Jabiru 2200 oil pressure problems!

[Oscar]

Appreciate the responses...Going to check clearance on the oil pump gears this weekend and will take a good look at the relief valve for wear or insufficient seating. I am puzzled by the Jabiru at 420 hours on a 2000 hour TBO. I am curious about the machined seat on the CAMit mod. My engine casing has a snap ring groove which secures the outer washer and the pressure relief assembly. How do they do the machined seat? The other thing that puzzles me about Jabiru is 3 washers under the spring(max according to manual) from the Factory.....Has anyone ran across that?

FR, in the CAMit mod., the snap ring (we call them a circlip) is removed and a small o-ring is seated in the very bottom of the counterbored hole in the case - this is the seal for their new OP relief shuttle. It's a completely straightforward swap-over job: 20 minutes for anybody who is a competent mechanic. You can get the information 'from the horse's mouth' by contacting CAMit - their contact details are at: http://camitaeroengines.net/

 

 

[Oscar]

There is a thermo unit for the Jabiru from UKThought Ian was looking at something similar?

jj - I believe that it's on the list for testing in the test cell. As you can probably deduce from Dafydd Llewellyn's post above, the necessity for (calibrated) instrumentation and control of the factors that affect oil cooling performance require this level of precision and control in order to be an acceptable mod. to a certificated engine, there are too many variables in a flying installation to get the authoritative data. The UK one you mention is by all reports damn good, but it needs this sort of test data to get the 'acceptability' for installation on anything other than experimental-class aircraft.

 

 

[Dafydd Llewellyn]

Appreciate the responses...I am curious about the machined seat on the CAMit mod. My engine casing has a snap ring groove which secures the outer washer and the pressure relief assembly. How do they do the machined seat?

The machined seat is an integral part of the CAMit oil cooler/filter adapter. See photo. I don't know whether the plunger that goes with it is a standard Jabiru part, or a modified one to fit this seat. I'm not sure CAMit sell that part separately - it may be part of their jab engine rebuild program rather than an after-market item - you'd need to contact Ian Bent and ask him. I do know that the combined assembly works very well.

 

The oil pressure gauge in the test cell is an Aviasport gauge, which uses a VDO sender (but a different part number to the original one supplied by Jabiru). Here's the calibration result:

 

 

 

 

[freeman28139]

Guys, I am surprised with all of the information. I really appreciate it. The CAMit info is interesting. I plan to give them a call. I can't help but be suspicious of the relief assembly. I have thoroughly enjoyed my Jab up to this point, good performance and temps have been good all the way. The thought of a rebuild is troublesome. I am hoping to find a economical, yet, good solution.... I will update my findings as I go. Thanks for the info once again.

 

Phillip

 

 

[facthunter]

No relief valve is perfect. It has to seal at a fairly constant figure. It's purpose is to limit the maximum the oil pressure reached and protect the system. If the engine is operating with the pressure limited/regulated by the relief valve, it has to be pumping oil at a rate surplus to the flow through the engine, at the revs and oil temp prevailing.

 

Loading up the spring pressure will not affect pressure if the flowrate isn't high enough. If the ball doesn't seal it is another place for the oil to bleed away and not do it's job, just as if the pump is worn or the inlet blocked or leaking air "IN".

 

Ball valves might give irregular readings. Sliding plunger type can get a small piece of metal to jamb them in various positions. A failed spring will cause dangerous pressure loss.. A "WAVE washer in the oil pump is sometimes used to allow a sideplate to move and allow oil to leak away at that point, when the predetermined pressure is reached. Nev

 

 

[Oscar]

Phillip, the standard Jab. relief valve has some known 'quirks' - that's why CAMit re-designed it for their engines. However, the standard VDO sender and gauge are both also known to be less than bullet-proof, which is why we're using an Aviasport on my engine. If you can get hold of another gauge and sender to try as a temporary, it MAY give a different reading (of course, then you have to decide which one/s are telling the truth - it's always worth changing just one thing at a time if you can do that!).

 

 

[Dafydd Llewellyn]

Here's my dead-weight oil pressure gauge calibration rig. It uses a Citroen rear suspension cylinder, which is a lapped fit (rather too good a lapped fit; it really needs to be brought up to its design operating temperature - I would assume around 70C - to work sufficiently freely. Amazing what one can do with a mousetrap and a piece of string . . . and some certified test weights, of course.

 

 

 

 

[Dafydd Llewellyn]

For what it may be worth - I wonder to what extent the fluctuations one sees with the standard oil pressure sender location may be due to the pressure relief valve in the oil filter opening and closing. We haven't been able to get a figure for the filter back-pressure at which that valve is supposed to open.

