Author Topic: Fuel injection systems  (Read 23185 times)

Offline Roger B

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Re: Fuel injection systems
« Reply #135 on: July 23, 2017, 11:20:32 AM »
The next step was to make the pump plunger and injector needle from 2mm and 1.5mm silver steel respectively. They were cut to length end the end of the pump plunger was threaded M2 before hardening. The pump plunger was lapped to 1.98mm diameter and the bearing surface of the needle was lapped to 1.48mm. The 50░ point was ground on the end of the needle as before.
When I tried to grind the shank of the needle down to 1mm diameter the finish was bad and the end snapped off  :( I tried again with the same result  :headscratch:
I looked back to see how I successfully made the first one and what was different.
The solution was as follows:
Harden ~20mm of the 1.5mm silver steel, don't cut to length yet.
Grind and polish the point.
Grind the shank to 1mm diameter with the lathe at 250rpm in reverse and the grinding wheel at ~5000rpm.
Reduce the depth of cut from 0.05mm to 0.025mm.
Feed in at the chuck end and cut towards the point.
Polish the shank.
Lap the bearing surface to 1.48mm and cut to length.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #136 on: July 23, 2017, 12:33:00 PM »
Next I needed to change to milling mode to cut a screwdriver slot in the end of the nozzle so I could insert and remove it.
Whilst in this setup I cut a slot in the end of the operating plunger for a small ball race to run on the cam and cut the slot in the control gear for the piece that will turn the plunger and set the helix position.
I then went back to lathe mode and lapped the bores of the nozzle and pump body.
Next step put it all in the ultrasonic bath to remove the diamond paste residue.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #137 on: August 06, 2017, 04:37:59 PM »
Having removed the contact breaker from the diesel engine I wanted to try the roller follower for the injection pump. The follower housing was held onto the crankcase with a small milling clamp and a steel ruler was used as a return spring. Unfortunately, but not unexpectedly (which is why I did the trial) it tended to run at an angle  ::)

I could either slot the plunger and add some sort of guide pin or key or change the design to a swinging link type follower  :headscratch:

<a href="http://www.youtube.com/watch?v=vjbnAhMha0Q" target="_blank">http://www.youtube.com/watch?v=vjbnAhMha0Q</a>
Best regards

Roger

Offline Brendon M

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Re: Fuel injection systems
« Reply #138 on: August 17, 2017, 09:00:57 AM »
I am up to date again Roger, keep at it :)

I found the procedure for forming the injector needle quite interesting.
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Offline Roger B

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Re: Fuel injection systems
« Reply #139 on: September 03, 2017, 04:46:02 PM »
Thank you Brendon  :)

I made the union and nipple for the injector in the same way as before. This time I drilled the cone in the nozzle a little deeper and filed a flat on the nozzle to allow a couple more threads to engage.

I then ground the helix in the plunger and trimmed it to length, again as previously. The next bit was the tappet to go on the end of the plunger and transmit the rotation from the rack gear. This was sawn and filled from a piece of 4mm square silver steel so I can harden it. Having just purchased a set of edge finders I tried one out to centre the hole in the tappet.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #140 on: September 03, 2017, 05:52:57 PM »
Problem  :( When I assembled the system it would not turn freely and jammed completely in a couple of places  :headscratch: After a series of checks I found that the bore was not concentric with the running surface for the rack gear by ~0.2mm. This was a result of drilling from the other end to give the delivery valve seat a better chance  ::)

OK, start yet another injector pump body with a different machining sequence. This time I turned the spigot for the rack gear and then drilled and reamed the bore. As a further, hopeful, refinement I started with the drill as far into the chuck as it would go and then moved it out in stages as the hole got deeper. The process was the optimum one from my experiment with the floating reamer holder.
Run at 2000rpm
Center drill deep enough to leave a countersink.
Drill 1.85mm
Ream 1.95mm with a controlled feed of 0.08mm per rev.
This seemed to work, the 1.96mm pin gauge passed straight through, the 1.97 mm barely entered. It was also concentric to better than 0.02mm and when reversed and mounted in a collet the run out of the bore was not detectable   :)
Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #141 on: September 03, 2017, 09:13:20 PM »
Quite an improvement in precision  :ThumbsUp:

Hope that you will have much more "luck" with the next test  :)

Offline Roger B

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Re: Fuel injection systems
« Reply #142 on: September 30, 2017, 05:23:28 PM »
Thank you Per  :ThumbsUp:
I lapped the bore as previously and this time it all fitted together and turned without jamming  :) All the bits that had been in contact with diamond lapping paste went in the ultrasonic bath for cleaning and I machined the unions and delivery valve.
I tried to repeat the oil pressure tests that I had done with the previous pump. The much shorter leakage paths were obvious and as it leaked it reached the spill point and collapsed. Maybe it will work, maybe it's a step too far  :headscratch:
I had to slot some of the holes in the mounting plate to get the correct positions of the pump plunger but otherwise it all seemed to fit together  :)
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #143 on: September 30, 2017, 05:32:55 PM »
I tried the horizontal engine with the original fuel pump and injector as a check before I experimented with the new system. It didn't run as well as before  :(  :headscratch: but I was able to test the new injector which worked much  the same as the original.
When I went to install the new pump I noticed that the soldered joint holding the fuel inlet nipple had cracked  ::) The solder hadn't penetrated at all  :( I cleaned the parts and resoldered them, maybe this caused small air leak that upset the first trial. I then installed the helix pump and tried to get it to run, without success  :(
Many problems: The delivery valve leaked so the fuel feed pump would blow past it. A quick clean solved that, but I was not getting any pressure feed from the pump at all. If I took the spring out of the injector it would dribble but no jet/cloud  ::)
I need to recheck that I have phased the rack to the plunger correctly but otherwise back to the drawing board  :headscratch:
« Last Edit: October 12, 2017, 05:21:03 PM by Roger B »
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #144 on: October 11, 2017, 05:33:00 PM »
A bit of a post mortem on the problems  ::)

I had drilled the delivery valve too deep so that there was not enough pressure on the ball  :facepalm: The bore was also too big due to a drawing error. It should have been 3.1mm for a 3 mm ball. I had put 3.2mm on the drawing and the drill I used resulted in a 3.3mm hole. Solution: make a new valve body  :ThumbsUp:

The tip of the plunger was again too small yet it was a tight fit  :headscratch: Problem: the length of Silver Steel I was using was not straight and round. Solution: Try using the pin gauge.

I annealed the end of the gauge, holding it in an old pair of pliers to act as a heat sink, and was then able to thread it. I tried it in the existing pump body using a light machine oil and with a 4.5kg weight it sunk in around 10 seconds. This is a pressure of around 140 Bar / 2000psi. As the gauges cost CHF 10 and will make two plungers I will continue down this route.
« Last Edit: October 12, 2017, 05:21:53 PM by Roger B »
Best regards

Roger