This is just one of multiple ways you can plumb a custom oil tank. I used one of our DIY Oil Tank Kits and decided to do a vertical oil tank, with the return line coming in at the top of the tank. This saves time instead of cutting each piece and making the fittings and bungs, but you can easily do this with some assorted size steel or aluminum tubing and round stock. For an oil tank for a British motorcycle such as a Triumph or BSA, you need to route oil to the top end of the motor from the return line going back to the oil tank. On a stock tank this is done with a 'T' fitting, and that is what we do here. The DIY Oil Tank Kit comes with the plumbing ready to go, or if you make it yourself you just want to use 5/16" ID tubing for the main return with a piece of 1/8" to 3/16"OD tubing for the smaller arm of the 'T', which is where you use oil line to run up to your rocker boxes.
The first step is to decide what type of oil tank you are going to build and where you will locate the filler neck, mounting bungs, return fitting, feed fitting and vent. Once you draw a rough blueprint or mark it on your tank you are ready to begin.
Here I used a drill press and a 1-1/2" metal hole saw to cut the holes needed for the filler neck and the oil feed fitting, both of which were 1-1/2" OD. This would have been easier if I took the time to swap out the machinist's vise on my drill press to a larger one, but I was able to hold it in place while quickly drilling the holes. Use cutting fluid when doing this to extend the life of your drill bit and cut the steel easier.
With the holes drilled, prep the metal for welding with a bit of sand paper to get any rust off and then wiped it down so it was clean and oil-free. Slide the filler neck inside the hole you drilled and tack it in place, do the same with the oil feed bung, then once you are sure they are straight go ahead and weld them all the way around, making sure you get good penetration and you don't leave any pinholes for oil to leak from.
For the oil tank vent, which equalizes pressure inside the tank while oil is returning, we are going to simply weld the vent fitting over the hole in the top, facing it backwards so a piece of oil line can be run towards the rear of the bike to vent.
If we were running the oil return from the bottom of the tank, you use this 'snorkel tube' so that the hot oil returns to the top of the tank, and the cooler oil at the bottom is sucked from the feed fitting. Since I am setting this up to return at the top of the tank I am going to cut the tube shorter and weld it to the fitting.
Then drill a hole in the body of the oil tank where you want the return fitting to be located. Just be sure that it will be high enough to return oil above the actual oil level of the tank. It is nice to locate it so when you look through the fill cap you can visually confirm that there is oil returning to your tank when the bike is running.
Weld the top and bottom to the body of the oil tank before welding the return fitting, this way you can easily rotate the body of the tank and do the finish welding without having to worry about the return tube sticking out.
All that is left is to weld the mounting bungs in place. Here we used two mounting bungs that will match up to two steel bungs that go through the vertical seat post tube on the frame, giving a very secure mounting location.
Now you have a finished oil tank. There are almost limitless possibilities as to what you can come up with, this was just one idea that took an afternoon to make a reality. You can read a complete guide how we mount an oil tank on the motorcycle with very detailed steps and images.