Thursday, March 5, 2015

Rullo Custom Cycles: How to install a fuel sight gauge on a motorcycle tank

We have been installing our Motorcycle Gas Tank Fuel Sight Gauge kits on our customers' bikes for over 12 years. There are other brands out there as well like the Lowbrow Customs kit that we have in our store, but the installation will generally be the same. This article is a general installation guide. Proper precautionary steps should be taken to avoid serious injury. If you are new to welding and fabrication, we advise that you pay a professional to do the install.

  1. Prep your gas tank
  2. Mark where you will install the included bungs
  3. Center punch and drill
  4. Clean heat affected zone
  5. Install bungs and tack in place
  6. Finish weld bungs
  7. Plug all openings in tank and pressure test
  8. Finish install

1. All welding applications begin with safety first. Installing a fuel sight gauge on a new gas tank involves much less preparation than an existing gas tank. If your gas tank has had gasoline in it previously, it is imperative that the tank be completely drained and cleansed of any residual gas or fumes. Explosions when welding are never a good thing. Additionally you will need to remove any paint that is in the way of the heat affected zone that you are installing the fuel sight gauge. You will be repainting after the install.

2. When you have your gas tank in bare metal and are certain that there are no residual fumes, you can mark the tank for where you want the fittings to be installed. Locate the fittings where you prefer them to be. This is somewhat discretionary for appearance, but keep in mind the reason that you are installing this kit. We mark these with a sharpie or paint marker first and visualize how the final install will appear. This is the time to make any changes.

3. Center punch your markings so that you can drill the gas tank accurately. We use a spring loaded center punch. The bungs that are included with our fuel sight gauge kit are a tophat style bung. You will drill a 5/8" hole in which you will install each bung. We use a step drill to make this simple and accurate along with cutting oil. Test fit the bungs to make sure the flanges sit flush against the body of the tank and clean any oil off of the tank. Clean out any metal debris from the inside of the tank.

4. Use a sanding disc to clean the gas tank around the holes that you drilled far enough out that your heat affected zone when welding will not be contaminated. The flange of the tophat bungs included with your fuel sight gauge are 7/8" so keep in mind that you will be cleaning far enough outside that radius to keep from contaminating your weld. We suggest that you also sand the flanges to bright metal as well. The bungs included with our kit have a nice machine finish, but other brands do not.

5. Install the included bungs and tack them in place. Your gas tank wall thickness is in the range of .05" to .0625" or so. The flange of the fuel sight gauge bungs is .125", so you should set your amperage for a fillet weld. We TIG weld these fittings. A useful guide and calculator for necessary amperage for your weld can be found on Miller's website. 

6. Finish weld around each bung. We weld incrementally around each bung to avoid distortion due to overheating the gas tank or bung. Keep in mind that proper amperage needs to be used to assure good weld penetration without burning through the sheet metal of your gas tank.

7. After allowing your welds to cool, pressure test the gas tank. To read our "How To Pressure Test a Tank" article click here. This is a necessary step as any leak needs to be addressed before you line, prep, and paint your gas tank.

8. After lining, prepping, and painting your tank you will install the 90 degree chrome or brass fittings into the welded bungs. With the design of the included bungs, you should have little to no distortion of any threads. If you got the bungs too hot you may have to chase the threads with a 1/8" NPT pipe tap. These are tapered threads so keep this in mind if chasing them. Put some Teflon tape on each 90 degree fitting and tighten each fitting. Do not over-tighten the fittings, but these need to be leak-free and point in the direction necessary for attaching your tubing. Place the included clamps on the included fuel line and then push the tubing onto the 90 degree fittings. Any trimming of the tubing should be done with a tubing cutter or you can use a razor blade. Once your fuel line is in place crimp your clamps or tighten the worm clamps included with your fuel sight gauge kit. Check your work and check for leaks. 

That's it, you should have your new Rullo Custom Cycle Fuel Sight Gauge Kit installed. You'll be looking cool while being able to visually check fuel level. 

-Steve Rullo - Visit us at and check our Knowledge section for other informative articles.

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