# Atkinson Differential Engine - Making it work?



## dsage (Feb 27, 2020)

Even if I get plans from reputable sources I always re-draw them in my 3D modelling program. By the time I get finished modelling the engine I have a full understanding of how it goes together, and I almost always find errors or omissions in the drawings which I am able to correct. Back in 2015 I acquired the book by Vincent R. Gingery " Building the Atkinson Differential Engine" pictured below.
 I had already built the "Atkinson Cycle Engine" also by Mr. Gingery with success. So I thought it would be a good addition.
Right from the beginning I was not impressed with the book. It starts off with how to make patterns to make your own casting and the dimensions required there and follows on with machining the castings. There are several places in the book where dimensions are confusing to say the least. To top it all off in the assembly instructions it states that you need to fiddle a bit to make it all work and even suggests that some parts might have to be re-made in order to get the mechanism to operate properly. Following that it is suggested that a very long run-in period of turning the engine over with an electric motor might be required.
To me none of that should be necessary. In my opinion if the plans are worth anything and you build it according to the plans the engine should be capable of running with not much more than typical fuel and ignition adjustments.
One of the advantages of a 3D model is that if the parts are constrained properly you can actually manually animate the engine by say turning the flywheel which will make all the other pieces move. Being that this engine has a very strange mechanism it was interesting to "operate" the model and see how it achieves the typical 4 cycles. You can turn the flywheel a few degrees  and take measurements and figure things like compression etc.
What I noticed right off is that the engine was going to have VERY low compression. I figured about 2:1. I checked my drawings with what was in the book (factoring in the confusing drawings) but I still could not realize better compression.
 I concluded that something had to be wrong with the drawings so I put it on hold and decided I'd ask one or two builders of the engine I'd seen running at shows what they had found to be wrong and what they did to fix it. I asked one fellow and he just said simply that he had to change something but he couldn't remember what. I contacted another fellow that had one running on YouTube. He said he made a wooden model first before he built it but had no details on what might have been altered.
SO I decided I wasn't going to build it and the files have been sitting on my computer for 5 years.
Then about a year ago on this forum I saw a post by Gordon entitled "Atkinson Frustrations'
https://www.homemodelenginemachinist.com/threads/atkinson-frustrations.30272/
Gordon had built the engine and was asking for help to make it run. One of his many comments was that the engine had poor compression. There was also another contributor (Ramoye) who was having the same problems.
So it appeared my drawings might have been correct. It was agreed that the plans were sketchy at best and unfortunately both of the Gentlemen  had been through making a lot of new parts with limited success.
I decided that maybe I should analyze the model more closely to see what changes could be made to the mechanism to correct at least the compression issue.
This was no easy feat because almost any change of only a few thou in positioning of parts can make a HUGE difference in the operation in the differential motion of the two opposed pistons. I went through a couple of weeks of change something / observe the motion / see if it looks reasonable / make measurements to see if compression improved and mostly to see if there were collisions of parts and if the engine was still able to be built.
In the end I think I've (more or less stumbled) come up with a configuration that MIGHT work. Unfortunately a lot of the changes are not suited to being made to an existing engine built from the original plans. Too many parts would have to be re-made.
BUT I can certainly build a new engine from my plans to see what happens.

***** WARNING - This project may be a complete failure - but I think I can trust my drawings to build it. Although my analysis of the operation of 3D model may end in disaster when it tries to run. *****

SO follow along on what might turn out to be yet another unsuccessful  Atkinson Differential Engine build.
I'll get started in a couple of days.


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## awake (Feb 27, 2020)

dsage, I have followed your earlier posts on this with interest, and and very much looking forward to your build!


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## Gordon (Feb 27, 2020)

I am really looking forward to seeing your results. It certainly is one of the most frustrating engines I have ever built. I have played around with a lot of changes and have not found anything which makes much difference. I have played around with my 2 D cad moving stuff around to simulate actual intake, compression, ignition but have not found anything which makes much difference. Occasionally I can get the engine to run for a short time but then it will not even try the next time even when nothing has changed in parts or adjustment.  

Gordon


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## dsage (Feb 27, 2020)

Well..... We'll see what happens. It might be a complete failure. But I think I've gained enough knowledge of what affect various part positions have on the operation that maybe I can "adjust it" (with minimal part changes) to get it to be happy.
My fear right now is that on the power stroke the right piston moves down the cylinder quickly as it is supposed to but the left piston begins to follow too soon after. I guess that effectively makes one piston fight the other with the expanding pressure. It's not too bad but it's one of those things that remains to be tested. I think I can make "adjustments" to reduce that effect when it fails.
Another concern is that it may not have much "Suction" on the intake stroke. i.e no incentive to bring in any fuel. You need a good "suction" to make a carb vapourize the fuel. This is not unique to my changes. I don't think the original design had much either.
Obviously this is all a crap shoot. This may end up being a shelf queen.
I am thinking of you (and others) in that it may be possible to modify an existing engine with my changes. But at this point I need to test some of my assumptions.


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## Gordon (Feb 27, 2020)

Suction on intake has not been a problem in that when it is turning over there is fairly good suction at the carburetor throat. I also wondered about atomazation and tried a vapor carburetor but that does not make any difference. Obviously this engine was never going to power anything useful. It barely keeps itself running. I would certainly like to know what other YouTube posters did to make the engine run.


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## dsage (Feb 27, 2020)

It's good to know that suction won't be a problem. In that respect I also wondered how much time it had to take in a charge with the small hole into the cylinder they specified. That's why my plan is to make the hole into a slot to take advantage of what my simulation shows is the whole portion of the intake stroke where it appears the pistons are moving apart from each other (creating vacuum) and cut the port off  before they start to move in unison to the left.
I tried a vapour carb on my other Gingery Atkinson engine when it stopped running reliably for some reason. In the end it was an ignition problem (you know the saying "most  fuel problems are ignition" and vise versa).
Anyway I found the vapour carb to be just as much trouble to get the fuel air mix correct. Although they don't have the problem with raw fuel being ingested.
 I use propane on my Parcell and Weed engine but even with it's special mixer intake valve it's a chore to get it just right to fire. There is a VERY narrow range of mixture where propane is combustible.
So I'm glad I'll be able to stick with a carb which is pretty adjustable.
Time will tell.
Being able to power anything requires horsepower and that's mostly dependent on compression. I'm hoping my changes will boost the compression without adverse effects.
The other Atkinson engine was a pretty sketchy design as well. Mine has very low compression. It runs and will run fast but it doesn't have much power.


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## dsage (Feb 28, 2020)

I decided to start with the flywheel. When I made the Atkinson Cycle engine I made a pattern and my friend and I cast a flywheel for it from aluminum. The first attempt had a lot of casting flash so we made a second one that turned out much better. Luckily I kept the first one and was able to use it for this engine (they are the same - close enough anyway). I had experimented with powder coating this flywheel back when it was first made because I'd heard that powder coating cast material can be an issue. It was true. If you just follow the normal procedure and put it in the oven cold, when it heats up to the typical 400deg or so the gasses in the casting come out an bubble up the curing coating. It leaves a rice crispy like finish of bubbles. The trick is to  heat the casting first above the normal baking temperature and coat the part while it's hot and put it back in the oven.
Apparently this works - I have yet to try it - but if you've ever tried removing power coating after it has cured it's very tough. So I figured it best to just use conventional paint this time.
I first turned the rough (and powder coated) casting to true it up and to remove the powder coat. A lot of hand work was required to remove the casting flash that was mostly around the spokes. I blasted it with ground glass and applied a bit of body work to make it pretty, primed it with etching primer and painted it.
In the picture the wheel is hanging inside of my 3x3x3ft paint booth from a rotisserie that turns the part slowly. This not so much a proper paint booth it's more of an exhaust booth with a reclaimed furnace fan ducted outside. It does a really good job at removing paint fumes, anodizing fumes and powder coat dust (or any other smelly stuff) from the shop but it also sucks a lot of air out of the house along with dust from the shop. So a painted part can sometimes end up with a bit of dust in the finish. I just add an extra coat of paint and if it's a problem I can buff the finish after.
The flywheel is held into the crank shaft with a collet. Although a lot more work than a key and set screw they work well. The flywheel needs to have a matching taper turned into the hub.


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## propclock (Feb 28, 2020)

Great looking flywheel Dave I am following with great interest.


