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912 oil purge proceedure

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dashwood

Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada

Posted: Mon May 03, 2010 6:08 pm Post subject: 912 oil purge proceedure

the manual says to remove the top plugs and turn over engine to purge oil system. what it doesn't say is do you have to protect the coil by leaving the resistor wires connected to plugs and leave them grounded out to cylinder jugs. or .. just let leads dangle and plugs on the bench. i understand the mags will be off when swinging prop but is there potential for damage to ignition

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Ross Alexander: CH701 driver 912ul 788tt
It only takes two things to fly, airspeed and money

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Mon May 03, 2010 7:10 pm Post subject: 912 oil purge proceedure

The danger to the ignition is only when it is live and a plug is ungrounded. There's a diode in the module that will fry if you do this, which is why you're taught to use an ignition spark tester between plug wire and plug to check for spark. When the ignition is off, as you put it, the mag is grounded, hence no problem. You are doing the purge turning the engine over by hand, aren't you?

Rick Girard



On Mon, May 3, 2010 at 9:08 PM, dashwood <dashwoodlock(at)hotmail.com (dashwoodlock(at)hotmail.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "dashwood" <dashwoodlock(at)hotmail.com (dashwoodlock(at)hotmail.com)>

  

 the manual says to remove the top plugs and turn over engine to purge oil system. what it doesn't say is do you have to protect the coil by leaving the resistor wires connected to plugs and leave them grounded out to cylinder jugs. or .. just let leads dangle and plugs on the bench. i understand the mags will be off when swinging prop but is there potential for damage to ignition

  

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dashwood

Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada

Posted: Thu May 06, 2010 8:42 am Post subject: Re: 912 oil purge proceedure

thanks for the info. i have a small leak somewhere between the oil cooler outlet elbow and the inlet to the pump. i will be opening up this area to replace this flex hose. question. i will not be draining the cooler rad or the pump ???  i was wondering what happens to this small amount of air that will now be in the system.  is it pushed about the galleries and into the crankcase and what keeps it out of the lifters which is the whole point  of the purge. or is a purge even necessary  for this small amount depending on how much pukes out of the pump.

edit update.... as soon as i opened the hose the pump held its oil but the rad puked oil and was draining the reservoir. i had to temp plug the outlet to stop from loosing all that valuable oil.

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Ross Alexander: CH701 driver 912ul 788tt
It only takes two things to fly, airspeed and money

Last edited by dashwood on Fri May 21, 2010 3:52 am; edited 1 time in total

rampil

Joined: 04 May 2007
Posts: 870

Posted: Fri May 07, 2010 3:19 am Post subject: Re: 912 oil purge proceedure

It depends!



How will you fix the leak without removing the hose (at the bottom)

of the oil system. If you just tighten the hose connections, then no,

no purge, otherwise yes.



Wit the leak at the bottom of the system, there is always positive pressure

in the hose. How can air get in against the pressure gradient?



If the air is there somehow, bit the bullet, do the purge

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dashwood

Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada

Posted: Tue May 18, 2010 4:07 am Post subject: Re: 912 oil purge proceedure

ok i changed the line from rad to pump . did the purge. oil leak and trail has stopped.. guage was fluctuating from 28 to 32lbs before and is now steady at 29.5lbs.  2 years ago it was steady always at 45lbs with a fairly steady decline over this time.  have ordered the vdo engine mounted pressure sender and will replace soonest . is the next step to look at the releif spring and spacer washer. i always use the rotax oil filter and oil changes ever 50 hours... am averaging 100+ hours / year..always 10/40 winter or 10/50 summer full synthetic mobile 1.oil.

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Ross Alexander: CH701 driver 912ul 788tt
It only takes two things to fly, airspeed and money

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed May 19, 2010 2:52 am Post subject: Re: 912 oil purge proceedure

Ross,



On all the 912UL engines I've owned, the gradual reduction is oil pressure readings was due to the oil pressure sending unit slowly failing. I would expect when you replace the VDO unit, you will see higher oil pressure readings again, similar to original. 



