20 cc Horizontal 2 Stroke Diesel

[Roger B]

Thank you again Per.

I made a cover for the cooling tank to reduce the splashing. The large hole was made with a Conecut which luckily also ended up with a nice profile, possibly due to the piece of wood I was using as a backing.

I than made a larger bore exhaust using 14mm bore plumbing fittings. One elbow was annealed and shaped to match the existing exhaust flange. It seems to run better than before but is still mostly four stroking. If I lean off the mixture any more it just stops. I also tried an extension on the exhaust pipe but I don't think that it made any real difference.

<a href="https://www.youtube.com/watch?v=xRUs5ny1NRg" target="_blank">http://www.youtube.com/watch?v=xRUs5ny1NRg</a>

[Admiral_dk]

It sound more "natural" to me now - but we can agree that it is not a fast runner in it's current state.

[Brendon M]

Roger, I've been away from the forum for a while, and I see you've got your engine running. Congratulations!

For what it's worth, the second video sounded like a small petrol 2 stroke engine.... Albeit using mechanical injection

[Roger B]

 Hi Brendon, This is just running as a two stroke petrol engine to check the crankcase compression and porting. I still need to make the diesel cylinder head and finish the injection system before the real diesel trials begin   

[Roger B]

The next step is to make the diesel cylinder head. This is another piece of cast iron from the bar used to make the cylinder. The combustion chamber was cut to depth with a 10mm endmill using my depth gauge held to the side of the tailstock.
When I removed the petrol cylinder head from the engine to check the fit of the new head I was surprised to find oil in the combustion chamber  My lubrication system is obviously adequate.
The gap between the head and the cylinder at TDC was around 0.3 mm so I should be able to set a suitable bumping clearance with a 1mm thick gasket.
I then turned the boss where the injector will fit on the top of the head and checked that the injector would just reach into the combustion chamber.

[Roger B]

The cylinder head cover was made from a slice of 50mm bar out of the goodie box. This was turned down to 3mm thick using some spacers on the jaws and drilled 10mm for the injector mounting boss. I had to move to the next set of steps on the jaws to allow clearance for the drill. The piece was then mounted on a slitting saw arbour to turn the outside down to 45mm. The shaft of the arbour doesn't quite fit through the chuck but by taking light cuts the overhang was not a problem.

[Stuart]

Roger

I don’t post very often but be very careful if you get lube oil on top of the piston , it just could start to diesel on the lube oil not the fuel

I have once seen it on a full size engine and I don’t what to see it again ,they shut off the fuel but it just kept going full blown runaway

Followed trials and tribulations in getting this far best of luck with the outcome

[Roger B]

Thank you for the thoughts Stuart. I am aware of the risks with, especially two stroke, diesels. The air intake on this one is a 10mm hole that is conveniently placed to be blocked with a thumb if nothing else will stop it. The exhaust port is also at the bottom of the cylinder to allow excess fuel and oil to drain out (originally as a precaution against hydraulic locking).
The deposit in the cylinder head was more like grease and had to wiped out. I guess that it is some form of degraded oil (I use cheap supermarket multigrade).

Back in the early 80s I had a hired Mercury Capri in the States that was hard to stop. In drive it would 'diesel' for 30secs - 1 minute. If I put it in neutral it would probably have still been running in the morning 

[Roger B]

A circular water cooling passage was milled in the head using a 3mm 3 flute mill down to 6mm depth and finishing with ball end cutter. I wanted to drill the holes in the cover together with the head and the easiest way was to start with one of the injector fixing stud holes so I could put a screw in and fix the two parts together.
Due to lack of clearance between the head and the chuck the holes were not drilled completely through. I wanted to drill out most of the water passages, but unfortunately the second hole broke through into the first one. The passage were milled 10 mm deep with a 3 flute mill and then cut through into the circular passage.

[Roger B]

The cylinder head was then taken over to the bench drill for the hole to be drilled right through. It was then put the other way up in the mill and re indexed at the 0° hole. The rest of the water passages were then milled out. The transition between the water passages was smoothed with a ball cutter in the Proxxon and some riffler files. I need to make some studs and then back to the injection system.

[Roger B]

I found that the injector fixing holes didn't quite line up with the head  The bracket may have moved slightly during silver soldering as both holes were offset the same way from the center. I moved them ~0.3 mm across with and end mill and then counterbored again.
Back in lathe mode I radiused the cylinder head cover using a 2mm radiusing milling cutter as a lathe tool. The flat was luckily (or maybe by design) at the right angle to the cutting edges 
I then countersunk the injector nozzle hole for a sealing O ring. The O ring is 5mm id, 1.5mm section so I choose a large end diameter of 8mm. The injector studs are from all thread and I made a few M3 5mm AF brass nuts then put it together.

The 0.35mm nozzle hole in the injector is enough to destroy the compression at hand turning speed and whistles quite well. With the needle in the injector I can't turn it over compression by gripping the flywheel 

[Jo]

You are doing well Roger 

I am equally pleased that my old Hobbymat is still performing for you 

Jo

[Admiral_dk]

The 0.35mm nozzle hole in the injector is enough to destroy the compression at hand turning speed and whistles quite well. With the needle in the injector I can't turn it over compression by gripping the flywheel 

It sounds like you got this part solved to running quality - another tick on the list 

[Roger B]

Thank you both  The Hobbymat is doing fine 

When I tried the fuel injection system in place it clashed with the cylinder oil feed so I made a right angle fitting to give more clearance. I made a holding block out of hexagonal steel bar to allow me to turn the head on the bolt part and then to index the hexagon.

[Roger B]

I am also working on reduce the size of the injection pump (over on the fuel injection thread) but even so clearance was still limited so I thinned the head on the bolt by 1mm and counterbored the block by 1mm to give a little more space around the delivery valve.