J

JEG

Active Member
I am in the process of purging engine prior to first run, regulated 12lb pressure to vent, 50 lb pressure showing on Skyview when cranking but no oil showing at the in line to the canister. I have tried several times with no luck. I am able to purge burp engine with plugs installed. Any ideas would be appreciated. John
 
Hi John,

I'll be happy to help you through this. It is easy, but sometimes a little
mis-understood. I just had a guy call me yesterday from TX with the exact same question.

Give me a call up to about 2100 hrs Tucson, Az Time.
 
JEG said:
I am in the process of purging engine prior to first run, regulated 12lb pressure to vent, 50 lb pressure showing on Skyview when cranking but no oil showing at the in line to the canister. I have tried several times with no luck. I am able to purge burp engine with plugs installed. Any ideas would be appreciated. John
Click to expand...

If you are doing as described in the S.I., without spark plugs installed, you will not see any oil getting sent back to the tank.
The oil is pushed back by crank case pressure (which can't develop, with no spark plugs installed).

Put the plugs back in, and burp the engine again, and you will be good to go (don't forget to also confirm that all of the lifters are pumped up).
 
He has pressure hooked up and that substitutes for crank case pressure. With the plugs in you can't turn it fast enough and that's why they have you take them out and use external air pressure. The oil should come out of the tank inlet hose which is the one off the bottom of the engine. It isn't a huge steady stream, but there should be some. Most don't turn the prop long enough and a little speed certainly helps. I turn the prop fast enough that I usually see about 45-55 psi on the panel. I turn it at about a rate of one revolution per second. It's a fairly fast rate, but works great. If it is a new engine you may just need to rotate the prop a little longer and more than once. I hate to take chances with a new engine so I will turn the prop 80 revolutions and do that twice. Take a couple minutes break after the first set so you can catch your breath and then you won't need the paramedics. :) I always get oil out the inlet in some amount. I have never had a soft lifter doing it this way.

Doing this twice isn't always necessary, but I hate to take chances with $18K new engine at stake and for an extra 2 minutes of my time. It's the better safe than sorry train of thought and it gets the job done 100% of the time.
 
Not going to argue with you Rog... but you are wrong (at least with how we do it on the RV-12's).

The air pressure sourced at the tank does nothing for pressurizing the crank case, so oil will not come out the return hose unless you do what the S.I. tells you to do... move the disconnected hose below the bottom of the engine with the end in a catch container.
This way it will gravity drain the oil from the engine case.
With the the hose routing on the RV-12 this is difficult, and really of no value anyway.
If you only turn the prop until oil pressure comes up, it doesn't put very much oil in the engine. Then just reinstall the spark plugs, burp the engine and you are ready to go.
 
A quick question?

Since the RV12 has separate ignition switches can you use the starter to spin the prop?:rolleyes:
 
Hi Scott,

rvbuilder2002

"The air pressure sourced at the tank does nothing for pressurizing the crank case, so oil will not come out the return hose unless you do what the S.I. tells you to do... move the disconnected hose below the bottom of the engine with the end in a catch container.
This way it will gravity drain the oil from the engine case."
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This is a little long winded, but I hope it helps others that are just getting started to understand a little better and some of this I'm sure is redundant for some.
Return hose routing on some aircraft does make the return hose angle difficult under normal circumstance, but when I I'm taking responsibility for that first start I change that routing for the oil purge and then route it back. If the muffler is in the way leave it off until after the oil purge.


You are correct and I agree, but I don't think you took it far enough.
We are usually only concerned about crankcase pressure to return oil to the tank when under normal operations and the hose on the bottom of the engine is hooked up to the oil tank. This is the only way oil gets pushed back into the tank when the engine is running. This is a test question on exams.

Okay let's go with the idea for a moment the air pressure does nothing as you said. Then why do it, why does Rotax want you to hook it up at all? Why not just dump oil in the tank, leave the plugs in and rotate the prop? (I know this isn't what you meant, but I think we need to be careful with our wording with new owners) The crankcase is the entire case with all its parts that need lubrication and I think you are only considering the bottom of the case (wording) where case pressure returns oil back to the tank. You need the case pressurized with the oil to move it through the rest of the crankcase.

You're correct that once oil gets through the system to the bottom of the case it becomes gravity fed down the hose only if you have it pointed downward during the oil purge process. If the hose is up in the air then gravity won't get oil out uphill and the case starts to fill with more oil because it can't gravity feed out. The air pressure does pressure the engine with oil and along with the oil pump while rotating the prop helps push oil through to the point where it drops into the bottom of the case next to the outlet hose on the bottom. This is now open to the atmosphere during the purge and not going back to the oil tank. If you never see oil come out of this hose where is it going? Most likely if it never comes out it hasn't completely traveled through the system because we didn't turn the prop long enough
(#1 problem) or ran out of oil in the tank or you have your hose sticking up in the air and gravity doesn't work any more (#2 problem).

