Primer Fuel Line Failure

[kiwibob]

Bob, thanks for the heads up & great photo. I'm kind of with you regarding the need for the primer system. I've got 360 hrs on my 2014 CarbonCub & I have honestly NEVER touched the primer except to insure that it's locked during my takeoff check.

In 500 hours on my Carbon Cub never occurred to me that I would not need the primer so I always used it on first start of the day. Obviously worth trying without it especially in a temperate climate.
Thanks for the post and the tip about the pipe.

[Pete D]

Loctite 567 is good and used during the builds.

EZ turn fuel lube should be used on any fuel systems. (light semi-translucent peanut butter colored)

Loctite 576 on oil systems (engine oil and brakes) (bright white color)

Mix them up, pretty much guaranteed a leak.

[Daveembry]

UPDATE: TALKED AGAIN WITH MITCH TODAY ABOUT THIS AND HE CONFIRMS TO NOT USE THE FUEL LUBE BUT TO USE THE LOCTITE 567 FOR ALL APPLICATIONS REQUIRE THREAD SEALER INCLUDING FUEL CONNECTIONS.

Pete. We need to get with Mitch and change all the manuals then as this is what’s specified fort metal threads . Also Mitch has said due to problems with Fuel Lube (EZ Turn) he recommends not using it and has repeatedly said to use the Loctite 567 in the engine threads and on all fuel fittings. Guess we better get the correct answer.

EZ turn fuel lube should be used on any fuel systems. (light semi-translucent peanut butter colored)

Loctite 576 on oil systems (engine oil and brakes) (bright white color)

Mix them up, pretty much guaranteed a leak.

[turbopilot]

UPDATE: TALKED AGAIN WITH MITCH TODAY ABOUT THIS AND HE CONFIRMS TO NOT USE THE FUEL LUBE BUT TO USE THE LOCTITE 567 FOR ALL APPLICATIONS REQUIRE THREAD SEALER INCLUDING FUEL CONNECTIONS.

Ok, let me see if I am following the recommendations here.

I installed a steel 1/8 NPT plug in the cylinder where the primer discharge nipple (AN4022-1) was located. I just used some anti-seize compound on that fitting and tightened it down.

On the gascolator I removed the brass primer fitting and replaced it with an 1/8 NPT brass plug but no Loctite or anti-seize compound.

So you are recommending Loctite 567 for both plugs?

[Rudy]

UPDATE: TALKED AGAIN WITH MITCH TODAY ABOUT THIS AND HE CONFIRMS TO NOT USE THE FUEL LUBE BUT TO USE THE LOCTITE 567 FOR ALL APPLICATIONS REQUIRE THREAD SEALER INCLUDING FUEL CONNECTIONS.

Pete. We need to get with Mitch and change all the manuals then as this is what’s specified fort metal threads . Also Mitch has said due to problems with Fuel Lube (EZ Turn) he recommends not using it and has repeatedly said to use the Loctite 567 in the engine threads and on all fuel fittings. Guess we better get the correct answer.

EZ turn on the tapered thread fuel fittings has caused multiple fuel leaks for me.

[Daveembry]

Sorry for the confusion! Let me explain my understanding of the use of the different thread sealants. I am coming from the "kit builder" perspective, so everything I know has come either from the written construction manuals or directly from Mitch Travis, the builders help man.

Mitch is working with kit builders like me.....who may or may not be A&P's or have any prior experience in building aircraft. I say that because there may be subtle differences even though he thinks even the factory floor may have made this switch (but he will confirm that and with engineering).

The way I understand it, "FUEL LUBE" was a brand name for a thread sealant used on any fittings that required thread sealant that came in contact with fuel. They no longer manufacture under that name and the current product used is "EZ TURN, FUEL RESISTANT LUBRICANT" manufactured by United-Erie, a division of Interstate Chemical Co. It is rated for high temperatures as well whereas Loctite 567 is specified to 150c or 302f (which seems too low to me for engines?)


