Mc Donald Model tractor

[Roger BParticipant @rogerb61624]

Very impressive work on the gearbox

There seem to be very few people building land vehicles powered by self built engines. There are a lot of ETW Wallabies out there but very few 1831s. I have seen a number of Lanz Bulldog derivatives. I think someone makes casting sets.

I am working (very slowly) on a couple of models. One will be powered by a 12cc four stroke twin. I have almost got the engine running to my satisfaction with a constatnt depression carb. The simple carbs tended to struggle when a load was applied. This will be a freelance design.

The engine on it's test bed

The second one is based on the Field Marshall horizontal single cylinder two stroke diesel. I am slill learning/experimenting with the injection system. I have acheived some firing but not sustained running.

[Four stroke FredParticipant @fourstrokefred]

Hi Roger,

Your engines look very good and I am particularly interested in the single cylinder unit as I will know doubt encounter the same type of problems when I make the engine for this tractor. It’s a single cylinder two stroke “semi” diesel with hot bulb ignition and reed valve induction. Many problems to solve but that is what makes life interesting. Keep up the good work.

Fred.

[Roger BParticipant @rogerb61624]

Thank you This is my first go at a two stroke and bought a number of challenges. The prototype has angled ports, drawing these and the susequent maching was interesting. I strarted with an aluminium piece with the same dimensions as the cylinder but much shorter. This gave me a chance to see what was going on and reduced the amount of scrap. Using small long series milling cutters results in some deflection.

I cheated with the reed valves and bought a comercial set (spare part for a scooter, less than £2) which fitted in the space that I had.

I initially ran the engine as a spark ignition petrol engine to confirm that the red valves and ports actually worked.

Lots of fun

[Four stroke FredParticipant @fourstrokefred]

The last couple of weeks has been spent making the gearbox internals and now the white 3D printed parts have been replaced by metal items. I did change the selector mechanism as it was becoming over crowded at the front end. Working out all the movements of the selectors and mating them to both the gears and the “gate” at the rear was quite a fiddle. As designed the gears would not match the “gate” on the full sized tractor and that would never do!
Fred.

[Adrian R2Participant @adrianr2]

Hello Fred – How fares the McDonald project? Is the gearbox assembled yet?

[Tony Wright 1Participant @tonywright1]

My version !😃 well almost .Steam Powered similar size to a Mamod tractor.

Tony

[Jeff DaymanParticipant @jeffdayman43397]

they look great Tony, good fun!

[Four stroke FredParticipant @fourstrokefred]

Good Day fellow modellers,

Lovely to see your work and read your comments. I have spent the last two weeks tidying up my shed and as a result
tractor building has come to a halt but I am about to restart as I have now made some work space. The gearbox is now working and is ready for assembly but before I do that I have to cast and fit two small covers and the steering box. In the clearing up I did find a worm and worm wheel just the right size and right direction for the steering. The mudguards have been rolled to shape and material for the wheels spokes purchased. I am looking forward to making and fitting the rear wheels as this will then give an idea of the the size of the model.

Fred.

[Adrian R2Participant @adrianr2]

Thanks Fred, looking forward to seeing some more pictures in due course.

[Four stroke FredParticipant @fourstrokefred]

This week I have designed and made the patterns for the steering gearbox and also the two small side covers for the left hand side of the gearbox. The photo shows the complete 3D printed steering box in the top left, the four start worm and worm wheel and the other small patterns ready for casting.I have been using the metal from hard drive cases as these have been die cast and when melted down seem to flow well. The next stage will be machining up and then fitting the parts.

[Four stroke FredParticipant @fourstrokefred]

[Four stroke FredParticipant @fourstrokefred]

Yesterday they were patterns and today they are castings and tomorrow I hope to machine them up and fit them to the gearbox. These castings still need some cleaning up but appear to be ok. With the air temperature in the 30Cs and the furnace going full blast it was a hot job.

Fred.

[Adrian R2Participant @adrianr2]

Good stuff. I don't think I'd fancy furnace work in 30C, well, not unless you have one of those closed and insulated electric ones. On the plus side less chilling from the moulds I guess.

[Four stroke FredParticipant @fourstrokefred]

This week I cast the steering wheel in aluminium having made the pattern on the 3D printer. As the wheel is dished this caused some head scratching when casting. When the print was made I included a thin membrane to separate the two sand layers – this would also allow the metal to flow over the whole wheel and was cut out when the casting was made. The photo shows the steering wheel on the left, the pattern in the centre and a support cone that the 3D printer makes to support the print – this being used in the casting process.