The faster prop rotations do help the overall processes verses slow. We care about every thing up to this exit point. The only thing seeing oil coming out the hose does is give us an indication oil has traveled through the engine to its exit point. If you never see oil how do you know it has gone all the way through and pushed out all the air spaces?


Here is the oil route as it is forced through the case. You block off the inlet on the tank. The other line on the oil tank is the outlet line that goes to the oil cooler and or thermostat. With pressure on top of the oil it is pushed out the outlet hose (point of least resistance) through the radiator. Then into the oil pump and through the oil filter where it is then forced with this pressure and pump through the oil ports into all the other internal areas of the engine, i.e. fills the lifters, travels through the rods, bearings, lubes the bushings, ect.. until after its journey it falls into the bottom of the crankcase along with the trapped air that is being replaced by the oil moving through the system. The air and oil have to go somewhere. They shouldn't just stay in the bottom of the case. If your hose off the bottom of the engine is hanging down or at least horizontal to the ground then not only will the trapped air pass through, but the oil that has gone through the system will flow out the hose. It isn't pressurized oil as it may barely flow or sputter out and this is your gravity feed at this last spot in its journey through the engine.

So the air pressure on top of the oil in the tank is pushing oil into the oil pump and forcing it through and into all its cavities as you turn the prop. All of this is the crankcase and not just the bottom end. The oil pump also pumps the oil as you turn the prop, but gets a big assist from the pressurized oil coming into it.
Your using that air more or less as a pneumatic advantage and a force to push oil into all its tight spaces and fill voids of air pockets.

Think of a garden hose that has been unused. You close off the nozzle on the end and turn the water on. You believe it is full of water up to the nozzle, but would you bet all the air is out of the hose and there isn't any air pockets? If on a brand new engine you haven't filled and lubed everything on that first start then scoring happens and one or more lifters may not be filled with oil at first start especially if that engine has been sitting a long time waiting to go on and aircraft.

It becomes a gamble and I'm a better safe than sorry kind of guy. Parts are too darn expensive and that first start may cause dry spot scoring or damage that may not show up today, but shorten the engine's life or parts.


So for me I let the hose hang and rotate fast and long enough until I see oil. It doesn't have to be a lot it just has to be there.
 
OK Roger all that being said , would a little suction on the line help speed the process.
 
H Jeg,

Would it? maybe, but I have never heard of anyone doing it and never seen anything in writing. It may lead itself to air vacancies on certain parts of the engine. I truly don't know. You shouldn't have to do this. Like Scott said once it goes through the system and gets to the bottom of the case it is a garvity feed out the hose. Might be a tad of loose air helping it along.

I have never had trouble getting oil out the hose. The biggest factor that I get when people call is that they didn't rotate the prop long enough. Speed isn't critical, but it does help.
You also don't need a lot of air pressure. I typically only use 10 psi. The manual says 5-15 psi. More isn't necessarily better. I think technique plays a bigger part.

We only have 4 indicators that lead us to believe we have done a decent job in on our oil purge. No single one is enough, but joined together the sum shows us it got done.
1. Oil pressure on the panel while rotating the prop. This doesn't mean everything has oil. It does mean the pump has oil because that is where the pressure sender is located. It also means oil is meeting resistance going through the system somewhere and you now have some back pressure.
2. Oil coming out of the return line that you have hanging down. At least you have some indication that oil has traveled through the system. It doesn't mean it is everywhere you want it, but just another single indicator.
3. Rocker arms are all solid and do not sink inward when you put pressure on them to test the lifters for air.
4. Quick and solid oil pressure on start up of the engine. Just another single indicator. If you didn't have any pressure it would be time to shut down and purge again. I have never had to do this.

I don't think an oil purge gets every last bit of air out, but if it isn't in the wrong places it works its way out when the engine is run and isn't harmful.

My offer still stands. If you want to talk about it please feel free to give me a call. Tell me exactly how you did it from start to stop and I bet we can work it out to make it work well with good results.
 
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Roger, you seem to be ignoring the point (probably haven't yet done the procedure on an RV-12) that with the way the oil hoses are installed on an RV-12, it is not possible to lower the return hose so that oil will gravity feed out the bottom of the engine.
It really doesn't matter, since it is also not possible to get a normal oil pressure reading while doing the procedure, and not have oil going into the bottom of the crank case. If the system is under pressure, oil will be expelled from around bearing surfaces, etc, and drop into the bottom of the engine.

I realize it is not exactly to the letter, the way Rotax describes doing it, but all an RV-12 owner needs to do is pressurize the tank as described, spin the prop briskly (reason for removing spark plugs) until oil pressure is detected; continue for another 10 seconds or so and you are done. Re-install the spark plugs... burp the engine, and it should be ready for first start. As long as it takes a bit of turning to burp the engine after completing the procedure, it is a pretty obvious sign that there was some oil in the bottom of the crank case as a result of the purge procedure.

