Mc Donald Model tractor

Fred,

I don’t post here very often but have been following this from the start. It’s a great account of a fantastic ‘journey’ (how I hate that phrase but it fits here). The result must surely be well deserving of a gold medal if you were ever to enter it in the exhibition competition. Fantastic job sir, well done.

Paul.

I never thought I would be able to say that there are only two more parts to make plus any I have to remake. The photo above shows the two stage reed valve induction unit. These reeds were originally designed for small motorbikes where at low speed only the the two small petals open but as revs rise the secondary kick in ( the larger part). The steel protruding plate prevents the reeds from contacting the flywheels. The second photo shows the chain drive from the engine to the gearbox. Commercial chain is used and it does not require a tensioner - more by luck than calculation. I did have to remove a link and make use of a half link as a joiner. Having careful separated the link that had to be taken out I was ready for the next step but no I accidentally picked up the link I had just taken out and fitted it to the chain. That’s how to waste time with out really trying! I still have to make and fit a chain guard and also connect the clutch lever to the clutch.

Fred.

The above photo shows the finished and fitted chain case and that in theory is the last part to be made as I have also made and fitted the push rod for the clutch/ brake. The next stage is to have a working engine but I expect that will take quite some time as there will be some problems to over come. I do have a small pencil type gas blow torch for heating the bulb and will adapt that to fit and hopefully it will produce combustion inside the engine! Trying to make this engine work is a bit like stepping into the unknown as there are so many variables that have to be solved and no instruction book to follow but that is why we take on projects like this, it’s the challenge. The one aspect that I am not looking forward to is having to completely strip, detail and paint the model and when that task is done the model will be finished. If and when the engine bursts into life I will record the occasion for posterity and I will then be walking on air for the t week or so - fingers crossed. Thanks to all of those who have added comments and given me the incentive to keep working on this project.
Fred.

Good luck for your first running trials

Have you tested the injection system yet? Do you get a reasonable spray pattern?

Roger that is part of the next weeks test program but I am prepared to remake or adjust parts if required.

Fred.

What an achievement even to get it to this stage!! With all the time and design you have put into this project plus a little bit of luck and a following wind any adjustments needed to get the engine running will hopefully be minor. I have thoroughly enjoyed you postings here and look forward to seeing you post a video of it running with a nice chug - chug - chug sound of it ticking over. Hope it all goes according to plan.

Martin W

The photo shows the gas tank and burner in position. The head of the burner and the filler in the tank came from a small pencil type gas torch with the tank being made from brass and copper. I do have to set the length of the flame but have made the stand so the this can be adjusted to suit. All the cheese head screws on the model have now been replaced with hex heads ( as near to scale as possible). The oil pump has had its stroke reduced by 30% and the injector set at 20degrees before top dead centre. All gaskets have now been made and fitted but I do still have to check and test the cooling system. I read in a motorcycle magazine about a fellow who had just restored a bike and was not sure if he should kick into life or sit, admire and enjoy the product of all that labour for a while! That’s how I feel about the Mc Donald but as I do need to see and hear it run ( if it will) before I start the painting process I will try giving it a whirl in the not to distant future!

Fred.

Absolutely fantastic work (and pictures). It deserves to run on looks alone.

Nice to see some engineering on this site!

FANTASTIC!

The research,k the work to make the parts, and to assemble them so close to prototype.

It looks wonderful.

Given your standard of workmanship and finish, it ought to be a runner without too many problems.

Howard

This weeks efforts saw the gas cylinder in place and the gas jet set and working as it should do. Two problems did raise their heads and need to be addressed. The first was the oil in the the oil box siphons down to the engine when left over night. I think this can be resolved by the addition of two small springs to hold down the ball check valves in the pump body and not rely on gravity or the weight of the steel balls to form a seal. I have discovered that my electric razor has springs of just the right size and shape. Just call it recycling! I will need to drill and tap a drain hole in the engine crankcase to allow excess oil to be drained out.
The second problem is trying to start the engine by holding on to the scale starting handle. On the full size tractor the flywheel is rocked back and forth until enough momentum is generated to overcome the compression. Holding onto the small retractable handle on the model is not the easiest of processes and the fingers soon tell you so ! To overcome this I will have to make a starting dog that will attached to the flywheel side of the engine and allow an electric drill to be used. These are just some of the small problems to be overcome and there may be more to follow.

Fred.

