Latest 3300

[Guest DonC]

Does anyone have a late 3300 (post ser # 2390) Mine has done 85 hrs now and seems quite a

 

bit down on power compared to a well worn one it has replaced.

 

Will only pull 3,000 rpm straight and level (in a J230) and cht is noticeably hotter.

 

Retarding the ignition timing to 20 deg btdc sounds like a backward step to me!

 

 

[Jaba-who]

Are all cylinders running hot?

 

 

[Guest DonC]

Are all cylinders running hot?

Don't know mate, can only afford one cht!

 

 

[Jaba-who]

Has it ever run better than 3000 rpm?

 

And

 

Is it using a standard jabiru prop?

 

Just trying to cover some other bases before blaming the engine completely.

 

Jab props are usually a bit coarse so it could be a prop issue.

 

 

[geoffreywh]

You can happily blame the engine ! I have a shortened Original Jab prop here you can try if you like...Ended up shelling out 1800 for the sensenich. 3300 WOT is now easy to achieve. That, plus updated pushrods/rockers and LOTS and LOTS of other things pm me for details if you like....

 

 

[Guernsey]

You can happily blame the engine ! I have a shortened Original Jab prop here you can try if you like...Ended up shelling out 1800 for the sensenich. 3300 WOT is now easy to achieve. That, plus updated pushrods/rockers and LOTS and LOTS of other things pm me for details if you like....

Not sure what you are saying here, are you blaming the engine or saying a better prop increased the revs. Also what does WOT mean.

Alan.

 

 

[Guest DonC]

Engine never did more than 3000 from new - now 90 hrs

 

Standard prop

 

 

[Guest Andys@coffs]

Not sure what you are saying here, are you blaming the engine or saying a better prop increased the revs. Also what does WOT mean.Alan.

WOT = WideOpenThrottle......errr flat out....balls to the wall...etc. When the need for WOT comes unexpectedly can often be accompanied by an inverse movement of your sphincter

 

 

[Jaba-who]

I'm not blaming it completely but don't discount the prop effect completely

 

I have had two jab props that both were unable to get over about 2750 on static testing. (from brand new build & engine) And we had another on a second machine with same problem.

 

Changed it to a sensenich prop and instantly got 2850. We have had several other jab props here that were also coarser than desired.

 

I spoke with jabiru and they conceded the measuring system (which is supposed to be done a standard way) is not done by the guy who makes jab props ( they are not made at jabiru but subcontracted out to a third party) and that they are coarser than say sensennich props of the same specs.

 

 

[Guest DonC]

I'm not blaming it completely but don't discount the prop effect completelyI have had two jab props that both were unable to get over about 2750 on static testing. (from brand new build & engine) And we had another on a second machine with same problem.

 

Changed it to a sensenich prop and instantly got 2850. We have had several other jab props here that were also coarser than desired.

 

I spoke with jabiru and they conceded the measuring system (which is supposed to be done a standard way) is not done by the guy who makes jab props ( they are not made at jabiru but subcontracted out to a third party) and that they are coarser than say sensennich props of the same specs.

Sorry mate, I should have been clearer, only the engine is new, the prop performed well on the old engine

 

 

[Guernsey]

We have a Bolly ground adjustable prop giving us 3,000 revs WOT in flight, should we re- adjust pitch to give us 3,300 or some other figure in between. We want to maintain our high cruise speed (not worried about climb performance as we have the 6 cylinder Jab) so we are thinking that the extra revs at a finer pitch should maintain this performance, however which would be better FOR THE ENGINE

 

Any comments would be appreciated.

 

Incidentally Andy we have removed the Sphincer from the engine and it now runs much smoother and cooler.

 

Alan Marriette.

 

 

[geoffreywh]

You should be able to achieve max revs at W.O.T. level flight at a set altitude, say, 1000ft?.....( or even a little more)....... if not? Then the engine may not be as good as it can be, or you have too much pitch....The engine REALLY REally wants/needs to be revved, to labour the motor is to kill it by allowing it to overheat ( I don't know about non-Jabiru installations) ........So as far as I can make out 3000 rpm is a minimum cruise engine speed and the engine should be propped accordingly.....As far as a Bolly adjustable prop goes. I would adjust it to give me, say 3400 at WOT and cruise at 3000, WHATEVER the speed is, is irrelevant to the engine.....

 

 

[Guest Andys@coffs]

Incidentally Andy we have removed the Sphincer from the engine and it now runs much smoother and cooler.

