two fuel filters?

[frankmcm]

I just spent an enjoyable few hours over the past week preparing our Jab for annual inspection.

 

Inpector wanted a few things fixed, like a frayed air intake hose, and the UC bolts replaced, and an improved mounting for the oil cooler.

 

For the first time I got inside the workings of the aircraft, and the experience left me much more knowledgeable about how it is held together, and more confident that I can keep on top of any problems that may develop.

 

One unexpected finding was a fuel filter buried between the tank and seatbacks, out of sight and forgotten during the past 4 years, and not changed in that time because we didnt expect there would be one there. There is another filter plainly visible in the forward footwell.

 

The fuel system schematic shows a " finger filter" at the tank outlet, just upstream of the electric pump. I am not sure I would recognise one if I saw it, but I am glad to have located this one as it was pretty discoloured internally. I will make sure to replace this annually.

 

Any thoughts on the design?

 

 

[turboplanner]

I grew up with race car design where every item on the car had to be quickly demountable and replaceable, tuning items had to be readily available and instantly visible, and nothing as critical as a fuel fliter was hidden away where no one would notice it. Wonder how many engines run lean because of clogged filters?

 

 

[jetjr]

In some Jabs the header tank is under the PAX seat. A second filter may have been added to keep any junk out of here?? Sure should have been changed though. These paper filters do fall apart after a while dropping small bits of paper into system. Just had one do it in a car I have. Filter was ~ 4 years old but done maybe a few hours work.

 

In my Jab the firewall mounted one is under a cover, sort of end to the console and ridiculously hard to get to.

 

The finger filters are very coarse.

 

 

[Jaba-who]

I have a vague recollection that the old construction manual (before about 5 years ago) had two filters fitted in the line in one of the several conflicting diagrams so maybe this one was following the book?

 

Mine is in the same spot as jetjr's and every 100 hourly I swear I am going to move it somewhere more easily got at. It's a real problem where it is.

 

 

[jetjr]

Yes I think every 50hrs where can it be positioned better, but without going into the engine bay its fairly tough, Ive redone hoses so its as close to the firewall fitting as it can be, its still a PITA. Im thinking about mounting pump onto the floor so at least the cover can come off easier.

 

Around the time these were built Jabiru were using Gascolators and no header tank, AC had "sharks fin" in centre of roof which housed vents. After some issues this setup was removed and header tank setup as currently sold was introduced. Initially under PAX seat then moved behind rear curtain for less lead needed in tail for W&B

 

Plenty were converted from one setup to the other - before the header tank install, the position behind the seats would be ideal for filter location.

 

 

[frankmcm]

Yes I think every 50hrs where can it be positioned better, but without going into the engine bay its fairly tough, Ive redone hoses so its as close to the firewall fitting as it can be, its still a PITA. Im thinking about mounting pump onto the floor so at least the cover can come off easier.Around the time these were built Jabiru were using Gascolators and no header tank, AC had "sharks fin" in centre of roof which housed vents. After some issues this setup was removed and header tank setup as currently sold was introduced. Initially under PAX seat then moved behind rear curtain for less lead needed in tail for W&B

Plenty were converted from one setup to the other - before the header tank install, the position behind the seats would be ideal for filter location.

I just want a safe and practical setup. Currently I have to move the tank to reach this filter, and until recently I didn't even know it was there at all.

It has been suggested that I get rid of it and just rely on the single forward filter. Tempting.

 

 

[jetjr]

If your concerned ask Jabiru?

 

 

[Bruce Tuncks]

I can't see any reason why one fuel filter wouldn't be enough. It is only there to stop particles bigger than the filter mesh size getting to the carby. I've never heard of any problems with the single filter system which has been used for years now.

 

I was once told by a Jabiru factory engine man ( I think his name was Jamie ) that he had never seen a blocked fuel filter on a Jabiru. Personally, I've seen a blocked filter on another aircraft with a fibreglass tank, but it was a far smaller filter and the material looked like muck left in when the tank was built.

 

....Bruce

 

 

[facthunter]

IF you don't filter the fuel that goes into the tank, and many poeple don't, I reckon there is merit in having a coarse mesh metal filter in the bottom of the tank. and possibly a water separator as well. The final filter has to be capable of removing particles that would be big enough to affect the operation of the carburettor, and is much more likely to block up if something like the lining of the tank sheds glass fibres, and would need servicing regularly, wheras the coarse one wouldn't. I have had a chain come off a filler cap and fall into the tank. That sort of thing is why I would like the coarse filter. Nev

 

 

[Jaba-who]

Hi Nev.

 

The set up already includes finger filters in the main tanks (that's standard in Jab main tanks ) that would trap such things as bits of chain and other foreign objects that get into the main tank. What I am pretty sure is involved here is an extra paper filter between the main and header tanks.

 

What Jabiru currently uses (apart from the aforementioned finger filters) is a single paper filter (Repco z15, I think, model) between the header tank and the engine, usually just after the electric fuel pump.

 

I have pulled apart a couple of the fuel filters in the past when I replaced them and never found anything in them. Also never heard of them clogging up on anyone else's machine. Have a talk to Jabiru but I am confident they will say it's OK to just remove that extra filter and run on one filter.