Essex hot air engine from MyfordBoy's castings

[deverett]

I've had the castings lying about for more than 3 years. As they are aluminium, I can't really claim that they have been waiting to be normalised. MyfordBoy did a very good series of videos on how to make the engine and it was after watching them that I decided to get the castings. They are of excellent quality, some other casting suppliers could learn from him.

I met David Abbott (MyfordBoy) at the last 2 Bristol shows and both times he asked me if I had made a start, but meekly replied that it was on the 'to do' list. Conscience pricked, when I got home I blew the dust and cobwebs off the castings and made a start.

There is no point in giving a blow by blow account of my work because I mostly followed MB's construction videos. All I have done here is to mention any major differences in my way of working. The squeamish might baulk at some of his methods, but using that rare commodity Common Sense, I have no issue with his ideas.


Cylinders

I smoothed the castings around the parting lines before mounting them in my 4 jaw independent chuck. MB obviously has more faith in the accuracy and holding power of his 3 jaw chuck than I do of mine. I was able to clock both flanges reasonably true prior to turning the extensions slightly oversize after drilling a centre hole to take the supporting revolving centre.

Once that was done, I put up the steady to hold the extensions while they were drilled, bored and reamed. Putting the revolving centre back into the extension end allowed me to turn them to the correct size. The extensions are supplied overlength and they will be trimmed down later on.

Before reversing the castings onto the faceplate, I turned up the 2 plug gauges required for the bores.
The remainder was as per MB's video.


Engine frame

All pretty straightforward, really. I followed the video.

Dave
The Emerald Isle

 

[idahoan]

Hi Dave

Good to see this build, I too have a set of these very nice castings ageing under the bench. Looking forward to seeing your progress on this one.
I built a full sized Essex hot air fan replica from Myers castings a number of years ago. Someday I hope to have the Essex engine completed to go along with it.

Dave

 

[deverett]

Dave
I remember seeing your Essex fan at GEARS. A very impressive piece although at the time I did not appreciate it, unfortunately.
Dave
The Emerald Isle

 

[deverett]

Crankshaft bearing

The extension was smoothed off before holding in the 4 jaw SC chuck. I didn't have the correct size reamer, so after drilling I used a boring head to get the correct size bushing hole, running the boring tool through a couple of times to work any spring out.

Then over to the milling machine as per MB, but I did not have suitable clamps to hold everything like he did. Instead, I put a long bolt through the bushing hole to hold everything tight.

To get the platform level, I had previously marked the leg in two places and used a height gauge on them to set the casting level.

The platform really is horizontal!

The rest was done as per MB.
The drawings gave no dimensions for the lightening hole so I traced the hole in the frame casting and used that for sizing.

Dave
The Emerald Isle

 

[deverett]

Carrying on with the crankshaft bracket...

I cocked up drilling the top and bottom securing holes in the end of the power cylinder. Instead of doing them as per MB, I relied on measurements from the drawing. Somehow they ended up 1/16" too far apart. Isn't JB Weld wonderful stuff!

The middle hole was in the correct place, so with the bracket attached to the cylinder with this one screw, I lined it up by putting a length of bar through the bearing bore and used a scribing block to set the bar parallel to the mill table. Then it was just a case of marking the new hole locations with a transfer punch, drilling and tapping.

.
When the bracket was secured to the cylinder, levelling off the foot was done as per MB.

Dave
The Emerald Isle

 

[deverett]

Water jacket

Straightforward, but I did make several checks to ensure the screw holes were in the correct position. There is not a lot of room for error in the water chamber. The build notes from MB gives suitable warning.

The core plugs were next. A gash piece of ali long enough to make both plugs was turned to fit the holes and then transferred to the milling machine to put the square on each end. I didn't glue them in just yet; I'll wait until the engine is painted before putting them in place.

Dave
The Emerald Isle

 

[deverett]

Transfer cylinder

My transfer cylinder is a piece of 2" stainless steel with quite a thick wall so to start with this was machined down at each end and in the middle to the required 26 thou.

