Atkinson Differential Engine - Making it work?

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Some differences in design. I tried the Gingery design first and this looked better but still not a good engine.


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I did not seal it at all. I used a different set of drawings and the cylinder is made from a solid piece of cast iron which dissipates the heat better. Ray Moye made his using the original Gingery and I don't think that he used any water either. He had his running for several runs of 30 minutes. I can send you my 2d drawings if you want to see what the differences are. Pivot points are different and the arms are quite a bit different.

I thought you used the Gingery drawings. Thanks for the offer but I'll stick with my drawings. No sense in getting confused.
(Save me going back to the other thread) Who was it that was having problems along with you? I thought his was a no-go as well.
If it was Ray, what did he do to get it to run for a half hour?
I'll hold off on the water hopper sealing. I'm hoping it will run good enough to get hot. When it does I'll take care of it.
Some more simple parts made. Nothing critical.
Oscillating arm links - Slightly different process at first since the stock could be held in the vise for drilling the holes. But then - fasten the stock to the board indicate the end holes and mill the profile. Added bushings and pins and installed them.
I also made the tie rod at the front. It really is just a couple of collars with set screws to hold all the moving pieces from sliding off the shafts. I suppose the bar across the front stabilizes the distance between the shafts. I just made the two collars and milled a recess in the side of each and JB welded the cross bar in place. Again, not a large amount of stress on it. The shafts are quite short and 1/2" diameter so they're not going to be flexing much.
In a couple of pictures you'll see some long brass screws. They are the only thing I had at hand to substitute for a set screws that won't damage the shafts.







Another change I made was to increase the length of the left connecting rod from 1.625 to 1.755 (130thou longer). This moved the left piston to the right. Along with increasing the compression it also throws a lot of other things out of whack on the other strokes. For one thing the spark plug had to be moved to the right so it was still between the pistons at maximum compression.
As I might have mentioned before I'm not sure these modifications were ALL necessary. Certainly a couple of them seem to achieve the same result and maybe more of one change might have eliminated the need for another. There were just too many variables to manage and observe, each having significant effect on the motion works. It's just what I ended up with trying to balance the end result which was to increase the compression. Some changes had more negative results than others so they were applied sparingly.
There are always multiple ways to make a part. The connecting rods are 3/4" in one dimension. I had a block of 1" thick aluminum just about the right size to get both rods out of. Instead of facing it down to 3/4" thick and using the method of holding I used for many of the other pieces, I used another method that might be of interest.
I drilled and reamed the holes right through the block with the holes over a table slot. I milled the profiles 3/4" into the 1" thick block. I filled the profile with plaster of paris and let it cure. Then I flipped the block over and milled off the 1/4" from the back side. leaving the finished parts locked into the block. With a bit of effort the parts can be pushed out of the plaster of paris. A bit of warm water cleans them up nicely.
A few manual milling operations produced the forked end, the radius where the end meets the beam and some edge chamfering to make them pretty. I inserted the bushings and they were done. One of odd things about the original plans is that almost every moving connection has a bronze bushing (a good thing) EXCEPT for the small end of the connecting rod at the wrist pin. Just where you'd think you'd need it most. I chose to add one there as well. I put a small hole in the small end also where I can manually oil the wrist pin. It will need to be oiled since there is no crankcase oil vapour or pressurized oil system as in a typical engine.






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Interesting technique with the plaster of Paris - I love to see creative jigs and work holding ideas like this!

And it all continues to look superb!

<Edited because autocorrect produced a somewhat off-color version of what I intended to say!>
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Thanks to both of you. I saw the plaster of Paris idea in Home Shop Machinist (or similar). Works really well for CNC type jobs where work holding is a challenge. I use it as the need arises.

Yes you have to watch that auto-correct :)
I think the email notification went out before you edited it though.

