all constant and none moved when torque-checked to 20 ft-lbs. So far, so good. This little mill has run the 600 hours in 2-1/2 years, on cross-hire.

 

Jabiru engines are built to run and run hard. Babying them is bad for them as it is for most aircraft piston engines. It's a good way to sludge up your Lycoming or Continental, and it also causes cylinder-wall glazing. Remember, your engine is air-oil and fuel-cooled...yes, the incoming fuel-air charge actually cools the cylinder-head as it is inducted. That's why aircraft piston engines tend to be set to run rich, especially on takeoff.

 

Regard the current incarnations of Jabiru cylinder-heads as 500-600 hour items. Somewhere about those hours be prepared to haul them off, do the valves, de-coke, check the cylinders and any upgrades to hydraulic-lifters, push-rods, rocker-arms etc. They are an easy engine to work on and the parts for a top-end job are cheap and available more or less "on-demand". Doing this is cheap insurance and may prevent a catastrophic engine-failure and a forced-landing.

 

FWIW, the leakdowns were 70/80, 70/80, 71/80 and 69/80, very good for an engine with 600 hours on it (100 since top-end work).

 

I also fly an aircraft with a Rotax 912 ULS engine, a reliable but complex engine with expensive spare parts and consumables (compare a Rotax oil filter with a Ryco Z386 for a Jab 2.2). I have great confidence in both engines because I do the maintenance, or I stand and look over the shoulder of the chap who is putting the spanners to it, and I ask questions.

 

It's hard to know too much about your engine.

 

 

[JabSP6]

Deadstick. I would like to have a chat with the bloke about the mods that have been done in NZ. This is exactly the sort of thing i am looking at doing here myself. I too had to have some porting done to the new Fine finned heads for the same reason. Very inconsistant machining from 1 head to another. It is good to see that other people are experiening the same issues i am confronting. I am hoping for good results once i get the motor back together if i can talk to some people and gain some good feedback of their experiences. I had an Engine builder look at the heads and another comment he made was looking at the flow of the ports, the size of the piston and stroke, he has concluded that the size of the exhaust valve is too small compaired to the size of the Inlet valve to achieve the correct air flow. He had some formular that worked all this out which is abit out of my league but has suggest and Exhaust valve 3mm bigger in diameter would improve the effectiveness of these heads. He said that by machining out the seats slightly this would easily allow the fitting of a bigger valve that could be made to suit. It's just a thought that i am throwing out there. Any comments or ideas about this?

 

 

[biggles]

Another impartial and well researched post that we have got accustomed to from our friend - 'Diesel' !

 

Bob

 

Bob

 

 

[JabSP6]

Guys.

 

I don't want to be a stickler for the rules but this is a Jab forum. I am really not interested in hearing about the rotax motor or how cheap the parts are. I am looking for options other than the standard replacements and factory rebuilds for the Jabiru motor. If anyone can give some advice on the actual topic of this forum this would be much appreciated.

 

Andrew

 

 

[Vev]

Improved engine life

 

G’day Andrew,

 

After rebuilding my top end at 350 hrs I went out and spoke to a number of Jab engine experts around the world (mostly Jab Distributors) and found a number of things that I think will help extend the life of the jab engine.

 

Most of the problems in Jabs is due to overheating ... sticking rings, worn guides, exhaust value pitting/breakage, broken through bolts (detonation) etc etc is all heat related.

 

The new fine fin heads have 50% more surface area along with a wider setting between the valves .. there is also a lot more finning material around the exhaust port which make quite an improvement in terms of getting heat away from the top end. Additionally the new hollow push rod and rocker gear has greatly improved lubrication system and will help extend the rocker gear life many times. One mod I have come across and have implemented into my own engine is to use K-line valve guide inserts, whilst I haven't done enough hrs on them yet to personally give them the thumbs up, the South African Jab Distributor has done thousands of hrs and say they are the bees knees.

 

The new piston and ring set up provides more clearance in the ring groves which should help stop ring sticking and the new piston have larger drain slots in the oil ring grove too ... this combo is a good step forward to reduce ring and bore wear. Jab have also changed the cylinders in the last few months; these are now 0.5m longer to lower the compression to overcome detonation and stop thru bolts breaking.

 

As I said, most problems in Jab engine relate to getting too hot ... the biggest factor to fix over heating is fuel mixture. It is imperative that you have the latest jetting (including needle) in your carby .. Without the right jets you will most certainly run lean and do damage. Fuel distribution in the 6 cylinder is a problem and has also claimed the life of many engines ... however there is a simple fix for the 6 cylinder (not the 4). In the induction track of the manifold there is an aerofoil which acts as a divider to direct flow inside the manifold … this aerofoil doesn’t work. The factory has discovered if you remove this and simply replace it with a 12mm round tube it improves fuel distribution and EGT becomes balanced across the cylinders… it really does work!:big_grin:

 

There is another mod to the Bing Carby, although I have not done this myself, .. the South African Jab Distributor has increased the emulsion air induction size and drilled the emulsion tube air holes to 4mm … I believe this as improved things in terms of better atomisation. I know Jab in Bundy have verified this and suggest you talk with them to get the exact details.

 

I have also tried exhaust wrap for 250 hrs and came to the conclusion that this didn’t provide any real benefit .. it reduced the inside cowl temp but think it may have put heat stress on the exhaust valve.

 

Lastly, fly them hard, particularly during run-in to ward off glazing … they love heaps of fuel going through them to cool thngs down.

 

Hope this helps … Jack

 

 

[JabSP6]

JACK. This is very good info mate and i appreciate you taking the time to tell us about these changes. I do recall hearing about the change to the deflector in the plenum but had forgoten all about it. I will make sure I do this. Also the Carby mod is a new one that I will be asking about. Do you have any more info on this as I would like to know a bit more about what they do before I go asking the question. I am curious about the valve inserts. Can you give me a part number or suggest where I can purchase these items. Are they made from a different type of material and do they run tighter tollerances. It has been suggested the standard guides are an aluminium/bronze guide are are not as good as a Phosphorus/bronze guide. Thanks again Jack

 

 

[dazza 38]

I have learnt more from Jacks Post, than all the reading i have done in regards to the Jabiru engine.Thank you Vev.