Jab engines

[RFguy]

Hi Steve L

The rotax soft start you refer to is NOT what we are referring to on Jab engines.

 

The Jab (and others) issue is the tendency of the starter motor with its enormous torque , and small ring gear ratio, the tendency to try and tear the flywheel off the crankshaft.

 

The rotax soft start I understand is designed to make life easier on the gearbox.

 

-glen.

 

 

 

 

Edited October 14, 2020 by RFguy

[440032]

Try and tear the flywheel off the crankshaft??? WHAT????????????

Yet more utter nonsense from someone who does not even own, operate or maintain a Jabiru engine. Sorry RF dude, you are just way out of line with your nonsense on Jabiru engines.

Yes, I myself do own, operate and maintain a Jabiru engine for the last 16 years. Unwarranted and uninformed Jabiru bashing needs to stop.

 

[skippydiesel]

55 minutes ago, 440032 said:

........................................................Unwarranted and uninformed Jabiru bashing needs to stop.

 

What and spoil al the fun?  --------- what would we argue about ?  Rock on say I

[RFguy]

I am not bashing Jabs. I am pro -Jabiru....... Go and look at my other other Jab stances.

 

There are many defficiencies in all aircraft that can have improvement applied.

 

 

 

[Yenn]

I had problems with the Bing carbie on my Corby with Jab 2200 engine some time ago. I used to be a good mechnic, but years have passed and I have lost a bit of confidenc, so I sent the carbie to jabiru. They overhauled it, replaced one or two items and sent it back. I could have left it with them for a longer time so they could fit it to an engine and run it, but decided I would forgoe that luxury.

I fitted the carbie and found that it needed no choke to start it, in fact sometimes it needed throttle. I tried to adjust the slow running to reduce rpm and found the slow running needle valve screwed right in, opening it caused roughness, so I just reduced the throttle setting.

I was getting black spark plugs and a much higher fuel consumption, but it was delivering power OK.

Now I have decided to look further at the problem, I removed the carbie and fuel level was good, nothing obviously wrong. I removed the choke / starting system and the only obvious problem was that a short piece of the paper gasket was missing. I could not find the missing piece, but I may have broken it during removal.

Jabiru say that they never remove the choke, so they don't stock the gasket.

I made a new gasket and today replaced the carbie. Result, it now needs choke to start and runs well. When running application of choke results in a slight rpm increase.

I only ran it up to 50% power and will conduct full power tests and a test flight probably tomorrow.

I would have thought that a broken gasket in the choke system would have resulted in lean running. I will have to look further at how the system works.

Has anyone else had any experience with the bing carby similar to this?

[skippydiesel]

Yenn - it seems to me you do yourself a disservice - nothing wrong with your mechanical skills/diagnosis. I have not long found out how use emoji's - so here is one for you 😇

[facthunter]

The choke is a by pass mixing chamber. Not a choke in the normal sense It's most effective when the throttle is nearly closed. The failed gasket in you case must have allowed air in which is quite likely.as the fuel must be sucked there. Nev

[alf jessup]

On 15/10/2020 at 12:12 AM, Steve L said:

My 912 has soft start on it. I believe it retards the timing until a few seconds after start. Surely it could be adapted to most engines.

Steve, the soft start allows the engine to fire 4 degrees after TDC which will save the sprag clutch from any damage, once it reaches 1000 rpm it reverts back to 27 deg BTDC like the standard ignitions.

I have to replace my sprag clutch soon as my battery got a bit tired a while back and it kicked back a few times and damaged it.

you will never have a problem with soft start modules.

[skippydiesel]

Yes the "Soft Start" will have a beneficial impact on your Sprag Clutch longevity and  all the other components of your starting system. 

I relaced the Sprag Clutch on my 2000 commissioned 912 ULS @ about 600 hrs - no data to support my feeling on the matter but I am of the opinion that persisting with weak battery performance (may have had kick back's  but dont recall any) was the main cause.

I installed a partial "Soft Start" - retaining my old ignition modules but replacing the original fly wheel with the Soft Start one - great improvement. The fly wheel is the cheapest part of the Soft Star upgrade.

I now only give a battery one chance to "come good" , from an overnight charge, using one of those multi stage battery chargers . If it doesnt get back to top performance (14.2V), it is immediately replaced with a new one.

To help maintain the battery and extend its operational life, I now give it a "tickle up" about once per 2 months - again with an overnight charge with the multi stage charger - so far so good. 