I am now flying a Jabiru 2200A engine (still like the 912 just bought a different airplane with different engine). The Jabiru engine uses a similar VDO oil pressure sender and succumbs to the same problem over time. I have a mechanical oil pressure gauge as a back-up to check on the electric VDO reading. The mech gauge is currently reading about 5 psi more than the VDO sending unit gauge.



http://sites.google.com/site/riddletr/a&pmechanix

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Buffalo, NY (9G0)

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed May 19, 2010 2:53 am Post subject: Re: 912 oil purge proceedure

Ross,



On all the 912UL engines I've owned, the gradual reduction is oil pressure readings was due to the oil pressure sending unit slowly failing. I would expect when you replace the VDO unit, you will see higher oil pressure readings again, similar to original. 



I am now flying a Jabiru 2200A engine (still like the 912 just bought a different airplane with different engine). The Jabiru engine uses a similar VDO oil pressure sender and succumbs to the same problem over time. I have a mechanical oil pressure gauge as a back-up to check on the electric VDO reading. The mech gauge is currently reading about 5 psi more than the VDO sending unit gauge.



http://sites.google.com/site/riddletr/a&pmechanix

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Wed May 19, 2010 5:39 am Post subject: Re: 912 oil purge proceedure

Thom is right about senders slowly dying down, but the only sure way to tell is put a mechanical pressure gauge in line and double check it. 

I would also recommend getting the new oil pressure cap screw, spring and oil pressure control cone. This takes ten minutes to install and many people have found that it steadies the pressure and increases it. This is the new addition for the 2000 hr. TBO for certain engines, but is highly recommended for all 912's. I have done about a dozen of these so far and it has helped everyone.

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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

craig(at)craigandjean.com
Guest

Posted: Wed May 19, 2010 8:55 am Post subject: 912 oil purge proceedure

 	  Quote: 	
		   I would also recommend getting the new oil pressure cap screw, spring and

oil pressure control cone.
	




How "new" are these? Is there a service bulletin? Do you know the part

numbers and approximate price? 



-- Craig



--

dashwood

Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada

Posted: Fri May 21, 2010 3:47 am Post subject: Re: 912 oil purge proceedure

is this regulator spring mod advisable without the pump gear extension mod. i understand they are changing the pump driver pins from roll formed to solid shaft and extending the gear teeth to increase flow and pressure by the pump alone. one would assume with the spring only you are only putting gallery pressure back to where it should be originally assuming the older spring settup is allowing blowdown. is the cheaper fix now for low pressure but is the pump a ticking hazard

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Ross Alexander: CH701 driver 912ul 788tt
It only takes two things to fly, airspeed and money

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Fri May 21, 2010 5:01 am Post subject: Re: 912 oil purge proceedure

Here are the part numbers and approximate cost. It is recommended whether you get the extended TBO or not. It is just better than the old ball bearing.



Cap screw 841-983  $31.41 (Longer shoulder and harder metal)



Spring  838-122  $7.81



oil pressure regulator cone  857-230  $30  (completely different from the ball bearing) looks like a mushroom with a hole in the top.

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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

dashwood

Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada

Posted: Sat May 22, 2010 6:20 pm Post subject: Re: 912 oil purge proceedure

again is it advisable to wait till the 600hr mark to make oil pump changes. does heavier regulator  parts put more stain on the older version pump or should everything be changed sooner than later. don't mean to flail on but oil flow and quality is a biggy.

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Ross Alexander: CH701 driver 912ul 788tt
It only takes two things to fly, airspeed and money

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun May 23, 2010 7:04 am Post subject: Re: 912 oil purge proceedure

Make your changes now. They are not heavier parts or strain on the system. They are just better designed parts that make the system run at more consistent pressures.

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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

dashwood

Joined: 24 Jan 2009
Posts: 73
Location: sw ontario canada

Posted: Sat May 29, 2010 8:08 pm Post subject: Re: 912 oil purge proceedure

firstly thanks for all the good advice. I changed the pressure sender today. test flight before change reading 31 lbs. only swapped senders and cleaned wire contacts. tested runup pressure instantly 65lbs. found it difficult to remove the wire because the terminal post on the old unit was spinning inside the casing. proly part of the problem.

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Ross Alexander: CH701 driver 912ul 788tt
It only takes two things to fly, airspeed and money

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun May 30, 2010 5:41 am Post subject: Re: 912 oil purge proceedure

Hi Ross,



Most of the time when people are having oil pressure issues it is the oil pressure sending unit or a bad ground. It usually is not really an engine oil pressure problem. That's why I advise most people to put a mechanical gauge in line and double check the real pressure and it will usually tell you right away what the problem is. Glad it worked out.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

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