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## dsage (Feb 29, 2020)

Most of the engine framework and moving components can be made from 1/4" extruded aluminum so I bought standard 6061 extruded material that comes in a range of widths. In order to simplify the order I purchased a 6ft long piece of 1/4" thick  x 6" wide material. What I didn't expect was that a plate that width would be cupped. Not a lot - maybe 15thou across the width (not as bad as it looks in the picture) but it was not acceptable when a couple of pieces had to be stacked such as the two tier base plate. So I had to cut each stock piece and put it in my hydraulic press to take the cup out of it. Once each piece was "flattened" to an acceptable amount it was machined to size. In the original engine the base plate is a single casting 1/2" thick. It was easy enough to get the tiered shape by stacking two 1/4" pieces rather than machining the step into a 1/2" piece.
The other issue was that the material was only nominally 1/4" thick but measured .260" . Not a big deal except perhaps when things start to stack up like in the front of the engine where the oscillating arms are stacked on top of the links etc. etc. The  spacers will need to be adjusted else it will affect the position of the cylinder.  And so it goes. I'll have to adjust my drawings.
I started making pieces from the bottom of the engine up. The first picture is of milling the four feet to go under the engine.
Then I proceeded up to the base plate. This is where I noticed the finished plate was about 10thou larger in both X and Y than it was programmed to be. I'm using a mill-drill converted to CNC. I guess I beat it up quite a bit making the George Britnell V-twin (actually two of them). I found the gibs on both axis loose allowing the table to shift around. I also found the quill had quite a bit of side play. I have an adjustment to fix that. So I spent a half day playing around getting the machine back in shape. I had to trim the previously made base plate to the correct dimensions.
After the "tune up" some test pieces were coming out right on size. In reality there isn't much on the engine where the outside dimension really matter since the original design is made from castings which can be notoriously off dimension. Hole placement is the only critical aspect of the build and they are now right on.
Sorry nothing of great interest to show so far. I'll be making plates for a bit.


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## dsage (Feb 29, 2020)

Nothing too exciting today either. I just turned out some more plates. The side panels, like the rest were originally castings. They would have to be made from 5/8" thick material. Instead I used my 1/4" plate and some 3/8 x 3/8 (which I had to machine down from 3/8 x 3/4) for the corner supports. I purposely made them a bit long so they could be fastened to the side panels with screws and then trimmed to the height of the side panels.


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## dsage (Mar 1, 2020)

Things are starting to come together. I assembled the base plate and side panels. You might note the one upright has drilled and tapped holes ready to accept the front plate. I forgot to do the others but that turned out to be fortunate because it was a bit presumptuous of me to think that the panels were all going to fit nice and flush at the corners given material and machining tolerances. After making the front and back plates I clamped them in place and used  a transfer punch to mark the proper place for the holes in the uprights.
The front and back plates is where I'm committed to my design. One of the major changes was to move the left oscillating arm pivot point down from the standard location. I found this changed the geometry of the movement to increase the compression significantly.
One of the tricky parts of CNC machining is holding the material. You have to come up with a secure fastening method that also (hopefully) allows you to do all the machining in one setup. It's especially tricky when you have a crappy mill drill machine like me because without the ability to raise the knee you have to get the height of the head correct to accept all of the tools used to complete the job. Raising the head during the job is not accurate. I have an assortment of different length collets, drill chucks and cut off reamers so I can drill and mill without losing my reference point.
The easiest way to mill on-the-flat is to screw the stock down to a piece of MDF (which is surprisingly flat).
The job required reaming the holes for the shafts so in the picture you'll see I've pre-milled pockets into the board so the reamers can pass fully through the stock.
The original casting had bosses for the shafts to pass through. I turned some bosses separately and glued them with JB weld to the surface of the plate. I also machined the water jacket mounting boss plate and glued it in place. There is no stress on these parts. They are essentially just spacers so the JB weld should be sufficient.
I extracted the locations for these pieces from the machining code and wrote a program to cycle around to the locations and stop at each. The bosses started with only small holes in the center so I could use a fine scribe pointer to get the boss centered over the proper location and press it down into the JB weld.
You'll see in the picture that both the front and back plates are stacked so the holes in both plates are perfectly aligned. The first step was to drill all the holes in the front panel and to ream the shaft holes. Some of those holes are used to hold the panel itself to the board because milling the profile will release it from the stock plate. This is another tricky part of CNC because you have to hold the stock and also hold the finished piece without having clamps in the way of the profiling process. (I avoid tabs for various reasons).
Yes I forgot the slot in the front of the water jacket plate before the picture. But that has to be done only to the front plate so I fastened it down to the board separately and finished that step. I didn't take a picture. I also made a couple of the shafts to stick through in order to get the front and back aligned before fastening them to the side panels.
SO it's finally coming together.


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## dsage (Mar 1, 2020)

I pressed in some bushings for the crankshaft and added the shaft and crank disk.
The bushings are 660 bearing bronze that even with a brand new reamer is resistant to reaming on size. So a bit of honing with an expanding lap took the last tenth or so out of the bore and surprisingly the shaft went right through the holes in the front and back plates. I was expecting that because the two plates were not perfectly flat (why mentioned previously) that when they were separated after being clamped for machining that the plate would spring back and the holes may not be aligned, perhaps tilted forward or back or side to side. Luck was with me.


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## johnmcc69 (Mar 1, 2020)

Looking good Dave!

 John


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## dsage (Mar 1, 2020)

Thanks. All the critical stuff is coming. I hope it works !!


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## awake (Mar 1, 2020)

Great progress!


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## dsage (Mar 1, 2020)

Thanks. A few more pieces to make and then I get to the water jacket placement, cylinder, pistons etc and work will slow down. I'll have to make and check placement of almost everything to be sure it's turning out according to my drawings. Small changes in the placement of those items appears to throw the whole mechanism out of whack.
Maybe like the original Hubble telescope mirror it will be "perfectly wrong".


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## dsage (Mar 2, 2020)

The oscillating arms are a prime example of why I always re-draw plans that I plan to build. On page 36 where you are creating the castings for the arms they give dimensions for the patterns. On page 81 they give dimensions for where the holes should be drilled in the castings. Unfortunately the hole in the tip of the oscillating arm turns out not to be concentric with the radius of the end. I just doesn't look  "nice" to have the hole off center. Assuming that the placement of the holes is important to the geometry of the  movement I kept those dimensions and adjusted the end radius to be concentric. Of course this throws off the general shape of the arm slightly because the curves joining the various bosses are no longer arcs as laid out on page 36. On paper one could (I suppose) just join the features with a French curve but that would make it more difficult to machine if you're using a rotary table. I kept the curves close to the original shape so as not to introduce interference between the arm and the cylinder (for instance). Since I'm CNC milling it, it makes no difference the shape. If producing the parts manually from my drawings, simple arcs and a bit of hand work could reproduce the shape I arrived at.
As with the front plate machining the machining process was to locate the position of the bosses on the wooden plate and mill pockets into the board so the reamer could pass through the plate.. The bosses were glued to the plate and the holes were drilled and reamed. Then those holes could were used to hold the arm to the board when it is release from the plate upon machining. Since the bosses were glued to the plate they needed to be faced off after to be the correct height above the plate since they are effectively spacers standing the arms off the front plate.

There are only a couple of more simple pieces to produce and then the work is going to slow down as I make the water jacket, cylinder, pistons, connecting rods etc. and position them accurately according to plan. Most of my changes in the geometry were made in these remaining pieces and their positions are critical.


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## Gordon (Mar 2, 2020)

You are making amazing progress in a very short time. FWIW I made the bosses with a shoulder to fit into the main part and attached them with four 4-40 socket head screws Worked well without depending on Loctite.  Example: 1.25 dia boss w/ 1/2" bore and 5/8 dia shoulder to fit a 5/8" hole in the main part with 1" bolt circle.

The problem with the hole location in the oscillating arm was one of the first problem I ran into also. I am amazed that of the many folks who have made this engine I could not find any mention of this or several other discrepancies I found.


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## dsage (Mar 2, 2020)

I guess maybe I should / could have taken that approach with the bosses. My thinking was that there should be no stress on them. They are more or less just spacers and the torque transfers through the arm itself. Then again I'm not a structural engineer. I guess if they break loose I can screw them in place (even from the front)
I'm somewhat in a "let's just build it and see what happens mode" because I'm thinking I shouldn't spend a lot of time on what might become a shelf queen.
You might see that my plates are all held in place with flat head / counter sink screws into non- countersunk holes. This helps locate the plates exactly where they need to be because the plates can't shift around under the screw head. I hate it when there are so many pieces that can be adjusted and you are trying to get reamed holes to line up. 
I plan to replace those with socket head cap screws one at a time when everything is running smoothly.

I have a question for you: I didn't read the book on this. I've given up on the book and it's sketchy suggestions.
What did you do to seal the water hopper? I'm pretty sure I don't want to take it all apart again to put sealer between the plates. I 'm also concerned about painting it for the same reason. I'm paranoid that taking it apart and adding sealer and paint will shift stuff enough that it will be a nightmare to get things aligned again.
I'm thinking I'll just put clear silicon on the seams from the inside, not paint the inside (can't paint silicon) and then just paint the  outside. OR maybe I'll just bead blast the whole thing and leave it plain?? 
Usually I anodize my aluminum pieces but it's VERY time consuming, my tank is too small for the larger pieces and I'd have to take it apart.
Suggestions welcome.