[facthunter]

 IF you engine does fire after TDC there's NO way it will kick back unless it's overheated.  Most engines never fire after TDC normally. The engine slows  a lot and gets hot and has a very labouring  steady exhaust note.. The impulse starting magneto's are a delayed firing mechanism that automatically ceases once the engine starts as the trip mechanism centrifugally disengages. Firing against the starter is hard on the starter and the engine itself. Your starter spins more easily with the throttle closed as they don't FILL.the cylinders with gas so if you want to save things spin the motor first then switch the ignition on and open the throttle slightly.  Nev

[Yenn]

I am still waiting for a replacement gasket, but in the meantime i have reduced the idling speed by turning back the adjusting screw 1 turn, On the test flight the engine stopped on approach, nose too high, revs dropped and suddenly stop. No worries i was high enough but started it and continued.

I turned adjuster up half a turn and next flight, it stopped again and being the lazy sod that I am, I said stuff the engine and landed without it. It started easily after I stopped, but i did learn something from it. There was about a 4 knot cross wind and as we slowed down it became much harder to to maintain heading, there was a very definite lessening of rudder effectiveness. So much so that I reckon with a real engine out situation I would not want to have to deal with a cross wind. The landing would be OK, but better brakes would be desirable.

When I get the gasket, if that does not solve the original problem I have an idling jet replacement. That was sent by Jabiru, when i ordered a needle jet. It seems for carbies I would be better off dealing with Flood than Jabiru.

[facthunter]

They wouldn't be jetted the same. With no propwash you'd be best to carry a bit of extra speed. Whether we use it or not the engine power is an extra  control. (Energy management too) If it looks as though you are not going to to clear the downwind fence safely , a burst of power is the only way to do it.. Nev

[kgwilson]

If the paper gasket you made works why bother paying for one from the manufacturer. You used to be able to buy gasket paper material in different thicknesses. Maybe that is not the case now. I made all sorts in my younger days & they worked well & only had to be replaced when I pulled things apart again. Then RTV was invented & that solved lots of gasket issues (not for petrol areas though).

 

As FH stated the Bing choke is a separate by pass system with its own jet and not a butterfly airflow choke normally seen. If the throttle is not at idle even open a little bit it will not work. The choke will supply a rich mixture for idle running and it reduces the tendency to flood the engine. If the engine doesn't start then a lot of people try to use throttle and end up flooding the engine.

 

A comment on starter clutches. I am on my 3rd. The first began to stop engaging when the pinion was grinding at the edges of the ring gear but not fully meshing. A new one fixed the problem but the old one which I still have looks in perfect condition and works when I fire it manually. It just won't work when installed. I thought it must have something to do with the sprag clutch but that seems to work properly as well. The second one failed because the pinion was only pressed on to the shaft with out a keyway or spline like the first one. The one I have now has the pinion splined onto the drive shaft. Most modern cars have a pre engage mechanism to lessens the sudden clash of gears and high torque. This used to cause worn or broken teeth on ring gear in 4 or 6 places & mechanics sometimes removed the ring gear and shifted it around a bit on the flywheel so it  engaged in a different spot. The Jabiru starter clutch was originally a Honda as many motorbikes use this type of starter because they are smaller and lighter. Now its a clone as the Honda genuine articles are expensive. All starters put stress on the crankshaft bolts and these have been known to shear. Jabiru had 6 x 3/8 cap screws loctited in originally then they moved to nordloc washers with higher torque & now with the Gen 4 engine there are 3 dowels and 3 cap screws to improve torque shock. Lycomings & other engines with the starter at the front have a much larger flange on the crankshaft to absorb the torque.

 

 

[facthunter]

Some places like this will work with NO gasket IF the surfaces are dead flat. You can lap them on a piece of plate glass but I'd get a few of the "proper" ones, preferably. Cutting them out is too finicky. All this is done with laser cutting I believe and is very cheap if you get a few done. Engines prone to stalling are risky. If the idle isn't reliable the plane is supposed to be US till it is rectified.  Too fast an idle will make the plane "float" on landing. Nev

[kgwilson]

Adjusting the throttle idle takes a bit of time. After I built and tested my aircraft I thought I'd got it right but hadn't & when I pulled the throttle to idle, with a bit more force the engine would stop. I did a few dead stick landings and adjustments before I got it right.

[Blueadventures]

4 hours ago, kgwilson said:

Adjusting the throttle idle takes a bit of time. After I built and tested my aircraft I thought I'd got it right but hadn't & when I pulled the throttle to idle, with a bit more force the engine would stop. I did a few dead stick landings and adjustments before I got it right.

This is what throttle lever / vernier  etc stops are for so we don’t stretch or damage the carb lever setting stops.

 

[coinz]

16 hours ago, Yenn said:

I am still waiting for a replacement gasket, but in the meantime i have reduced the idling speed by turning back the adjusting screw 1 turn, On the test flight the engine stopped on approach, nose too high, revs dropped and suddenly stop. No worries i was high enough but started it and continued.