It's not rocket science (unless you designed a way to put a BRS system on your RV-12, but there is another thread for that discussion ;))
 
Hi Scott,

"Roger, you seem to be ignoring the point".

I'm not ignoring just saying there is always a way around an obstacle. I try to think out of the envelope.

The RV12 Rotax isn't any different than other Rotax engine mounting. Yes some things are a little different, but a part removal here or a muffler removal there and it shouldn't be a big deal since it is a fairly rare event. I have to do these things all the time for all kinds of aircraft mountings. It isn't hard to
re-route the return line off the engine or just add an extension hose. I haven't seen a Rotax engine yet that with some work (some more, some less) that the return line can not be routed properly especially since it is a first start. The last two years I have been doing 20 hose changes a year and have to purge all of them and have never had a problem and believe me some can be a challenge. If an RV12 is a home built then the purge can be done almost anytime just before start with parts cleared out of the way. Just as Vans advises, knowing a certain assembly order makes a job easier. I haven't seen one of the RV12 ELSA's I can't do a normal purge on. If you have to remove a part or re-route the the hose for a little bit it isn't an issue and it is important enough to do it. When I work on other aircraft if I need to pull the muffler or snake a hose out that has never been an issue. I like easy, but that doesn't always happen.

"since it is also not possible to get a normal oil pressure reading while doing the procedure."

I get 45-55 psi during every oil purge, first time or after a hose change. It has to do with the speed you rotate the prop. Get a younger guy to spin the prop faster. :)

"As long as it takes a bit of turning to burp the engine after completing the procedure, it is a pretty obvious sign that there was some oil in the bottom of the crank case as a result of the purge procedure."

You can get a gurgle on the engine if you rotate the prop afterward, but still have a soft lifter if it isn't checked. Oil may not and usually doesn't flow equally everywhere and that's why I rotate more times and do it twice.

I have seen and recently worked on an SLSA RV12, no reason a regular oil purge can't be done on an SLSA or ELSA RV12 with a few considerations.

This job for me is so important with an $18K engine it isn't worth the risk to take a short cut.

I just finished an oil purge a couple of days ago from a hose change and have another probably Wed. this week from a hose change. If I get pumped enough I'll try and make a video and record the pressure and procedure with oil coming out the hose. It won't look like a Rotax video, but might be worth some laughs because usually after I spin the prop that many times at that speed I feel like I need oxygen when I'm finished. LOL.
 
Post #6

Scott or Roger,
Can either of you answer "Jetguy's" question in post #6. Thread has been very informative!
Steve
 
Jetguy said:
Since the RV12 has separate ignition switches can you use the starter to spin the prop?:rolleyes:
Click to expand...

You can (I have done it) but I don't advocate it because it is not in the published S.I. procedure.

With plugs removed (especially if you do it with the top and bottoms removed), the engine turns over very easily and than you don't put wear and tear on your starter motor and run your battery down.
 
roger lee said:
"since it is also not possible to get a normal oil pressure reading while doing the procedure."

I get 45-55 psi during every oil purge, first time or after a hose change. It has to do with the speed you rotate the prop. Get a younger guy to spin the prop faster. :)
Click to expand...

I guess you are having difficulty with how I write (I don't claim to be very good at it), because you are totally quoting me out of context.

I never wrote it was not possible to get normal oil pressure during the procedure (and I do every time also)...

What I wrote since it is also not possible to get a normal oil pressure reading while doing the procedure, and not have oil going into the bottom of the crank case.
You said you were concerned about confirming that. I was simply saying the concern was unfounded, because it is not possible.

Do what you want you want when doing the purge procedure, but there is no benefit in confirming that oil is draining from the bottom of the engine. It is not possible for oil to not be there if the engine has been turned over and full oil pressure attained.

I guess owners will have to just make up their own mind how they will do it.

Once you have actually done it on an RV-12, maybe you can post for everyone what clever process you used to get the return line disconnected from the tank and fished out of and then back into its proper routing path (all just to get it below the engine, to confirm that oil drains out of the bottom), and of course, not have to charge your customer an extra hour of shop time to do it.

Over..... and Out
 
Thanks all for your responses to my issue. Seems like there are lots of different ideas on just how to accomplish the task. Knowing I have plenty of oil pressure while cranking and I am able to burp the engine I should be able to loosen the lower crankcase hose fitting and there should be oil. Perhaps the engine need to be running and the case pressurized to return this oil to the canister?????????????? What say you . Again many thanks . Jonn
 
JEG said:
Thanks all for your responses to my issue. Seems like there are lots of different ideas on just how to accomplish the task. Knowing I have plenty of oil pressure while cranking and I am able to burp the engine I should be able to loosen the lower crankcase hose fitting and there should be oil. Perhaps the engine need to be running and the case pressurized to return this oil to the canister?????????????? What say you . Again many thanks . Jonn
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JEG, when you burp the engine, you are returning the oil to the tank.That is the purpose of that procedure.
That is why I said if you burp it after doing the purge and it takes a few turns of the prop, it is proof that there was oil in the crank case after the purge procedure.

