primer problems

Maintenance, parts and services related to Cessna 120/140's

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primer problems

Postby 6785 » Sun Nov 07, 2010 4:07 pm

Cannot get my engine started, 85hp primer feels funny,seems like pressure is not there when pushed in
Are they repairable?
Aircraft Spruce wants $170.00 for a new one.
Any suggestions?
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Postby Randy Thompson » Sun Nov 07, 2010 4:13 pm

The engine should start without the primer. Close the throttle all of the way and crank. It may take a while but if it does not start you might have fuel blockage that keeps the primer from working, too. I am assuming that you have a Stromberg carburetor.
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Postby Ray Hunter » Sun Nov 07, 2010 4:53 pm

I agree. You shouldn't need the primer. In summer, I handcrank for 8 blades..then get in and it starts up afer 2 blades with the starter. In winter, same thing. Preheat, hand-crank, starts up instantly.
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Postby John C » Sun Nov 07, 2010 6:48 pm

To answer your question... ;)
What brand is yours?
Most primers have an o-ring seal that can be replaced. Lukenheimer (sp?) have only a stem packing. They all have inlet and outlet valves, but they generally don't give much trouble, unless some dirt gets in and keeps them from seating.
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Postby AmazonJet » Sun Nov 07, 2010 9:07 pm

I rebuilt mine. It does come completely apart although I had to use a flame to get it to unscrew.

Also, if no fuel is getting to it, it will not have a hydraulic reisitance feel as you push it in.
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Postby skot7ac » Sun Nov 07, 2010 11:18 pm

Sounds like it might be time for new o rings. It is certainly both easy and pretty inexpensive to do. I "borrowed" this from the 170 page, pretty sure that it's the same primer but I won't hang my hat on it. The links did not work for me, but the info is pretty good.

I ran across the following while browsing Cessna Single-engine service letters and thought it might be a helpful reference to anyone in need of a fuel primer rebuild. Service letter 78-73 says that using NAS1593-012 o-rings "provides smoother primer operation, improved sealing, and longer service life" than the original AN6227-7 o-ring. They recommend replacing them at the next 100 hr. inspection. According to Geniune Aircraft Hardware Co. NAS1593 o-rings are made of Viton. Aircraft Spruce doesn't show the NAS o-ring but does sell MS29513-012 o-rings that "are resistant to fuel and are ideal for applications such as fuel ... primers." I then stumbled on McFarlane's website which seems to have the latest and greatest o-rings ever (for 13 times the price of an MS29513-012): "The MCM83248 series o-rings are 'fuel proof' FAA-PMA replacement o-rings. Only McFarlane has FAA approval to replace the old, less fuel resistant nitrile (MS series) and synthetic rubber (NAS series) o-rings with the latest fuel proof fluorocarbon o-rings! Flurocarbon rubber is commonly known as Viton. It is an advanced rubber that has extremely good fuel and heat resistance and is ideally suited for aircraft fuel system applications." So for the primer the o-ring you need is MCM83248/1-012. Here's a link if you need to order: http://www.mcfarlane-aviation.com/Produ ... 8%2F1-012& Or, if you're willing to risk the FAA checking whether you bought your Viton o-rings from a place that might not have the FAA's blessing to replace the original, you can get them for 36 cents from Sacramento Sky Ranch. (Quite a deal as they are normally priced there at $89 each!) http://www.sacskyranch.com/acatalog/Sac ... s_302.html
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Postby Otterpilot » Mon Nov 08, 2010 11:21 am

Are there any o-rings that would work in a Lunkenheimer (sp?)?

I don't recall a groove for an o-ring when I opened it up. I rebuilt mine a few years ago with teflon "thread" from the aviation department at Ace Hardware. This worked great for a few months. The original leaking is gone, but there is quite a bit of pumping required to prime the line again before it works. I do still get the occasional drip when I use it though.

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Postby John C » Mon Nov 08, 2010 3:09 pm

The Lukenheimer doesn't need an o-ring. Your issues are due to the packing still leaking. Teflon packing is nearly infinitely compressible. (And you really don't want any if it to get loose in the fuel system!) You need something with more "body". Cotton string impregnated with fuel-lub will work.
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primer

Postby 6785 » Mon Nov 08, 2010 9:04 pm

I thank you guys for the info you have given me.
Worked on my primer today,found that is has 2 o rings
However there was no fuel to be seen
Question, where does the second line get its fuel from?
2 Lines are going from the primer to the fire wall, one goes to the engine compartment
The other line disappeared to where?
Any info would be greatly appreciated :D
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Postby Randy Thompson » Mon Nov 08, 2010 9:12 pm

The one that gives fuel to the primer is connected to a tee coming out of the gascolator. The other feeds the fuel to a fitting in the intake manifold or spider. Does your engine run?
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primer problems

Postby 6785 » Tue Nov 09, 2010 3:34 pm

Got my problem solved guys technically I had NO problem.
Found that my fuel valve was on the OFF setting.
Sorry if I caused any inconvenience to any one. :oops:
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Postby Otterpilot » Wed Nov 10, 2010 12:09 pm

Well at least it happened before starting, instead of at 30' with no runway in front of you!

I at least got some great info from it. Back a while I read threads on primers and got the teflon idea for the Lunkensphincter (sp?). I like the fuel lube and packing string much better. What came out of it looked similar to that. Just did not have a clue about how to execute it. A buddy has the fuel lube, and all I have to do is find a rugged enough material now.

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Postby Mike Smith » Wed Nov 10, 2010 3:03 pm

Sounds like a checklist is needed and should be followed.
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