Furnace

I was able to get hold of a piece of 3" stainless steel tube to use for the furnace, instead of having to roll up a piece of steel plate and solder it into a tube. There are plenty of bits available on eBay.

My S7 has 1/4" extra centre height compared to MB's ML10 and this allowed me to mount the tube directly on the cross slide. I had previously marked the position of the 3 holes and deeply centre-popped them. It was easy then to support the tube by centres in the dimples, shim it up to the correct height and clamp ready to drill/bore for the transfer cylinder.

I drilled/bored the first hole to size, then carried on through the tube without moving the cross slide for the second hole.

The extra clamp clamped the first one. Not sure that it did very much but I felt happier with it there.

For the inspection hole, the tube was mounted to an angle plate on the cross slide.

I had not been looking forward to this operation and had been putting it off for a while, but it came out alright in the end and I breathed a sigh of relief.

After the three holes were done and cleaned up, I had a trial assembly of the furnace and frame.

Looking good so far, at least to my eyes!

Dave
The Emerald Isle

 

[deverett]

Trial assembly

Next job that to be done is to secure the two cylinders and frame together. MB relied on measurements to drill/tap the holes in the cylinders, and used a stack of washers to measure the height of the engine frame above the transfer cylinder. At the time of watching his video I didn't really understand what he was describing so I resorted to a simpler (for me) method.

The crankshaft bracket is not flush with the outside of the power cylinder, there is a gap between the bracket and cylinder edge so after temporarily assembling the transfer cylinder, I adjusted the height of the frame manually until it matched the crankshaft bearing 'underhang'.

The assembly was held with a couple of small clamps and put on the mill table; the furnace was then aligned vertically with a square. A quickly made small pointed punch was used to transfer the holes from the frame to the cylinders which were then drilled and tapped.

Dave
The Emerald Isle

 

[deverett]

Securing engine to base

The holes in the base had previously been drilled. The engine was clamped to the base and using a transfer punch, the position of the screw holes in the cylinder standards were marked.

Dismantling the engine, I put the cylinders in the machine vice on the mill and after levelling them, drilled and tapped the screw holes.

Slower perhaps than MB, but I was pretty much assured of success my way. I didn't want to use any more JB Weld!

Dave
The Emerald Isle

 

[deverett]

Some cast iron machining coming up next, but before this I made up the small end bearing from steel as per MB and this was put on one side afterwards.

Cylinder Liner

I didn't have a long enough piece of cast iron to get the cylinder liner and piston from. I did have two suitable shorter pieces - one piece for the liner, the other for the piston.

With reduced overhang of the shorter piece, I held it in the 4 jaw chuck. The outside was turned to a nice slip fit into the power cylinder casting, ready to be secured with Loctite in due course. The bore was left about 2 thou too small ready for the lapping process described by MB.

Piston and Extension

Wanting to get the cast iron machining out of the way, I next did the piston. The CI was again held in the 4 jaw chuck. The bore was left the correct size and the outside was left 10 thou oversize until the cylinder liner was lapped.

Next up is the piston extension. MB suggests a cheap rolling pin as a source of stainless steel. They are usually 2" in diameter, so to reduce to the required 1.862", the tube is cut lengthways and MB silver soldered it with a simple lap joint. The same process is used for the displacer piston. He obviously found it satisfactory, but I thought a joggled lap joint would be better - more 'professional'!

Never having joggled a joint before, I practiced on the waste piece of tube.

A piece of steel the same thickness as the tube material had a saw cut put in it.

The cut steel tube was marked where the joggle was to go and then put through the slit. It was just a simple task of putting the steel plate and flattened out tube in the vice and squeezing.

Hey presto: one joggled piece of steel.

So, now to put my new skill to the test. Some years ago I made a set of rolls to the GHT design but they have had very little use until now when I was able to roll the piece back to quite an accurate tube.

MB silver soldered the tube and two end plates in one heat, but I didn't trust my silver soldering ability to do that, so I did it in three separate heat sessions - tube, end plate 1 and end plate 2.