I didn't think about (and I didn't analyze) the position of the hole in the tip of the arm and it's affect on the operation. I don't think it would matter much. I was more concerned with the looks of it. The books whole avoidance of the issue and not mentioning it is what annoyed me. It brings doubt to the drawings at a time when you are trying to make things right.
I presume it was because it was easier to make the patterns using basic round curves.

Thanks for your interest.


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## Gordon (Mar 2, 2020)

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.


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## Gordon (Mar 2, 2020)

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


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## dsage (Mar 2, 2020)

Gordon said:


> 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.


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## dsage (Mar 2, 2020)

Oops. We must have been typing at the same time. I'll have a look at your picture


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## dsage (Mar 3, 2020)

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.


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## propclock (Mar 4, 2020)

Looks great Dave


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## dsage (Mar 5, 2020)

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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## awake (Mar 5, 2020)

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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## Ramoye (Mar 5, 2020)

Looks great Dave.

Ray


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## dsage (Mar 5, 2020)

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).


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## propclock (Mar 5, 2020)

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.


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## dsage (Mar 5, 2020)

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


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## stragenmitsuko (Mar 5, 2020)

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 .


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## dsage (Mar 8, 2020)

I only have experience with two of them (both Atkinson engines). And I think you're correct.


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## dsage (Mar 8, 2020)

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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## propclock (Mar 9, 2020)

Great Dave, getting vewwy vewwy crose. 
Got a carb in mind?


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## dsage (Mar 9, 2020)

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.


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## RonC9876 (Mar 10, 2020)

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,


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## dsage (Mar 10, 2020)

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.


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## Brian Hutchings (Mar 11, 2020)

dsage said:


> 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.
Brian


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## dsage (Mar 11, 2020)

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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## propclock (Mar 11, 2020)

Thanks Dave , very informative.


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## dsage (Mar 22, 2020)

Making of the clear cylinder turned out to be a good idea as it demonstrated visually that the drawings were accurate and also gave me some more thoughts on changes that might be beneficial. But it was not perfectly accurate for making measurements.
One of the stumbling blocks was, other than trusting the drawings, I couldn't figure out how to measure where to put the ports in the cylinder. The light went on when I noticed that everything could be measured from the tail end of the pistons and knowing the dimensions of the pistons I could measure exactly where the front of the piston was going to be (which is where the ports are located). The only thing that could throw that off is the height of the cylinder above the base plate because altering that dimension pushes the pistons in or out of the cylinder. I trusted the drawings for that measurement.
In any case it took quite a bit of checking to be sure I had everything setup and measured before possibly trashing a good cylinder.
The first picture shows milling the hole in the water jacket that the cylinder slips through. My machine is very sloppy especially when milling steel.  I also had to use a very long 1/4" end mill in order to reach through the water jacket to mill the other side to ensure they were concentric. In the end even though  it worked the hole turned out to be too small and out of round. Not a disastrous outcome because I then used a boring head to bring it perfectly to size (and round). (Time for a new machine).
After marking the cylinder with the port locations I used a 3/16" end mill to make the ports. You'll notice I've decided to make the exhaust port a slot as well and that decision came from observing the motions which indicated that (if the combustion was poor) there might be a point where the exhaust is being compressed again at the right side of the cylinder. So I thought maybe I'd "open the exhaust port a bit early. This whole port placement is sort of like a two stroke engine which I have no experience with. It's all a guess.
In any case the next series of pictures shows that my measurements for the placement of the spark plug hole landed it right between the pistons at "TDC" where I had hoped. The next picture is of the exhaust port slot placement where the left piston and right piston come very close together (about 1/16 apart). The right piston is almost gone to the right of the slot while the left pistons rings are visible. There will be no problem getting all the exhaust out.
The next picture shows the start of the intake motion. There is a bit of motion where there will probably be a bit of vacuum build up because the exhaust valve will be closed and the intake port is not uncovered yet. But I think a bit of vacuum build up will be ok when the intake port is finally uncovered.
The next pictures shows how (I hope) the slotted intake port will allow for a longer intake time and it's length is designed to take advantage of all of the motion that "appears" to be when the pistons are still creating vacuum before the port is covered up.
My next question is going to be what to use for valves. There is no need for conventional poppet valves because in this engine neither of the valves has to seal against compression and only residual combustion pressure. Those pressures all takes place between the pistons when they are both at the left end of the cylinder far away from the two ports.
I could use poppet valves but the springs would likely need to be very very light.
So I started thinking maybe a free floating ball and seat might be easier than messing about with spring pressures as the ball valves would be self governing.
Then I thought of reed valves. They might be most effective and are certainly used in two strokes but I have no experience with them. The good part is that the valves will be enclosed in pieces that are fastened to the cylinder over the slots so they can be experimented with. Also if I find the slots need to be modified I can just cover them up to a certain extent by the pieces that hold the valves.
Ideas are welcome.
PS> You might notice that the cylinder is at this point held in place by JBWeld spots. Since the cylinder is so thin I didn't want to risk silver soldering it in place and distorting it. I'm going to completely JBweld it in place eventually and form a nice fillet at the joint and eventually paint the water jacket (and maybe the cylinder assembly).


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## dsage (Mar 26, 2020)

I guess my thoughts on using reed valves is going to have to be implemented. I hadn't noticed that raising the cylinder to increase compression ended up with the intake valve making contact with the oscillating arm. Also sliding the exhaust manifold over to line up with the new slotted port put it in contact with the intake manifold.
Below are a couple of pictures of the collisions and then a few pictures of new manifolds using reed valves. The reed valves are in orange inside the manifolds.
There is still a bit of interference with the carburetor requiring it to be cocked on an angle to get the fuel hose on it but that might be solved with a 90deg hose pipe.
I pondered over what to use for the actual reed material. It needs to be very flat and springy so it will cover the port, seal properly and spring out of the way when pressure acts on it and reseal reliably. Then I thought of a small piece of feeler gauge. I made the dimensions of the manifold interior such that I could just cut the end off of a standard 1/2" wide feeler gauge and clamp it in place. This will also give me the ability to choose a thickness from a set that suits the application.
The problem right now is that I don't want to cut up my current set and considering that we are supposed to be isolated at home it's probably a bit irresponsible to go out to a store to buy a new set. If only they stocked feeler gauges at the grocery store 
The idea might have to remain as drawings for a while. Sometimes not a bad idea because I might think of a better idea. I could probably make one of the manifolds (they are fairly simple) and substitute the feeler with piece of mylar sheet to test the idea.

COLLISION OF THE INTAKE VALVE






INTERFERENCE OF THE INTAKE AND EXHAUSTS MANIFOLDS






CLOSE UP OF INTAKE MANIFOLD WITH REED VALVE (flat orange)






BOTH MANIFOLDS WITH REED VALVES (carb on an angle to accommodate the fuel hose connection)


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## awake (Mar 26, 2020)

Here you go - delivery to your front door:



			https://www.amazon.com/OEMTOOLS-25025-Blade-Master-Feeler/dp/B000BYGIR4/ref=sr_1_8?crid=30V170FRHGTMV&dchild=1&keywords=feeler+gauge&qid=1585250822&sprefix=feeler+g%2Caps%2C198&sr=8-8
		


Of course, there are plenty more options available from Amazon if you want something different, but the one shown is cheap (you are planning to cut these up, right?) and better yet is an Amazon Prime item. Of course, even with that, how quickly it will arrive in these perilous times is a question.

And of course, plenty of other on-line stores you could order from, starting with HF - but then you have to pay the shipping. 









						Feeler Gauge, 32 Piece
					

Amazing deals on this Feeler Gauge 32Pc  at Harbor Freight. Quality tools & low prices.




					www.harborfreight.com


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## propclock (Mar 26, 2020)

Following . Enjoying  your process. And progress.


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## dsage (Mar 26, 2020)

Awake:
Yes I guess that's an option. I never thought of it.
Thanks


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## awake (Mar 26, 2020)

A totally selfish gesture on my part - I want to see where you take this design, and how it turns out!


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## Gordon (Mar 26, 2020)

dsage said:


> I guess my thoughts on using reed valves is going to have to be implemented. I hadn't noticed that raising the cylinder to increase compression ended up with the intake valve making contact with the oscillating arm. Also sliding the exhaust manifold over to line up with the new slotted port put it in contact with the intake manifold.
> Below are a couple of pictures of the collisions and then a few pictures of new manifolds using reed valves. The reed valves are in orange inside the manifolds.
> There is still a bit of interference with the carburetor requiring it to be cocked on an angle to get the fuel hose on it but that might be solved with a 90deg hose pipe.
> I pondered over what to use for the actual reed material. It needs to be very flat and springy so it will cover the port, seal properly and spring out of the way when pressure acts on it and reseal reliably. Then I thought of a small piece of feeler gauge. I made the dimensions of the manifold interior such that I could just cut the end off of a standard 1/2" wide feeler gauge and clamp it in place. This will also give me the ability to choose a thickness from a set that suits the application.
> ...


