Commando banjos.

Commandos have banjos and oil pipes 3/8" in diameter. Early Commandos (1969) with central oil tank require 1/2" I.D. hoses. The metal pipes built up from 3/8 to 1/2. I am guessing the increased diameter is a tube that has been soldered on. Correct? I want to remove the extra tube by unsoldering (MAP torch) and pulling them off. Reasons: it is far easier to find 3/8" oil line and 1/2" looks way out of proportion. Is it possible to unsolder the extra tube with out unsoldering the tube from the banjo?

assembled with soft solder. East to remove

You will flow more oil having bigger oil pipe even if it drops down in diameter at the banjo , you might end up with cavitation at the pump , especially when cold .

Shelby-Right said:

You will flow more oil having bigger oil pipe even if it drops down in diameter at the banjo , you might end up with cavitation at the pump , especially when cold .

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True, but insignificant, and I doubt the gear-rotor oil pump will develop sufficient negative pressure pressure to get into the region of cavitation.

So, the OP has nothing to worry regarding his plan.

Slick

I know I wouldn't do this on my T160 , thats why triumph increased the diameter on later T160s , take a look at fluid dynamics there is slower flow around the outer area of the inside diameter of pipe flow and faster flow through the middle if you know what I mean.

Shelby-Right said:

I know I wouldn't do this on my T160 , thats why triumph increased the diameter on later T160s , take a look at fluid dynamics there is slower flow around the outer area of the inside diameter of pipe flow and faster flow through the middle if you know what I mean.

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Yes, I think I know what you mean. I have a doctorate in fluid mechanics. That slower flow you refer to around the outer periphery is called "boundary layer" flow, and is ALWAYS slower than core flow, regardless of pipe diameter.

I stand by my assertion that changing the tube diameter results in an insignificant change in flow, providing the length of the changed section is short relative to the tube diameter. In this regard, short is defined as <10 times the tube diameter. Thus, if the base diameter of the tube, or pipe, is 3/8 inch, then the length of the changed section (the 1/2 inch section) can be up to 3.75 inches before there is a significant change in flow. Significant is defined as >5%, but in practical instances, the change is typically more nearer 2%.

This issue comes up time and time again as many obsess over inducing a severe flow restriction whenever they contemplate introducing something into an oil line. Actually, it matters not if the fluid is oil, fuel, or air.

Let me state the generalized fluid mechanics rule of thumb:

An increase (decrease) in tube diameter, will result in an insignificant (less than 5%) increase (decrease) in flow providing the length of the increased (decreased) section is less than 10 times the base diameter of the tube.

Want data? See note (6) after the data table in:

Slick

Thanks I'm definitely going to up size mine on the T160 (to the later size mid production size ) I notice cavitation on cold day cold start as the oil pressure goes down when the revs go up , viscosity when cold , good when hot , tank screen is clean etc .

The oil pipe from the motor...both tubes...is 3/8".
Then the diameter increases..the hose...to 1/2".
Then necks back down to 3/8 before it enters or leaves the oil tank.
I would really be surprised if that affects oil flow. Why they did it that way is a mystery. After this all commandos were 3/8" all the way.

My worry is that when I melt the solder on the pipe I will also melt the solder where the tube meets the banjo, an inch or less away

Put one end in water, or wet towel .

If anyone is worried about making oil holes smaller just look at the feed hole in the timing crankcase under the oil pipe assembly, it's slightly large than 1/4". I would not make the pipes 1/4" ID all the way but dropping from 1/2" to 3/8" over 1.5" is not going to add much if any to the restriction of the 1/4" on the crankcase entry point.

kommando said:

If anyone is worried about making oil holes smaller just look at the feed hole in the timing crankcase under the oil pipe assembly, it's slightly large than 1/4". I would not make the pipes 1/4" ID all the way but dropping from 1/2" to 3/8" over 1.5" is not going to add much if any to the restriction of the 1/4" on the crankcase entry point.

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Exactly! This reduction in the oil junction block follows the same Law I waxed on above, the reduced section is short, and insignificantly reduces the flow. Fuggettabout it!.

Another factor to consider is the oil pump's appetite for oil..... if the
hose can supply more oil than the pump can move, it matters not if there is a small reduction in the maximum supply potential of the hose!

Slick

Mission accomplished. The pieces soldered on to the oil pipes junction block assembly were easy to remove while the solder on the banjos was tougher stuff. But not impossible. All set to install tomorrow.
My theory is that Norton had a s***load of 1/2" oil line laying around and the grunts were ordered to use it up. So they made 1/2" adapters and soldered them to the components until the oil line was used up.