First part - soldering up the tube was acceptable, but oh what a disaster when I tried the first (bottom end) cap. Scrap one extension.

Fortunately, there was enough spare tube to have a second try. Still going with three heats but this time, putting the thick top end in first to help give some rigidity.

This time I called it a winner.

The displacer was done the same way (without the ****-up!). MB shows a small hole in the top end cap that prevents an air lock during the soldering process, later to be plugged. I just drilled the central hole for the displacer rod right through the cap and will rely on sealant round the thread to make the displacer air tight.

Dave
The Emerald Isle

 

[deverett]

Con rod

Looking at the drawing for the con rod without watching the video, I would have tried to make it from one piece of brass. MB made his by using a piece of brass for the main part and the bearings at each end were made from bronze.
I took the opportunity to copy his idea but by keeping the spigot that fitted into the main holes short, an oil reservoir was created. Maybe he did the same, but this was not made clear in the video.

The bosses were formed on a rounding jig and the embryo rod was then fixed to a piece of bar for the waist to be formed. I finally finished the bosses with filing buttons to get the blended shape.

Piston assembly

Looking at the drawings, I could not understand how the piston was assembled and I thought that there was an error in the assembly drawing. There was no way the wrist pin (drawn at 1.600") could be put inside the piston extension (with a central hole of 1.230") before the extension was soldered up. My thought was that the small end bearing was shown facing the wrong way.

When I contacted MB and pointed out the error of his ways, he stated that the assembly was correct. He also sent me a picture of an original engine con rod secured to the wrist pin in the small end bearing with a set screw. Having already made the con rod, I left it as per his drawings.

The only explanation was that the wrist pin was drawn too long so I had to shorten it from 1.600" down to 1.200". This allowed the assembly to pass through the piston extension hole and be assembled as drawn.

Time to have a trial assembly of the piston and con rod.

Dave
The Emerald Isle

 

[idahoan]

Hi Dave

You are making good progress, I have been following along but have neglected to comment, sorry about that.
Everything looks great!

I did check my prints and the length of the wrist pin is correct.

Dave

 

[deverett]

Hi Dave

I did check my prints and the length of the wrist pin is correct.

Dave

I don't think so, Dave. The diameter of the hole in the piston extension is only 1.230" and the pin is drawn at 1.600" (or at least that's how I read it!) Anyway, shortening the pin worked for me and it hasn't fallen apart yet.

Dave
The Emerald Isle

 

[idahoan]

I guess what I was trying to say is your print said 1.600 which was too long, and my print says 1.120 so I'm assuming that I have updated drawings?

Dave

 

[deverett]

MB must have updated his drawings, perhaps other builders noticed the problem. My drawings are Rev. A.

Dave
The Emerald Isle

 

[idahoan]

Most of my drawings are also rev. A but that particular sheet is rev. B

Dave

 

[deverett]

Displacer con rod

The drawings did not give a straight length of rod required, although all dimensions of the rod as bent were there. I got some copper wire from a scrap piece of mains cable and bent it up as per the drawings to act as a template; when straightened out it came to just under 19".

Looking at the drawings, I initially thought the bends were at 45 degrees and bent the copper wire so, but there was clearly a problem with the result. Measuring the drawing with a schoolboy plastic protractor, the bends were in fact 52.5 degrees as close as I could tell.

Starting out with a 5 ft length of 3/16" stainless steel in the lathe I put a 2BA thread on one end. I don't know what grade of stainless it was, but it was a real pig to thread.

Which end to start the bending? I did not want to end up with a short straight length after the 90 degree bend for the second thread. The dog leg bends at the flywheel end were easier to do so that is where I started, leaving the other end and thread to think about later. Initially, I tried to bend the embryo con rod using a piece of 2" diameter bar as the former and pinched former and rod in the vice and bent by hand. First bend was OK, but the second one would not go where I wanted it. Straightening rod always leaves a slight kink where the previous bend was, so after a couple of tries, I gave up on that idea and my length of rod was now about 10" shorter after I cut the bad bit off!