I am amazed at how many errors there are in a design which has been around for such a long time. I encountered the same problems. I took some off from the oscillating arm and shortened the valve a little. I mounted the exhaust valve horizontally.


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## dsage (Mar 27, 2020)

Gordon:

Concerning your comment that you noticed the same issues, I went back and checked my backup drawings. When I drew the engine as per the book drawings there was no issue with the the intake valve colliding with the oscillating arm. It was close but not a problem.
It was only after making changes such as moving the cylinder up that it showed up.
So I'm at a loss why you saw that problem.
I haven't built the reed valve manifolds yet. I'm still deciding if I'm going to implement them.
I should have noted before that I don't have any piston rings installed yet and I do notice some compression on the compression stroke.
I haven't made the rings yet and will probably leave them to almost the end when I'm done playing around with the cylinder and I'm sure I won't be needing to remove the pistons.


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## rsholl (Mar 27, 2020)

Hi Dave Sage,

I've been trying to follow your build, definitely very interesting stuff but I'd expect no less from you.
As for the reed valves, my first thought was to the small reed valve used in the Cox model airplane engine. I see they have change some but about mid way down on the link is the new reed valves. On the old engine, they just used the small cir-clip to hold them in, they actually floated a small amount. Anyway, I figured if they worked in the little Cox .049 engine at 21,000 rpm they might work for your application. BTW, the Cox dealer is in Canada.





__





						Back End > 049/051 Parts > Cox International
					

Cox 049/051 Back End




					coxengines.ca


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## dsage (Mar 27, 2020)

Thanks Roy. I'll check them out.
I should probably post a cut-away (or something) of what I came up with so far. Maybe I'll get some constructive criticism on what I have.
Maybe tomorrow.
Thanks


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## dsage (Mar 27, 2020)

Below is what I have designed for the intake manifold with a reed valve.
The charge from the carburetor comes in through the hole in the back but it can't proceed until the vacuum pulls the orange reed valve (down). The reed is the cutoff end of a feeler gauge.
There is quite a bit of space around the sides of the reed so the charge can travel around it. There is also a bit of space at the curved end (not really visible).
There is a bit of a cavity below the reed to accumulate the charge. But the cavity is mostly there to make space for the clamp that holds down the one end of the reed.
The trick will be getting the thickness of the reed chosen properly. But there will be a range of thickness available in a full set of gauges.
The reed could be any material instead of the metal feeler gauge. Maybe a thin piece of mylar would be better?
Looking at rsholl's  suggested page from the Cox website. Plastic seems to be the material of choice.
I was trying to avoid burrs on the edge of the reed caused by cutting it that would keep it from sealing. (Just being lazy).
With the feeler gauge there would only be one cut and it would be under the clamp. A typical feeler gauge is 1/2" wide with a full radius on the end.
Also not really visible is that the clamp has been narrowed to about 1/16" width between the hold-down screws which are #0-80. Hopefully so leave the most flex possible.
The whole thing could be scaled down to reduce the mass of the reed. I just started with the original manifold size.
Comments are welcome.


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## propclock (Mar 27, 2020)

I forgot about the circular reed valves"with ears" on the old cox engines. They worked well.
Just for what it is worth. As a kid I gathered old .049 engines that had poor compression
due to ingesting dirt etc. They would not run on the original "cox" fuel. Fairly high nitro?
But being a " Mad Scientist"  I added some of my fathers Ronson Lighter fuel  to the mixture. Amazing !! even really really worn out engines would run??  They would 
run backwards most of the time so I guess they were " Dieseling" ? I really don't know
but I thought I should pass this along.  I got a lot of fun out of "dead" engines. 
What is in "cox" fuel or Ronson lighter fuel circa 1966? I have no idea. But it works!
Sorry Dave the  reed brought up old memories that I thought might be useful to others.


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## dsage (Apr 10, 2020)

Sorry. It's been a while since the last post.
Spare time is high but motivation has reduced.
I used the slower (and stronger) JB weld to affix the cylinder into the water jacket. So it was time to make the bosses that go over the port holes in the cylinder for exhaust and intake.
One thing that is nice about a CNC machine is that you can produce a large radius on the face of a piece of material without having to set up a rotary table or by some other cumbersome method. Of course you have to make a drawing of the exact conditions for the tool path.
The bosses need a radius on them so they sit nicely on the side of the cylinder.
In the first picture after the machine is set up  it makes multiple passes in an arc to the full depth of the boss. The second picture shows the result. The third picture is the finished boss with blind #2-56 tapped holes for the carburetor body to screw to. I used JB weld again to glue the bosses to the cylinder. As you will remember, the hole in the boss is round but the hole in the cylinder is a slot. But because of the thickness of the cylinder wall the air will follow the slot to the hole in the boss.

















I also started work on the reed valves since it looked like they might work.
The next picture is of the finished exhaust valve body with the recess where the reed will sit. You can see a couple of #0-80 tapped holes that will hold the clamp that holds the reed along one edge.
The reed covers a hole in the bottom of the recess. I purposely offset the hole thinking that air pressure would have more leverage to push the reed open.
In the second picture you see yet another method of holding material while it's machined. In this example the aluminum plate is contact cemented to the piece of MDF and the finished parts - once cut free of the stock - will be held by tiny finishing nails the heads of which turned out to be just the right size for the 1/16 cutter to cut around without hitting them. These parts were about the limit for my worn out machine. They are about 0.6" long, 1/16" wide and 1/16 high. It's always good to make  more than you need in case one gets messed up.
The last picture shows the finished exhaust reed valve. I used a piece of clear mylar for the reed and marked an X on it in case it was not visible in the picture. You can see the tiny clamp on the left used to hold it down.
I hold no hope that this reed will survive hot exhaust. It's more of a test to be able to manually crank the engine over to see if the two reed valves operate. They do seem to work quite well when you try to suck air  through them.
There is no need for them to withstand high pressures since they never see compression. Their only purpose is to route outgoing exhaust and incoming air.


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## propclock (Apr 10, 2020)

Yea ! Dave.


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## awake (Apr 10, 2020)

Now that's some tiny, fiddly work. If it were me, I'd say you need to make extras because, inevitably, one of them is going to wind up missing ...


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## dsage (Apr 10, 2020)

awake said:


> Now that's some tiny, fiddly work. If it were me, I'd say you need to make extras because, inevitably, one of them is going to wind up missing ...


As far as the tiny clamps are concerned I made one extra. I should have made more. But I have the CAD file so it's just a matter of glueing and nailing down another piece of aluminum, setting the reference point and pressing go.
(At least that's what everyone says is the case for CNC - isn't it ?) 
Luckily I can just loosen the clamp and slip in another reed so hopefully the clamp(s) won't go missing.
Thanks for tuning in.


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## dsage (Apr 11, 2020)

All of the moving pieces of the engine are finished so I decided to assemble it - hopefully for the final time. I plan to use a one-way clutch bearing on the end of the crank shaft for starting the engine. They work best if the shaft is hardened. The shaft is made from 1/2" O-1 oil hardening drill rod. I've had a Banggood induction heater around for quite some time so I thought it might be a good time to give it a try on the end of the shaft.
The fist picture is all stuff required to completed the job.
The induction heater that I having running on four car batteries batteries (48 volts)
A magnet held in the vise grips to tell when the drill rod becomes non-magnetic (the metal has reached the desired temperature).
A tin can full of cutting oil to quench with (it smokes but won't catch fire - and I have it around the shop)
The shaft with a wet rag around it to limit the heat to the shaft end.






The end of the shaft is stuck inside the coil. It heats up pretty quickly. It never really got as hot as I would have heated it with a torch but it did become non-magnetic and I let it stay hot for a couple of minutes.






A quick dunk and swish in the oil to cool it off. There was minimal scale on the surface easily removed with steel wool. I tested the shaft with a file and it was very hard. I tried tempering it but it was very hard to see the colour of the shaft being that it's inside the coil. I think it also heats up much quicker with the induction heater since there is no way to reduce the heat. So after annealing it ended up being a bit soft. So I went through the hardening process again and just left it hard. I suppose it might only be surface hardened because I normally heat the metal much hotter and for a longer period of time. But in this application surface hard is good enough.


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## propclock (Apr 11, 2020)

Way cool again. I bought one of those induction heaters and a big switching power supply.
So far it has just been a dust collector. I believe you have motivated me to finish an enclosure for it , Thanks for the motivation/ training.


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## awake (Apr 11, 2020)

Interesting induction heater - didn't realize they were available on sites like Banggood.