EZ Turn is a specialty lubricant/sealant used for fuel and oil line valves & is resistant to high temps. Especially effective where high octane fuels and aromatics are present. EZ Turn is also extremely efficient as a gasket paste & anti- seize agent. EZ Turn will not gum, crack or dry out. Excellent for tapered plug valves, aircraft engine manufacturing, and marine applications. EZ Turn is the functional equivalent of fuel lube.

It is extremely sticky, much like petroleum jelly but a much thicker paste. The problems with the "fuel lube" product is that you can not get it into the fuel lines or system as it will stop it up as it isn't soluble in fuel. The manuals say when putting it on the male end of a fitting, not to let any on the first 3 threads of the fitting. This is to prevent any from getting into the system.

I think the problems that have occurred has been a result of messy application and not the product itself, thus.....perhaps the recommendation from Mitch that builders stop using it and use the Loctite 567 for all applications. The new CC363i engines are coming with the white, 567 thread sealer in the fittings I believe. It's recommended for course, metal threads. I'm not sure if Pete meant to say "576" in his explanation or it was a typo. They do make a "576" but it's a darker thread sealer?

I think both serve the same purpose but the 567 is more of a paste an not nearly as "sticky" and thick as the EZ TURN which I think makes it safer for use in fuel system fitting perhaps just due to the fact that it won't block the fuel system if not installed on the threads correctly (like by amateur kit builders???) so that it gets into the fuel system. I am told it is also non-soluble in petroleum products (fuel/oil/hydraulic fluids).





Off-white, low disassembly strength methacrylate thread sealant, ideal for sealing coarse threads up to M80/R3”. UL approved.
LOCTITE® 567 is an off-white, low strength, thixotropic methacrylate thread sealant. It cures in the absence of air and by contact with metals when confined within threads up to M80/R3”. It is best suited for use on coarse metal threads and its breakaway torque rating is 1.7Nm. Viscosity is 280,000 - 800,000 mPa·s and service temperature -55 to +150ºC. UL approved.

• Provides an instant low pressure seal
• Doesn’t creep, shrink or block systems
• Single component - clean and easy to apply
• Thixotropic and high/very high viscosity
• UL approved

So that is my understanding of it. Any tapered, metal fitting should have a sealant. The non-tapered, metal fitting do not require sealant as the threads themselves are sealing. I know the engine plugs in the ones I've used have always had a sealant on them.....

Ok, let me see if I am following the recommendations here.

I installed a steel 1/8 NPT plug in the cylinder where the primer discharge nipple (AN4022-1) was located. I just used some anti-seize compound on that fitting and tightened it down.

On the gascolator I removed the brass primer fitting and replaced it with an 1/8 NPT brass plug but no Loctite or anti-seize compound.

So you are recommending Loctite 567 for both plugs?

[Mark Keneston]

When installing those in new builds I have also always used a good spiral wrap on the entire copper line. Not sure if that helps or not but might help stabilize the vibrations some??? If not, it's good protection against any abrasion that might happen.

Agreed, need a much smaller loop and then secure it so there is no vibration. MK

[turbopilot]

Agreed, need a much smaller loop and then secure it so there is no vibration. MK

Can't comment about a smaller loop. My installation was as secure as it could be. One clamp on firewall and one clamp on the engine nearest to the firewall.

This failure appears to be a fatigue fracture of the cooper line. With the rocking of the engine it is just a matter of time before the line fails. Good news is that a failure between firewall and engine is not a significant safety of flight issue. Failure between the gascolator and primer pump is a very big deal.

In any event I have completely removed the primer system from my aircraft. Just dead weight.

[seastar]

Just as another input --- my engine will not start the first time of the day, no matter the temperature without priming at least four strokes of the plunger. My engine will not start at all much below freezing without preheat. I keep electric heat on the engine all winter but still need to prime.
Pumping the throttle does not help.
since I can't remove the primer line I need a valid solution to this apparent failure mode.
Is there one?

[seastar]

I just noticed that the break in the copper tube occurred at the smallest bend radius.
I wonder if that point were over bent or some how stressed too much?
I can't see any damage to the tube in the picture but something caused it to break where it did.
Maybe defective tube?