Engine Plumbing: Fuel Lines

For the first major task following mounting of the engine, I began installation of the fuel lines. I thought this would be pretty easy, but it took two full days and I learned a few things.

At first I was going to use aluminum tubing, much like I did in the fuselage, and as shown in the first photo below. It took a while to make all the bends in the tubing between the bulkhead connectors, gascolator, and fuel pump – much more than I expected. The required bends are pretty tight, some of them were compound, and were generally beyond the capability of the bending tool I had, so I had to improvise a bit, bending a few by hand.

After spending all that time forming the bends in all the tubing, I found it extremely difficult to install firesleeve over the aluminum fittings, especially the elbows. After doing a little digging for tips from other builders, I quickly learned that aluminum tubing is not typically used forward of the firewall, since it wouldn’t survive prolonged heat exposure. More typically, hoses or stainless steel braided lines are used. So, after wasting hours trying to form all the lines perfectly to shape, I uninstalled it all and restarted the task using the high pressure hose and stainless steel fittings included with the kit.

I started with these aluminum lines and it did look nice & neat

Once I switched over to using the rubber hoses provided with the FWF kit, I was able to complete the hose assemblies. I wound up with two assemblies: the first hose goes from the firewall to the gascolator, and the second connects everything else. The hoses attached to the AN6 SS fittings pretty easily, but the brass barbed tees were much more difficult. I found that warming the hose with a heat gun helped a bit.

Installing the firesleeve was also a bit tricky. A learned a few tips from reading the datasheet for the firesleeve, which is made by Eaton:

  • Blowing compressed air into the open end of the sleeve makes it easier to slide over the hose
  • Pulling back or cuffing the end of the sleeve helps to accommodate attachment of the fitting and ear clamps
Cuffing the end of the firesleeve

Curiously, the Eaton datasheet also says the ends should be dipped in “End Dip”, but there was no mention of this in the Sling KAI. The End Dip protects the fiberglass strands from becoming soaked with oil and/or debris, which in turn could be flammable. During a recent trip to Torrance, I spoke to Shawn, the engine expert at the Sling Build Assist center, and he had a unique solution – at the ends of the sleeve or at joints where the firesleeves meet, he applies a high-temperature RTV epoxy to seal the joint. Pretty clever, and it definitely neatens up the appearance! Also as seen in this photo, he wraps another hose over the firesleeve (simply a split piece of 5/8″ heater hose – Gates 3270), but he did admit this is done purely for cosmetic purposes.

Detail of fuel hoses on a Sling TSi build in progress at Torrance
Sling Build Assist Center uses this Permatex epoxy to seal the firesleeve ends
Fit & placement checks before I cut the vapor recovery hose

After a while I got pretty efficient at the hose connections. Once I was satisfied with the fit of the connections, I wrapped the ends of the firesleeve with safety wire. My safety wire loops weren’t as pretty as those in the build manual photos, but they should suffice. I am very confident that there will be no leaks in any of these hoses – the barbed fittings and the double-ear clamps are quite substantial, I suspect they would work fine even at hundreds of PSIs of pressure.

Typical tee junction appearance after setting the clamps
The same tee junction after uncuffing the sleeve and wrapping the ends with safety wire
Fuel return line, with cross-over for the vapor recovery

Normally this hose assembly would have one more tee for attaching a fuel pressure sensor, just before attaching to the inlet on the #1/#3 cylinder fuel rail. However, I discovered that my engine was fitted with a special banjo bolt on the fuel pressure regulator, which allows for easier installation of a fuel pressure sensor. This is an optional modification as documented in SI-PAC-024.

The sensor fitted to my engine was a Honeywell MLH010BGB06A, which is an absolute pressure sensor. Unfortunately, this is not one of the pre-configured sensors for the Garmin G3X; the install manual instead calls for a differential sensor made by Uma, type 1EU70D. Luckily the Uma sensor is exactly what Sling included with the FWF kit. Both the Uma sensor and the special banjo bolt have 1/8″ female NPT fittings, so I bought a short 1/8″ NPT nipple and will try attaching the Uma sensor in place of the Honeywell sensor at this banjo bolt.

Honeywell fuel pressure sensor attached to the fuel pressure regulator
Uma differential pressure sensor

One last item of note: I found the opening to be too small to feed the engine connectors through to the ECU (which is mounted to the instrument sub-panel. I never really looked closely, but the pear-shaped hole was indeed smaller on this firewall than standard, so I opened it up with a nibbler, sanded it smooth, then installed edge protection.

Tracing the area to be removed

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