[Four stroke FredParticipant @fourstrokefred]

Earlier on I said that I had found a worm gearing system that suited the the steering box well the truth is it was the correct size but unfortunately it was right handed and no good for the tractor – must have had a seniors moment, If I had used it the driver would have turned the steering wheel to the right but the tractor would have gone left ! After checking on the internet I discovered that most commercial worm wheel sets are right handed. The challenge was then to make my own that fitted the criteria and today I think I did just that. I still have to check and finish the matching pair but hopes are high. Yesterday I assembled the gearbox and joined it to the chassis, Gearbox is10kg and chassis 8kg.

Fred.

[Henry BrownParticipant @henrybrown95529]

More great work Fred, really enjoying your adventures!

[Tim StevensParticipant @timstevens64731]

I have a message for Roger – I hope he is still reading this story

I suspect that the Field Marshal is going to be a real problem to get running nicely. This is because its working depends on the shape and size of the exhaust system. As the exhaust port opens, the rush of gas is intended to overshoot, rather – drawing fresh air into the pipe as the 'bang' reaches the narrowing at the far end. This causes a reflection of a pulse back towards the engine, and this pushes the fresh air back into the cylinder, just in time to be trapped by the exhaust port closing, improving the compression and turbulence, for more power. This process needs to be 'timed' with the engine rpm, of course. But the timing of pressure reflection in the pipe depends on the length of the pipe. So a half-sized pipe on a half-sized model will need to rev at twice the RPM to work properly. So, your tick-over will not sound anything like the low beat of the original. If you can get it to work at all …

If I can help explain further, please send me a Private Message and I will do my best.

Regards, Tim

[Dominic BramleyParticipant @dominicbramley60728]

Looks great Fred!

I'm really enjoying following this build!

Cheers

Dom

[Roger BParticipant @rogerb61624]

Thank you Tim,

I fully understand the problems of scaling real life and am learning the additional problems that come with two strokes. I will be happy if I can get a operating range between 2000 and 4000 rpm. A 500rpm idle is out of the question. It sort of runs but the injector atomisation requires some more work.

**LINK**

[Four stroke FredParticipant @fourstrokefred]

Thanks for the comments and I am pleased that you enjoy reading about the construction of this model. For me it’s going into the unknown that is exciting as I enjoy the problem solving as well as the construction. The part I am working on is the model of the day and in the end they all add up to the completed model. I am looking forward to making the engine as I know there will be plenty of problem solving there.

Fred.

[Four stroke FredParticipant @fourstrokefred]

Today I worked on the steering box gears including making the hob and hobbling the worm wheel. Photographs show progress. It was a steep learning curve but satisfying to think that I didn’t have to buy them after all. I may have to hob the gear wheel a little more but that’s for tomorrow

Fred.

[Four stroke FredParticipant @fourstrokefred]

As you can see the steering box is now finished and now has its position on the side of the gearbox. I had to make the steering wheel shaft and temporarily fit it to the box as it I had to set the shaft at 66 degrees to the horizontal top of the main gearbox. The steering arm that fits onto the worm wheel shaft has been shaped but has yet to have the square hole made at its pivot point.

Fed.

[Four stroke FredParticipant @fourstrokefred]

Just to wet the appetite the photographs show progress so far ( but still a long way to go). The small part between the wheels is the steering arm that attaches to the steering gearbox. This part has a 6mm square hole in one end and it took most of a day to make as I made and used square broach but the end result was that the hole is a good fit on the square shaft and that was the aim of the day.

Fred.

[Four stroke FredParticipant @fourstrokefred]

Just to wet the appetite the photographs show progress so far ( but still a long way to go). The small part between the wheels is the steering arm that attaches to the steering gearbox. This part has a 6mm square hole in one end and it took most of a day to make as I made and used square broach but the end result was that the hole is a good fit on the square shaft and that was the aim of the day.

Fred.

[Four stroke FredParticipant @fourstrokefred]

This is this weeks”model”. It’s the gear change lever and as small as it is it’s fiddle and takes time. It’s a case of fingers too big and parts too small! The next part to be made is the clutch lever and as I didn’t have all the dimensions I had to make a visit to the farm armed with camera, rule and sketch pad. I am lucky in that the property is only 15 km away.

Fred.

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