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 Post subject: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 9:02 am 
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T-6 wobble pump losing prime problems.
Thank you for responding.
Here is the senario. The pump has been replaced twice. Engine driven pump,selector valve and all hoses and clamps. System has been pressure checked for leaks. The primer system has been inspection and pressure tested for leaks.
Prime the system up and get wobble pump pressure. Ground run engine and bleed system completely. Check the wobble pump pressure twice a day for 10 to 15 days and it is good. Then out of no where the pump loses its prime (usually when the owner/pilot shows up).
Been chasing this demon for over a month and out of ideas. Is there anyone out there in the Warbird Community ever seen this problem. If so, any ideas or imput on a fix.
Your help is appreciated.


Last edited by rwahlberg on Fri Jun 29, 2012 1:58 pm, edited 1 time in total.

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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 1:10 pm 
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Either an internal seal leak or you have a loose conenction between the engine driven pump and wobble pump or between the wobble and the tank selector or a leaking selector. Check for evidence of a minute fuel leak before you start tearing things down to overhaul or replace to save yourself some time..


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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 2:01 pm 
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rwalberg wrote:
T-6 wobble pump losing prime problems


Do you mean that the wobble pump doesn't work well and takes a long time to suck fuel and build pressure?

What fuel line set up do you have? one line to the carb with the fuel pump in line or the stock 2 line setup with a Y on the carb and 2 lines from the wobble pump.

How long has this been an issue? Did it happen after any maint was performed?

Does it do this on all the tanks? R/H, L/H and Aux. Is it any better if the tank is filled full?

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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 3:08 pm 
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The wobble pump loses it prime and no matter how long you pump, it will not pull fuel from the tank on any tank selection.
I have the stock two line with the Y to the carb.
The owner complained the first wobble pump was weak and he wanted it changed. ordered an overhauled pump, installed, bleed system. it worked fine. He flew from Pearland Tx. to Sun and Fun Fla. and while he was there this problem came up. So, he ordered another wobble pump and an overhaul engine driven pump and had it installed there.He flew back to Pearland and everything was fine and then out of the blue the system kept losing its prime again and agian. I inspected the shut off valve and it was leaking really bad. Replaced it with an overhaul unit and replaced all the flex hoses and clamps. As I stated earlier, it will hold its prime and then just lose it and will not wobble up pressure. Have to prime system again and again. Any ideas???


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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 3:25 pm 
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rwalberg wrote:
The wobble pump loses it prime and no matter how long you pump, it will not pull fuel from the tank on any tank selection.
I have the stock two line with the Y to the carb.
The owner complained the first wobble pump was weak and he wanted it changed. ordered an overhauled pump, installed, bleed system. it worked fine. He flew from Pearland Tx. to Sun and Fun Fla. and while he was there this problem came up. So, he ordered another wobble pump and an overhaul engine driven pump and had it installed there.He flew back to Pearland and everything was fine and then out of the blue the system kept losing its prime again and agian. I inspected the shut off valve and it was leaking really bad. Replaced it with an overhaul unit and replaced all the flex hoses and clamps. As I stated earlier, it will hold its prime and then just lose it and will not wobble up pressure. Have to prime system again and again. Any ideas???

Sounds like it is sucking air some point anywhere from the selector to the fuel unit.
Check connections in the wing/firewall behind the triangle panel in the R/H wheel well. Look for blue goo from fuel leakage. Check all connections along that feed line. You could also check the line condition by pulling the L/H stress door on the center wing section. There might be a splice with a rubber hose and hose clamps in there thats not stock. A hose connection could lose tension over the years.
While pumping the hand pump does any fuel spill from the carb?
Also I have pulled apart a new pump unit that had rust issues internally as there are steel plates inside. Also there are flapper units on hinges. Also a cast brass piece that rotates. It seals against the steel plates and has the flapper doors as part of assy. The unit rotates one way a distance than hits a stop, then reverses direction and stops. The flapper plates regulate fuel flow as the unit rotates. It basically alternates as an increasing chamber that fills with fuel and then dispenses the fuel as it reverses direction and the fuel is pushed out.
There is also some leather strips that act as a sealing device internally.
That is why a unit could have some corrosion growing internally, even if new or overhauled in the past, that could reduce it's sealing and ability to suck over time.

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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 4:37 pm 
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I have taken the pump apart and no corrossion, good leather seal strips against the shaft.Flapper doors are clean and have good seats, shaft seal is good, shaft end cap seal is good, strainer end cap seal is good. Bypass valve is cleaned and polished so it will not stick. The only line I haven't checked is the on under the lower wing strees panel. Might have to venture into it come monday.
Yes, with mixture in cut-off, fuel spills out of the carb while wobble pumping.
The fuel line in the triangle panel is good.


