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Thread: Leaking Primer

  1. #51
    NRW-Aviator's Avatar
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    Default Imperial Brass Primer Pump

    Today I changed the o-rings go the primer pump, but now Iīm at a point I donīt know to go on. Thereīs a diaphragm at the aft end of the body. And this diaphragm isnīt flexible anymore. Where can I buy that diaphragm?

    Attachment 8488Attachment 8489IMG_1776.jpg
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  2. #52

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    Default Engine sucking gas from not sealing primer?

    Quote Originally Posted by walt.buskey View Post
    OK. I finally figured out how the Kohler 2406 primer pump "positively" locks out any fuel passage.

    The tapered metal shaft that protrudes into the pump barrel from the end of the plunger is spring loaded!! It's a fairly stiff spring, and I hadn't noticed it earlier, but it definitely has a spring bearing against it from within the plunger.


    The way I figure it's supposed to work, and this is where there could very well have been a problem, is that the OUTSIDE knurled nut has to be screwed in all the way until it rests on its internal shoulder, against the top of the threads on the pump barrel, BEFORE final installation. THEN, the large nut on the back side of the instrument panel is supposed to be tightened up to secure the pump to the sheet metal of the instrument panel.


    Of course, it's a lot easier to tighten the pump to the instrument panel by tightening the OUTSIDE nut (incidentally, in the same manner as almost any "vintage" automotive ignition key or add-on dash switch), but it needs to be done the other way around to ensure that the bayonet locking mechanism applies sufficient pressure to the tapered metal shaft --in that last 1/8" of forward travel during "lock"-- to ensure that it seats into the inlet hole at the far end of the pump barrel with tension on the spring. The spring pressure on the tapered shaft then assures that the seal is complete. (It is a metal-to-metal seal, no o-ring.)

    Attachment 3919

    Apologies if you all knew this already, but I had not been able to find an adequate description of just how that thing was supposed to block any fuel from being "sucked" through the primer lines when the engine was running; I had already discovered that the ball & spring check-valves will allow a steady, small drip when the plunger is removed from the primer. I have a feeling it may well have been "loose" in my PA-22. At any rate, primer lines are now disconnected --pump removed-- and both ends securely capped. Now to see if the engine still tends to run rich....

    An interesting side-point: in a troubleshooting manual for the Marvel-Schebler MA-40SP carb--- Top of the list for probable causes for a rich-running engine: Primer Pump....
    Researching and brought this back from the dead.. Walt never came back (that I found) on this thread and said if this was what was causing his running rich problem. Well every since my annual was completed a few months ago (the mech took the primer plunger out and replaced some orings and put it back together) I wonder if he did not get the plunger tightened in the sequence Walt describes above, because I have a new hard start issue I didn't have before the primer was worked on. She won't start easy and I have to lean quickly to get her running good after it does cough itself to life cranking and cranking about 5 seconds to get it to begin to run. Before the primer was worked on it would start right up and run good.

    Original thread post http://www.shortwingpipers.org/forum...ll=1#post54104

  3. #53

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    Default Re: Engine sucking gas from not sealing primer?

    A shout out to Walt, thank you very much! That was the problem with my essex primer, she is all better now.

  4. #54
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    Default Re: Engine sucking gas from not sealing primer?

    So what was the issue?

  5. #55

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    Default Re: Engine sucking gas from not sealing primer?

    The symptoms were, my plane went from starting up like a champ before the annual, to starting like it was sick and on it's last leg after the annual. The mechanic took the primer plunger out during the annual and replaced the o rings and put it back together. If you read the quote from Walt I posted above, he talks about the needle shaft on the end of the plunger being spring loaded and if you press in on the tip of the shaft it moves back into the plunger, it needs to be seated all the way into the hole in the back of the primer barrel WITH that spring tension on it, when you unlock the primer that spring load on the needle should pop the plunger out about an 1/8 inch, not just sit there for you to pull it out. When my mechanic put it back together he only screwed the front nut on a few threads and tightened the back nut on the barrel behind the panel up to the front nut, you need to make sure the front nut is tightened all the way down onto the barrel before tightening the back nut, that way the plunger gets the extra stretch it needs to get the needle shaft deep into the seal in the back of the barrel... which I think puts pressure on the ball spring in the barrel sealing the primer lines from being able to suck gas into the intake. After reading more from a post your dad wrote, I think maybe the ball springs in the barrel are the primary fuel shutoff for the input and the output primer lines on the barrel, and this needle shaft pressing on the back of the barrel is a secondary backup to make sure the primer output line is sealed. So now I am thinking that the little spring under the ball is worn out and not doing its job, not sure about that. You or your dad can probably clear it up better for me, but I think it was sucking fuel or air or probably a mixture or both into the cylinder when it shouldn't have been.

    Here are quotes from the original post, your dad gives a great explanation of what goes on inside the primer, and Walt explains his fuel rich problem (simular to the problem I was having). The quotes are below, but here is the link to the thread you can read, they jump around from two separate problems Walt was dealing with, I just pulled the quotes that dealt with the primer problem. http://www.shortwingpipers.org/forum...ll=1#post53391

    Quote Originally Posted by Gilbert Pierce View Post
    The plunger "needle" on the tube pushes a spring that forces the check valve ball against the seat to seal off the primer outlet when the plunger is in and locked. If you get trash in that seat fuel from the head pressure in the wing tank will leak thru the check valve and out into the primer ports, into the intake tubes behind the intake valve then down the intake tubes thru the carb and out onto the hangar floor. If you think your carb is leaking, disconnect the fuel supply to the primer and cap it off and see if the fuel leak stops.