I can only imagine what some of the email notifications come through as for my posts. Sometimes I read what I post and go back and make major changes after to make it more readable (I hope).
Way cool, I never saw the plaster of paris trick before. How long does it take to cure? Also I was wondering what screws you use on your parts
when you screw to the wood board. Conventional machine screws or wood screws? I have a lot of surplus epoxy so that is what I use.
Very interesting build Dave, Thanks.
It depends on how thick the plaster is. The grooves I filled were 3/4" deep and 1/4" wide. From experience I left it over night and it did the job fine. After removing the parts it was solid but still damp about halfway through the 3/4".
I also mix it pretty thin so it will flow so that slows it down. I believe it's actually a chemical reaction (like concrete) not so much a drying thing.
Drops of plaster on the bench harden in about an hour. And it gets pretty stiff in the mixing container in about 15 min.
I just use wood screws so I can drive them in on an angle if I have to to according to the wood thickness vs screws on hand.
I have used other methods such as super glue with accelerator, contact cement. There is also that fixturing plastic that comes in beads and melts in hot water. You can pack it in while it's soft, let it cool and soften it again to pull the parts out. Obviously a bit sketchy if the machining creates too much heat.
Tabs are the preferred method but for complicated reasons my crappy machine won't mill tabs reliably.
What ever gets the job done without having to do it over :)
I think it's safe to say that while Dave Gingery was kind of a genius , Vince Gingery is only trying to cash in in the "gingery name . I've seen several books with errors , incomplete ...

Love the build Dave , keep 'm coming .
My plan has always been to use Drawn Over Mandrel (DOM) tubing for the cylinder so I picked the nearest standard size available to give me a piston close to what was in the book. The OD of the tubing was 1.25 OD. The inside measured as 1.120. Pretty thin walls but it makes no difference. I didn't want to get involved with boring a cylinder.
I've used DOM in the past in 2-1/4" ID for the Parcell and Weed engine and found it to be very good. As specified it is seamless (it has no ridge on the inside) and is very round.
This time, although the tubing did not have a visible seam on the outside and no seam or ridge on the inside, it did have a score mark the length of the tube inside. It was quite visible but you could barely feel it. I figured I could lap it out so I used a brake cylinder hone for a while and it got better but progress was pretty slow. I added some 40 micron diamond paste to the hone and went at it some more. About a half hour later I had increased the diameter by only 1 thou. The mark was still visible but could not be felt.
So I made the pistons to suit the cylinder - a typical 2 thou under the cylinder diameter. They dropped through the cylinder nicely and if you block the end of the tube they sit in the cylinder as long a you care to do that until you release the end of the tube. There is also a bit of spring action on the piston if you press on it while it sits in the cylinder. SO I'm pretty convinced the score mark is not going cause a leak. Especially with the rings installed.
The pistons were made to be 1.117 dia. Both pistons are the same.
I didn't like the 94 thou wide ring grooves spec'd in the book. IMO big fat rings have too much friction, are too stiff and really don't seal any better. So, more according to the Trimble calculations for making rings I made them about 1/25 the diameter of the piston. I already had a 47 thou wide grooving tool that I made for the V-twin so I used that.
I also moved the rings down a bit on the piston to give a bit more crown in case I need to remove a bit from the crown to provide running clearance. In the picture you can see the two pistons and the finished cylinder.
I'm thinking what I might do is loosely wrap a piece of clear mylar around the two pistons to create a clear cylinder and mount that into the water jacket. Then I'll turn the engine over slowly to visually see if the running clearances I calculated are present.