Last week I thought a small spring would resolve the problem of the oil leaking back into the engine - well it didn’t! A rethink of the problem was required and the photos show the results. I did make a new cam and shaft, ratchet ( with 38 teeth) and this time the new pump had a single piston of 4.8mm dia and a stroke of 2.5mm. A new ratchet with 38 teeth was machined and fitted. A screw valve gives a positive shut off to the oil from the tank and this leads to a tee outlet and finally to the copper pipes. The next job is the starting mechanism ( electric drill and drive dog).

Fred.

You may want to think about some means of restraining the tractor when using to drill for starting. This gives you a hand free for adjusting the injection volume and timing.

I finally got my four stroke diesel to run at the weekend and it was trying to escape from the 'workmate' type bench I use for trials.

The last few days have been spent setting up the cooling system and testing it for leaks. I discovered that the full system holds 1 litre of water but over night it developed a couple of minor leaks and one not so minor!The small leaks were easily cured by tightening the bolts or using Loctite 518 gasket but the other one was not quite so easy to cure as it was internal. The cause was either porosity or small shrinkage crack internally with the result that some water reached inside the crankcase. The cure proved to quite simple - radiator sealant. The instruction said to run the engine and then pour in the liquid while the engine was hot. As my engine has yet to run I flushed it with boiling water and then followed the instructions on the bottle. The end result was a sealed system and as it is not under any pressure it should be satisfactory. The starting socket has been made to fit the flywheel side of the crankshaft. I hope I have the same result as you did with your engine Roger ( congratulations on your achievement).I am not sure of the weight of the finished tractor but expect it to be 49-50 Kg and when testing I will make sure it is in neutral gear and well anchored down!

Fred.

Thank you

Here's a brief clip of it running. Still lots more to improve.

**LINK**

Good work by both Roger B and Fred. (Good is a major understatement )

WHAT achievements

Howard

The development continues. As a test of the porting I set up a Hall effect ignition system with a small magnet embedded in a brass case in the back of the flywheel. The engine already has a spark plug positioned in the head as on the full size tractor this is used for starting in cool climates. I used a commercial engine starting spray in the air intake and cranked the engine over with an electric drill. To my surprise and pleasure it fired up which proved the porting and reed valve were working. The exhaust noise was very load - I had almost forgotten how noisy two stroke engines can be on an open pipe! I made and fitted some baffles and lightly pressed them into the exhaust pipe but on restarting the engine these were to be seen heading to the sky at a rapid rate of knots . After fitting a small bolt to hold them in place the noise level was reduced to a more acceptable level and gave some back pressure to the exhaust pulse.The current injection system uses a small gas jet but this size of hole was still to large and an excessive amount of fuel squirts into the pre combustion chamber - another problem to solve. Having spent a night thinking how to make a very small hole I came to the conclusion that a small hypodermic needle may be the answer as these are available down to .003 inside diameter. A needle could be silver soldered into the gas jet but only experimenting will see if this improves the situation and that’s todays task.

Fred.

Great that you got it running I initially ran my two stroke diesel as a spark ignition engine to prove the porting as well. I have drilled nozzles down to 0.2 mm (8 thou) with my basic equipment. Did the original tractor have an open injector or some form of needle/pintle?

Good Day Roger,

It seems that we are both travelling the same path related to Diesel engines and have the same problems to solve. I will have to check what type of injector was used on the full-size tractor. I am now in the process of redesigning a pintle style injector as the previous injector gave a stream at full stroke and a dribble when shut back. I used a .007” hypodermic needle soldered into the gas jet and have smaller ones on order but they will not arrive until the end of November. What is lacking is the punch that cause the fuel to break up into small droplets and to make this happen I will need a spring loaded pintle and a pump capable of creating the pressure required to lift the pintle off the seat. Experimentation and reading continues and I hope success is just around the corner!

Fred.

I have been playing with fuel injection systems for many years. My current system seems to work and seems to be reproducible. This is based on 20 – 25 cc engines and uses a 2mm diameter injection plunger with a helix metering groove. I initially tried a needle type injector but the leakage by the needle was too much. I am now using a mushroom/pintle injector which seems to work well on petrol, as manifold injection, and diesel. I have built a test pump which I can operate with a spring balance which implies an injection pressure of around 90 bar. Be careful with fuel at these pressures and keep it away from your skin. I usually check the results against a piece of paper.

Here is an exploded view of my injection system. The injector needle is 1.4 mm diameter. There are more pictures on here:

https://www.flickr.com/photos/153503473@N05/

And a spray patten is here:

**LINK**