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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 5:04 pm 
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rwalberg wrote:
I have taken the pump apart and no corrossion, good leather seal strips against the shaft.Flapper doors are clean and have good seats, shaft seal is good, shaft end cap seal is good, strainer end cap seal is good. Bypass valve is cleaned and polished so it will not stick. The only line I haven't checked is the on under the lower wing strees panel. Might have to venture into it come monday.
Yes, with mixture in cut-off, fuel spills out of the carb while wobble pumping.
The fuel line in the triangle panel is good.


Have you checked the line from the wobble pump to the primer? My experience is if you've got air there, it's leaking, or someone leaves the primer unlocked on the ground you'll dry out the wobble pump.

Chris


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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 5:26 pm 
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An old timer trick with wobble pumps that don't pick up fuel is to run some 60 wt. oil into the pump. After working the pump, filling with more oil, etc, it began to pick up fuel and has worked ever since. It worked on mine. I surmise that the leather is worn or dried out and the 60 wt. caused it to expand and seal. The system is so simple that it is very frustrating when it doesn't work!


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 Post subject: Re: T-6 wobble pump
PostPosted: Fri Jun 29, 2012 5:59 pm 
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rwalberg wrote:
I have taken the pump apart and no corrossion, good leather seal strips against the shaft.Flapper doors are clean and have good seats, shaft seal is good, shaft end cap seal is good, strainer end cap seal is good. Bypass valve is cleaned and polished so it will not stick. The only line I haven't checked is the on under the lower wing strees panel. Might have to venture into it come monday.
Yes, with mixture in cut-off, fuel spills out of the carb while wobble pumping.
The fuel line in the triangle panel is good.

Carb will dump a bit of fuel on occasion until the float needles seat. Until this seats the pressure will low and then rapidly rise when it seats.
If it constant dumps some fuel it may be the carb doesn't seat and you won't build pressure with the handpump then.

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 Post subject: Re: T-6 wobble pump
PostPosted: Sat Jun 30, 2012 10:06 pm 
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To quickly prime the pump in a pinch you can blow (with your lungs) into the tank vent for the selected tank while someone wobbles the pump. I have found that the left tank is easier to pickup the prime than the right. We have to do the same thing to our ClarkAT Tug sometimes. One of our T-6's has an electric pump in addition to the wobble pump, it sure takes the drama out of building up fuel pressure to prime.


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 Post subject: Re: T-6 wobble pump
PostPosted: Mon Jul 02, 2012 7:42 am 
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Ken Dwelle wrote:
To quickly prime the pump in a pinch you can blow (with your lungs) into the tank vent for the selected tank while someone wobbles the pump. I have found that the left tank is easier to pickup the prime than the right. We have to do the same thing to our ClarkAT Tug sometimes. One of our T-6's has an electric pump in addition to the wobble pump, it sure takes the drama out of building up fuel pressure to prime.



We have learned that trick and it does work in a pinch. Thanks.
Any input on the electric fuel pump install? What type pump?
Where can you get one? Is it legal to install with a STC?


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 Post subject: Re: T-6 wobble pump
PostPosted: Mon Jul 02, 2012 7:57 am 
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The plane set all weekend with the fuel selector in the off position. Turn to left tank and wobble pump dead. NO PRESSURE. this is very frustrating.


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 Post subject: Re: T-6 wobble pump
PostPosted: Mon Jul 02, 2012 8:09 am 
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rwalberg wrote:
The plane set all weekend with the fuel selector in the off position. Turn to left tank and wobble pump dead. NO PRESSURE. this is very frustrating.

PM sent


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 Post subject: Re: T-6 wobble pump
PostPosted: Mon Jul 02, 2012 1:18 pm 
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Warbird #1 sez "never turn the fuel valve to off to keep the cork wet" and "never change tanks unless you're over an airport", NATA #1 agrees

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 Post subject: Re: T-6 wobble pump
PostPosted: Mon Jul 02, 2012 9:41 pm 
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[quote="rwalberg"][quote="Ken Dwelle"]To quickly prime the pump in a pinch you can blow (with your lungs) into the tank vent for the selected tank while someone wobbles the pump. I have found that the left tank is easier to pickup the prime than the right. We have to do the same thing to our ClarkAT Tug sometimes. One of our T-6's has an electric pump in addition to the wobble pump, it sure takes the drama out of building up fuel pressure to prime.[/quote]


We have learned that trick and it does work in a pinch. Thanks.
Any input on the electric fuel pump install? What type pump?
Where can you get one? Is it legal to install with a STC?[/quote]

We have a 337, with field approval. It's a Delco motor driving an AN pump on the firewall. If you PM me your contact info I can provide more.

Ken


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