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Lunkenheimer primer re-build

L

Longwinglover

Registered User
Charlotte, NC
Hi, all,

I've got a couple of Lunkenheimer primers to rebuild for a J3 project.

These things are STONE AGE simple. There are NO "O" rings in them to replace, but there is a "packing" around the shaft. This is where my main question lies. The packing is coming out of one of the primers and needs to be replaced. What do I use as a packing material? This stuff looks like cotton mop string. Is there any need for fuel lube on the packing?

There are also two "check valves" (inlet and outlet). Is there any need to open / clean these?

Thanks in advance.

John Scott

Primer_1.jpg


Primer_2.jpg
 
teflon coated string from truevalue. I rebuilt mine 3 years ago and is still working fine. I believe it was in the plumbing section.
 
Primer question

The other day it was around 50 and it took some time to get my cub going. Giving up I pulled a couple of lower plugs and they were bone dry. Av-gas was leaking out on the ground from the carb. I have a primer pump installed, but the 2 lines are cut just inside the firewall. It was that way when I bought the cub. I had thought I would never hook up the primer since I live in mostly in warm weather. I think next time I will pull two upper plugs and squirt some av-gas into the jugs and see if it starts with less effort. If it were your cub would you hook up the lines or pre-heat and forget the primer? Thanks teeweed
 
John
There is also a graphite impregnated string that is sold in the plumbing section.
 
Dan, I'll look into the Teflon coated string. Do you remember about how long a piece you used? What I eventually pulled out was about 4" long.

Dave, I'll look into the graphite impregnated too. Wonder if the graphite would wash out with the gas?

This stuff really looks like cotton twine. I'm probably over thinking this and need to take my own advice about rocket science not being invented when these were produced! I wonder how cotton twine gooped with fuel lube would work?

John Scott
 
I do not remember a length but I did wrap enough around the plunger so it was fairly difficult to insert. It does look like cotton string except it is coated with white teflon.
 
Hi, I need to rebuild my Lunkenheimer also.

Is this the white teflon rope found in the plumbing department? I bought some, but am reluctant to try it in a fuel application till I get a positive response. I have asked all the automotive stores about teflon tape for a fuel application and they look at me like I am crazy.

Any tricks to doing the packing if what I have is the right stuff?

Thanks
Mark
 
Check valves.. YES.. you've got the thing out.. clean them. Had more than one customers engine stumble because it was sucking fuel thru the primer at certain manifold pressures.
 
So it's been a couple of years, does the teflon packing from True Value hold up? Jim
 
I have flown my J4 about 500 hrs in 7 years with this teflon string packing. works great. Also used it in my dads J5. But I am not a aircraft expert so don't take my word for it.
 
The pin in the end of the plunger has a spring behind it and all is retained by a flat sided "nut". You might take this apart, too, and clean out any debris or corrosion. When the springs behind the checkballs deteriorate, is there a source for them? jrh
 
Anyone have any idea what size the compression nut is that goes on this Lunkenheimer primer? It is not 5/16-32. It appears to be 8mm, I cannot exactly determine pitch as it does follow any pitch gage I have. Source, part number, anything? 5/16-32 shown in pic for comparison.
 

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1/8" tube compression fitting from Ace Hardware fits mine perfectly - -

Edit: Oops, my primer is the Kohler / Essex - -sorry - - -
 
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Steve, Thanks for checking but the AN805 nut is 5/16-32, the Kohler primer outlet is 5/16-24, my primer appears to have a tapered thread not straight. The pic Longwinglover posted of his Lunkenheimer primers almost appear to have a straight thread. Maybe mine is an oddball. Perhaps someone from across the big pond will chime in with an opinion, I found a source of metric fittings in the USA if I knew what size/style to ask for. I believe it is 8mm OD.
 
Jim the AN805-2 union nuts I got from Spruce fit both of mine and it looks just like yours in the picture. I put my thread gauge on it and it is 32. The fitting you show in comparison is a courser thread like a primer nozzle.
 
I've got new 805-2 nuts and also AN929-2 nuts, neither is correct. It is not quite 32 pitch, maybe 36, although it is hard to measure cause it's so short and appears to be very slightly tapered. There is a British thread, MBSPT, that is very slightly tapered, as I said I believe this is metric of some sort. Thanks for the effort. Jim
 
can anybody give a brief description of how to "install" the packing? We had been sizing o-rings as it had one on it when I bought it. They were only lasting a few flights. No wonder....
 
Start and end the packing like the tapered ends on a coil spring from your car. Stuff as much as you can into the packing gland...tighten the packing nut good’n tight.....until the valve shaft locks up, then back it off until the turning resistance feels right. If the nut bottoms out before locking up the shaft....not enough packing....
I’ve never worked with Teflon coated packing..wonder if it’s as mooshable. As graphite packing?
e169ce58e001360ad1a28248a049a8e5.jpg

Oleo strut spring...as an example of how to taper the ends of the packing. Use a nice sharp wood chisel to cut the packing.

Sent from my iPad using Tapatalk Pro
 
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