Mc Donald Model tractor

One flywheel completed and as you can see it is heavy and should give plenty of momentum to the engine and hopefully help it to run slowly. I now have to go back to the injector cam and think that through. I was pleased to hear that there is a little flexibility in the actual timing of the injected fuel. I have two drawings of the system and think that one may be a later development but as I can’t take the full size tractor apart I will have to choose the one that suits me! The one I originally designed allows the bob weights to move the eccentric via two linkage arms thus giving and advance/ retard but keeping the ‘ stroke’ constant. The fork alters the quantity of fuel to be injected but would slightly alter the timing as there is gap between contact of the ram on the eccentric and the fuel piston. The wedge shape on the Lanz avoids this. As these engines will run in the reverse direction ( more by accident than choice) does the governor advance the injection point before top dead centre? More thinking required!

Fred

A hot bulb type engine following the Akroyd Stuart design injects the fuel very early, around 150° before TDC, to allow for vaporisation. As the compression ratio increases and the engine moves towards Diesel's design the injection point moves nearer to TDC. The firing point on a hot bulb engine is more dependant on the cylinder head design than on the point of injection.

As long as the injection system is fairly symmetrical the engine will happily run in both directions. Some full size injection pump cams are deliberately asymmetrical to avoid the possibilty of starting in the wrong direction.

Thanks for the information Roger all very useful. I forgot to mention that the button on the front of the flywheel is the starting handle that springs back into the position shown when not in use.

Fred.

The photographs show progress on the governor. I still have to add the spring adjusters and test to see what speed the cast iron weights throw out to the outer limits. The eccentric is made from bronze and will have a steel eccentric sleeve/ rod when it is made. Having studied the injector pump arrangements on the Lanz I now understand how it works - the outer eccentric gives the pump stroke and the inner concentric one gives the advance/ retard but I have made mine as shown on one of the sets of drawings for the Mc Donald. If I find after test this does not work I will have to change the design. The reason for choosing this is because there is very little room for two eccentrics and there are less parts to make! The next part to make is the injector pump.

Fred.

The photo shows progress this week and it doesn’t look like very much! It’s what you can’t see that has taken the time as it all happens behind the bob weights. I have made and fitted the cover and added various parts.The injector plunger that activates the pump can be seen protruding from the the top and on the left is the arm that operates the oil pump. Further to the left is the inspection hatch that enables the governor springs can be adjusted. Having drawn all these parts they were then 3D printed to give an idea of the full size model parts. The drawing of the parts on the screen gives a false impression of size but having them in your hand is reality. The injector pump and valves will be the next part to be made as weather condition have halted any attempt to make castings ( we work in the open air).
Just a few facts on our weather that may interest you - parts of the east coast of Australia has been hit by a band of very heavy rain but fortunately most of it has missed our area. One Queensland river rose 25 metres, another place had 700 mm in one day and we had hot steamy nights with 27C being recorded at 3.0am! We are looking forward to cooler and drier times.

Fred.

This is the injector pump with the cover removed to show what is happening inside. The brass fittings are one way valves that allow fuel in from the tank and then pumped out to the injector nozzle. As the cylinder is almost horizontal gravity is used to seat the ball valves with small 12 BA pins used to prevent them from “ jumping” to far off the seat similar to the check valves used on model steam locomotives.The handle on the right controls the amount of fuel being pumped to the injector and is connected by levers to the drivers end of the tractor. The knurled part holds an “O” ring in place to help form a seal between the 1/8” piston and cast iron cylinder. I now have to start to think about the cylinder head and that will be a really interesting part to design and make but that for next week!

Fred.

​​​​. The

I continue to be amazed

MichaelG.

That's a neat metering solution.. ..still watching with interest, thanks for posting so much of the detail..

Thanks for your comments. After all this time and effort there is no guarantee that it’s going to work but it’s good fun trying and a great learning process.

Fred.

These are the 3D drawings of the cylinder head with the injector on the top and the hot bulb on the under side. The top photo shows the hot bulb and special peg spanned and the lower part of the combustion chamber all made from steel.I may need to experiment with more hot tubes of various thicknesses and lengths but will have to wait until the rest of the engine is made to test what will actually work. The match box gives some idea of scale. The next stage is to make 3D patterns for the main part of the head and then cast them in aluminium.

Fred

Still following along and enjoying

Is there room to fit an automotive diesel glowplug in the combustion chamber for the first trials? It could remove some of the uncertainty as you know it will be hot enough to ignite so you can concentrate on the fuel injection.

Good Day Roger
Thanks for your comments. On the full size tractor there is a place for a plug ( glow or spark) and I have incorporated this in my model and is the hole on the left hand side of the cylinder head. I was told these were used for the starting process in places where the climate is cooler and it is harder to keep the bulb hot. I can fit a 1/4 x 32 commercial glow plug and may use that for initial testing.

Fred

This photograph shows progress so far on the cylinder head with the 3D printer pattern on the right and the real part on the left. The larger of the two holes on the front is for the decompressor valve and the hole below is for the escaping gas. The recess on the left is for a glow plug and yes this was fitted to the full-size tractor and used in cooler climates to help with the starting. In some cases they may have used a spark plug and a trembler coil to provide a cascade of sparks. I will also post a photo of the combustion chamber and the underside of the head/ hot bulb. The bulb is detachable and I may have to experiment with lengths and thicknesses but that’s for later.

Fred.

This shows the pre combustion chamber and the hot bulb with its special peg spanner. The castings still have to be cleaned up and made presentable.

Fred.

Was cartridge start an option for these beasts? That would be an interesting thing to reproduce at model scale.

Really interesting work Fred, please keep posting.

Andy

I don't think that hot bulb engines used cartridge start as you didn't have to get them over compression. They were typically bounced off compression in the wrong direction and hopefully started running in the correct direction of rotation.

Cartridges as far as I know were used for starting full diesels where they had to be got rapidly over compression.

If I get my diesel running well I suppose a blank .22 cartridge could be an option

Thanks for the comments from those who are following the progress on this model and good to hear that you are making a Diesel engine Roger ( what is it?) They do present a real challenge but that’s what makes life interesting. The Mc Donald did not use a cartridge type start. The flywheel has a retractable sprung loaded handle and the engine is “ rocked” until it bounces of compression and fires up. I hope the model will do the same but I expect there will be teething problems and I will just have to try to solve them one at a time.

Fred

I mentioned a little bit about my diesel at the start of this thread however things have moved on. I have been experimenting with fuel injection for some time and have successful manifold injection systems for Petrol/Gas/Benzin. The diesel injection system appears to reach around 100 Bar but good atomisation is proving difficult. The initial engine was a horizontal two stroke based on the Field Marshall design.

The two stroke diesel would start and run on standard automotive diesel fuel. I believe that an amount of the running was on fuel that had passed by the piston and was vapourised in the crankcase. This was backed up by the amount of oily black clag that comes out of the exhaust and the lack of response to the fuel rack position once it starts.

I am now rebuilding it as a four stroke to allow me to better separate the different parts of the operation cycle. The bottom end and conrod will be retained along with the lubrication system. It will need a new cylinder block piston and cylinder head. This is being documented on Model Engine Maker:

https://www.modelenginemaker.com/index.php/topic,10605.0.html

Here is a video clip of the two stroke nearly running and the initial layout of the four stroke. The stops were due to me reducing the fuel injection quantity. It has a tendency to run away but the air intake is easily blocked with a finger.

https://youtu.be/1OP6LxPb2uU