20cc Four Stroke Diesel

[Roger B]

Thank you Craig       I think that the challenges you faced with the Otto Langren are much the same as I face with the diesel, you can’t scale nature or tolerances and you have to work out which details are critical.

Before I cut any more metal it was time for a quick sanity check, I removed all the two stroke parts from the engine and bagged them up for later experiments. The cylinder block was then rested in place and the positions of the camshaft drive and injection pump were confirmed. Finally I checked the position of the top of the conrod at TDC which was 12.3mm as opposed to 12mm on the drawing.

The cylinder head fixing holes were drilled 4mm and the valve guide holes were drilled 7.9mm and reamed to 8mm. The fixing holes lined up with M4 screws

Next up I have to work out the best way to clamp the cylinder block for boring the 16mm camshaft tunnel and sort out the lubrication system for non 2 stroke use.

[Roger B]

The set up to bore the camshaft tunnel was not easy  The 50mm width of the block is the same as the quill stroke on the mill, the block was to big to fit on the faceplate and the M6 T nuts that I had would not fit the milling table. In the end I milled the M6 T nuts down to fit and used the mill. I started off with stub, standard and then long 2.5mm drills, dropping the milling head 1mm to ensure breakthrough. This was followed with a 13.5mm drill, again having to drop the head to get a breakthrough.
To get the full 50mm stroke with the boring head I found an additional sleeve for the clamp bolt, the usual one only allowed 40mm. Previously I had purchased a couple of cheap 8mm insert boring bars so I could cut them down to sensible lengths to reduce chatter.
The first cut seemed ok but this will take a little while at 0.15- 0.2mm depth of cut. I have 16mm reamer to finish off.

[Kim]

Wow... you had to make a lot of 'tool adjustments' to get this one made.  But you found a way to get 'er done!
Enjoying following along, Roger! 

I didn't follow the thing with the 50mm (vs 40mm) sleeve and clamp bolt thing.  What does the sleeve do that allows you more stroke length? Is it a Proxon specific thing?  Or am I just not understanding in general?

Kim

[Roger B]

Thank you 

Its a Proxxon thing, a nut that fits the drawbar thread won't pass the top of the quill so it needs a spacer. I should really make a 55mm long spacer next time I am in lathe mode.

[Kim]

Ah!  I get it now.  Thanks for the explanation, Roger.  Makes perfect sense now. 

Kim

[Roger B]

We went off for a while to enjoy some warmer weather and sun in southern Switzerland  Now back to some engine making. The camshaft tunnel was bored out to 15.8mm and then reamed to 16mm. The next step was the bores for the cam followers. these were drilled out to 11.5mm and then reamed to 1mm. Finally I milled a 16mm pocket so I could have a chance to press the bushings in place. Just a few more holes to go 

[RReid]

What a beautiful sunset shot! Even prettier than your engine work, which is pretty darn pretty. 

[Roger B]

Thank you Ron  Ascona is always a beautiful place however the mist over the lower part of the lake made that sunset special, some of the other pictures almost look like posters.

I have decided to keep the oil pump feed to the crankshaft bearings and will run a low oil level in the crankcase. This will keep the camshaft lubricated via a 4mm drilled passage. The previous crankcase drain will go directly to the inlet of the oil pump.

Having finished the camshaft tunnel I put the pieces together with a temporary shaft to check the chain centres. It is a little slacker than I would like, but not a real problem as the lower pass is the tension side. There is a little interference between the chain links and the oil pump body which can be easily solved.

The camshaft bearing supports were turned from a dog end of 30mm diameter aluminium. A piece of 10mm silver steel was a good running fit so all seems to have remained concentric and parallel.

Next up is the fixing holes for the bearing supports and some water connections for the cylinder body.

[Roger B]

The camshaft bearing supports were set up in the Proxxon RT to drill the fixing holes. The holes were then spotted through to the cylinder block and tapped M3. The fixings for the cooling water were drilled and tapped M8x1. Unfortunately I picked the 7.5mm drill rather that the 7mm so the thread depth is limited  but it will still hold.

The bushes were then pressed into the bearing supports and faced off to length. A quick trial assembly showed enough clearance and the cam lobes were fairly central. A little off centre is good as it forces rotation and even wear 

[Roger B]

The next step was to make the camshaft sprocket fixing and fine adjustment. I was prepared to mount the sprocket in the 4 jaw independent chuck to open out the bore but a quick trial in the 3 jaw was true enough, no visible run out, so I used that. I drilled 9.5mm and again no visible run out so I opened out to 9.8mm and then reamed 10mm. The jaws were changed to the external (???) set and the sprocket boss was thinned down. A bush was then turned from a dog end of mildish steel and parted off. The 2mm keyway was cut using my bench drill as a press and the bush was then moved to the Proxxon drill for drilling and taping 2mm for the grub screw. If there is a key I prefer to seat the grubscrew on that as it does not mark the shaft. The bushing was then transferred to the RT to drill the ends of the adjustment slots 2mm.

[Roger B]

The sprocket was then drilled and tapped M2 with the RT in the same position. The RT was moved to the Proxxon mill, centred, and the slots were milled with a 2mm endmill at 11 000 rpm in 0.5mm steps. The trial assembly seems to work and will allow easy setting of the cam timing. I now need to make a similar bush for the injection pump cam and mill some keyways in the camshaft. The cams will be fixed to the shaft with Loctite.

[Roger B]

A little bit more on this. The tappet bushes were turned and reamed from bearing bronze and as they are deeply recessed I made a mandrel for pressing them in place. The injection timing adjuster was made in a similar way to the camshaft one except the slots were made completely in the Proxxon mill rather than starting in the drill and moving to the mill.

[Roger B]

The last picture of the injection cam drive and a start on the tappets. These are made from 10mm silver steel with the camshaft end carefully polished with a fine diamond file and the pushrod hole drilled 6mm. These will then be hardened and polished again.

[Roger B]

With the Hobbymat back in milling mode I started on the injector seating in the head. It was clamped at 30° and centred on the bore centre pop. The seating was machined with a 14mm endmill in 1mm steps, hoping my drawing and calculations were correct. The injector hole was drilled from above and arrived almost on centre on the lower face.

The injector hole was opened out to 5mm followed by an 8mm bore for the O ring and a 10mm bore to clear the injector body. A quick trial fit suggests that the calculations were correct. The picture is with the sealing O ring uncompressed. It should protrude around 0.5mm more.

[Roger B]

I'm still doing some bits on this one. The tappets were turned from 10mm silver steel, hardened and polished. The ports and pushrod holes were drilled in the cylinder head and the block and head were cleaned in the ultrasonic bath. Next, I think, will be the valves and guides.