For tempering, I generally use the kitchen oven - just make sure the part is very clean and won't emit any fumes.


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## dsage (Apr 11, 2020)

Banggood has everything  
Quality is another issue. But it hasn't blown up yet in about 3 uses.
I hadn't thought of using the kitchen oven. I have one in my shop that I use for powder coating with an exhaust fan going outside. But the shaft is JB welded (seems to be the theme on this engine) to the crank disk. So the JB weld might be weakened by the heat. Even though they rate the slow stuff for 600deg (peak). This joint might be a problem in the future but it's easily tacked with my TIG welder if it lets go. I was just lazy when I stuck it together.


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## awake (Apr 11, 2020)

"Quality is another issue" - I've always thought it interesting that that particular vendor's name starts with "Bang"!


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## dsage (Apr 12, 2020)

It's finally time to make the piston rings so I can do the final assembly. The method I use is a combination of both the Chaddock and Trimble processes. Using the suggested calculations from those guys the rings end up being fairly thin which I like. It makes them easier to install and I think they seal better than fat rings.
Making the rings is pretty quick. I use grey cast iron turned into a tube according to the calculations. And then I part them off and lap them to thickness.
Making the holder to heat treat them is a lot more time consuming. There is a calculation for the diameter of the pin that holds the gap open while heat treating. It's a pretty theoretical dimension. I may have got it slightly wrong as I think the maximum diameter of the pin is supposed to be on the center line of the ring ends. But in the end it really makes little difference (IMHO) as long as they are springy when completed.
I only made the jig to hold 5 rings even though I parted off 10 (minus one off spec).
The rings are stacked in the holder and a cap is installed that keeps them in place and seals the container from air. A bolt holds it all together.
I heat the whole thing carefully with a torch to a dull red colour (no more) barely visible in a dark room and held for several minutes.
There is a whole process you are supposed to follow concerning time and temperature but it works fine (for me) approx as described. After heating they are left to cool until room temperature before opening the container. The rings have no scale. They are just dis-coloured and clean up nicely with some very fine steel wool.

While I had the engine all apart I bead blasted all the pieces. I actually used ground glass because it was already in the cabinet and it's a pain to change. It was a bit too coarse for a final finish in my opinion but it is perfect should I choose to paint it. (I probably won't - I don't want to take it all apart again).
In one picture you can see the installed reed valves. The exhaust valve has what's supposed to be a muffler stacked on top of the valve. The exhaust exits through three holes facing down (not visible).

You'll notice what looks like staining on the metal. That's just oil from assembling it. It is easily removed with some brake cleaner making the whole thing a uniform colour.

Some upcoming parts to make are holders for a magnet and a hall sensor so I can trigger the ignition. The ignition will be easy. I'll be using one of my coil driver modules and a car ignition coil.
A carburetor of some sort - I don't like the one in the book.
And finally a cap to glue on the end of that water jacket that I keep forgetting about,

I'm happy to report that the engine has fairly good compression and the valves seem to be doing their thing.
More on that later.


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## stragenmitsuko (Apr 12, 2020)

So they actually work do they .
Good to know . The induction heater that is


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## dsage (Apr 13, 2020)

stragenmitsuko said:


> So they actually work do they .
> Good to know . The induction heater that is


Yes. Seems to work. But I can't compare it to any other. I ran it at it's maximum (spec) voltage of 48volts and, as mentioned I thought it would heat the 1/2" rod hotter. I had hoped for orange or bright orange. Maybe the rest of the rod was sucking up the energy since it was wrapped in a wet rag. 
My batteries are marginal too. I didn't check the voltage under load.  Might have been some of it.


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## dsage (Apr 13, 2020)

I figured out the ignition pretty quickly. I'm using a hall sensor and magnet to trigger one of my coil driver modules.
I made a thin clamp to go around the crankshaft to hold a 1/8" dia magnet. The magnet will rotate with the crank.
Another disk holds the hall sensor and is mounted and cupped around the crankshaft bearing boss and is held in place by a set screw. The initial timing setting is done by setting the pistons at TDC and rotating the magnet clamp to the trigger point of the ignition. After initial setup the timing can be changed slightly one way or the other by loosening the screw on the sensor disk and rotating the disk slightly. This fine tuning can be done while the engine is running. All things considered IMHO it's a pretty compact solution.
You can see in the pictures how I mounted the ignition driver on the back of the engine behind the flywheel. The cut down Ford COP coil is mounted on the side of the engine. A battery holder with 4-AA NiMh cells plugs into a power connector. I didn't add a power switch because it's safe to leave the module powered up.
The ignition gives a nice hot spark at the 1/4-32 spark plug.

I still need a carb to try it out. That may take some time.
Getting close.


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## awake (Apr 13, 2020)

Eager to see & hear it run!


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## propclock (Apr 14, 2020)

Nice Dave , glad to see you are using your own ignition, Now my 1.414 cents worth.
Hall sensors draw several ma of power Reeds draw nothing unless the magnet
happens to stop on it. Also what, if despite your pessimism, this thing really takes off
and dances off the table?   Yea I know you have that big beautiful flywheel to stop it
 But why mess up that beautiful paint job ? add a switch and a power on LED 
Just my opinion.  I hope it dances , but not off the table.  Good luck Dave.


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## dsage (Apr 14, 2020)

Hmm. Good point on the switch.
I hadn't even thought of how to turn the engine off once it's running . My bad.
I must have been day dreaming and lazy as usual.
Ok. I'll add the switch - and maybe a light. Which I guess means a small panel to mount them. You're making work for me Paul.
To go along with the recurring theme of JB weld,  I'll glue it on the side of the engine 

I did a compression check this morning.
It has 70lbs of compression. That's good.

I'm working on an adapter so I can use a known good carburetor from my V-twin. It will be ugly (but temporary).
There are enough unknowns with this engine. I don't want to add confusion when it doesn't run.

I still believe there will be problems. The reed valves perhaps one of them. (The exhaust reed for sure).


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## propclock (Apr 14, 2020)

Compression!!!! its all just playing now,  congratulations!!


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## bluejets (Apr 14, 2020)

dsage said:


> The rings are stacked in the holder and a cap is installed that keeps them in place and seals the container from air. A bolt holds it all together.
> I heat the whole thing carefully with a torch to a dull red colour (no more) barely visible in a dark room and held for several minutes.
> There is a whole process you are supposed to follow concerning time and temperature but it works fine (for me) approx as described. After heating they are left to cool until room temperature before opening the container. The rings have no scale. They are just dis-coloured and clean up nicely with some very fine steel wool.



There is an additional process the rings should go through to bring them back to true round after the heat treatment otherwise they will leak.
Allowance must be made for this during the initial turning by allowing a few extra thou on the outside diameter.

Involves stacking the now-heat treated rings in a purpose made tube.
Then a fitting , similar to the clamp for heat treatment, clamps the rings together.
Assembly is returned to the lathe and the rings brought to true round and size.

Whether or not you agree or do it is entirely up to you.
I know it works.

Last pic shows a highly inviting path for the spark to jump to the frame from the plug cap.


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## dsage (Apr 14, 2020)

Thanks. I'm aware of that "extra step". The full process if you read the Trimble and Chaddock articles is to make them that thou or two oversized in the first place so you have something to skim off.
I don't subscribe to it because there is more runout in my lathe and especially the mandrel used to hold them that it's next to impossible (for me) to reliably "skim" off" a thou. It probably would do more harm than good. 
I make the rings exactly the ID of the cylinder - to within part of a tenth - polished to size if required. Then I use the gap to adjust for a fit. They were round when they were made - they'll be round when they are compressed - again just IMHO.
I've made so many rings  I can't count them and have never had an engine that smokes nor required any run-in to seat the rings. If your rings need seating in you screwed something up - again IMHO.

Actually the metal tip of the spark plug is well above (maybe 1/4") any metal. Then you have the insulated cap on top of that. The spark plug gap is only about 10 thou. So I don't think there's any chance of an arc through the cap to the frame when the gap is so inviting.

BTW in a previous post I noted I have 70lbs of compression with no run time on the rings. They don't leak.

Thanks for your concerns.


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## bluejets (Apr 14, 2020)

dsage said:


> I don't subscribe to it because there is more runout in my lathe and especially the mandrel used to hold them that it's next to impossible (for me) to reliably "skim" off" a thou. It probably would do more harm than good.



I would say this is a setup problem rather than blaming the lathe.
All machines have some degree of inaccuracy and it is up to the operator to compensate.
Even an old sloppy machine can produce accurate results.

However, as I said initially as I expected a negative reply, up to you.


