Putting AN fittings on ends of the hard fuel line

[jclayc]

Can I add a stainless steel tube sleeve, tube nut and a 37 degree flare on the ends of the hard fuel line so I can run AN fittings w/ flexible lines. I don't like clamps as much as fittings.

And 1/4" being the closest diameter for our fuel lines, that translates to -4 AN.
Is that ok to run from tank to tunnel, etc. or should I add a fitting to the 4an tube nut to change it to 6an fittings and lines?

[Glenn]

FYI, the factory didn't use clamps, the pressure is so low, they weren't needed.

Two reasons to use AN fittings on the fuel supply:
1) You are using high pressure as in fuel injection.
2) You have money to waste and you like the bling.

The 2-3psi from the stock mechanical fuel pump will not cause the German fabric covered line to come off. Adding a ABA style band clamp is extra protection if you want. It's belt and suspenders.
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[jclayc]

good feedback Glenn, thank you.

[ashman40]

While I don't disagree with anything Glenn posted above, I have looked into terminating the tunnel hard lines in AN fittings. If this is something you are intent on doing... here is a video that covers a few options for terminating tubing with AN fittings. It presumes you have SAE size steel tubing and may not work with the OE metric tubing. You may have to source AN fittings that work with metric tubing.

Link


The compression fitting is the easiest as you just need a set of wrenches once the lines are cut to the proper length. No need to deal with a flare tool and getting the correct flare on the end of the tubing. But if you plan to use the stock metric hard lines maybe the flared tubing option is the better one as the seal will be made to the tubing material which has been flared and not depending on the crush of the incorrect 1/4" ferrel being installed on a 5mm tube.

While I agree that the correct size hose for 5.5mm/0.25" tubing should be -4 AN fittings as this is the equivalent of 4/16 = 0.25"... the actual ID of the -4 AN fitting would be closer to 0.17" which means you are adding a restriction in the overall flow by going with -4 AN fittings.
Also, you may find it difficult to source the needed -4 AN fitting/adapters you need. I found it easier to source -6 AN compression fittings that would attach to the end of 0.25 OD tubing than to find -4 AN compression fittings for 1/4" tubing. -6 AN hardware is a much more common size for both fittings, adapters and hoses when it comes to automotive use.

So out of convenience you may want to look at -6 AN hardware.
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[richparker]

On my 2275cc, bling bling 💎

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[Glenn]

[67rustavenger]

Some bling on this pile too. The local race tracks frown on more than 12" total of rubber fuel line here.

EDIT: I used a -6an adapter fitting on the hard line at the frame horn connection.
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[esde]

One argument for AN fittings, is that after a few months, it is often impossible to get fuel lines back off of a barbed fitting. I'm assuming it is the current fuels that dry and harden the hoses, but I almost always have to cut them off of a barb. With a JIC or AN connection it's just two wrenches and apart. Of course this doesn't do anything for a stock pump or carb..
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[Glenn]

I only have a few inches of hose. I use stainless hardline like it came from the factory.

ABA Band hose clamps.

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[richparker]

[scrivyscriv]

I totally disagree with Glen on bling and extra wasted money. If there’s any system that was under-engineered, it was the fuel system. I really don’t know if it’s the modern ethanol fuel, or the “rubber” currently available, but fuel leaks and engine fires have been a problem for air cooled for as long as I can remember. If there’s anywhere that money isn’t wasted, it’s on fuel system upgrades and fire extinguishers.

I think it’s a wise move to eliminate any clamped joints in the fuel system - under the tank isn’t a big deal, but anything aft of it would benefit. A braided teflon tubing would be ok in the engine bay as long as it isn’t subject to significant flexing over its life. I would not use any rubber or Teflon over the heat exchanger; that needs to be metal tubing, preferably with a short length of silicone and fiberglass heat sleeve crossing the exchanger. I can’t think of any downsides to using a threaded connection anywhere in the fuel system.
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Robert in Memphis
Dünkelgrügen 1967 Java Green bug thread
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[Glenn]

Use hose that is ethanol safe.
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[jclayc]

[scrivyscriv]

Mine's not running yet, but here's how I set my fuel line up. I've got a 4AN straight bulkhead fitting at the front under the tank, and I flared the line coming out of the frame horn for a 4AN standard tube nut and sleeve. I'm using aluminum fittings but in this scenario I don't think it matters that much steel vs. aluminum. I may see some ethanol corrosion on the aluminum down the road so that's something I'll have to check in the future.
I'll run the frame horn line to the left hand body sheetmetal right beside the engine, to a bulkhead fitting. There is no real benefit to putting 6AN tubing on a stock engine; it's easier to keep everything the same to avoid adapter unions with their extra potential leak points.

Keep in mind most braided hoses are rubber, and you're not guaranteed a high quality rubber if you buy based on price. As Glen says, make sure your rubber is rated for ethanol. Otherwise you can get a teflon braided hose, but teflon does take a set over time and can crack if it's flexed much after it takes a set. I don't see a problem with either material for our fuel lines, as there is no flexing anywhere.. just vibration.
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Robert in Memphis
Dünkelgrügen 1967 Java Green bug thread
Engine rebuild thread
If you're ever in the Memphis area, you are welcome to stop by for advice and help.

[zerotofifty]

For An fittings, I d stick with the correct sized tubing, You might find on the interweb what the tolerance is for 1/4 tube to work with AN fittings, and if the metric VW fuel lines is within those limits then go for it, but otherwise it maybe problematic to use an AN fitting for 1/4 inch on a non 1/4 inch tube. If you want AN, you can run a whole new tube of the correct diameter. Keep in mind that vibration isolation maybe needed at the engine to chassis connection area.
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[scrivyscriv]

You can easily see how well the tubing matches up against a fitting once you flare it. There is more than enough allowance at the fitting interface to make up for differences in wall thickness that I wouldn't sweat it here at all
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Robert in Memphis
Dünkelgrügen 1967 Java Green bug thread
Engine rebuild thread
If you're ever in the Memphis area, you are welcome to stop by for advice and help.

[ashman40]

[scrivyscriv]

[jclayc]

Great follow ups, thanks.

scrivyscriv - I thought about running bulkhead fittings and new tube inside the tunnel but just couldn't talk myself into re-running the hard line, so I think I'll flare both ends for tube and nut using -4an.

ashman40 - Regarding the availability of 4an vs 6an filters, etc... good to keep in mind but I also see lots of filters, regulators and pumps with 1/8 NPT female threads where I could use a 1/8 NPT to 4an fitting.

I'm still thinking through questions like 4an vs 6an for the flexible lines and whether or not to run hard or flexible line in the engine bay itself but, regardless, I hear you on wanting quality lines. Although I have quality line and have built AN hoses in the past, I used raceflux pre-made lines on my old CTS-V racecar for peace of mind and may do the same again. We'll see.