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The best shape is a tall vertical cylinder to de-aerate (let the bubbles come out of suspension) and make the longest path back to the feed outlet. This is hard to conceal, though (duh).
If you can weld, aluminum tubing is fairly cheap in common sizes. 10” tall × 4” OD (1/8” wall) holds 2 qts. + some air space (needed). I'd rather see 3 qts. + air space. |
Several sources made a roughly triangular aluminum tank (for the T120?) that fits nicely behind the post but narrow enough in the front to allow carb clearance, you see them used on eBay time to time. Shown here are two views of a tank sold by WebCo for the unit Triumph B range 650 twin. Click either picture for a larger view. |
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If you have a space problem to the wheel, a better shape (but harder to build) is a really big radius tube cut lengthwise into a 1/2-round and closed off with a flat plate. Width = diameter, depth (front to back) = radius. For example: 8” diameter (1/8” wall) means 8” wide, 4” deep, 10” tall holds 236” or about 4.1 quarts, plenty of room for oil and outlet for big case breather hose. Could also have space to neatly hold battery, spares, tools, electrical parts. |
Attractive but more complex shape using both sections cut from 6” (or ?) tube, 1” tubes and flat plate. Front curve is less than full diameter to angle sides away with smooth transition - angle depends on desired width, etc. Rear curved inlet is for tire clearance.
Even more complex with nose clearanced for frame tube intrusion, but still common shapes. Click the picture to see a larger view.
If you're going to make it look seamless (grind and polish welds) use at least 3/16” wall.
My welder suggests sides only, tacking 1st to make sure it fits the chassis. Top and bottom can be thick to accept threads or you can buy threaded bungs to weld in (Moroso).
Extra bungs on top and bottom to accept lord mounts makes it cleaner and helps with vibration. Alt is ears or loops for surgical tubing - works well but not pretty and must be tensioned. |
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Drain must be lowest, typically back left corner. Don't use the feed outlet as a drain, or it will pick up sludge - should be a stand-pipe 1/2” off floor minimum.
I use big fittings for all lines (3/8-27 NPT) and reduce as needed.
Vent and inlet go in as high as possible, can enter from bottom (cleaner looking) but then must be extended above max oil level with vertical pipe - subject to vibration fracture and must be very strong and secured to wall near top. |
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