Back to the drawing board. Taking short cuts doesn't work, so the next job was to make up a simple bending jig that would hold the rod and put in controlled bends, hopefully in the correct place.

To assist with the bending, I scribed two lines on the bending former at 52.5 degrees and this helped to get good bends.

The final 90 degree bend was put in and the excess length of bar cut off. 2BA is just a few thou smaller diameter than 3/16" so a file was used to get the diameter of the rod down so that it could be threaded. Not so hard after all!

Dave
The Emerald Isle

 

[deverett]

Ball Joints

These are the last two pieces to be made. MB used a form tool to make his ball joints. I used a ball turning tool for mine.

And this is how they turned out. Crankshaft end ball fitted.

Dave
The Emerald Isle

 

[deverett]

The engine is now complete and has been painted.

The important bit: does it work. Unfortunately the answer at the moment is No, but I have high hopes it will in the future because it does seem to want to go.

The displacer con rod needed a bit of tweaking to remove friction.
I have compression.
The problem is that the displacer is canted on its rod and is rubbing in the cylinder bore.
I've tried removing the cant but the displacer construction is too strong and can't be un-canted. I've tried to re-silver solder it but that was a failure.
I've looked all round Cork for one of the cheapo rolling pins but there are none to be found, so I've ordered one from England and will make a new displacer.


Turntable

During the construction of the engine, I made up the turntable. No construction pictures as I followed MBs video instructions.

One of the uses for the turntable was for shop window displays, so in preparation of a working display, I made up a platform. This is a piece of 1/2" MDF that has been covered in red felt.

And a smaller one that could be mounted above this one.

And here is what I would like the display to look like when ready to be powered by the Essex engine.

15 Matchbox vintage commercial vehicles fit neatly round the two levels.


I'll report back when I have the engine running.

Dave
The Emerald Isle

 

[deverett]

New displacer

I've finally managed to make a new displacer.

The original displacer was rubbing on the cylinder wall because the end cap securing the barrel was not perpendicular to the displacer rod. I tried to straighten it out and file away the high side, but I just made a hole and in trying to solder up the hole, the situation became beyond repair. Scrap 1.

So, new displacer required. I ordered another of those cheapo rolling pins as previously, but the wily Chinese had upgraded them by filling them with some sort of weight to actually make them useful. Absolutely useless for my purpose. I searched for a source of thin stainless steel in small quantities but without success. Then Marvin Hedberg suggested the use of a pumice BBQ cleaning brick.

These BBQ cleaners are very light and seem quite fragile. I determined that the displacer rod would also be the spine of the displacer and the brick would have two end caps. The block was cut down to a suitable size with a hacksaw for machining and then mounted vertically in the mill to drill a hole right through.

The displacer rod was turned down a few thou for the length of the displacer and the end tapped for a retaining screw. One end cap was JB Welded in place. When cured, more JB Weld was smeared along the displacer rod and the BBQ block was slid on.
When set, the corners of the block were taken off with an old Surform plane - done outside of the workshop.

The embryo displacer was set up in the lathe and turned to the required diameter. Lots of newspaper was put in place and a vacuum cleaner nozzle was held close to the action area to catch the grit.

I used a carbide insert tool about 20 thou cuts and moderate speed. It machined beautifully.

When to diameter and length, the other end cap was JB Welded and screwed in place.

The block as originally supplied seemed quite fragile with lots of loose dust/grit in the package, but after machining it didn't want to crumble although care still was needed to prevent chipping.

I realised afterwards that the outer end cap was not strictly necessary - the JB Weld would have been sufficient for securing the body to the rod.

The grit from machining is extremely abrasive and thorough precautions need to be taken to prevent it getting into places where it shouldn't. I spent quite a long time after machining in cleaning the lathe, but I still found traces much later on. Cast iron dust is quite benign compared to this stuff.

The new displacer was fitted and the engine started up straight away. Very satisfying.

Dave
The Emerald Isle