ROTAX 912 Oil Change and oil pressure sender questions

[FastEddieB]

Apparently, changing the oil on a ROTAX 912 is a little more involved than your average oil change.

Last oil change, we drained the oil tank, pulled the filter and the magnetic inspection plug, then let the plane sit overnight. Next day we installed the plug and filter, filled the oil tank, pulled the prop through about 30 revolutions and started the plane up.

It took a long time for the oil pressure to come up, but it finally did.

Since then I've been advised,

1) to fill the oil filter with oil prior to installation

2) to drain and refill the oil tank before changing the filter*

Questions:

1) With the oil tank filled (if I do that first), can I expect oil to come out when I pull the magnetic inspection plug and/or oil filter?

2) Similarly, I have to change out my oil pressure sending unit, which started leaking on our Sun 'n' Fun trip:



With the oil "burped" into the oil tank, can I expect oil to come gushing out when I pull the old sender? If so, can I safely do it with all the oil drained out, without the fear of introducing air into the system?

Thanks in advance.

*neither of these are mentioned in the ROTAX maintenance manual, though I believe subsequent service instructions may mention one or both.

[roger lee]

Hi Eddie,

You shouldn't let it sit overnight without the oil and oil filter. If you do then an oil purge would be needed.
Here is a normal procedure to follow.
The engine should be warm. Rotate the prop until it burps. Then drain the tank. While that is draining pre-fill the new oil filter from the 3 qts. you have ready. You should always pre-fill the filter. It will fill to the top and then the level will recede because it soaks into the paper element. Refill it again until the level is about 2/3 full. Put a slight film of oil on the filter gasket. Do not use silicone or anti seize to lube the rubber oil ring. Put the drain plug for the tank back in place. Remove the old filter and immediately install the new filter. Refill the tank with whats left over of the 3 qts from filling the filter. Pull the magnetic plug and inspect. Replace the mag plug. Rotate the prop 20 times. Safety wire the magnetic plug and oil drain plug. The oil level should be right at the top of the flat fill mark. No matter if it looks a little lower do not add more oil after the 3 qts. or you will be too full.

One last thing, never rotate the prop when the oil tank is empty or the filter is off or you will inject air and will then have to do a purge.

The oil sending unit can be removed without any air issues. First I would try and tighten it. It is rare that it leaks on the seam. If it really has a leak then of course it needs to be changed. Put a little thread sealer on it and re-install. Put a rag under it and the magnetic plug because both will drool some oil. When I pull the plug I plug the hole with a rubber stopper or my finger until I put it back in just to keep from making a mess.

Lockwood has two senders for this. They are identical VDO senders on the inside. One has a heavy metal ring,supposedly for anti vibration and the other one without the metal ring. The metal ring one does not last any longer than the plain one. The metal ring one is about $240 and the standard VDO gauge is about $40. $40 works for me and I have never purchased the metal ringed sender.

[FastEddieB]

Roger,

Thanks for that.

I have the $40 sender on the way (my Sky Arrow is Experimental so it should be fine).

Once the cowling was off I could see the situation better. I sure don't see any leaking from the threads* or on the back side of the sender:



Someone expressed concern that leaving the oil draining overnight with the filter and magnetic plugs out could lead to a collapsed lifter. To be totally safe, I'm planning on having Tim Dawson of OpTIMum Improvement come over to help me with the oil change this time, and also check the lifters, check the compressions, clean the oil tank, swap the sending unit and talk me through the purge procedure.

The ROTAX engine IS a curious beast!

*the oil pressure sending unit page in the Lockwood Catalog warns against using any kind of thread sealer, saying it could interfere with proper grounding

[3Dreaming]

The brass collar can be pressed off the old sender and placed on the new $40 dollar sender without to much trouble. It's funny on the thread sealer because Rotax says to put it on.

[FastEddieB]

It's funny on the thread sealer because Rotax says to put it on.

The "Heavy Maintenance" manual I have says:

After removal of oil pressure sensor, clean the thread. Apply LOCTITE 243 to thread of sensor and tighten to 15 Nm (133 in.lb).

