Jump to content
  • Welcome to Recreational Flying!
    A compelling community experience for all aviators
    Intuitive, Social, Engaging...Registration is FREE.
    Register Log in
JabSP6

How to improve the reliability of the 6 Cylinder Jab

Recommended Posts

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

Ditto

 

I have just done a top end overhaul on my SP6 (375hr) and had not heard about the aerofoil mod in the manifold. Thanks for sharing!

 

Cheers John

 

 

 

Share this post


Link to post
Share on other sites

Thanks guys .. glad if this helps.

 

Andrew,

 

The k-line value guide inserts are available at almost any auto head re-conditioner ... I believe they are an Al/bronze material. I have run with std clearance and these seem to be working fine, although, as I said, it will take a few more hours to confirm their durability, but others have obtained great improvements. The answer I believe is all to do with the spiral cut inside the insert which provides better lubrication between the valve stem and guide... The spiral simply hold the lubricant and prevents dry contact.

 

In terms of the carby mod ... I checked my notes and I have the "Air Density Sense Port" is drilled out to 3/16" and the emulsion tube holes is increased to 3mm from 2.5mm (not 4 mm as I said in my previous note). The guys at Jab in Bundy are well aware of this mod for the 6 cyl so I suggest you talk to them as I haven't done this to my jab.

 

The only other thing I should mention is your EGT should not exceed 1250 deg F ... some even say 1200 f as max. Whilst EGT's have their limitations in terms of accuracy, there is a direct correlation between reaching TBO and not. Putting in the recommended jetting and using plenty of throttle will take you a long way to managing engine temp at a good level.

 

Cheers

 

Jack

 

 

Share this post


Link to post
Share on other sites

Jack.I will talk to the guys at Jabiru when i get home on the weekend about the carby mods and i will keep you all informed. I hope that by performing these mods the carby might work ok with the standard jetting recommended. I was running the latest Jabiru needle with the recommended 285 Needle jet & 255 Main jet & 35 idle jet. This gave me a cruise temp of 750 degrees C and a maximum power temp of 780 degrees C. I have increased the needle jet to a 290 and the cruise temps are now around 700degrees and I increased the main jet to 265 to achieve a maximum power temp of 680 degrees. these are still a bit higher that what you have recommended so i will see what happens after the carby mods are done and the plenum chamber mod is done. I am still working on cooling the head temps and it has been suggested i fit baffles under the barrels to even the air flow around the cylinders and fit a lower cowl boomerang to improve the pressure differential. I will keep you updated on this mod also.

 

 

Share this post


Link to post
Share on other sites

Jabiru factory have not found a solution to the uneven fuelling - Ive been fighting this one with thier help for a while now and no success.

 

They admit its been an issue since day 1 in the 6cyl and some solutions work in some cases. Not one fix works for everyone.

 

There were a couple of intake plenums, some have more swept angle than others - I thought the tube deflector was the early version but Im not really sure.

 

Some talk regarding a deflector vane in air intake either as it leaves airfilter housing or in the cobra head near carb, but again this doesnt work all the time.

 

Seems to be possible air swirls as it comes through intake and carb, priorotising one side or the other

 

Port injection is the only true solution I know of.

 

Re valve guide wear, this isnt an issue with solid lifter engines I think?? Hydraulic type have some new rocker gear to improve geometry now I heard, aparantly it was pushing valves sideways a bit wearing guides. Some had significant issues with oil flow to valves too

 

New and older heads (fine vs thick fins) also have different valve/rocker geometry too

 

I reckon the 650-680 deg max EGT is perfect, but make sure its being measured on your worst cylinder. This cylinder location can change at cruise and WOT. Im convinced some guys lean off to reduce fuel burn at engines detriment. Especially if they arent watching all cylinders.

 

The tuning you are doing with jets is also very important I think, not many do it.

 

Im keen to hear regarding under cylinder baffles - its how other makes are setup

 

Playing with lower edge of bottom cowl makes big changes, not always the way you want, so take it easy. I fitted 2 tabs ~ 25mm wide by 200mm each and CHT went right UP !!! After fitting new oil cooler intake the new cowl insert had much larger full width extension and CHT dropped. Cant explain this.

 

 

Share this post


Link to post
Share on other sites

New manifold inbound

 

I was complaining about the same fueling issues with Jab the other day and offered to do some work towards a fuel injection system after they stated that they could not get the Rhotec system to work properly, anyway got talking with one of the design engineers who stated that they will have a new intake manifold system ready for trial next month and I could have one to test. I am in the process of fitting a MGL 12 channel EGT/CHT guage and sensors so will be able to check the spread and see if it improves. will let you's know how I go.

 

DK

 

 

Share this post


Link to post
Share on other sites
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?

