SS injector supply lines, an upcoming DIY attempt

[gnavs]

The fact that it's getting harder and harder to find new injector lines, or at least a decent used set, is starting to bug me. 
My background is instrumentation and as such I've bent enough SS tubing to feel comfortable about recreating a set but the issue now becomes the sealing end.  I've only ever used Swagelok compression fittings in industrial applications (supplied air lines, methanol injection lines etc) at relatively low pressures, at least compared to what our injection pumps put out.  I seem to remember reading somewhere that we'd need to be prepared to see operating pressures in excess of 1500 PSI, can anyone confirm this? 
Flared connections will undoubtedly be better at handling higher pressure but I'm not sure if you can create a good sealing flare with SS tubing. 
Anyways, I wanted to start gathering information, from you guys as well as some of the tubing suppliers like Swagelok, McMaster Car etc., and seriously look at making a set of lines myself this summer.
So, on to the questions.

- What is the operating pressure between IP and injector?
- Does anyone have experience with flaring SS lines?
- Can I get away with compression fittings?
- Does anybody know the thread size on the IP and injectors?
- What is the size of the standard injection lines? (metric something or other I'm assuming)

Feel free to add your thoughts.

TIA!

[Luckypabst]

   
155 bar = 2,248.08493 pounds per square inch

Don't forget to add in a safety factor as well... No telling what value the Bosch engineers used for this.

You may have cracking issues when flaring stainless. How about billet machined ends that are then brazed to the formed lines?

Chris

[Vincent Waldon]

If you track down the two original SAE papers on the development of the engine there are some details on the design considerations for the lines.  The three I kinda remember are:

- they are made of a special tubing with extra thick walls to handle the actual pressures involved.. per Chris' post
- they are all the exact same length... and IIRC a specific tuned length IIRC. 
- they are bent in that specific shape to (a) keep 'em the same length and (b) allow for some physical deformation due to vibration and, once again, the high pressures involved

[rs899]

I just ordered a set from, ahem, Prothe for $14.  I'll let you know if they are any good ( and carry some leaky Boschs in my trunk)

[monomer]

Stainless wouldn't work. Materials not suited for it. You'll also need a seamless tube, no annealing from welding.

I think there's enough to be found in junkyards....

[theman53]

IIRC the threads are m12-1.5 but don't quote me. Check the FAQ I am almost positive it was in there. Unless the injectors are more than spec of 155 or they got clogged or something the line will only ever see 155bar as the injector should open there and relieve the pressure.

[92EcoDiesel Jetta]

I am sure you can make your own stainless steel lines and get them to work.  But your effort involved may be huge. That effort  may be better spent fixing the leak in your Bosch lines. If they are not cracked, the grooves in the flared ends that is causing them to leak can be sanded out by hand. I have been successful on everyone I did using 400 grit wet dry paper with a twisting motion. I may make a cutter to make the  job easier.

[ktzdsl]

Thought I saw brand new lines on sale on ebay, about $75.00

[rodpaslow]

I've got three good ones sitting in my Garage, I'd be willing to send to anyone who wants them - for shipping cost. Trying to clean out my garage...
(the forth one (cyl #3) has a small leak)

[gnavs]

I see a lot of 1.6 lines on ebay but none for AAZ's, can they be made to work? 
Some points to consider, and I'm just spitballing.
I have enough experience bending tube that I can confidently recreate the factory lines.  The lengths and bends would be exact so any sort of "calibration" due to differences in line lengths should be negated.  Although, regardless of the line length you'd think that since you're moving a non-compressible fluid through the line and, providing there are no air bubbles, should get injection and pressure when required.  This is taking into assumption the SS line itself won't stretch and warp with each stroke.

According to McMaster Carr's website, 316 SS seamless instrumentation tubing is good up to 6300 PSI, depending on the ID and wall thickness.  This seems well within the range of expected fuel pressure.  There are a few options as far as wall thickness goes, up to 2mm, but even the 1mm thick walls are rated to 5100 PSI. 

What's the reason SS isn't suited for diesel fuel? Is there something I'm missing?