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I'll look over the carb in the book and maybe start there. I haven't even considered it yet.
Close - not really. It's all the little stuff that will take a lot of time.
Hey Dave: Happened to be browsing around this site and came across your engine build. Hope it all turns out and runs well. Sure looks up to your high standards as far as machining goes. If anyone can figure it out; it would be you. I will be watching for the video of the first run. Just getting around to painting my Maytag model 72 half scale. Only parts left to machine are for the kick starter. I will crank it over with a drill first to see if it runs. Lots of fun,
Thanks for your vote of confidence Ron. Compared to you I'm a bit of a hacker.
The pictures look better than the machining actually is. My machine has gotten so sloppy that it's making a mess in some places. A file helps.
I think I mentioned before that I may have to rename it the "Hubble" (after the telescope) that was made perfectly "wrong". I really have no idea if it's going to run.
Work s has slowed to a crawl now as I measure everything and make wooden mock-ups to get the cylinder placed in exactly the right place (or exactly the wrong place).
The CAD model shows that several thou off and there could (likely will ) be piston collisions.
Time will tell.
I'm sure your Maytag will run fine (just like the other one). Nice work.
Thanks to both of you. I saw the plaster of Paris idea in Home Shop Machinist (or similar). Works really well for CNC type jobs where work holding is a challenge. I use it as the need arises.

Interesting engine and a clever use of Plaster of Paris. It reminded me of a job (when I had to work for a living) where we had to hold jet engine turbine blades after worn areas were built up with weld and needed remachining. We used to place them in a temporary holding fixture that located on a couple of critical points. The space around was then filled with Woods Metal, which melts in hot water but is solid at room temperature. When the machining was finished, the whole thing was dunked in hot water which melted the Woods metal that could be reused.
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I started on the water jacket which is made of 1 x 2 structural tubing and a steel plate that matches up to the plate on the front of the engine. Same old work holding technique as previously with the stock screwed to a board.
But to ensure the placement of the water jacket actually works according to my drawings I decided to make a copy of it from wood and fit a clear cylinder made from rolled up mylar sheet.
For you interested in work holding, try this. In a photo below you'll see some 1/8 wood fastened to the board but it has no convenient holes to hold it down. I found this technique on the NYCCNC Youtube channel.
You take your piece of stock (material type is not important) and put masking tape on the back leaving no gaps if you need to use multiple strips.
Lay some masking tape down on the mounting board larger in area than the stock piece. Make sure all the tape is well adhered. It helps to clean the stock and the mounting board with alcohol or brake clean to be sure there is no oils to affect the tape sticking.
On the mounting board tape spread an even coat of thickened super glue - don't spread it too thin but be sure it's even.
On the work stock tape spray super glue accelerant.
I use a product called Mitre Bond which comes with the glue and the accelerant. It is meant for quickly tacking together mitre joints. Say a corner joint. You spray one mitre and put glue on the other. You line them up and the instant they touch the super glue goes hard - really hard. Beautiful stuff.
SO you line up the stock (with the accelerant) over the mounting board (with the glue) and set the stock down while quickly putting pressure on it. Boom. It's stuck. Put lots of pressure on it.
The reason for the tape is that you can pry the stock up off the board by lifting the tape. So the glue is really only holding the layers of tape together.
Since milling is all a shear force there is no way the action of milling is going to push the part around even though it's just the tape holding it. You should be careful that machining does not heat the part too much since the heat will soften the sticky on the tape. (little to no effect on the super glue).
The other reason for the tape is that it peals off the back of the stock (and the mounting board) leaving them clean avoiding nasty cleanup of glue from your part.. The glue on the tape goes in the garbage with the tape.
Yes I've heard of the double sided tape method but the tape tends to be much thicker and I've found the part squirms around especially if it's a small part.
Just another thing to try.
SO I made the wooden water hopper and I tacked the metal one together. I am not going to fully weld the metal one to avoid warping of the baseplate. I will spread a filet of JB weld on the seam (since it has to be water proof).
In the last picture you can see the assembled engine with the (barely visible) clear cylinder.
AND it proves that my 3D model is correct. (I had no doubt but it's nice to see what's going on).
There is about 72thou between the pistons on compression. There is almost zero gap on exhaust (as in the model). I may have to add a bit there (compromising my compression slightly). And the intake (assuming a properly placed slot shaped intake port) should give me about 1/2" of piston travel during intake.
Doing the math (rough only) theoretically I should have at least 6:1 compression.
We'll see. The geometry of the piston movements LOOKS ok but it remains to be seen if it will run or fight itself on combustion.
I have along way to go before I can actually fire it up.





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