Priming the oil pump through the relief valve?

[Stumpy]

Well now...away from home dealing with our rather extensive PNW wildfire season at the moment. Had an hour or two off so I wandered down where a couple fellows were working on a (gasp) Cub, A-65 on her nose. Apparently just done the annual. Supposedly she occasionally loses prime,
and had again....plus they'd let it drain overnight. Tail-up didn't do it.

So I said just pull the sender and squirt a little aeroshell in there. The IA, an old-school guy who generally knows his stuff, said "no, I was thinking about pulling the relief valve to check it out and give it a good cleaning anyway, so we can prime it from that end."

Now, I'd never given that any thought, but seems like it would work as good as the screen end. I had to go back to the smoke about then and didn't get to see if it worked fine.

Anyone else ever prime the oil pump that way? Any reason to not do it that way, like maybe "it won't work?"

[astjp2]

Re: Priming the oil pump through the relief valve?

The relief is on the opposite side of the case, the oil would have to go to the front, cross over to the other side then back to the pump. the -12 case transfers oil down both sides at the same time, the -8 goes up one, crosses over in the front and then back to the bypass. Just pull the screen and prime it that way and then get the accessory case/cover/gears replace/repaired as necessary. Harry Fenton talks about this on the Flybaby site. Tim

[Hank Jarrett]

Re: Priming the oil pump through the relief valve?

Just primed my A-65-8 through the pressure relief. Worked great and got good oil pressure right away. As the pumps wear you loose prime , especially with the tail down. The old timers say you can tell a plane with a worn pump because the cover over the pressure relief spring and plunger isn't safety wired. ;-)

I park my plane in the hangar with the tail wheel on a table so the plane is level. Makes it easier to work on the engine and takes much longer to loose the prime. If I had an experimental engine I would put a prime line on it through the rear case. Better yet, I designed a simple fix to maintain the proper clearance, but the cost to certify it is so high if I put it on every A-65 in the world I could never recover the cost.

Hank

[Guest]

Re: Priming the oil pump through the relief valve?

Well now...away from home dealing with our rather extensive PNW wildfire season at the moment. Had an hour or two off so I wandered down where a couple fellows were working on a (gasp) Cub, A-65 on her nose. Apparently just done the annual. Supposedly she occasionally loses prime,
and had again....plus they'd let it drain overnight. Tail-up didn't do it.

So I said just pull the sender and squirt a little aeroshell in there. The IA, an old-school guy who generally knows his stuff, said "no, I was thinking about pulling the relief valve to check it out and give it a good cleaning anyway, so we can prime it from that end."

Now, I'd never given that any thought, but seems like it would work as good as the screen end. I had to go back to the smoke about then and didn't get to see if it worked fine.

Anyone else ever prime the oil pump that way? Any reason to not do it that way, like maybe "it won't work?"

Putting it on its nose will not do anything to help.

Priming from the far end makes no sense. Priming from the far end will require a standalone priming pump. You need to force enough oil flow back to the gears that means you have to supply all the oil leakage from the bearings and rods. You need a rather high pressure to since after you force the oil back to the pump outlet. So its gonna be a big job and squirting an oil can in there will not work. But cleaning the relief plunger is a good idea.

Tim Popp is right on, prime it then get it fixed the real way, loosing oil prime indicates something that is not in a condition for safe operation.

That it needs to be primed indicates a problem.

Those "old school" guys and the guys who "know what's really important" to make it safe but don't go right by the book always make me wonder.

I ran into one of them last year who had not heard of Continental SB03-3 and the test orifice used with the diff. pressure tester. I am sure that there is a lot that I never heard of too but that one set me back.

Dave

p.s. Just saw Hanks post above and his success with priming from the plunger end. Makes no sense to me but if it worked then that's good. I eat my words on priming from the far end. Dave

[senior]

Re: Priming the oil pump through the relief valve?

Putting it on its nose will not do anything to help.

