Mc Donald Model tractor

[Roger BParticipant @rogerb61624]

What injector pressure are you looking for? I am using 90-100 bar (estimated) but you shouldn’t need anything like that.

I think that you need to reduce the length of your 0.35mm nozzle hole on two counts. Firstly the relatively long thin passage will tend to cause the atomised fuel to coalesce and secondly drilling a 0.35mm hole several millimetres long is a significant challenge. I would suggest the nozzle hole should not be much more than 0.7mm long (2 x d).

The long 1mm fuel passage will also be somewhat of a challenge to drill. I avoided this by having a long reduced diameter section on the needle but that makes whole thing longer and the fuel inlet somewhat clumsy.

Finally I moved on to the mushroom/poppet design which removes a number of the manufacturing challenges and avoids the fuel drain.

[Howard LewisParticipant @howardlewis46836]

As an aside, the length of the hole (s ) in the nozzle will affect the spray angle.

Since a model will probably not be expected to run at Full Load Rated Speed for long periods, if at all, one can probably be a little more lax over needle lift and sac volumes,

For the prototype machine, i would have expected Injector breaking pressure to be of the order of 65 – 70 bar

It was only in the late 30s that pressures reached the 120 – 130 bar level (Atmospheres actually, at the time)

Eventually pressures crept up through 180 Ats to 210 as Injection pumps and injector manufacturing techniques improved. (We expected a Leyland 0600 to be marginally better with CAV injectors.than with Leyland ones, probably based on slightly better lapped fits, leakage rates and tighter tolerances.

Since leakage is subject to pressure and time, higher pressures will increase leakage, both in the pump and the injector nozzle (Leakage is one of the features which checked in full size products ) In a model it will be difficult to better the lapped fits of the conventional products, But with 90 years of manufacturing experience and development. modern materials and technique. may allow that.

To produce scale models of F I E which function is no mean feat anyway.

Good on yer, chaps!

Howard.

[Roger BParticipant @rogerb61624]

I couldn't find this video clip yesterday. I didn't realise how old it was This is a confirmation of the quality of atomisation with a needle injector like the one above. As precautions there is a damp towel just out of view and a 1kg dry powder extinguisher by the door

[Four stroke FredParticipant @fourstrokefred]

This is the Mk5 injector! I designed 5 but only made 3 of which this is the latest and I am pleased to say that it works and gives a good fine spray. I always realised that this part of the model would be a real challenge and take time. The piston is made from bronze and the body from steel and both are lapped to give a good fit. The lapping part of the process took far longer than expected and with the hope that as the injector heats up in use the fit should tighten up and help retain the pressure. I will carry out further experiments to determine the final spring pressure and try different size gas jets to see what effect these have. It’s scale is with in that of the model and is not to overpowering. I have had plenty of practice at drilling small holes (1.0mm dia) and pleased to report that no drills were broken in the process ( although one did disappear out of the chuck and out of the window due to centrifugal forces). The two main parts are sparingly silver soldered together to avoid blocking the fine holes and passages. Although it is difficult to see on the drawing there is a fuel hole near where the needle pass through the support to allow the fuel into the lower chamber.

Fred.

[Roger BParticipant @rogerb61624]

That looks good Are the gas jets screwed in so you can easily change them?

[Four stroke FredParticipant @fourstrokefred]

Yes the gas jets are screwed into the lower body ( 4.5 metric) and I have a range of four different sizes to choose from. This makes it easier to clean and change sizes. The number 5 design allowed me to ream the bore through and lap before assembly but did involve some tricky silver soldering.

Fred.

[Four stroke FredParticipant @fourstrokefred]

You could say practical progress has slowed down but the thinking and reading continues. I have redesigned the fuel filter system as I have discovered that small jets and any form of a solid do not go well together and will block the system. I am hoping that the new filtration system will cure this problem – it is not quite to scale but looks ok. I still have to strike a balance with the bore and stroke of the fuel pump. A larger bore gives lack of accurate speed control but would give more fuel in a short time at the injector. A longer stroke with small bore gives more time/ distance for control of speed – more experiments required! I am not alone with this problem as I have read else where that other modellers have experienced the same problem with injected Diesel engine models. Christmas is just round the corner and as a result work in the shed will slow down. I had hope to have the model running by the end of the year but didn’t say which year! Take care and stay safe.

Fred.

[Roger BParticipant @rogerb61624]

Have you managed to get it firing in hot bulb mode yet or are you still experimenting with the injection system?

[Four stroke FredParticipant @fourstrokefred]

Roger I am still experimenting with the injection system and have had to modify the test equipment and filtering system.

Fred.

[Four stroke FredParticipant @fourstrokefred]

With Christmas and New Year over its good to be back in the shed. I am not sure what the plural for a group of injectors but this is the sum total made so far. The drawing shows the next stage of the development and next weeks work in the shed. Some of the above have worked but I need to have a consistent performance. I have tested them to 1,600 psi and feel that should be sufficient for the low compression engine. One problem that I did encounter was blockage in the small passages and jets and to overcome this I have now fitted a three stage filter system in the fuel line. The first stage is a gauze filter inside the fuse tank, the second stage is the fuel filter on the side of the cylinder and the third stage is a micro filter in the fuel line to the pump. I did have to remake the original fuel filter slightly larger as I wanted to incorporate a filter from a lawn mower. The plumbing is now complete. From what I have read on other forums I am not alone in trying to solve the problems of injectors and pumps. Painting has been put on hold as the weather is very humid at this time of the year and it’s not a process I enjoy! I feel that the development stage will take longer than I anticipated. The drawing does not show the blocking off of the passage ways necessary to make it work.