Alan Marriette.

Alan...youve done it, completely fixed the long standing questions of Jab reliability. No Sphincter means it cant sh%t itself.....fantastic

 

On a more serious note...overall engine speed does have an impact on engine life... running too fine a pitch and then having RPM too high will accelerate wear and has to increase vibrations etc. I'm pretty sure that J say that in the 3300 with their prop cruise should be 2850ish. higher than that tends to overheat in my beast..albeit that its an older solid lifters and thick finned heads but with newer oil cooler and bigger lipped back lower cowl.....

 

 

[geoffreywh]

Really 2850 is just not fast enough..............more IS better....

 

 

[Bryon]

..............more IS better....

Thats what the girlfriend says.......now all I need is for the missus to say the same thing

 

 

[Jaba-who]

2850 is the recommended rpm on static testing. (or it was when I did the reading and initial testing). In the air is a different story.

 

If you get more on static testing I guess it means your prop is over- fine. Which will predispose you to over- revving in flight. That then means lower top speed in cruise. Good for climb but not so good for cruise and risky for overspeeding in descents.

 

 

[Adrian Lewer]

Are you actually getting WOT ? have you checked whether or not your actually getting full throttle you might have some binding and just not getting the last 2-3 mm of travel ?

 

 

[facthunter]

I want what you're eating Byron.

 

Re the JAB RPM. Overloading the engine could be harmfull. ( too large or coarse a prop). and IF you don't achieve the stipulated static revs on the ground you will not tbe getting the full power either. As to running an engine at high revs in cruise, once you get a variable pitch prop you don't usully do that. You give it a bit of a rest. ( because you can). The CV type carburetter has the needle "tweeked" to give a rich mixture on TO at sea level. At altitude the needle will not open as far because you do not get the same mass airflow. ( It is less).so it doesn't get as rich. That is OK because the engine is not operating under the same load as at sea level.

 

I think Jabs like a lot of throttle as because it keeps them rich (and COOLER).. This is important when you are getting full power, but less important when they are at higher altitudes. The only time you can work the engine hard is at low heights. As far as bore glazing, a lot of what is said about that is smoke and mirrors. Something to blame)..Anytime your Jab is cruising above about 6,000 ft, it is loafing ( even on full throttle) Nev

 

 

[Guernsey]

I want what you're eating Byron.. As far as bore glazing, a lot of what is said about that is smoke and mirrors. Something to blame)..Anytime tyour Jab is cruising above about 6,000 ft, it is loafing ( even on full throttle) Nev

Not sure if I agree with you here Nev, although we have not experienced bore glazing on the Morgan there have been many posts plus a friend with a Jab 230 who have all experienced this when flying at less than 2,700 revs in cruise in order to save fuel. I have always respected your opinions so could you explain why you think the bore glazing occured.

 

Alan Marriette.

 

 

[facthunter]

Alan with a steel bore (which in the case of a Jabiru, and some others) is pretty soft, ( ie it is not Nitrided) and also has a very fine honed surface on it, it is pretty inevitable that the bore will develop a very polished surface on it fairly quickly. This type of surface does not retain an oil film well, and if the rings get scuffed they will not seal, you lose some power and the engine " breathes" a lot.

 

Nitriding the cylinders and having a more aggressive hone pattern would help hold the oil. and delay the "polishing/ glazing.' I have had experience where running an engine in too easily would result in a motor that always used oil. This doesnt happen with aero engines too much as you can't take -off without using a lot of power. Think about my statement relating to the altitude cruise. You are down on power because of loss of volumetric efficienct due to the reduced air pressure, so the engine does have an easier time. Revs in isolation does not mean that the engine is working hard, ( unless all other things are equal).

 

Most of the damage that I have seen in the cylinders of Jabiru's has been scratches probably caused by breakdown of the oil film , perhaps a combination of high temperature and the type of oil ring used. Jabs don't actually burn much oil, they vent most of it. ( unless the inlet guides are worn).

 

Having aircooled cylinders, and consequently higher running temps, it has to run more clearance on the pistons than is the case with say a Rotax 912 Inevitably the piston does not seal as well as it would if it ran less clearance. ALL aircooled motors experience this problem. It can be reduced by having the cylinders made from an aluminium alloy ( which will be weaker than steel) but will expand more closely to the same rate as the piston and will need a hard coating, (Nickasil or similar) on the bore surface. to prevent wear. Nev