Fuel Injection Systems Part 2

[Roger B]

Thank you both 

The fixing flange was cut from 2mm thick steel and silver soldered in place. It all seemed to fit so the next step was to mill scallops either side of the body to allow my box spanner to reach the fixing nuts. This design is full of compromises, I am trying to use parts from my first injectors which I know work in a confined space and I reduced the separation between the fixing studs from 16mm to 14mm to gain a bit more space in the cylinder head.

I used an 8mm round ended mill with 0.2mm depth of cut which seemed to work. The last details were finished with a file, often quicker than a milling setup. It fitted and i could tighten the clamping nuts 

Next up is the nozzle. I know I can drill down to 0.2mm in brass, I need to see what I can do in stainless steel  The first trial will be 0.35mm

[Admiral_dk]

Interesting new design    and I see what you mean about lack of space / planning ahead

Per

[Kim]

That is just impressive work, Roger! 
Kim

[Roger B]

Thank you both 

The nozzle was turned to length from some 5mm stainless steel, with a 0.5 x 0.5 mm step to clear the partially threads in the body. This was threaded M5 x 0.5 and checked for fit in the body and then in the cylinder head. This was then spotted and drilled 1.35mm then reamed 1.45 mm ready to drill the nozzle hole. I had decided to start with 0.5mm to reduce the risk. It appeared to be ok, there was a little resistance and then it appeared to break through. The drill looked ok 

The next step was to cut the seating with a D bit I made for the previous experiments. What I didn’t realise was that the tip of the 0.5mm drill had broken off and was still in the hole in the nozzle. This piece then jammed and wrecked the D bit 

[Roger B]

I made a few more unsuccessful experiments with 0.5mm and 0.35mm drills at various speeds up to 5000 rpm on the Proxxon lathe. Back to brass.

I repaired both nozzle drills, the bit are Loctited into the holders so a bit of heat releases them.

Repeating the procedure on a brass nozzle resulted in a problem free 0.35mm hole 

Now I need to make new D bit. This starts as a length of 1.5mm silver steel with a 90° point. The needle then has a 60° point to give close to line contact. Due to historic parts of the design I now need to lap it down to 1.45mm before filling the flat.

[RReid]

More fine and precise and teensy work. 

[Kim]

Bummer about the broken bits. 

Glad you were able to recover.  Sorry the stainless didn't work out either! But now you've learned.  What kind of Stainless are you using?  303?

Kim

[vtsteam]

I like your die holder lap! 

[Roger B]

Thank you all      The material was a piece from the scrap bin, probably similar to 303. I am not sure if the European materials are a direct equivalent 

When the blank was a good fit in the nozzle I used the previously made filling fixture the make a flat to just under half the diameter. The D bit was then hardened and polished in the polishing fixture with a fine diamond file.

I then used the D bit to finish the seating in the nozzle. The next stage was to cut a small step to clear the unfinished thread in the body and thread it M5 x 0.5.

It all fitted together but unfortunately I didn’t allow for the step and cut one thread too many  I don’t think it will affect the sealing of the injector to the cylinder head.

[Admiral_dk]

Bummer about the broken Drill-Bit -> D-Bit

Smart Jig for filing and polishing the D-Bit 

Is it hardned like a filing button ?

Per       

[vtsteam]

I like the D-bit jigs      

[Roger B]

Thank you both 

The jigs are made from  7.98mm diameter silver steel (nominal 8mm), the one for filling was milled down to 4.10mm and the one for polishing to 4.03mm so that the flat on the D bit will not quite reach the centre. Whilst still in the vice both were drilled and tapped for an M2 grubscrew. They were both then hardened.

[Brendon M]

Some impressively fine work, Roger! I still can't get over 0.35mm drills, it seems ridiculous that they actually work. 

[Roger B]

Thank you 

Next up was the needle. A 60° cone was turned on the end of a length of 1.5mm silver steel and the next 15mm was turned down to 1mm in 5mm steps. I have previously done this using a tool post grinder but I wanted to see if it could be simply turned.
The injector body was then lapped with 1 micron diamond paste until a 1.48mm pin gauge just passed through. The needle was then lapped to fit the body and finally the needle tip was lapped into the nozzle.

[RReid]

I'm impressed that you were able to turn such a small a diameter with that much unsupported length hanging out.