Yet I have seen it done & done it myself to a 65 that sat over the winter.
Ran for 20 secs no oil pressure.
Lifted the tail head level for 30-45 secs (seemed like an hr )
Fired it back up & presto, lots of oil pressure.

[Guest]

Re: Priming the oil pump through the relief valve?

Yet I have seen it done & done it myself to a 65 that sat over the winter.
Ran for 20 secs no oil pressure.
Lifted the tail head level for 30-45 secs (seemed like an hr )
Fired it back up & presto, lots of oil pressure.

Interesting.

Putting it on its nose as mentioned in the first post would be different that what you did. You did not have it on its nose.

Perhaps I should not have taken that literally?

When its on its nose (literally) the oil will be farther away from the pickup and may even be exiting the sump.

In the sixties I lived near an airport that had many Cubs and they were stored on their nose in the hangar around the sides of the hangar so I take on their nose literally regarding Cubs.

Lifting the tail up to level will raise the oil level up closer to the pump gears thereby requiring less suction to lift the oil into the pump inlet. So that makes some sense. Of course setting it back down will result in the oil also going back down but after some unknown period of delay.

Dave

[Guest]

Re: Priming the oil pump through the relief valve?

Senior,

You got me thinking. Sometimes what we attribute to cause and effect are not correct.

When you mentioned the time in seconds that you observed it got me thinking about the time constant of an oil pressure gauge, oil line and the air trapped inside the line.

I wonder this; how many, if any, of the engines that we think have priming problems actually have air trapped in the line such that the time it takes to compress the air so that the gauge shows a reading is very long.

Explanation; The oil line to the gauge is fed through a tiny tiny orifice so that if the line breaks the oil leaks out slowly. The air in the line compresses and decompresses through high viscosity (relative to air) moving through that tiny hole. More air in the line means a longer delay until the gauge reads. The same delay applies to decompressing the air in there. Well not really, when you start the oil is cold and moves slow through the orifice and when you shut down the oil is generally hot and moves more quickly so that boggles up part of this thought.

So I wonder a couple of things 1) if airplanes that have a priming problem had the air bled out of the line at the gauge by loosening the nut on the line until oil dripped out would the no longer see a problem at start up?, 2) if in a case like yours if you had just let it idle longer would the pressure come up anyhow?, 3) when you shut down how long does your pressure gauge show pressure after the prop stops with hot engine and with cold engine?

Just some wild thoughts over the morning's coffee, Dave.

[Hank Jarrett]

Re: Priming the oil pump through the relief valve?

The safest thing to do is to disconnect the oil P line and put a gauge on a short line so it doesn't have to pressurize the air in the line to the gauge. It is easy to bleed the line when it is next to the firewall. I pull four plugs and spin the engine by hand until I get pressure after a long storage. You do need to eventually bleed the oil gauge end to eliminate the air problem, but get oil pressure first and it is a LOT easier!

I did that several times after the last storage and got nothing until I pulled the pressure cover, spring and plunger and filled the cavity with oil. You aren't actually priming the pump, you are just getting some oil between the case and gears and the gears and rear cover. As soon as those are wet with oil the pump will pick up a prime. The smaller the clearance and heavier the oil the longer that area will stay "wet" with oil. The worse your gear to case and gear to cover clearances are, the faster you will loose prime.

I got into the habit of putting my tail up on a table when I was at an airport where my hangar floor flooded with every rain. I had a set of ramps I pushed the mains up on and the tail was on the table because I was sick of repacking my bearings every time the water got deep enough to get the bearings. It happened a LOT! I finally got sick of it and moved to an airport that actually has drainage. Nice dry paved floor hangar so I left the tail down. Suddenly I am loosing prime if she sits. My wear must be on the edge since it holds prime if stored with the plane level. Never had to put the nose DOWN and don't know if it would even help. I think just keeping the gap vertical may be helping so the oil doesn't flow out, but I am REALLY guessing now. All I know is keeping the fuselage level seems to help and tail down I loose prime.

