Injector HP Fuel Line - How to Make?

[a64pilot]

Line length really shouldn’t matter. Fuel is not compressible.
I’ve not measured, but am pretty sure that they are not equal length.

[ulpilot45]

All fuel injection lines are the same lengthy and set to a spec by the manufacture it relates to time and volume . Time verses metering how much time it takes to flow thru the line and the amount of time to do it.all calculated by the engine manufacturer. Where it is possible to build your own lines it's better to buy them when possible.

[kmacdonald]

Originally Posted by Wotname

Maybe they are these days - mine don't look swaged but they are old - say 40 years old.

The new common rail diesels use pressures of about 20,000 psi vs 1500 to 4000 in conventional diesels so there may be a difference in construction. I know the common rail line should not be reused if the seal is broken. A new line is called for.

[Wotname]

Originally Posted by jimbunyard

Hope nobody gets their panties in a wad here, but technically soldering or silver-soldering is brazing, i.e. the process of joining two or more pieces of metal together with a filler metal that melts at a lesser temperature than the metal being joined.

It is troublingly common on internet discussions for people with lots of experience to make declarative statements, with probably/usually good reasons for making them, and then stop dead, with no explanation and no information as to how to accomplish the job in the way they deem correct.

For instance, I know there are at least dozens of types of 'silver solder', probably hundreds, not counting those that are the same alloy but produced by different manufacturers. It seems to me that at the very least it would be helpful to include some kind of designation as to what alloy or brand or designation of which product years of experience has taught works best, as well as maybe a brief note regarding technique.
..............

I wasn't going to raise that rabbit hole - brazing - silver soldering - hard solder - soft solder and so on. I am content that I know the differences and also know some of the terms are not technically correct. I'll leave it to others to discuss these things

As for the filler rod - 2%, 5%, 10%, 15%, 20%, 40%, 50% silver - with or with out cadmium, phosphorus, zinc, tin - yep, let others argue the pros and cons

Now about those fluxes

[Wotname]

Originally Posted by jimbunyard

................

But back to the point about the length...imagine that you have two tubes, 1/2" ID, each filled with 7/16" marbles, one ten feet long, the other one foot long. If you push (inject) one more ball into the end of each tube simultaneously, a ball will be ejected from the other end of both simultaneously, regardless of the length.

Thus, I can only come up with two potential reasons for the 'all lines must be the same length' rule (which I always dutifully quote when asked).

The friction in the lines is enough to make a difference due to length (more length=more friction=different pressure), or the different volume in different length lines acts as a kind of accumulator, and allows a slight variation of pressure based on those different volumes, or a combination of both.

Or it could be something I've missed entirely.

It would be interesting if someone familiar with fuel injection theory could actually explain the real reason(s) clearly and conclusively...

Yes that would be good! I agree with your two possible explanations, both might be relevant.

I do observe that some effort has been made to equalise the length on the small marine engines I am familiar with so I guess it could be important - but....

[Wotname]

Originally Posted by Lepke

......
Considering tube cost, I can't see making my own.

Others have also bought up the cost considerations. There seems to be price disconnect between Australia and the USA - going by on-line pricing I've seen.

I don't know the Yanmar price but new unused not branded lines in Oz is $100 plus while similar product in USA is say $25. Big difference!

Sourcing mild steel hydraulic tube may be harder than I thought - at least for a reasonable price. I'll keep looking, no hurry on this project!

Presumably SS is not suitable - work hardens and cracks - no ???????????

[kmacdonald]

OK, let's bring metallurgy into the equation now.

[jimbunyard]

As long as the lines were supported as designed by the engine manufacturer, and I could get the ends affixed properly, I wouldn't have a problem using stainless. If I'm not mistaken, stainless is used as OEM by some common-rail engine manufacturers, due to corrosion problems with plain steel.

The idea that common rail injector lines are a use-once item is, I think, a combination of CYA and profit motive. I recently bought a set of remanufactured, nickel-plated CR lines for 200.00, with cores required. New aftermarket in SS was 400.00. Price for new OEM was 600.00.


https://www.amazon.com/Inline-Tube-L.../dp/B01CPPIR5W

1/4-304 Stainless Steel Brake Line Coil Tube, 20 Ft, Standard Automotive Spec 1/4 OD, .028 Wall Thickness. Fully Annealed. Our 1/4" stainless steel tubing is made from 304 grade (rated at 6000 psi) which is double annealed to allow easy flaring. This can be used with AN and 45 degree double flare fittings. The Rockwell hardness of steel tube is .60 and this stainless is .74 - so it is the softest on the market but still a bit harder than steel tube. Inline tube Stainless Steel Brake Line Coil 1/4" x 20 foot All Inline tube tubing conforms to the following: Wall thickness = .028 (.70mm) Elongation in 2” (50mm) = 14% Yield Strength: 24,656 PSI Tensile Strength: 42,061 PSI Working Pressure: 4,500 PSI Burst Pressure: 17, 900 PSI Hardness (Rockwell 30T Scale): 74. Clean finish inside and out Leak and vibration resistant.