I turned adjuster up half a turn and next flight, it stopped again and being the lazy sod that I am, I said stuff the engine and landed without it. It started easily after I stopped, but i did learn something from it. There was about a 4 knot cross wind and as we slowed down it became much harder to to maintain heading, there was a very definite lessening of rudder effectiveness. So much so that I reckon with a real engine out situation I would not want to have to deal with a cross wind. The landing would be OK, but better brakes would be desirable.

When I get the gasket, if that does not solve the original problem I have an idling jet replacement. That was sent by Jabiru, when i ordered a needle jet. It seems for carbies I would be better off dealing with Flood than Jabiru.

We had 4 or 5 engine stoppages on approach with my early series 1 Jab at Marion field,idle was always stable on the ground.Eventually i discovered it appeared to be a design fault with the carb throttle lever arm.Throttle cable runs from left side of the engine and curves around the front then goes back to carb .My eng no high 600's later on they modified that. The carb throttle lever being alloy and the idle screw having a ball end and meeting the lever at an angle about 30 deg off from 90deg  meant the lever was distorting when snapping the throttle back on approach.

2 hours with a dremel had the lever and ball meeting at 90deg at the idle position and a small dimple in the lever(the lever is only 1/8" wide  so a bit underdone for the task) for the ball to always center itself on the lever . Eng never failed after that.

colin   

[facthunter]

Glen , I'll go over the fire event with you over the phone. Happy to, but it's a "heavy".  Leave it till after Xmas. In principle it's relevant to all planes... Nev

[Yenn]

The reason for waiting for the gasket is that the one I made may be fouling the disk inside. I don't know. The gasket is less than 2mm wide in 4 places round the disk. Going without a gasket would I think cause the disk to bind. I could put a full paper gasket over the whole thing and have no starting enrichment at all, but I want to get one problem solved before I start on the next.

What surprises me is that at idle on the ground the engine runs fairly well with the throttle pulled all the way out, but with a forward speed of about 40 kts and the nose held high giving a greater angle of attack of the downgoing blade of the prop, that there is so much drag that it stops the motor.

The Jab engine setup is poor concerning the controls to the carbie. The throttle cable comes in above and very close to the fuel line and the choke control is the same but beneath. It is extremely hard to get it all out together and I have found the best way is to put the fuel line on first, then the controls and finally the firesleeve. The answer is to remove the original inlet to the carbie and fit an AN tapped fitting in a different direction. Or to run the cables vertically into the carbie as they were done on BMW motorbikes, the fittings are still there.

[Mhalc]

I have completed the first series of ground tests (test stand) of a supercharged 3300.  These tests were conducted using a Bing carby, at manifold pressures to 34”MAP (just slightly higher than a normalized engine).  Future tests (after the first of the year) will be used to identify a practical maximum for the Bing (which may turnout to be 34”MAP).  Followed by a series of tests using the Rotec 40mm TBI, with the expectations the TBI will handle higher manifold pressures.

 

[Yenn]

Mhalc. I had to go a long way back to find where your conversation started, but find it I did. I reckon the only prolem apart from jetting that you would have with a Bing is if the feed to the float chamber came adrift, which is a problem i have had a few times. The connection of thin tube to an awkward to get at nipple is not the best, especially as that tube tends to be forgotten and gets hardened with age.

A TBI would I suppose not need any pressure equalisation. I am seriously considering changing from the Bing to a TBI as I reckon they are much easier to tune and more reliable,

[Mhalc]

For my application (Gen4 3300) I have a 40mm TBI, but I have been approached for Gen2/Gen3 options as well.  So I have been working out suitable fuel systems for the Bing.  For the Bing, you need a higher pressure fuel pump, and boost referenced pressure regulator.  As the float needs (4psi + boost pressure) fuel pressure to operate.  Your are correct it has taken longer than I expected to get here, but I am starting to get good results and integration is progressing well.  I hope to have test flights in and fly to Sun-N-Fun this year.

[RFguy]

At least with the TBI you have control over the mixture- 

I guess the Bing satisfies 90% of the operators by getting the mixture close most of the time .-  But it doesn't suit the enthusiasts.

 

[Mhalc]

Yes the TBI has traditional mixture control and less sensitive to fuel pressure.  In the stock configuration, I have been using a HACman for mixture control with the Bing.  I fly regularly between 8,500’ and 12,500’ and the HACman performed well.  Still need to test the HACman in the supercharged configuration.

[facthunter]

Having a float in the fuel system is risky in an aeroplane, and more inappropriate as you fly higher. Nev