Sorry for the late reply I will get the guys number and PM you.

 

 

Share this post


Link to post
Share on other sites
I was complaining about the same fueling issues with Jab the other day and offered to do some work towards a fuel injection system after they stated that they could not get the Rhotec system to work properly, anyway got talking with one of the design engineers who stated that they will have a new intake manifold system ready for trial next month and I could have one to test. I am in the process of fitting a MGL 12 channel EGT/CHT guage and sensors so will be able to check the spread and see if it improves. will let you's know how I go.

DK

Hi DK,

 

Yes heard about new manifolds for both 4 and 6 ... I understand they are out on trial now (at least thats what I was told 2 weeks ago) in some ac off-shore and at some flying schools for testing. However the stop gap (6 cyl only) while this is being done is to put the round defuser in the manifold which works well.

 

Also of interest is Jabiru engines are currently being fitted with EFI ... these are the Israeli Army UAV engines. They adjust mixture via an EGT sensor, all reports suggest there isn't a huge improvement and is just adding complexity.

 

Cheers

 

Jack

 

 

Share this post


Link to post
Share on other sites
Guest JRMobile
I am in the process of fitting a MGL 12 channel EGT/CHT guage and sensors so will be able to check the spread and see if it improves. will let you's know how I go.

DK

Hi DK I would be very interested in any results you see from this trial. Please keep us posted on the results :thumb_up:

 

Cheers John

 

 

Share this post


Link to post
Share on other sites

Guys

 

Just to let you all know I have the motor back together and after some testing of around 6 hours over the weekend I have made my first flight today back out to work. The hour meter was right on 2.0 hours for the trip this morning including run ups and taxi times. I have fitted the EGT and CHT sensors with the MGL Gauge and I noted some reading during the flight. I took off from Bundy and climbed to 4500" at a steady 300"/min. this took around 20nm to achieve cruise height. I then levelled off and cruised out to Rolleston (205nm). Sitting on just over 2800RPM on the tacho my airspeed was 120knots. I have a 3 blade Patroney Prop fitted set at 14 degrees pitch. I then had a slow decent to rolleston starting 20nm out of around 300"/min. The temps were as follows on cruise

 

EGT 1/ 602 2/ 673 3/ 621 4/ 682 5/ 639 6/ 681

 

CHT 1/ 103 2/ 95 3/ 127 4/ 108 5/ 101 6/ 92

 

I have increased the needle jet to 190 and the main jet to 165 to make sure there is plenty of fuel for the first few runs while i try to get on top of the difference in the CHT's.

 

I have not yet done the mod of the Plenum chamber but when i do i will hopefully see more consistant figures across the EGT's.

 

I am also trying to redirect some airflow over the middle cylinders (4 & 3) by fitting deflectors in the ram air ducts like they have done from factory over the rear cylinders. i will be doing this when i get home on the weekend. this should even out the CHT's.

 

The SP6 tank was right on the 80ltrs (avgas) in the hanger before i took off and when i checked it again at the hanger at work it was right on the 40ltrs. I think this is a pretty good result. Average 20ltrs/hour including run ups and taxiing times.

 

As the motor gets a few more hours on it I am sure the temp will improve and i may need to look at the jetting again after I perform the Plenum Mods. I will keep you all informed. Andrew

 

 

Share this post


Link to post
Share on other sites

Hi Andrew,

 

Look fwd to hearing hows things go.

 

Re your jetting .. the 190 needle jet and the (i presume) 265 main is on the upper end of the recommended jetting so you will be getting a heap of fuel through.

 

Just wondering if you have changed the needle to the new one as well?

 

Cheers

 

Jack

 

 

Share this post


Link to post
Share on other sites

Jack

 

I am running things a bit richer than the standard specs for now to see how things go with the other mods that i have done, ie. ceramic coating etc. 190 needle is 1 size bigger and 265 main is 2 sizes bigger. The WOT EGT's vary about 80 degrees from richest to leanest but the highest reading is around 650. The cruise EGT also vary about 80 degrees but the highest is 685. So according to these temps the mixtures should be, depending who you talk to, fairly close but just on the rich side but i am going to fit an air fuel ratio sensor short term to the exhaust to find out exactly what it is doing. The needle is the Jabiru spec one with the one circlip groove and the 3 rings as a marking which i believe is the correct needle. Once i can even out the temps for both CHT and EGT i will look at possibly rejetting if needed. I would rather burn a bit more fuel than risk engine damage. The Oil temp on the way out sat around the 85 degrees. Some people say it must be around the 90 mark ad others say the lower the better. What are your thoughts on the temp of the oil?

 

 

Share this post


Link to post
Share on other sites

Oil temp and other...