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## propclock (Apr 14, 2020)

Rings and Religion, not worth your time discussing.  But
I have a cool way of adjusting the end gap. Learned from a master 
Dwight Giles. Put 2 ,600 grit circular  disks of wet /dry  back to back .
 ~3-4" diameter make a mandrel  to mount them on. 
Yes you can use scissors to cut them out  . Make a slotted  
I,use aluminum , shelf for your tool post .  In the lathe two  disks of W/D sandpaper spin in the groove . Some back up disks are needed 
for the W/D mandrel.  
Then you squeeze the ring against the rotating  W/D. The ring  resting on the slotted tool post rest. 
Nice square end gap , then  put the ring in you test fixture  measure the gap and continue until you are happy. 
You of course have a test fixture?   Just an accurate bore with a nice taper to test the ring end gap.  Use you piston to push it in square
 I have 2 V8s  48 rings.  It took very little time. .
 This is just for the end gap.  The how to make rings  conversation is where  it becomes , What software is best? 
The answer always is,   What works best for you. 
Anxious to hear first pops Dave.


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## dsage (Apr 14, 2020)

Sounds like a home-made version of a manual ring gap grinding tool that you can buy. I've used them for full sized rings. Totally manual with a handle you crank to turn (if I remember right) a two sided diamond wheel. Same process. Lay the ring on the little table and squeeze the gap. Test and repeat. I do something a little more crude but more or less the same process with like you say W/D paper.

As for first pops. Don't hold your breath please. In the end there were a lot of things I changed in the mechanism that could throw a wrench into the works. 
I won't be re-building it unless the solution is really simple. I'm sort of tired of this engine.


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## dsage (Apr 16, 2020)

OK. It's official !!
IT'S A DUD.
I made an intake manifold adapter for a carburetor from my V-twin engine that is known good (although it's pretty touchy) I put some fuel to it and gave the engine a spin with the drill. I made all kinds of adjustments on the carb and the ignition timing but I couldn't get even one pop from it. I finally hit it with some starting fluid and got one very quick pop. Only one in several tries. It also unloads the starter slightly when you apply the starting fluid as if there is something helping the starter. It may just be the lubrication of the fluid. It also smells a bit like exhaust when it's spinning with fuel. Probably all wishful thoughts.
It has good compression. If you put your finger over the sparkplug hole while cranking it loads the starter down.
The intake and exhaust reed valves "seem" to be doing what their supposed to be doing. If you put a paper towel in front of the carb it will be sucked in with no signs of blowing out. Same sort of thing on the exhaust port.
It shouldn't matter if the valves are leaking because they are not a factor in the compression. As long as the fuel is being picked up by the pistons on intake, the compression and ignition take place at the other end of the cylinder so leaking valves will not be a problem.
The only thing I can think of is the fuel is being sucked in but it's not making it to the other end of the cylinder.
Upon checking the spark plug it was found to be wet. So maybe the fuel is not a vapour any more after traveling along between the pistons. Liquid fuel would not ignite. Although you'd think the starting fluid would remain a vapour.
Food for thought.

It has tons of spark because I'm driving the COP coil directly (without a ballast resistor) from 4-AA NiMh batteries.
SO I'm at a loss. Usually you can get some encouraging pops and it's just a matter of finding the sweet spot in all the adjustments.

Gordon:
Sorry Pal. I did my best to figure it out. At least it does have compression so you can rule that out of the things that ail this engine. Now it exhibits the other problems you described on you post. One of note is that fuel is coming out the exhaust slightly.
For now it seems it is doomed to join yours on the shelf.

Sorry to have strung all of you along on this build.
I'm going to put it aside for a bit while I go on to other things that need to be done around this place.
I may visit it again in the future if I come up with some revelation that doesn't require re-building it.
I'll post more then.


And no I didn't get around to putting the cover over the water jacket or adding the switch to the ignition


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## propclock (Apr 16, 2020)

Bummer, makes no sense?


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## awake (Apr 16, 2020)

How disappointing! Maybe a midnight revelation will occur, and you will realize some simple adjustment that will fix all ...


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## stragenmitsuko (Apr 16, 2020)

A suggestion : 
try using propane as a fuel . 
Just a small needle valve into the intake circuit .
That would rule out the non vaporising or condensing fuel issue .


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## dsage (Apr 16, 2020)

Tony:
I briefly let the engine breathe in a bit of propane from a torch placed just outside the carburetor intake. It didn't seem to respond at all. But from my Parcell and Weed engine that runs on propane I know it can be VERY finicky as to the ratio of air to propane. The is a very narrow range where propane is combustable.
So there might be some hope there. But Gorden says he tried propane and a vapour carb (and almost everything else  ) and didn't have any luck.
It will be worth some more experimentation though.
Thanks

Andy: Yes I'll need to sleep on it.

See the next post.


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## dsage (Apr 16, 2020)

I made a really crappy Youtube video of the motion works. I just videoed my PC screen.
My explanation timing is bit off on the exhaust port but hopefully you'll get the idea. Don't forget the reed valves are over each port controlling which way gasses move. I deleted the valves from the model so you can see the slotted ports.
Also sorry I couldn't zoom it more but I had to leave access to the flywheel on the screen so I could rotate the engine.
Maybe you'll catch something I hadn't noticed.


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## dsage (Apr 17, 2020)

Stay tuned I'm not done with it yet  
After consulting a fellow club member there is some suspicion that my crude reed valves may be leaking.
I have another idea worth a try.


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## jquevedo (Apr 17, 2020)

i just finished building an Atkinson engine, designed loosely copied from Jan Ridders and inspiration form an engine built by an old friend Frank Kurtz,. 

Trying to get my engine running i experienced something similar to your situation, IO was using an ignition built from a designed published in Model engine builder ( loos very similar to the one in your pictures), 
My problem was the ignition, changed to a trusty CH ignition added a new Hall effect sensor and played with timing and guess what it started running, after that was playing with fuel and timing and the engine now runs quite nice.

Timing for spark is supposed to be around 135 Deg, i placed my spark at 110 deg to make it run, I Know all events in the engine are happening at the right time like opening and closing of valves, compression, expansion, intake duration are of the right duration and timing so  not sure why the need to advance that much the ignition spark but that is where my engine desired it to run.
Tried posting a short video of it running but this site does not allow .MOV files (?)

I understand the frustration but  once your head cools down you may want to think about the ignition, mine was giving very strong initial spark and then going dead silent and then spark again..


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## awake (Apr 17, 2020)

jquevedo, nice build on your Atkinson. I'd love to see the video. You are right that you cannot upload .MOV files to the forum - in general, video files are way too large - so most people put the video on YouTube and post a link.

Note that Dave (dsage) is building the opposed-piston Atkinson, which, by all accounts, is a much more difficult animal to tame. There are a lot of successful builds of the style that you have made (though yours is the first I've seen with a belt-driven OHC!), but as I understand it, very few if any of the opposed-piston style that will run consistently.


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## dsage (Apr 17, 2020)

jquevedo:

Nice looking engine I'd like to see the video as well. I have the Gingery version of that engine. But (as mentioned by Andy) this is differential engine - a different beast.
Yes. A lot of folks have problems with their ignition systems.
If anything is right about this engine it's the ignition system. It has a very hot white spark. The coil driver is laughing at such a calm application.
But thanks for being concerned about it. It is a common problem.

The timing on this engine only has a very narrow range because the pistons are only in front of the spark plug hole for  a certain number of degrees.

Thanks


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## RonC9876 (Apr 17, 2020)

Dave: Are you one of us guys that can’t get gasoline to burn? Sometimes it seems that way. I went through the same problems with my Novi engine. Your description of the smells of fuel burning and the unloading of the starter work load brought back the frustration of all that work and no results. That engine sat on the shelf for a couple of years. I know I told you all about it. Just a faster cranking speed was all it took and it was off and running. Something so simple but not understood. Keep on plugging. It will run eventually.


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## dsage (Apr 17, 2020)

Yes Ron. It seems it is so 
 Your solution to the Novi was certainly un-expected and strange.
I can give it a try but my next fastest drill is about 3600 rpm. The wacky mechanism might fly apart 
Once I get the motivation I'll try simply adding a light spring behind the reed valves to ensure they are seated.
Motivation is low today.


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## Gordon (Apr 18, 2020)

dsage said:


> Yes Ron. It seems it is so
> Your solution to the Novi was certainly un-expected and strange.
> I can give it a try but my next fastest drill is about 3600 rpm. The wacky mechanism might fly apart
> Once I get the motivation I'll try simply adding a light spring behind the reed valves to ensure they are seated.
> Motivation is low today.


I would be inclined to think that the spring tension on the intake valve would be too high, not too low. When you turn the engine over do you get a good suction at the intake? If you have good suction it should draw fuel into the cylinder. Correct mix is a different question.


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## dsage (Apr 18, 2020)

Gordon:
I did say I was going to try a spring behind the reed valve(S) meaning both just to be sure they are both sealing to some degree. As you say the intake should be very light but a slight pressure might be beneficial just to be sure there is no funny business going on.