 

 

[facthunter]

True but I don't think it is many pounds/ sq in. At that point you are bypassing unfiltered oil. It used to happen near start up first, (so I'm told) with a clogged filter or perhaps too small, or very worn bearings. Nev

 

 

[jetjr]

Theres a site somewhere where a guy has worked with lots of valve end profiles to try to smooth out severe pulsation coming from oil pump. He did have some detailed logging and data. Pulsation was very real and surprisingly violent. He got to ver 5 or more and did have some success.

 

Lots of gauge senders show wear on the wiper from vibration and oscillating pressures, why they fail a lot I guess.

 

It was thought these pulses were the cause of some extremely high pressure cycles fatiguing early 6 cyl coolers

 

I have had a piece of grit hold open valve, was seen pretty quick and pressure was low but OK.

 

Found it

 

Yahoo groups Jabiru engines

 

https://groups.yahoo.com/neo/groups/jabiruengines/photos/albums/439839736

 

Probably need to join to see images, there is a lot of historic fiddling with Jab engines there, photos worth a look.

 

 

 

[geoffreywh]

The info given here is very useful and valuable, BUT it's worth naught until the oil pressure is checked with a mechanical gauge...................DO THAT FIRST, it takes but a few minutes... unless you know the actual pressure that you are dealing with you are groping in the dark..........Those VDO ones are notorious for giving false readings....

 

 

[Dafydd Llewellyn]

Whatever form of gauge you use, it needs to be calibrated either immediately before or immediately after the test. Mechanical gauges generally hold their calibration for a long time, but electric sender types are not so consistent.

 

The reason people use the electric sender type in aircraft is because there are requirements to prevent the release of flammable and/or toxic fluids - especially as a fine spray under pressure - within the cockpit. The weak part of a mechanical gauge is the tube that connects it to the engine, or the Bourdon tube inside the gauge; both are susceptible to fatigue failure; and a failure means the engine runs out of oil, apart from whatever effect it may have on the pilot.

 

 

[geoffreywh]

Agreed, But for purposes of diagnosis, use a mechanical gauge.....If all is well then the mechanical gauge will agree with the electric sender one...If not you have somewhere to start...and you are dealing with known facts, not asumptions

 

 

[jakej]

yeah guys, the emphasis is on using a calibrated test gauge - it doesn't have to be a new one.

 

Jake J

 

 

[Yenn]

Doesn't matter how many washers you put under the relief valve. It only control when the pressure is too high, If you havn't got high pressure the relief valve can be set at infinity and you still have low pressure.

 

 

[Olav]

To Dafydd Llewellyn.

 

What kind of stick on insulating material did you use?

 

Just came to the same conclusion about insulating/protecting the oil sump from cold air flow, and then found your comment.

 

Winter in Denmark. Until now I have been choking the air inlet to the oil cooler by a big sponge. Easy to ground adjust before flight, but still primitive and not very accurate control.

 

I did try instead to tape up my oil cooler, but the oil was too cold. Now I have installed an oil thermostat and tested with no air flow restriction - but the oil is too cold.

 

So I have concluded that the oil sump surface alone is cooling the oil too much, so the sump must be insulated or protected against the cold air flow.

 

This way I can secure only the oil cooler will do the oil cooling job and only when the thermostat opens at around 85 deg. C.

 

Regards Olav.

 

 

[Old Koreelah]

To Dafydd Llewellyn.

What kind of stick on insulating material did you use?

 

Just came to the same conclusion about insulating/protecting the oil sump from cold air flow, and then found your comment.

 

Winter in Denmark. Until now I have been choking the air inlet to the oil cooler by a big sponge. Easy to ground adjust before flight, but still primitive and not very accurate control.

 

I did try instead to tape up my oil cooler, but the oil was too cold. Now I have installed an oil thermostat and tested with no air flow restriction - but the oil is too cold.

 

So I have concluded that the oil sump surface alone is cooling the oil too much, so the sump must be insulated or protected against the cold air flow.

 

This way I can secure only the oil cooler will do the oil cooling job and only when the thermostat opens at around 85 deg. C.

 

Regards Olav.

Olaf Dafydd no longer posts on this site (which is a great loss). I just phoned him and he said he'd covered the sump with common self-adhesive insulation for wrapping around water pipes. This was on an uncowled engine in a wind tunnel, so not the same as actual flying conditions.

 

As discussed on this and other threads, one problem is that the standard Jab oil temperature probe is very short and effectively only samples the temperature of the oil very close to the walls of the sump; that "boundary layer" of oil is likely to be quite a bit cooler than the oil circulating around the engine. To get a more accurate reading, you'd need a probe that's long enough to get past the cooler oil near the sides to samples the hotter oil further in.