 

The lower the better is NOT OK. The oil will pick up moisture from the products of combustion, if it is too cold and the oil gets cloudy. Most manufacturers like the oil to reach about 90 C.

 

With measuring all the temps, what variation do you think you are getting from gauge to gauge? How accurately do you think they are calibrated? There could be a considerable variation and EGT's may vary depending on how the exhaust exits the port. (relating to the location of the probe).

 

A lot of this kind of research was done in days past with heat sensing paints. Works well on cyl heads to give an overall picture. ..Nev

 

 

Share this post


Link to post
Share on other sites

hi Andrew,

 

Nev is correct ... engine lubricants need to operate in a range high enough to dry them as well as activate the additive systems, particularly in respect of anti-wear.... Too hot will cause oxidation of the base oil where it will break down.

 

I am assuming you are using Shell 15w-50? At 80-90 deg c you are in the sweet spot and all is good.

 

Cheers

 

Jack

 

 

Share this post


Link to post
Share on other sites

Nev / Jack

 

I am using Shell 100W PLUS aero engine oil which was recommended by jabiru. Should i be using 15w-50?

 

Winter up here does't usually get below 10degrees

 

 

Share this post


Link to post
Share on other sites

Andrew,

 

 

If you are running in a new top end you need to use a lubricant with minimum additive treatment such as AeroShell 100 (Not AeroShell W100 Plus) for the first 25hrs. If you don’t use a run in lube your engine may glaze the bores.

 

After the engine is run in I prefer a multigrade such as AeroShell 15w-50 ... the 15w is the equivalent viscosity at 40deg c, the "W" stands for Winter and tell you that is will operate well below zero. The 50 is the equivalent SAE viscosity at 100 deg C and tells you it will maintain good lubrication qualities at higher temps.

 

The multigrades are achieved by blending in Viscosity Index Improvers (polymers), where the oil is relatively thin and less restricted compared to a SAE 50 mono grade oil at low temps, thereby allowing the oil to travel around engine more quickly and reduce start up wear. This low temp performance is important in the Jab engine as not only does it assist in reduceding start up wear but it also helps with drain back from the rocker chest to the sump… the rocker chest is a source of thermal shock owing to the high heat of the cylinder head in the first few minutes at start up, which is more critical in the 4 cylinder engine but still an issue in the 6.

 

In summary … I would use the Shell W100 to run in and then the Aeroshell 15w-50 after that.

 

Hope this helps

 

Cheers

 

Jack

 

 

Share this post


Link to post
Share on other sites

Availability of Shell W-100.

 

Not sure but I think that the only 2 oils from Shell are the W-100 plus and the Multigrade. ( which Jab and Jack recommend). The 100 plus has an additive which is for Lycoming engines in particular (and other engines in general) which stops Camshaft corrosion during lay-over. I don't think this would be any problem at all for running in as its not affecting the lubrication qualities. (You can always get a second opinion.) Nev.

 

 

Share this post


Link to post
Share on other sites
Not sure but I think that the only 2 oils from Shell are the W-100 plus and the Multigrade. ( which Jab and Jack recommend).

Theres a "Blue " 100 labelled one too as Vev mentioned, used for breaking in new engines or after OH . I think some people call it a "mineral only" oil.

 

Not rare but a bit harder to find

 

W100 Red label

 

W100 Plus Orange label

 

15W50 silver

 

100 blue

 

Sports Plus - different shaped bottle and Orange label

 

Now I see theres W120 too - Annoyingly also in red label bottle

 

Ive used W100, W100+ and 15W50 and found 15W50 is best all rounder and definitely better in winter, W100+ seems to handle high summer temps a bit better though

 

As I have a, just arrived, rebuilt 3300 in my shed, on the build sheet they clearly recommend

 

"Non compounded Aviation oil Aeroshell 100, Mobil Red Band or BP Aviation Oil 100 for 25 hours, then drain and replace with compounded oil, Aeroshell W100, AeroShell 15W50 (for cooler climates), AeroShell W100+, BP Aero OIl D100/BP Multigrade Aero oil D SAE 20W 50"

Share this post


Link to post
Share on other sites

AeroShell Oils 65, 80, 100 and 120

 

AeroShell (straight mineral) Oils are available in four different viscosity grades (SAE 30, 40, 50 and 60). They are blended from selected high viscosity index base stocks and contain a minimum quantity of additives. These oils are especially appropriate during the break-in period of most new or recently overhauled four-stroke aircraft piston engines. Interesting numbering system Cheers

 

 

Share this post


Link to post
Share on other sites

I recall at the Jabiru Engine forum at the final Narromine the engine man said that Aeroshell 15-50 was better at ensuring that small particles got flushed out of the hydraulic lifters. This problem could let the lifters jam open and might occur as they run horizontally instead of the more usual vertical mode. Quite how this worked was not stated; maybe the semi-synthetic blend flushes better. I notice that the oil filler label now reflects this on LSA aircraft.