Fred

[Roger BParticipant @rogerb61624]

That sounds about right A quick check suggests I have at least 9 injector designs plus five injection pumps. You will get there and it's great when you do

[Steve AddyParticipant @steveaddy35670]

Absolutely awesome work Fred. I wonder if you have seen the YouTube videos of this Danish gentleman. Find Hansen YouTube Channel

[Four stroke FredParticipant @fourstrokefred]

Thank you for your comments Steve and yes I have seen the YouTube that you suggested. The quality of his work is wonderful. Although I have not added to this column for some time I have been working on the model and now have the engine running. I have make some changes to the method of the fuel injection and now use a spark plug for ignition just to make life a bit easier and also had to cure a small water leak. I now have the engine stripped for checking and make some modifications as access to the oil sump drain and water drain from the cooling system needed to be made easier to use. The full size tractor did use spark ignition to aid starting in cooler climates and then when warmed up the hot tube would take over.

Fred.

[Roger BParticipant @rogerb61624]

Glad to hear that you have had it running Did the governor system work or haven't you got that far?

[vic francisParticipant @vicfrancis]

Fred , your work is a remarkable combination of skill, determination and patience.This model is in my top ten wonderful models list of all time.

I am sure it's in my wish list as well! Congratulations 👏, very inspirational.

Kind regards, vic

[Four stroke FredParticipant @fourstrokefred]

Thank you Roger and Vic for the interest shown in my model. After 3 1/2 years work it was good to see and hear that there is life in the old girl ( tractor) and although it’s not finished the end is now much closer. I began to feel that I was going round in circles with the injector and pump and as the prime factor was to have a working model I had a rethink of the process. I think that I have cured the water leak into the engine. A small shrinkage crack in the transfer port was the culprit and this has since been sealed. To bring the engine to life I have added an ignition system driven by a Hall effect unit with the magnet housed in an aluminium holder in the steel flywheel. Call it a defeat if you like but I did need to have a working engine and this system was used on the full size tractor. While I had made a working injector ( one of six) I decided that I would take the easy way out and use indirect injection. Originally I had oil being injected into the reed valve but have now made this the entry point for the fuel injection shown in the photo. A thin brass pipe with the end blocked off and two .3mm holes drilled sprays fuel into the air stream when the reed valves open. I still have work to do but a short initial run looks promising. While I have the engine stripped down I have made minor alterations to allow easier access to the both the excess oil drain from the crankcase and water from the cooling system. I am looking forward to the next development session next week. Photo to follow.

Fred.

[Four stroke FredParticipant @fourstrokefred]

[Howard LewisParticipant @howardlewis46836]

Superb that you have now had the engine running.

What a thrill for you, (and your followers )!

Howard

[A SmithParticipant @asmith78105]

Always look forward to your posts Fred. Marvellous work.

Andy

[Martin Johnson 1Participant @martinjohnson1]

Hat off to you Sir.

Well done.

Martin

[Adrian R2Participant @adrianr2]

Indeed, marvellous work, and a running engine deserves a video if you can manage it in due course.

[Four stroke FredParticipant @fourstrokefred]

Thank you all for your comments. I am in the process of painting the model and now have many parts hanging on a washing line in the shed. I did make a very short video of the engine running but will try to make a better effort when the paint has cured through. Trying to identify the colour has been difficult as on the full size tractor there appears to be many shades of the green or the same colour with various degrees of fading!. I tried to match the paint with the paint chart in the shop but when you open the tim they never quite the same. I am using a two pack paint but must admit that this part of the project is not my favourite activity, especially the cleaning up. It seems that paint has the affinity to stick to yours truly. I do try to do all the work myself even if the end project is not quite up to professional standards but as they say “ I did it my way.” The next photo should show the finished project but that will be in a couple weeks time.

Fred.

[Four stroke FredParticipant @fourstrokefred]

The photographs show the end of four years work ( pleasure and pain!). Having chosen the colour from a paint card in the paint shop I had a bit of a shock when I opened the tin as it was more of a duck egg blue when viewed in the day light. I did start the painting process thinking that the colour would grow on me but that was not to be. A sleepless night followed and no it wouldn’t grow on me. Next morning a return to the paint shop and a meeting with a very helpful lady assistant produced a more acceptable colour. Painting to me is not a very enjoyable part of the process and all that cleaning up! After leaving the paint to harden up ( two pack) the process of reassembling began only this time all the cheese head screws were changed for hex head and bolts cut to the correct length. Fortunately all the parts went back in the correct order except for two of the radiator rubber connections – these are of different lengths and I had fitted a longer one where a short one was supposed to fit with the result that the fuel tank did not end up in the correct position. What have I managed to learn over the last four years and about four thousand hours. This model was a real challenge and pushed me to the limits but it made me explore areas of our hobby that I would not have taken if I had not made this tractor. I can now use CAD ( Fusion 360) and a 3D printer and can accept that challenges keep me thinking and give me some thing to look forward to each morning. There are just not enough hours in the day and best use must be made if every hour. This weekend I will be thinking of all those attending the Model Engineering Exhibition in Harrogate and wishing I was there to enjoy the experience – hope the weather improves. Perhaps next year I may bring the Mc Donald over and have a chance to meet fellow like minded model engineers. “Fred” is sitting on the tractor model and he will be pleased to meet you all. Thanks to all those who have offered help and followed this experience and I hope you enjoy your hobby as much as I do.

Regards,

Fred

[Four stroke FredParticipant @fourstrokefred]

[Four stroke FredParticipant @fourstrokefred]

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