Koul Tool’s Solution For Repairing Those Pesky, Leaking AN Fittings

It’s annoying. That straight length of steel tubing is now a perfectly bent fuel line with 45-degree double-inverted flare ends. The fittings thread in easily and you tightened them carefully and yet there it is – a leak. It’s that frustrating drip-drip-drip. 

In the past, we’d loosen and tighten the fitting several times trying to get that fitting to seat properly. We’ve even tried smearing valve lapping compound on the fitting and then running through the process of tightening and loosening the fitting multiple times to get the seat to finally get familiar. Sometimes this works, but other times it doesn’t, and we’re faced with making a new flare – or worse a whole new line. Much of this can be traced back to the procedure used to make the flare, but sometimes it seems like our flaring tool is possessed and is in need of exorcism. The other possibility is that maybe, just maybe, we were doing something wrong.

The good news is that there are multiple potential solutions. We’ll start with a few suggestions on how to execute a better flare and then show you a couple of new Koul Tools that can repair those leaking fittings. We don’t have space to detail all the different flaring tools that are out there – we’ll save that for a later date. There are some very nice manual and hydraulic tools out there using mandrels that do an outstanding job. But you can still do a good job with the old classic saddle-style flaring tool if you pay attention to the details.

We’ve spoken to several professional car builders and fabricators who say the way the tubing is cut can affect the quality of the flare. While a perfectly perpendicular cut is an absolute must, one builder claims he does not use a tubing cutter because it dents the tubing which affects the quality of the flare. Instead, he cuts tubing using a high-speed cut-off wheel. In a pinch, you could also use a fine-tooth hacksaw.

Tips for making a better 45-degree double flare include cutting the tubing with a high-speed cut-off wheel instead of the tubing cutter. Make sure the cut is perpendicular.

In auto shop class everyone is taught to deburr the inside of the tubing, but the tube’s outside diameter can also offer a raised sharp edge so take the time to carefully dress the tube’s outside diameter with either light sandpaper or a convolute wheel. Ours is mounted on a bench grinder and it works great for deburring and polishing the end of the tubing. Another trick with larger diameter tubing is to use a cartridge roll mounted on a die grinder to polish the inside of the tubing. This takes more time, but the leak-free results justify the effort. With the tubing polished and burr free, run through the double-flare process using a touch of oil on the tubing to help the tool do its job. 

The next step is to spend the time to deburr the inside and polish the outside of the tubing. A convolute wheel mounted on a grinder works well.

With the flare complete, you may still discover that the seal is not perfect. The aforementioned lapping compound trick has worked for us in the past, but recently we learned that Koul Tools has come up with a couple of slick devices that perform this job with much more accuracy. 

The first tool is called the Surseat with specific tools for either 45- or 37-degree sealing angles. For the record, most steel automotive fittings use a 45-degree seat angle, while nearly all AN fittings use a different, 37-degree flare angle. These are not interchangeable. 

Koul Tools offers a couple of ways to save your leaking fittings. The Surseat tools in the boxes use a hand-held fixture that can repair either 45- or 37-degree tubing flare seats. The smaller, blue Fitting Fixers use a drill motor to spin a diamond-dust mandrel that cleans male AN fittings.

The working end of the Surseat tool features a diamond dust-coated seat as the abrasive. With the tubing flare mounted in the tool, rotating the Surseat handle blends the proper angle into the seat. The tools in our example were designed for 3/16- and ¼-inch tubing but all the popular size tools are available up to ½-inch. The Surseat is small enough that it can also be used on the car without removing the hard line.

When challenged by a leaking flare, there’s an easy fix. Thread the fitting into the appropriate size Koul Tool fixture (this is a 45-degree, 3/16-inch line) and slide the mounting clip in place to retain the fixture.

The process is easy, starting with sliding the tubing inside a collet and clamping it in place in the fixture. After lubing the lapping head with WD-40, spinning the handle will clean the seating surface. Hard steel surfaces will require more turns than softer aluminum. After removing the tubing from the tool, clean the sealing surface with a Q-tip or swab to remove any abrasive and you’re ready to re-install the line as a leak-free piece of plumbing. 

For this fitting, we had to turn the mandrel several times to create an even seat but this will now do its job and not require gorilla torque to seat properly.

Koul also makes a separate tool called the Fitting Fixer designed to repair male AN fittings. Using this tool is even easier. Start by choosing the correct tool for the fitting size and thread the male AN fitting into the aluminum guide. Then chuck the lapping head into a drill motor and apply a small amount of lube like WD-40. Next insert the lapping head into the guide and over the AN fitting. Spin the drill motor for two or three seconds over multiple passes and then inspect the fitting. The goal is to remove as little material as possible to create a clean face. Clean the fitting and it’s ready to re-use.

This -4 bulkhead fitting has seen better days but the Fitting Fixer will tune it right up.

We threaded the -4 fitting into the Fitting Fixer and chucked the mandrel in our 3/8-inch drill motor. We added a little WD-40 to the end of the mandrel for lube and spun up the drill motor for 2 seconds per shot for five or six blasts, inspecting the fitting for a couple of sessions.

The Fitting Fixer did its job and removed a gouge that was present in the fitting. We cleaned the fitting thoroughly and then re-installed it on our oil pressure gauge.

This is a quick and simple way of saving fittings, especially more expensive fixed male fittings on items like oil coolers or dry sump tanks. If there is a downside to this repair, it is that the diamond coating removes any anodizing from the 37-degree surface. This is generally only a concern if the fitting is used in a fuel system using exotic fuels like methanol where corrosion is a significant problem for bare aluminum. 

Koul also sells other useful tools including its unique AN hose assembly tool for guiding the fitting over the braided stainless hose that makes this otherwise difficult and painful job very easy. We’ve used this tool dozens of times and it’s saved countless bloodlettings!

We also built this simple fitting tester mounting a simple tire Schrader valve in a fitting. We then install the fitting we want to test on the opposite end and pressurize the hose. Dunking the fitting under water will quickly reveal if the fitting leaks. Earl’s makes these test fittings, but we fabricated ours from an unused older fitting.

So, the smart move is to invest in one of these tools before that next dripping fitting comes along. When it happens, the solution will be sitting in your tool box just waiting for the opportunity to save the day. Just lock your tool box, because it’s likely your friends will all want to borrow these gems!

Parts List

Description PN Source
Fitting Fixer, small set 3/16” to ½” FF-3468 Summit Racing
Fitting Fixer, -6 AN FF-6 Summit Racing
SureSeat Flare lapper, full set 37 & 45 degree P-51 Summit Racing
SureSeat for small 45 degree seats, 3/16 & ¼ P-45 Summit Racing
SureSeat for small 37 degree seats, 3/16 & ¼  P-37 Summit Racing
Hose Assembly tool, -6, -8, -10 AN kit 681 Summit Racing

Article Sources

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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