When you do the burp procedure, you are pressurizing the crank case... just doing it manually.
 
For what it's worth, I was able to talk with a technician at Rotax by the name of Ralph. he talked very broken but I was able to understand perfectly. He says the Purging or burping process does absolutely nothing but evacuate oil from the case to the canister so a accurate oil level can be checked. He was familiar with RV 12 installation and doubts that oil will ever appear unless plugs are in and case pressure is established. He said that if you are indicating over 40lbs of pressure you can pretty much bet oil has circulated thru the engine.
He also indicated that you should run the engine before doing the valve lifter check. He also suggested wrapping the dip stick handle where you grab it with something so you can pull it up right after shut down by checking the oil level then it alleviates burping. He also suggested going to the RV Supply store and purchasing a T handle tool made for opening the drain valve on rv waters. Works great when opening the cap on the oil canister. I hope this helps you and again I thank you all for your input. John 120324 N337JG
 
Educate thy self through the all knowing Web!

so you can pull it up right after shut down by checking the oil level then it alleviates burping.
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This is not correct, you must always burp the engine to get a correct reading on the oil dip stick. It is a lot easier to do it when you are done flying for the day or when the engine is hot. It only takes about 5 blades to burp the engine when it is hot. It will take about 25 blades when it is cold to burp it. Might I suggest joining the Rotax-owner.com web site and watching the videos on it to reduce the learning curve on this engine which is different from other aircraft engines. Here are some titles you might want to watch:
Oil Level Check - EXP-SI-27-1997
Purging of Lubrication System
Carburetor Synchronization 1, 2, 3, & 4
Here is a EAA Webinar about Rotax 912 Maintenance and Inspection Tips:
http://www.eaavideo.org/video.aspx?v=2242926960001

Here is an EAA webinar about 912 Fuels and Carburetion:
http://www.eaavideo.org/video.aspx?v=2404699810001

A lot of good info here at these websites.;)
 
JEG said:
He says the Purging or burping process does absolutely nothing but evacuate oil from the case to the canister so a accurate oil level can be checked.
Click to expand...

John (and anyone else interested),
Just to clarify... in regards to a Rotax 912, purging and burping are not the same thing, and to prevent confusion when talking about the engine, it would be best to not use them interchangeably.

Purging is a maintenance process used after initial engine installation, and any time the oil system has been opened, to help evacuate any air from the entire system, as describe in a Service Instruction, using applied air pressure, etc.

Burping is what we do as a pre-flight process... turning the propeller to return oil from the lower crankcase back to the oil tank, to get an accurate oil level reading.
 
Jetguy said:
This is not correct, you must always burp the engine to get a correct reading on the oil dip stick.
Click to expand...

John, I think it is correct, and a lot of people do it this way.
If the oil level is checked immediately after shut down, pretty much all the oil is cleared from the crank case.
Nothing wrong with turning it a couple blades just to be sure, but I have never found it to cause much change, vs just reading it without burping first.

If it has been sitting stopped for a while, you must burp for an accurate reading.
 
We'll I stand corrected.:rolleyes: Learn something new everyday. I guess this falls in to the category of,
You can (I have done it) but I don't advocate it because it is not in the published S.I. procedure.
Click to expand...
All the seminars I've been to at OSH and here on this form never heard you could do it that way before, but Ill start trying it out and see how it works!;)
 
My apologies to Ralph @ Rotax, I misquoted him when I said Purging and Burping were the the same, and I do understand the difference. John
 
Rotax oil purge video

Here is a 26 sec. video of an oil purge. I rotate 90 times at 1 rev. per second. I always get 50-55 psi on the gauge and always get oil out the return. This was not a new engine, but one already in service that got some heavy maint. If I was doing this for a new engine I would do the 90 revs twice. I need a break in between the two purges or I need oxygen and medic. LOL.

The video was made short to the point and I'm sure it's funny, but it demos what you should see when done correctly. Turn the volume up you can hear them state the psi obtained. Notice you don't see a huge amount of oil out the return, but there should be some. The reason many don't really see any pressure or very low pressure is they don't rotate the prop fast enough. The reason they don't see any oil return out the hose is they don't do it long enough. New engines take more revs and longer than an engine already in service getting a purge.

http://www.youtube.com/watch?v=x4YkBLU7K9Q&feature=em-upload_owner
 
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