Upon a bit of investigation the intake reed with no spring pressure does snap shut on the exhaust stroke (there is nothing coming back out the carb). So it's probably ok to leave it as is. So I did.
BUT keep in mind that there is a lot of volume and pressure of air on the exhast stroke pushing on that valve so that's why it snaps shut.
Read on
Yes I have very good suction on the carb. BUT I think this could be a false indication of what's going on because if you put your finger over the carb - a complete blockage - then vacuum will build quickly making it look like everything is ok but it might be a different story under slight vacuum.
Read on
The exhaust reed is a different story. I added a spring behind it because there is a distinct possibility that if it is leaking only slightly then air could be sucked back in through the exhaust reed rather than through the carb especially on low intake vacuum and low flow that might not be high enough to snap the exhaust reed closed.

So I did add a spring behind the exhaust reed and there was a distinct difference in the sound while cranking. The engine did not even pop though. Now it might be a mixture issue.

I slept on it a bit and I think what I'm going to do is smoke test the engine i.e get a big fat cigar an blow the smoke through a small hose in front of the carb and see where it goes while cranking. I'll leave the spark plug out at first to see if the air/smoke is even being transferred to the spark plug end. After that I'll put the spark plug in and see if the smoke makes it's way to the exhaust port (or anywhere else it shouldn't be). This should also indicate compression issues if the smoke comes out the ends of the cylinder past the rings.

Gordon:
This might be something you can try on your engine and report back.

Gotta go find a cheap cigar. I don't smoke.

Later.


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## awake (Apr 18, 2020)

Dave, good idea. If a cigar is not handy, what about some burlap bag? Yeah, probably not something lying around either, but that's what my uncle used to used to burn in a little bee smoker (to calm the bees).


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## dsage (Apr 18, 2020)

awake said:


> Dave, good idea. If a cigar is not handy, what about some burlap bag? Yeah, probably not something lying around either, but that's what my uncle used to used to burn in a little bee smoker (to calm the bees).



A good idea. I tried just a wooden stick but it didn't produce enough smoke.
I found an old cigar in my golf bag - really old. I guess 30 years ago it was cool to smoke a cigar while golfing.
I blew some smoke through a small hose in front of the carb and it was tough to tell where it was going. Certainly some went in but it may have also been blown out. Again not enough smoke in one dose (mouth full)  to analyze it properly.
So I stuck the cigar right on the carb. My poor carb has nicotine stains now  but the engine did pump the smoke to the spark plug hole and when the plug was put back in it came out the exhaust.
But I'm still skeptical because the cigar requires a bit of draw probably increasing the vacuum and maybe masking a lazy valve.
What might be required is a densely smoke filled container for the engine to draw freely from.
An automotive EEVAP system smoke machine would be ideal. Might have to cobble something up.

Better still, I think I'm going to get rid of the reed valves and investigate fitting poppet valves in somehow.
Back to the CAD drawings.

It'll be a while.
Suggestions welcome.


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## mayhugh1 (Apr 18, 2020)

Your version is too well thought out (and great looking, by the way) to not run. After getting over the disappointment of it not immediately taking off, that area of your brain that just won't let things go will eventually figure it out. It'll signal you one evening just as you're about to fall asleep or one morning right after you wake up. - Terry


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## dsage (Apr 18, 2020)

Thanks Terry:
I think a running engine is in there somewhere. It's just a matter of figuring out what it wants. It's a weird one for sure.


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## Gordon (Apr 19, 2020)

dsage said:


> Thanks Terry:
> I think a running engine is in there somewhere. It's just a matter of figuring out what it wants. It's a weird one for sure.


With my engine getting fuel to the combustion chamber was not the problem. Flooding was the problem. I turned the engine over via Gingery method of a V belt to an electric motor which allowed fine tuning fuel mix on the fly. When I got it running for short periods the fuel mix adjustment was extremely fussy. Just a very slight adjustment of the mix went from starved to flooded. 1/32 to 1/64 of a turn. The problem is with the combustible mix. I believe that is a combination of limited compression and a very short combustion stroke which is not enough to actually create the proper mix. Actually your guess is as good as mine. 

Gordon


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## dsage (Apr 19, 2020)

Gordon:
Thanks. Those are good clues. I've decided to ditch the reed valve on the exhaust. I have a poppet valve almost designed (no chips yet). I'll see what happens with that.
For now I'm hoping the reed intake valve will be ok since there appears to be enough volume and pressure to hold it closed on the exhaust stroke.
Yes lots of guessing going on with this one.
I have lots of compression now. I hope that helps.
Thanks for the feedback.


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## Peter Twissell (Apr 19, 2020)

When engines are reluctant to for up for the first time, I have used butane gas to get them started.
Butane will ignite over a very wide range of mixtures, so it's easy to get going and then add in the liquid fuel.
I use a little pencil torch, filled with lighter gas. It has a regulator (of sorts) and I can pull the head off the end, leaving just a small outlet tube which can be pushed into a length of silicone tube to direct into the intake.


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## dsage (Apr 19, 2020)

Peter Twissell said:


> When engines are reluctant to for up for the first time, I have used butane gas to get them started.
> Butane will ignite over a very wide range of mixtures, so it's easy to get going and then add in the liquid fuel.
> I use a little pencil torch, filled with lighter gas. It has a regulator (of sorts) and I can pull the head off the end, leaving just a small outlet tube which can be pushed into a length of silicone tube to direct into the intake.



Good idea Peter. I'm glad you pointed out that trick. I have one of those torch pencils and will give it a try.
Thanks again


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## awake (Apr 19, 2020)

Dave, I found myself thinking about the video you posted above, early this morning when I woke up for my nightly OMB* call. Not sure why that was what popped into my head, but as I pondered it, I got to wondering about the way the spark plug is exposed just before it fires, and the fact that it is a very narrow space between the pistons that is acting as the combustion chamber. Is it possible that the mixture does not have a chance to come into adequate contact with the spark? This may be a complete red herring, but just in case ...

*OMB = old man's bladder.


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## dsage (Apr 19, 2020)

awake said:


> Dave, I found myself thinking about the video you posted above, early this morning when I woke up for my nightly OMB* call. Not sure why that was what popped into my head, but as I pondered it, I got to wondering about the way the spark plug is exposed just before it fires, and the fact that it is a very narrow space between the pistons that is acting as the combustion chamber. Is it possible that the mixture does not have a chance to come into adequate contact with the spark? This may be a complete red herring, but just in case ...
> 
> *OMB = old man's bladder.


Yes. This is a possibility. But what else can be done. If you want compression the pistons need to be close together. 
I tried changing the timing to various positions. Some way after TDC where the space would be wider (and of course less compression) and it didn't change anything.
FWIW There is a bit of space under the spark plug (not much) to gather a bit of charge that might ignite and carry into the gap. Wishful thinking though.
I'm guessing as (Gordon suggested) the whole thing is going to be very dependent on the mixture. I'm thinking it will need to be very lean to be more combustible. I think he also mentioned his engine was temperature dependent. That might indicate a change in mixture (like most engines) as it warms up.

Who knows.
One thing at a time I guess.


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## teeleevs (Apr 19, 2020)

dsage said:


> I made a really crappy Youtube video of the motion works. I just videoed my PC screen.
> My explanation timing is bit off on the exhaust port but hopefully you'll get the idea. Don't forget the reed valves are over each port controlling which way gasses move. I deleted the valves from the model so you can see the slotted ports.
> Also sorry I couldn't zoom it more but I had to leave access to the flywheel on the screen so I could rotate the engine.
> Maybe you'll catch something I hadn't noticed.



Seems to me in the video that the orange piston may need to have a little gap to uncover the spark plug sooner, also a trembler coil might work better, there would be no need for timing, just switch it on.


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## mayhugh1 (Apr 19, 2020)

Maybe try warming with a heat gun or hair drier?


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## dsage (Apr 19, 2020)

By a "gap" do you mean that maybe a little cutout or notch in the edge in the piston? Might be an idea. I'll keep in mind. Thanks.
It's hard to see in the animation (and it's not exactly like the real engine) but the piston does go slightly past the spark plug gap/tip.
Also I actually have to be careful to set the timing so the mechanism is just past TDC where the pistons just barely start to move apart. Otherwise the mechanism may not move in the right direction (or at all) when ignition occurs.

Your idea of a multi-spark ignition is a good one. I have such a driver already made and I use it on a hit-miss engine. It's a good idea to give it multiple chances to fire.
I'll look into moving it over to this engine.
Thanks for the suggestion.


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## dsage (Apr 19, 2020)

Terry:
Heat. Hmmm. A good idea. All suggestions are welcome.
Another one for the list.

To all:
Thanks for all the suggestions.


