Lucas Mechanical PI System Model

[55fairlane]

So continuing with the body. The inlet and outlet holes were drilled and tapped M5x0.5 and 2mm fixing holes were drilled in the end covers. These were then spotted through to the body and tapped M2. 1.2mm drain holes were drilled in each end cover to release any fuel that leaks past the metering system.

The control end cover required some thought. For the initial tests a simple screw adjuster is required but this must be convertible to a quick acting lever for engine trials. It is also important that the hole in the end cover is less than 2mm diameter to minimise the chance of the adjuster coming loose and the metering shuttle shooting out followed by a jet of fuel at 7 bar. I finally decided to press in a 4mm diameter bronze bush with a 1.5mm hole for the adjusting pin and an M3 thread for adjusting. Even if it becomes unscrewed the shuttle will only reach a maximum stroke of 2.5mm. For the final design I can press the bush back out and replace it with something else.

The drive end is drilled and reamed 6mm for a 4 mm bore bronze bush. Unfortunately the cover pulled out of the spring collet as the drill broke through. I was able to finish this off in the 4 jaw SC chuck as the concentricity requirement are not great.

For the next version I will develop an alternative machining sequence for the covers.

Man o live look at you go! This will be awesome when you get it all straightened out! Really enjoying the build

[Admiral_dk]

Thank you Dave. I'm doing fine now - but it took some time to get back to a decent speed off walking, biking etc. ....
And I completely agree on the 'Bouncing back time grows with age' thing - rather anoying .... isn't it 

Per       

[Roger B]

Hello Per, I’m glad you feel up to contributing again   

Here are the current drawings including the concept for a 6 cylinder version. I have attached the .DWG if anyone is interested (it is also a useful offsite backup).

[Roger B]

The stroke adjuster bush is turned from a offcut of bearing bronze. I just drilled the 1.5mm hole before pressing it in place as I think it would have collapsed if I had already opened it out to M3.

The drive end bush was turned from the same material and after being pressed in place it was reamed 4mm again. As the alignment was not perfect I used the floating reamer holder to avoid a tapered/bell mouthed bore.

The adjuster bush was then drilled and taped M3 for the stroke adjusting screw.

[Admiral_dk]

Slightly of topic - but does that Depth-Stop (in the second to last picture) work well for you Roger ...?

Every time I try any kind of stop mounted on the Drill-bit itself - I always end up in trouble .... 

I ask as it worries me a bit considering the precision required in this build ....

Per       

[Roger B]

Per, I have used this technique successfully on drills and end mills (generally when cutting the delivery valve seats on the 'normal' style injection pumps).

The bush/collar has to be the same size as the drill/end mill and the screw neeeds to be on a land.

I also use it as a depth guide rather than a stop so there is no real force applied.

[Admiral_dk]

Good to hear Roger .... it was just my immediate thought when I saw the picture 

Per       

[Roger B]

The next step was to machine the O ring grooves for the seal between the sleeve and the body.

The body was put back in the 4 jaw SC chuck in the same position as when it was bored. A quick check showed acceptable run out so I didn’t have to swap to the 4 jaw independent chuck.


<a href="https://www.youtube.com/watch?v=_d1Xz4tdWHs" target="_blank">http://www.youtube.com/watch?v=_d1Xz4tdWHs</a>



The groove was then cut with tool I had made earlier from a Proxxon boring bar. The groove in the sleeve was cut with the Applitec grooving tool and the other end was chamfered to allow entry into the body O ring.

The stroke adjusting hand wheel is a knurled aluminium disc, threaded M3 and tapped M1.6 for a grubscrew.

[Roger B]

The shaft is a piece of M3 allthread turned down to 1.4mm at one end for the stop pin. The adjuster was then assembled and the thread was parted off to give the required 3 mm maximum protrusion.

I would like to have a flat-bottomed hole for the delivery valve seat. For the helix pumps I use a 4.5mm end mill but I don’t have a 3.2mm end mill and so I will try using a 3.2mm drill with the end cut off square. Hopefully this will be adequate for brass.

I decided to make a trial using a piece of 7mm brass hex as will be used for the final version. The first hole was 2mm rather than 1.8mm and then ream to 2mm (as I would normally do for the ‘real’ part). It would have been better to start with the 3.2mm hole as the drill tended to snatch. The modified drill seamed to cut without chatter and the surface didn’t look bad, although difficult to photograph.

[Roger B]

I need to make a few trials with the fuel feed pump. There are various options for materials and construction. The initial attempt will be with brass gears in an aluminium body. I have used Delrin gears in my water pumps and steel gears in the Junkers oil pump. Delrin may be ok in Alkylate fuel but I think I prefer brass over steel as the lubricating properties are not so good.

I cut a couple of bits of aluminium for the body and cover. The main bearing will be an Oilite bush but as the ones I have are a little short I turned the flange off one to act as an extension using a 4mm tapered mandrel.

The gears as supplied have a small chamfer on the outside of the teeth which would cause additional leakage. I faced this off and then parted off 5mm slices.

To fix the driver gear to the shaft I lightly knurled the last 3mm of the shaft and then pushed it into the gear. It seems to be firm and runs reasonably truly.

Schillings suggested either silver soldering, with the potential problem of cleaning off any excess, or using coarse diamond dust to lock the two together.

[Roger B]

Next the body and cover were milled to size and the sealing face of the cover was milled flat (it was just the extruded surface). The bores for the shafts were drilled 3.8mm then reamed 4mm using the floating reamer holder. The separation of 12mm was set using the mill leadscrew.

The mesh of the gears seems a little too loose but I will continue with this for the moment.

[Roger B]

The ports were drilled 5mm with a separation of 11mm. I think they may be better with 10mm separation but once again I will continue with this. The inlet and outlet were drilled 4.5mm and taped M5 x 0.5.

To bore the cavities I mounted a piece of silver steel in a 6mm MT2 collet in the headstock and turned the end down to 4mm to fit the pump body. The body was then clamped to the faceplate and the bores were roughed out with a 12mm end mill.

Problem, the bores were over size     

I had used this technique before without problems but I realised that the previous pump had 6mm bores so the non-centre cutting end mill was not a problem. With 4mm bores it was being pushed off centre, hence the oversize bores     Start again