Petcock Relocation - Tech

Welding In A New Bung

writer: Toph Bocchiaro
photographer: Toph Bocchiaro

Choosing a new gas tank for your scooter isn't always the easiest proposition. There are a ridiculous amount of options-such as style and size-available. That's an important decision before even deciding on who and where to get the tank. Stock is...well...stock, and generally cheap and easy to get new or used. At the other end of the spectrum are full-on custom tanks, made to order for your application. That's great, but a custom tank might cost more than the basket case you're trying to assemble.

In the middle are aftermarket companies that make some bitchin' styles, but are often made for more generic applications, and not bike or model specific. Things like how the tank mounts to the frame and where the petcock is located are important things to keep in mind. For those handy enough to weld, these limitations are easily solved. The rest of us have to find someone competent enough to take a torch or TIG to a tank.

I happen to love the look of the retro Paughco Mustang series of tanks. Paughco has many different sizes and mounting options to choose from. I went with the low-tunnel, backbone-mounted three-gallon version. Fore and aft tabs mount the tank directly to the backbone. The style screams old Frisco to me and allows the motor to be the centerpiece of the bike. Not only do I happen to like the style, but I was forced into an alternative mounting option due to a stroker motor that necessitated frame surgery to squeeze it into the frame. The stock gas tank mounts had to be chopped in the process.

Once I got the tank custom mounted (August '07 Hot Rod's Bike-Works), I ran into another problem. The Paughco petcock bungs (they give you one on each side) were directly over the rear rocker box. There was no way to put a petcock into the space. In addition, the Paughco tanks take small 1/4-inch petcocks that don't flow enough gas for a high-output motor.

The plan was to have Gregg Grandon of Launch Padz do the petcock relocation and then prep the tank for powdercoating. A new petcock bung and high-flow petcock were added to the mix.

1. A profile of the sleek Paughco Mustang gas tank (model # 812, 147.95). This is the 3-gallon Extra-Wide Universal model with a low tunnel, early cam-style gas cap bung, and two internally threaded bungs for 1/4-inch petcocks. Tanks come in bare metal and pressure-tested.	2. These two petcock bungs (arrows) are going to be removed and welded up. A new hole and bung will be added to accept the new late-style EMS Ultra-Flo petcock.	3. A die grinder was used to cut the right side bung flush with the tank...
4. ...followed by the left side petcock bung.	5. We put the tank on the backbone of the bike to get an idea of where the new petcock would reside. We used a Sharpie to approximate the position of where the new weld in style Pingel 22mm steel fuel tank bung (bottom) would be placed. For bung placement, we split the difference between the two drawn circles.	6. Instead of using a drill, Gregg used the welder to poke a hole in the bottom of the gas tank. It worked clean and fast until the hole was about the size of the new bung.
7. Gregg tack-welded the bung onto the tank to make sure there was enough clearance between the petcock and the top of the rear rocker box.	8. After making sure the bung was in the right place and flat against the tank, a bead of weld was laid down around the petcock.	9. To plug up the holes where the old petcock bungs resided, Gregg inserted a piece of steel roundstock that was slightly smaller than the hole before welding the rod into place.
10. This filled in the hole, but left the rod protruding from the tank. Using a cutoff wheel, the rod was cut flush.	11. The same was done on the other old petcock bung location before both were sanded flat and blended into the surrounding tank metal.	12. After finishing up the welds, the petcock was threaded onto the new bung and the gas cap screwed in. An air line was attached to the petcock...
13. ...before pressurizing the tank with about 5 psi of air. While filled with air, soapy water was dropped over the newly welded areas to check for leaks. If it bubbled, we'd have to go back and fix the weld until the tank was airtight.	14. Following sandblasting, the prominent ridge down the center of the tank can be easily seen. This is the weld mark from the manufacturing process.	15. Since the tank was going to be powdercoated (and heated to almost 400 degrees in the process), traditional Bondo material wouldn't work. J-B Weld contains metal that would allow the electrically charged powdercoat to stick.
16. We went with the J-B Kwik because it cures in less than five minutes. After mixing up the J-B Kwik, we applied it to the tank with a homemade custom cardboard applicator. A putty knife works well, too.	17. After coating the problem areas on the top and bottom of the tank with J-B, we used an orbital sander (200-grit) to smooth out the J-B.	18. Since the middle of the tank was the high spot, the J-B was sanded away from the high spots and left on either side. A straight edge is handy for checking flatness as you go. If you mess up, it's easy to apply more J-B until you are satisfied with the outcome. Once you get close switch to 100-grit sandpaper.
19. Both of the old petcock bungs were treated to J-B smoothing, leaving a completely smooth tank bottom. The tank was now ready for powdercoating. Tune in next time for the completion of the powdercoating, along with the rear fender and installation.