    I thought I had a bad carb needle and seat but turned to be the something in the check ball seat keeping it from sealing. When talking to the carb repair shop about sending him my carb he said " you did check your primer didn't you?" Ding Ding-out to the hanger and disconect the primer input. The leak stopped. Reconnected the primer, pushed is about 10 times to clear and the leak was gone. Same me about &700.
    Quote Originally Posted by walt.buskey View Post
    Attachment 3801Attachment 3802Attachment 3803Attachment 3804

    Thanks, Gilbert. I didn't have a problem with fuel dripping on the floor, I'm trying to track down a condition that's existed since the fellow who sold me the airplane first bought it, seven years ago. He was told, and this was just after an engine overhaul/"restoration" of the airplane, "Don't run full rich, it'll foul the plugs; keep the mixture pulled out a bit and it'll run just fine."

    Which is what he's done for time he owned it, about 6 years and 750 hours, and apparently it has run just fine... the primer pump also didn't work (from the same time period), and he was told to use the accelerator pump on the MA-4SP carb, which has also worked OK for him. I have to admit, the engine does seem to start quite well.

    Problem is, my CFI doesn't like that situation, and I can't say I do either. So I'm trying to track it down.

    In my primer pump, I only saw two check valves, which I took to be on the inlet & outlet lines to facilitate the pumping action. Each of those check valves was accessed by a screw, one on the top and one on the side (photo 2) of the pump body. Beneath the screw was a rather soft (5/16" or so long) spring and a ball beneath that (photo 3). Is there another check valve in there at the end? I also had a slow drip of fuel when the plunger was removed and the pump body was hanging below the instrument panel, about one drop every 40 seconds or so.

    So far I have disconnected each of the three primer lines, one at a time, and pumped 2 or 3 slugs of fuel through, then cleaned the fittings with a clean paper towel. I also inspected the fittings going into the head, pulling out some small pieces of crud buildup in the hole. Not much, really, just a few specks. Also blew out each of the lines (by mouth) to make sure they were clear.

    The one line on the left side, however, looked different: instead of a ball-type end where it hooks up to the engine, it looks like a ferrule was used, and it looks rather messed up. Hard to see in the pic, I know. The other end of that same line, which is a 1/8" flare where it connects to the tee, looks like it's been split. Both ends are looking like they were mis-aligned and then over-tightened. I'm planning to replace that line; the other two lines on the right side looked fine.

    Appreciating any & all help, this site has been a great resource. My learning curve is wicked steep, but I'm getting there. WBB in NH
    Quote Originally Posted by Gilbert Pierce View Post
    It is not my intention to insult anyone's intelligence, I was accused of that when I gave detailed reply a while back. If you have not a primer apart as you have Walt, some folks may not realize that pulling the primer out causes a vacuum in the primer chamber. That vacuum causes the fuel on the inlet line to unseat the inlet check ball pulling it back from the seat against the spring and pulling fuel in from the gascolator into the plunger chamber. At this point the spring has the outlet check ball seated and shut off. When you push the primer in the pressure of the fuel you pushing against aids the spring in seating the inlet check ball and pushes the outlet check ball off the seat and that sends the fuel to the primer nozzles.

    At the end of the stroke the primer is pushed all the way in and locked. Both check balls should be seated preventing gravity fuel flow from the tank to the primers. That small shaft on the end of the primer plunger insures the outlet ball is seated.
    Quote Originally Posted by walt.buskey View Post
    OK. I finally figured out how the Kohler 2406 primer pump "positively" locks out any fuel passage.

    The tapered metal shaft that protrudes into the pump barrel from the end of the plunger is spring loaded!! It's a fairly stiff spring, and I hadn't noticed it earlier, but it definitely has a spring bearing against it from within the plunger.


    The way I figure it's supposed to work, and this is where there could very well have been a problem, is that the OUTSIDE knurled nut has to be screwed in all the way until it rests on its internal shoulder, against the top of the threads on the pump barrel, BEFORE final installation. THEN, the large nut on the back side of the instrument panel is supposed to be tightened up to secure the pump to the sheet metal of the instrument panel.


    Of course, it's a lot easier to tighten the pump to the instrument panel by tightening the OUTSIDE nut (incidentally, in the same manner as almost any "vintage" automotive ignition key or add-on dash switch), but it needs to be done the other way around to ensure that the bayonet locking mechanism applies sufficient pressure to the tapered metal shaft --in that last 1/8" of forward travel during "lock"-- to ensure that it seats into the inlet hole at the far end of the pump barrel with tension on the spring. The spring pressure on the tapered shaft then assures that the seal is complete. (It is a metal-to-metal seal, no o-ring.)

    Attachment 3919

    Apologies if you all knew this already, but I had not been able to find an adequate description of just how that thing was supposed to block any fuel from being "sucked" through the primer lines when the engine was running; I had already discovered that the ball & spring check-valves will allow a steady, small drip when the plunger is removed from the primer. I have a feeling it may well have been "loose" in my PA-22. At any rate, primer lines are now disconnected --pump removed-- and both ends securely capped. Now to see if the engine still tends to run rich....

    An interesting side-point: in a troubleshooting manual for the Marvel-Schebler MA-40SP carb--- Top of the list for probable causes for a rich-running engine: Primer Pump....
    Last edited by Semper Fi; 09-04-2015 at 08:57 PM.

  6. #56
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    Default Re: Leaking Primer

    Ok, reading the thread I thought maybe Walt had PM'd you some information. I merged the threads so that all the information is one place to help the next guy.

  7. #57
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    Default Re: Leaking Primer

    Ms29513-012 (3/8 id x 1/2 od x 1/16 w)

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