 

 

Share this post


Link to post
Share on other sites

Hi Modest Pilot,

 

Yes I heard the same reports about lifter flushing, although I can't say I have experienced this improvement but it could be quite true. However despite the fact that the 50% blend of semi-synthetics in the 15w/50 Shell lube, I would think it unlikely that the synthetic base oil will flush any better ... in fact the solvency of synthetics is mostly poorer than mineral oils. If the multigrade lube is flushing the lifters better it is more likely to be a combination the better flow characteristics by nature of it being a multigrade and a very effective dispersant additive in the oil.

 

Cheers

 

Jack

 

 

Share this post


Link to post
Share on other sites
Guest JRMobile
EGT 1/ 602 2/ 673 3/ 621 4/ 682 5/ 639 6/ 681

 

CHT 1/ 103 2/ 95 3/ 127 4/ 108 5/ 101 6/ 92

 

I am also trying to redirect some airflow over the middle cylinders (4 & 3) by fitting deflectors in the ram air ducts like they have done from factory over the rear cylinders. i will be doing this when i get home on the weekend. this should even out the CHT's.

 

Andrew

Hi Andrew

 

I would appreciate any feed back on the fitting of deflectors for the cooling on cylinders 3 and 4. As you know most of us get our CHT from #6 as it was supposed to be the hottest.

 

I'm go in today to adjust the tappetts / retroque the heads after 10 hrs, and am using AeroShell 100 straight mineral Oil.

 

Thanks for the feedback todate.

 

Cheers

 

John

 

 

Share this post


Link to post
Share on other sites

John,

 

I fitted the deflectors from left over fibre glass from the J430 kit on cyl 3 & 4 (the hottest) and found the CHT temp reduced by about 15 deg on those particular cyl. I recall that before the mod cyl 3 hit 180 deg on climb out in summer while cyl 6 was only 150 deg. My temps are pretty even now...around 155 deg in cruise at 2850 RPM. cyl 6 is still the coolest. If you are only monitoring cyl 6, it would be interesting to move the sensor to cyl 3 for a comparison.

 

Hope this helps.

 

Garry

 

 

Share this post


Link to post
Share on other sites

Even Cooling over the Heads

 

Garry & John

 

I have done a few things in relation to the cooling of the cylinder heads.

 

I was after a bit of advice in the deflectors you are talking about. i have looked into the Ram air ducts that sit on the barrels and heads. From factory there is a deflector right over the centre of Cylinder 5 & 6. As i now have my rear cylinders running around 5 - 10 degrees cooler then the front cylinders and the middle cylinders running around 15 - 20 degrees hotter than the front cylinders i was thinking of fitting a smaller version of the deflectors above the centre of the middle cylinders and just modify the length until the rear temps even out to the fronts and hopefully this will also reduce the centre cylinders to eventually have all around the same temp. I have also heard that you can fit a deflector under the barrels above the pushrod tubes to deflect the air coming between the cylinders around the bottom of the cylinders. i guess this would help even out the temps from the top of the engine to the bottom. just wondering which way you have done your mods?

 

I was also wondering if anyone has got any photos of their lower cowls so i could look at how i can modify mine to give a better negative pressure in the engine bay. the previous owner has done some drastic changes to mine from standard which to me looks like it would creat a lot more drag and turbulance than improving the airflow direction to achieve the negative pressure required.

 

Wags

 

 

Share this post


Link to post
Share on other sites
Guest JRMobile
I have also heard that you can fit a deflector under the barrels above the pushrod tubes to deflect the air coming between the cylinders around the bottom of the cylinders. i guess this would help even out the temps from the top of the engine to the bottom. just wondering which way you have done your mods?I was also wondering if anyone has got any photos of their lower cowls so i could look at how i can modify mine to give a better negative pressure in the engine bay. the previous owner has done some drastic changes to mine from standard which to me looks like it would creat a lot more drag and turbulance than improving the airflow direction to achieve the negative pressure required.

 

Wags

 

[ATTACH]12320.vB[/ATTACH]

 

Hi Andrew

 

The pic above shows the mod to the cowl for the larger oil cooler fitted earlier this year, you can just make out the lower cowl. While we were doing this mod I was advised to remove the deflectors between the cylinders as they were an impedance to the air flow.

 

I hope to have a look at the idea of fitting deflectors above 3 & 4 this weekend.

 

Cheers John

 

1844333264_NewOil.JPG.c01f9c50f9d641877bc67bd27e2e6f0b.JPG

 

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later for your post to be seen If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...