[Wotname]

^^ Thanks JimB, sourcing short lengths of 1/4' and 6mm SS tube certainly appears to be easier than mild steel - at least for the short time I have been looking.

[Compass790]

Originally Posted by jimbunyard

Hope nobody gets their panties in a wad here, but technically soldering or silver-soldering is brazing, i.e. the process of joining two or more pieces of metal together with a filler metal that melts at a lesser temperature than the metal being joined.

It is troublingly common on internet discussions for people with lots of experience to make declarative statements, with probably/usually good reasons for making them, and then stop dead, with no explanation and no information as to how to accomplish the job in the way they deem correct.

For instance, I know there are at least dozens of types of 'silver solder', probably hundreds, not counting those that are the same alloy but produced by different manufacturers. It seems to me that at the very least it would be helpful to include some kind of designation as to what alloy or brand or designation of which product years of experience has taught works best, as well as maybe a brief note regarding technique.

The 'length issue' with injector lines has always been a little mysterious to me. To begin with the OD cannot, by definition, affect the amount of fuel injected, unless it is either so thin that the injection pressure expands it, which to my inexperienced mind would cause it to fail, rather sooner than later, or if the wall was so thick that it increased the length, which would of course mean that the length was what was causing the difference.

But back to the point about the length...imagine that you have two tubes, 1/2" ID, each filled with 7/16" marbles, one ten feet long, the other one foot long. If you push (inject) one more ball into the end of each tube simultaneously, a ball will be ejected from the other end of both simultaneously, regardless of the length.

Thus, I can only come up with two potential reasons for the 'all lines must be the same length' rule (which I always dutifully quote when asked).

The friction in the lines is enough to make a difference due to length (more length=more friction=different pressure), or the different volume in different length lines acts as a kind of accumulator, and allows a slight variation of pressure based on those different volumes, or a combination of both.

Or it could be something I've missed entirely.

It would be interesting if someone familiar with fuel injection theory could actually explain the real reason(s) clearly and conclusively...

Good points you make. I agree with your theory as i cant see small differences in length being critical. The bigger the i.d. the thicker the wall thickness has to be to resist the pressure so I'd be careful to match those or exceed the wall thickness.

[EngNate]

Originally Posted by EngNate

Yes, line length matters, as does I.D. and wall thickness. I'd buy the OEM replacements if performance matters.

Indeed, I say dryly, the line expands under pressure. Sum = The interior volume expands as the pressure rises to the injector opening point, affecting both the amount of fuel delivered and the timing. Diameter, wall thickness, length and material are all part. The relationship is between the expansion and the volume of fuel metered, not the volume of the line. The volume of the line matters too, as the fuel does compress. Very small differences in metering and timing between cylinders will rob the engine of efficiency and produce smoke and soot and foul the affected injectors making it worse and worse. These simple parts have more engineering in them than one might think.

That's my story and I'm st-st-sticking to it. I'd bet my own money that the OP will eventually buy the OEM replacement(s).

I've bought Caterpillar injection lines and for what they cost I could not have paid myself minimum wage to make them

[Compass790]

Originally Posted by EngNate

Indeed, I say dryly, the line expands under pressure. Sum = The interior volume expands as the pressure rises to the injector opening point, affecting both the amount of fuel delivered and the timing. Diameter, wall thickness, length and material are all part. The relationship is between the expansion and the volume of fuel metered, not the volume of the line. The volume of the line matters too, as the fuel does compress. Very small differences in metering and timing between cylinders will rob the engine of efficiency and produce smoke and soot and foul the affected injectors making it worse and worse. These simple parts have more engineering in them than one might think.

That's my story and I'm st-st-sticking to it. I'd bet my own money that the OP will eventually buy the OEM replacement(s).

I've bought Caterpillar injection lines and for what they cost I could not have paid myself minimum wage to make them

I'll take yr bet. How much are you willing to wager?

[kmacdonald]

Originally Posted by EngNate

Indeed, I say dryly, the line expands under pressure. Sum = The interior volume expands as the pressure rises to the injector opening point, affecting both the amount of fuel delivered and the timing. Diameter, wall thickness, length and material are all part. The relationship is between the expansion and the volume of fuel metered, not the volume of the line. The volume of the line matters too, as the fuel does compress. Very small differences in metering and timing between cylinders will rob the engine of efficiency and produce smoke and soot and foul the affected injectors making it worse and worse. These simple parts have more engineering in them than one might think.

That's my story and I'm st-st-sticking to it. I'd bet my own money that the OP will eventually buy the OEM replacement(s).

I've bought Caterpillar injection lines and for what they cost I could not have paid myself minimum wage to make them

I agree. Buy OEM and be done with it. Designing an engine and rebuilding one are two different things.

I guess if he makes his own and there are issues he will know one place to look.

[EngNate]

I win, I come there and you take me on a cruise, you win you come here and I take you. You like to fish?


Keep us posted!

[Compass790]

Yep yr on. Have been to B.C. already & luved it. I'm a hunter- gatherer throwback. Hope ya aint a giant tho as our boat only has 5'10" headroom but whadda I care, I'm going to win!