The issue at the moment seems to be the sealing end itself.  Compression fittings should handle the pressure but I'm not sure if prolonged vibration could have a negative effect.  The other option is flaring the SS tubing, which may have its own challenges.  I've stumbled upon a few threads in muscle car and speedboat forums where this topic has come up.  The key points to flaring SS tubing are
- cut the tubing with a hacksaw, not a tubing cutter as this will harden the end you're trying to flare
- chamfer the hell out of the inside
- scuff up the outside with a wire brush
- use a drop of oil on the flaring tool

Even then I'm sure this would take a few tries before getting it right, hell it took me 3 or 4 tries to get my brake line flares perfect.

I'm still optimistic on this, I don't see why it can't be done but maybe I need to fail miserably before I learn any better.  Seems like that's the best way.

[Smokey Eddy]

I would be very interested in you doing this semi-commercially as one of my lines has sprouted a pin hole leak and a machine shop wanted $100+ PER LINE...

I just had a browse of the lines on ebay as gnavs mentioned and am surprised at the prices for being new un-used OEM lines flared with nuts and everything ($50-$70 + ~$10 shipping). I have a 1.6 pump on an AAZ and I have been using 1.6 lines. They never really sealed perfectly and they required some lets call it "tooling" to get them to line up correctly. The seller seems pretty focused on making sure you have the exact lines for the application. Cars being made in different countries apparently makes a difference?

I don't mean to hijack the thread here so anyone who can answer me please pm me; can I just buy the 1.6 NA lines for $20 less or will i need to man handle the lines to fit regardless? I seem to recall i had to bend them a tiny bit to make them fit perfectly and if its just a slight alteration that's not exactly detrimental to the lines is it? My line has started to leak at a place where it has never been bent (very odd).

Lastly, OP, do you think you could make lines for less than $50? I'm sure you would have several folks on here interested if you could supply new lines using your set as a template.
I'd also rather give a fellow vwdiesel.net user my $50 over someone on Ebay.

[bajacalal]

Although, regardless of the line length you'd think that since you're moving a non-compressible fluid through the line and, providing there are no air bubbles, should get injection and pressure when required.

That pressure "wave" takes time to travel through the line. Even though the fluid is not compressible, it takes a few milliseconds for the pressure to reach the injectors once the pressure is delivered on the injection pump side. Milliseconds can translate to significant differences in degrees of timing when the engine is actually running.

[Smokey Eddy]

I've got three good ones sitting in my Garage, I'd be willing to send to anyone who wants them - for shipping cost. Trying to clean out my garage...
(the forth one (cyl #3) has a small leak)

Dang thats the same one that leaks on my set.

If the lines are not originally stainless steel then what are they made of?

[gnavs]

That pressure "wave" takes time to travel through the line. Even though the fluid is not compressible, it takes a few milliseconds for the pressure to reach the injectors once the pressure is delivered on the injection pump side. Milliseconds can translate to significant differences in degrees of timing when the engine is actually running.

That's exactly what I figured.  The longer the line the longer that wave will take to reach the destination but I would imagine as long as I kept the new lines relatively close to the original length that "reaction time" would be negligible.  Either way, like I said, I'm comfortable enough with bending tubing to make them the same +- a couple mm.  Should even be able to use the OEM injector line clamp holder thingies.

Regarding price, at this point I'm not sure.  The original set will likely be a bit more than any future ones simply because of the R &D (or more accurately trial and error) that will go into it.  Parts can be ordered via McMaster Carr, and if I can get away with compression fittings rather than flared connections it'll make things even easier.  If I do go ahead and start making them for fellow vwdiesel.net folks I can order the right stuff in bulk and hopefully keep costs down.  Extra bonus if I can source the stuff from my instrumentation buddies (lots of scrap tubing and fittings "go missing" in that industry) but that all seems to be Imperial stuff.
So far, according again to McMaster Carr, a 2m length of 316SS tubing is around $100 for use with instrumentation (compression) fittings and a bit cheaper to go with tubing that would end up being flared.  What's cheaper, messing around trying to flare SS tubing or spending the extra dough for compression fittings?   

The thing I need to confirm now is the nut size on both pump and injector ends.  I'll be up working on my car again this weekend (hopefully wrapping up exhaust and taking it for a brisk drive) so I'll try and get some measurements on the stock stuff and go from there. 

[gnavs]

Tools for this project also need to be taken into consideration. 
Muthaflippin tube benders are several hundred $$, and a good flare tool runs the same.  Time to hit up kijiji...