Hank

[Guest]

Re: Priming the oil pump through the relief valve?

The safest thing to do is to disconnect the oil P line and put a gauge on a short line so it doesn't have to pressurize the air in the line to the gauge. It is easy to bleed the line when it is next to the firewall. I pull four plugs and spin the engine by hand until I get pressure after a long storage. You do need to eventually bleed the oil gauge end to eliminate the air problem, but get oil pressure first and it is a LOT easier!

I did that several times after the last storage and got nothing until I pulled the pressure cover, spring and plunger and filled the cavity with oil. You aren't actually priming the pump, you are just getting some oil between the case and gears and the gears and rear cover. As soon as those are wet with oil the pump will pick up a prime. The smaller the clearance and heavier the oil the longer that area will stay "wet" with oil. The worse your gear to case and gear to cover clearances are, the faster you will loose prime.

I got into the habit of putting my tail up on a table when I was at an airport where my hangar floor flooded with every rain. I had a set of ramps I pushed the mains up on and the tail was on the table because I was sick of repacking my bearings every time the water got deep enough to get the bearings. It happened a LOT! I finally got sick of it and moved to an airport that actually has drainage. Nice dry paved floor hangar so I left the tail down. Suddenly I am loosing prime if she sits. My wear must be on the edge since it holds prime if stored with the plane level. Never had to put the nose DOWN and don't know if it would even help. I think just keeping the gap vertical may be helping so the oil doesn't flow out, but I am REALLY guessing now. All I know is keeping the fuselage level seems to help and tail down I loose prime.

Hank

Hi Hank,

I don't question your statement in red above it does bring one more thought to the table.

When the airplane sits tail down some oil remains at the rear of the oil screen cavity merely because it is lower than the front of the cavity.

So given your statement then when I raise the tail of a plane that had been sitting normally then the oil that had been captured at the rear of the screen area moves forward and drips down onto the oil pump/gears just as if I had pulled the screen and squirted some in there doesn't it?

So the pump would work better after I raised the tail to level.

Is this what is taken place that causes the pump to work after raising the tail to level (like Senior described)?

Dave

[Marv]

Re: Priming the oil pump through the relief valve?

Looks like a tricycle gear is the answer.LOL Marv

[Hank Jarrett]

Re: Priming the oil pump through the relief valve?

Drude,
It could be. Like I said, I am REALLY guessing at this point. I just know it worked well before my long down time and I am hoping it will again. I REALLY don't want to need a new rear case which is what I understand is needed when you can't hold pressure any more.

Hank

[mikeg]

Re: Priming the oil pump through the relief valve?

Raising the tail should do it provided the oil filter housing has oil in it. Raising the tail allows oil in the filter housing to run into the oil pump and wet the gears. Fill the oil filter housing with oil through the oil temp bulb, if it is empty. Sounds like pump clearances are too loose. You can remove the rear cover (contains the oil pump), for repair, with the engine still installed (remove the mags, remove the oil tank, remove the rear cover). Been there-done that.
Mike

[Guest]

Re: Priming the oil pump through the relief valve?

Do these engines that have oil pump priming problems (ie. start up oil pressure problems) also have a problem with low oil pressure after the oil comes up to temperature?

[astjp2]

Re: Priming the oil pump through the relief valve?

Now all I need is to get an STC for good oil pump gears....and a new cover....tim

[Stumpy]

Re: Priming the oil pump through the relief valve?

Well, 43319 has never had a problem with losing prime, but I've had to deal with it on other's. Reckon will continue to pop the temp sender out and prime the way I always have as opposed to what I watched in process ;-). I usually just put a tube on the end of a cheap vet syringe, insert the tube (small enough dia to easily fit through the sender hole), and squirt 70-80 ml in...no mess no fuss...that pretty much fills things up in the screen department and never had it fail to pick up pressure instantly on startup.