Topic: Running smaller oil lines

[Turbogrimace]

I am looking for different ways to clean up the stock oil lines.  I am using an aftermarket bag and currently running a plate with npt fittings and barbs at the engine side.  I was thinking of tapping the stock oil line fittings for and npt fitting.  A lot of people have used this but you have to run a smaller diameter oil line.  Does anyone have any information on this?

I would like to find out if it's going to starve the engine if I go to a smaller diameter line.  If there are any other alternatives, let me know too!

Thanks!

[754]

What size hole in the off engine NPTs ? Should be around 7/16 or 1/2, I am thinking.

 On Amen frame bikes, we would cut the aluminum end off the stock line and weld on AN -8 fittings, then run braided lines to the Amen tank.

 I forget the ID of the stock line, but it is smaller than one would think looking at it..

 The size of lines used on oil coolers should be correct size..

[76CB5WI]

This has been covered but I wanted to leave this line
spec on here for oil line replacement.
Good diameter and tight fit even without crimps just use your
original elbows. CB750 line pressure is only 40 psi or so.
Reducing not recommended.
I got this at
a farm implement dealer.

8GTH 1/2 SAEr6/EN854 400 psi

Its tractor hydraulic  hose black vintage clean look and flexible.
Braided steel fab lines..overkill in my opinion.

[Turbogrimace]

754

Did you weld a barbed end to it or use threading?  Did you use clamps? I was thinking of welding ends to it, that did look a lot cleaner when I saw it on a bike.

[TwoTired]

Some things I know.

1 - Oil supply is related to the life of the engine.
2 - To move more fluid through a pipe you can increase diameter and/or increase the inlet to outlet pressure differential.
3- Since the walls of the pipe offer resistance to fluid flow, longer pipes offer more resistance to flow (can be overcome with larger diameters and/or higher pressure differentials inlet to outlet).
4 - The oil reservoir is vented to the atmosphere.  This is the reference pressure that the system "sees" at all times, engine running or not.

 Case A- Oil line to the oil reservoir from the engine has a mechanical pump making more pressure than atmospheric.  This makes fluid move from engine sump to oil reservoir.  This is a scavenge pump, and if the oil at the inlet screen is deficient, air gets pumped into the reservoir along with whatever oil is available.  If the oil line restricts flow and the pump cannot make enough pressure to increase volume to supply levels, your "dry sump engine" turns into a wet sump, and the oil reservoir level depletes.

 Case B - Oil line from oil reservoir to engine oil pump has atmospheric pressure at the reservoir pushing the oil toward the engine.  The oil pump provides negative pressure to the oil at the pipe outlet.  Restrict this line diameter and the flow volume reduces (unless you somehow increase the pressure differential).  If the oil supply to the oil pump can't keep up with outflow, then the pump cavitates, mixing the air into the oil and making a froth, ...that gets distributed to oil filter and engine bearings.  Frothed oil does not lubricate the engine nearly as well as un-frothed oil.

If you know the worst case (highest) negative pressure that the pipe outlet will see relative to pipe inlet (atmospheric), the highest viscosity fluid that is expected to flow through such pipe, and the diameter of the pipe, you can calculate at what point oil starvation of the engine will occur.

It real life testing, you could simply keep reducing the supply pipe diameter until the engine bearing begin showing failure symptoms, and then go back to the larger supply pipe diameter that Honda supplied.

My advice to you, is to not reduce the oil line inside diameters below that supplied by Honda, unless you are also modifying the oil pumps or the engine oil demand requirements.
But then, I'm conservative that way, as I don't wish to destroy vintage engines unnecessarily.

[Turbogrimace]

I understand the flow dynamics, but I was just curious what the tolerance was for smaller lines.  I know a lot of people are running them, but I dont know a lot of people who have run them on high performance engines or if they've paid attention to any increase in wear.

I'd like to use the stock oil line fittings on the engine side and maintain the stock line ID, but I wanted a line that looked less like an old birds nest and would hook up to my aftermarket tank.  I was thinking of threading the outside of the oil line fittings and slapping a female npt on there.  THat would allow me to keep the ID of the stock line.  I'm going to swing by a hydraulic line shop this weekend and see what they can do. 

Thanks a lot for the info guys.