This is what the Lockwood catalog says:



I'll probably try the blue Loctite, but very lightly applied so as not to interfere with grounding.

Thanks for the head's up on the "Collar Transplant"!

[roger lee]

Hi Eddie,

This product was recommended by a couple of different Mfgs. a few years ago to seal threads and prevent leaking. High or low pressure, oils, gas, hydraulic fluid it just doesn't matter. I use it for almost everything with a fluid in it on my plane and others where threads are concerned. I have never had a leak.



PRODUCT DESCRIPTION
LOCTITE® 567 provides the following product characteristics:
Technology Acrylic
Chemical Type Methacrylate ester
Appearance (uncured) Smooth, creamy, off-white pasteLMS
Components One component - requires no mixing
Viscosity High
Cure Anaerobic
Secondary Cure Activator
Application Thread sealing
Strength Low

LOCTITE® 567 is designed for the locking and sealing of metal
tapered threads and fittings. The product cures when confined
in the absence of air between close fitting metal surfaces and
prevents loosening and leakage from shock and vibration. The
high lubricating properties of this compound prevent galling on
stainless steel, aluminum and all other metal pipe threads and
fittings. LOCTITE® 567 is recommended for industrial
applications in the chemical processing, petroleum refining,
pulp/paper, waste treatment, textile, utilities/power generation,
marine, automotive, industrial equipment, gas compression
and distribution industries. It is also recommended for industrial
plant fluid power systems.
UL Classification
Classified by Underwriters Laboratories Inc.® as to fire
hazard only. Loctite® PST® 567 Pipe Sealant with PTFE. Fire
hazard is small. No flash point in liquid state. Ignition
temperature 465°C. For use in devices handling gasoline,
petroleum oils, natural gas (pressure not over 300 PSIG),
propane, and butane. 976P

[FastEddieB]

Roger,

Thanks for that.

I almost always have blue and red Loctite around - the 567 is new to me.

I'll run that by my mechanic as a substitute for the blue Loctite.

Do you have a source for that that I might find locally? I have NAPA, Advanced, O'Reilly's and Home Depot nearby.

[FastEddieB]

Last Friday I had Tim Dawson (ROTAX mechanic, http://www.optimum-improvement.com/) come up from Dahlonega to help me with the oil change and a few other things.

We changed out the oil pressure sender with the $40 VDO equivalent, then changed the oil (from Pennzoil Motorcycle oil to Aeroshell Sport 4 Plus), following Roger's instructions. Since we had changed out the oil pressure sender, and to show me how, we went ahead and did the purge procedure, using some jury-rigged fittings Tim had put together. We checked compressions and then started up the plane. With the purge, the oil pressure came up instantly, of course. Tim then showed me how to check the tappets for proper bleed-down, and they all seemed fine.

Anyway, we're hoping we took care of the leak. After the test flight, there was still a tiny bit of oil towards the rear (normally front) of the engine. I'll have to keep an eye, because we really cannot see where it might be coming from.

Thanks all for the help!

[drseti]

After the test flight, there was still a tiny bit of oil towards the rear (normally front) of the engine. I'll have to keep an eye, because we reall y cannot see where it might be coming from.

Eddie, I always have a bit of oil around the front (normally front) of my 912ULS, after every flight. I've also been unable to tell where it's coming from, though I assume the gearbox. Thing is, the gearbox was overhauled by Lockwood shortly before I bought the plane, and I know they replace seals. So, I'm beginning to think this is normal.

[roger lee]

Oil from any where on a 912 is not normal and can be fixed.

[FastEddieB]

I had the cowling off today to trouble-shoot the "GEN" light issue (see other thread).

After replacing the suspect oil pressure sender, my small leak continued. I used an old trick of cleaning the damped area and spraying on foot powder to trace the leak.

Voila'



The oil is emerging from the head of one of the case bolts. Tim Dawson is investigating, and thinks there might be a faulty o-ring involved. We're taking a look tomorrow.

Also, I've had a slight coolant smell. I think I found that as well:



We'll try to address that tomorrow as well, and I'll report back.