Member postings for Four stroke 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.

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.

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.

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

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.

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.

Thanks for the comments Martin and Diogenes it’s good to receive feed back. I started this as log of the tractor construction to keep as a record for myself but it just grew and grew! It has been useful as there have been times when I have had to repeat a process and I have been able to check back in the log to see how I did a process or set up the first time round. I think it’s also good for other model engineers to see what is normally hidden on a model like this and perhaps get ideas or may be even inspiration. I remember my first visit to the MEX back in the early 1960s and how that inspired me and set a standard that some day I may achieve. A model such as this is a challenge and the problem solving stimulates the brain and at my age you need to keep that active! You asked what will be the next model and the answer is that I do have several model to finish. One is a 67cc V8 and the second is a working scale model of a 250cc. single cylinder racing motor cycle. I have the frame already made but at the time I had neither the ability or equipment to complete the model - like wise the V8 has already had the parts cast and partly machined and it about time it was finished. Also there is a 5” gauge Terrier class loco and a 3 1/2” gauge Tich that needs attention but as my interest in steam has diminished they will have to wait. I will just have to live longer or find a 28 hour days! The shed / workshop is a wonderful place to be and when I am in there any aches and pains just disappear. Having a hobby like this has given me new circle friends who share the trials and tribulations of the journey and the learning curve continues to grow. I have reached the stage with this model where it appears to be nearly finished but some of the small tasks and problems do take time to resolve. Structurally the end is in sight but then there is the interesting stage of experimentation with all the settings and hopefully it will go. There is no guarantee that “Go” will happen as there is no instruction book but it doesn’t stop one from trying. Perhaps at some time in the future I may bring the finished model to a MEX but that depends on many factors some beyond my control. If it does happen I look forward to meeting you all face to face. The photo shows the tractor at a local club day display last Saturday.

Fred.

The list of jobs continues to reduce. This weeks work included the connecting up of all the water inlets and outlet pipes but the main effort went into machining and fitting the cast iron liner. Machining the bore was a long task as the final cuts were very small and lathe speed very slow ( about 20 minutes per pass )Having machined it to the required size both inside and out I was ready to press the liner into the cylinder. Guide lines were marked to line up the ports with the port holes in the liner. All went well with the fit being just right and in line with the top of the cylinder but a check revealed that the liner had rotated slightly as it went down the bore - oh bother! Next job was to make an extractor jig to remove the said liner. Double checks we’re made and this time all was well with all ports in the liner matching up with the ports in the casting. The piston complete with rings can now move up and down the cylinder. The next major job is working on the cylinder head. I also have to make and fit the rod that connects the clutch lever to the clutch and make and fit the chain drive to the gearbox. Photo to follow.

Fred.

Boring, that was the order of the day - boring the cylinder liner that is. The bar of iron was 60mm diameter and had to reduced to 55 mm and bored out to 45mm diameter. Waste was high but that was the only material I had in stock. I still have to finish the bore, outside diameter and then machine the ports.The fuel tank is now in its final position and has now been fitted with a filler and cap. The bonnet has had the holes cut for the exhaust ,inlet and fuel filler and the support stays added. The fuel lines and lubrication pipes have also been added. The list of jobs that still require attention is now shorter but it’s all the small jobs that seem to consume vast quantities of time. Beware this hobby of model engineering is addictive!

Fred.

This week it was a case of one step back and two steps forward. On assembling the air intake I discovered that the air pipe was obstructing the water pipe on the header tank of the radiator. The cause of the problem was the casting that joins the air box to the back of the engine. I had made the casting on the centre line when actually a part of it was offset from the centre line - this can be seen with the two castings in front of the tractor. The one on the right was the first attempt and the one on the left shows the amount of offset require. This was not easily seen on the full size tractor and only another visit and more photographs resolved the problem. After making a new pattern and core box it took me 4 attempts to make the new casting with the cause of the problem being the placement of the in gate. As they say if at first you don’t succeed try ,try and try again! The fuel line and filter have been fitted and the holes in the bonnet cut. There are still plenty of small jobs to do and that includes machining the cast iron liner from a 60mm diameter bar - boring.

Fred.

Today more 3D printing and casting. These are the saddle’s for the fuel tank and when cleaned up will be bolted to the top of the engine.

Fred

Last night I watched a video of a slow running model hot bulb engine made in Holland (I think).It was beautifully made and ran like a Swiss watch. The builder had aimed for a slow running engine and certainty achieved that.The compression ratio was 8:1, a heavy flywheel was used and the injection was fairly early on in the compression stroke, all points that I am hoping to transfer to the Mc Donald. The photographs shows the advance/ retard mechanism with the two grub screws that are use to set the position of the eccentric that works the injector pump. When the final position has been made a keyway will be cut in the eccentric to give it a permanent position - the keyway has already been cut in the shaft. The oil tank has been set up and appears to work OK and the right hand side of crankshaft has been pressed together and scotch keyed in place.

Fred.

This weekends workshop time was spent on the injector set up ( but not the timing). These small parts take longer than expected to both make and then set up and there seems very little to show for the hours it has taken, but it’s all to do with the vision of the end product. Each division on the throttle “gate” is 5 degrees and equates to half a mm of movement on the injector plunger via all the levers. If this amount of movement is excessive there is provision for the leverage to be changed but experimenting will determine if that is required.The crankshaft has yet to have the flywheel keyway cut but as this keyway may also drive the eccentric for the injector I have held off the process.

Fred.

The casting proved to be satisfactory and has been machined as can be seen in the photographs. This week I started the process of assembling some of the parts of the engine to make sure they all line up with where they are supposed to go and made a stand to hold the unit making life a little easier.The assembly includes the crankshaft /piston as I have now made a temporary liner which will later be used to check the port positions before making the real one from cast iron. The top photo shows the method used to machine the exhaust manifold - tricky but satisfying when finished. I have made the exhaust pipe a sliding fit and it will be held in place by a small grub screw as this will enable the pipe to be removed for ease of transportation and a reduction of volume should I every go the UK (MEX). I now have to make the fuel tank supports, fit the lubrication system ( the arms shown are 3D prints but will later be cast in aluminium) and add the water inlet and outlet holes. This tractor has a chain drive from engine to gearbox and is tensioned ( on the full size machine) by raising the front engine mount but as this is carried out the air and exhaust pipes are no longer vertical! I may tension the chain on the model by using a slipper tensioner but have to wait until the chain is fitted before I come to a decision. There are still problems to solve but life in the workshop is never dull.
Fred.

A “ model” motorcycle - makes a change from tractors!

Fred

No this is not a repeat of a previous photo but the new casting set up and having the end of the bore faced off. The lower part of the crankcase has already been machined and has had the bearing plate and injector fitted (not shown in the photo.)The process is slow due to the fact that setting up an article of this shape and size just takes time. Drilling four holes took half an hour ( 25 minute setting up and 5 minute drilling). Due to the set up in the lathe the process of facing the end of the cylinder is slow and it takes 10 minutes for every pass, any faster and centrifugal forces come in to play with disastrous consequences! I hope by the end of the week to have the bore machined to the 50mm diameter ready for the cast iron liner. I will probably make a dummy aluminium liner that is a sliding fit so the I can mark out the ports before making the working liner in cast iron.The photographs that I have taken with the previous two efforts have been very useful for reference when setting up this casting for machining. Last weekend I went to the local car, truck and motorcycle show and took my 125cc OHC twin Benelli (1982) - a great day out.

Fred.