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## Nikhil Bhale (Apr 20, 2020)

Hi Dsage,
I am new to this site and new to this hobby so my idea may be completely wrong.
Can you use starting fluid to see is the engine runs?
I work in offshore industry and we spray CRC contact cleaner on TC inlet sometimes if engine is not responding.
It works most of the time.

Nikhil


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## dsage (Apr 20, 2020)

Thanks
Yes I tried starting fluid, propane and butane and of course the regular fuel (naptha). Still no action.
Those things work on engines that were known to be previously working. In this case the engine has never run and it is quite likely it has other issues.
I'm currently working on a better exhaust valve. Maybe that with make it act more normally.
Thanks for your interest.


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## bluejets (Apr 21, 2020)

bluejets said:


> Last pic shows a highly inviting path for the spark to jump to the frame from the plug cap.



Did you investigate this..??


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## dsage (Apr 21, 2020)

BlueJets:
No. There is no need to investigate it. Go back and look at the SECOND LAST pic (post 66) you're referring to OR even more obvious the first and second pics of post 76 and you can see for yourself there is lots of clearance - even without the silicon rubber spark plug cap.


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## bluejets (Apr 21, 2020)

Yes well if you say so.
I have seen spark jump a lot further than that at times in free air.
Especially since you say you have a really strong spark and you are not even getting a murmur of a bang.
Have you tried it without the boot on the plug?


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## dsage (Apr 24, 2020)

I've been spending some time making proper poppet valves for the engine. Both exhaust and intake.  I had to scale the intake height down to avoid the interference with the oscillating arm and did the same for the exhaust valve body. Internally they are about the same as the book valves.
The engine sounds more "normal" as it cranks over now so maybe I can rule out the valves as the issue now. Intake suction and exhaust pressure seem more usual now.

As suggested, I also added the multi-spark (buzz coil) type coil driver. That puts multiple sparks into the cylinder over the full duration of rotation where it could possibly fire. (Thanks for reminding me to try that).
I tried starting it again with no carburetor at all. Just spraying starting fluid into the open hole in the valve body. It did not appear to be trying to start but the cylinder was getting warm and I noticed a puff of smoke once from the exhaust valve. So maybe now with a proper mixture it will respond. I also forgot to try the other suggestion of butane from my small torch.

SO
I went back to my drawings for the carburetor that is supposed to go on this engine and noticed it has an extraordinarily small air intake hole in it. It's only 0.078" diameter. Which to me seems crazy especially when the piston is a bit over 1" in diameter. The rest of the passage to the cylinder is 0.25" diameter. The only reason for such a small hole I can think of is that maybe the air passing through it would be moving at a pretty high speed. Maybe the air blasts into the fuel jet that is right behind the hole and makes for better atomization? I suppose also with such a small hole it would work like a throttle and keep the engine from running away (it has no throttle). It all seems pretty sketchy to me.
One thing that is for sure, the carb I was using from my V-twin that has an air intake well over 0.25" probably isn't going to work. Even though it does have a throttle that can close the air  passage down.

A question for Gordon:
Have you fiddled with the carburetor and the size of the hole? Any insight into it's use. I don't care much for it and was not considering using it. But it's very simple so maybe I'll make one up and see how it goes. Maybe I'll add a variable opening somehow.
At that point my engine will be pretty much as per the book except for the increased compression and modified port timing.

Below are pictures of the exhaust valve followed by both the valves installed on the engine.


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## bluejets (Apr 24, 2020)

My Atkinson cycle engine will run with the carburettor main throttle 1/8" diameter closed completely off and running on just the air bleed hole 40 thou.
Piston is 32mm diameter and no, it is NOT sucking from elsewhere.


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## dsage (Apr 24, 2020)

bluejets said:


> My Atkinson cycle engine will run with the carburettor main throttle 1/8" diameter closed completely off and running on just the air bleed hole 40 thou.
> Piston is 32mm diameter and no, it is NOT sucking from elsewhere.


Not to confuse the two engines:.
MY Atkinson CYCLE engine also runs as you suggest. That's why it has an air bleed hole (for idle) But it also has a throttle.
But we are talking about the Atkinson DIFFERENTIAL engine in this thread and the carburetor it's supposed to run on.. It's a whole different beast and I'd rather not confuse the two.
BUT you bring to mind another idea. Maybe this was your intent?
I could possibly try the carb off the CYCLE engine to see if it works.
Thanks for the idea.


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## bluejets (Apr 25, 2020)

Yes, engine type is irrelevant, point was the capacity of the cycle engine I built used around 32mm piston and it will run on very little air volume passing the throttle and needle valve, in this instance, through an idle air bleed hole of only 40 thou diameter. 
In the photo you can see the main throttle inlet is capped off and only relies on air draw through the air bleed hole.


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## dsage (Apr 25, 2020)

Point taken. I can give the carb a try if it fits.


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## Gordon (Apr 25, 2020)

The carb needs high speed air flow because there is such a short intake cycle.
Attached is the carb I finally had the best luck with. I used 1/4" throat dia but since the throat is constricted by the main jet the air flow is high speed.
I give no guarantee that anything will work on this temperamental beast. 
I will have try to figure out how to embed PDF files in the message body. 

Gordon


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## dsage (Apr 25, 2020)

Thanks Gordon.
 I'll look it over. Looks easy enough to build too. So it could be another in the arsenal.

Thanks


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## dsage (Apr 25, 2020)

Gordon:
As pointed out in the first post in this thread I always model drawings I receive to be sure I understand them.
Can you tell be what diameter of the small hole is that the needle tip goes into?
The #50 comes down and the 1/16 comes up but what is between is not dimensioned.
Thanks
Also the 0.190 needle assembly must be loose in the 13/64 (0.203) body hole - No? Or are you just letting the two hexes seal it.









What I have so far. You can see where the hole should go at the end of the needle to join the two existing holes.


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## Gordon (Apr 25, 2020)

dsage said:


> Gordon:
> As pointed out in the first post in this thread I always model drawings I receive to be sure I understand them.
> Can you tell be what diameter of the small hole is that the needle tip goes into?
> The #50 comes down and the 1/16 comes up but what is between is not dimensioned.
> ...


Per the note: It is #60 drill. It is 1/16 dia x 7/16 dp and then drill #60 through to the #50 hole on the top. The #60 is actually the fuel passage into the main body. The #60 in the side is actually the jet. The jet must be pointed downstream.

Yes the .190 hole is sealed by the hex of the needle assembly and the #10-40 lock nut on the top. I have put some sealer on those surfaces if I thought that I was getting too much leakage.

That is the problem with making drawings for yourself and and not for distribution. I understand what I am trying to do but it is less clear to others. I generally am just trying to record or clarify my build or check out the design.

As you can see opening up the throttle body makes more air flow % and less velocity.

Note: I used brass hex because that is what I have but it does not have to be hex.

Gordon


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## dsage (Apr 25, 2020)

Ah Yes. I didn't read the whole note. Makes sense now.
I noted some useful details of your carb that I think can be used to improve the original carb. The original looks easier to make if I remove some of the outside details. Also the air flow can be played around with by replacing the simple piece in the front with the hole in it.
Yes the notes on the air path are interesting.

Thanks.


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## teeleevs (Apr 25, 2020)

bluejets said:


> My Atkinson cycle engine will run with the carburettor main throttle 1/8" diameter closed completely off and running on just the air bleed hole 40 thou.
> Piston is 32mm diameter and no, it is NOT sucking from elsewhere.


I will ask one question, how much compression does it have?  I have a small engine that has never run, Putting a timing light on it revealed that the spark would fire each side of top centre but miss the full compression one, it too would get warm when driven by the lathe but so too does a bicycle pump, conclusion too much compression. I am still to investigate that.


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## dsage (Apr 25, 2020)

teeleevs said:


> I will ask one question, how much compression does it have?  I have a small engine that has never run, Putting a timing light on it revealed that the spark would fire each side of top center but miss the full compression one, it too would get warm when driven by the lathe but so too does a bicycle pump, conclusion too much compression. I am still to investigate that.


70 pounds. measured with a compression gauge.  But that doesn't really tell the whole story.
Theoretically - just by the measured spacing between the pistons when intake stops and when they come together at maximum compression I calculated approx 7:1 but that's by no means accurate. The measurements were just something I used to compare between changes to see if I was making headway. It's about where I quit trying to make it better and things started colliding etc.
I does bounce back when spun into the compression cycle. That's usually a good sign (sometimes).
Yes I don't make much of the cylinder getting warm. It was just an observation. Although I did see a puff of smoke from the exhaust once - just once.

In your case perhaps your ignition is not strong enough to fire the plug under full compression.
Not the case here.

Thanks


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## dsage (Apr 29, 2020)

I've been busy trying a few things. All of them failures. I tried a slightly modified version of the book carburetor. Conclusion - complete junk. I should have used the time to build the one Gordon presented a few posts back. The book carb doesn't have a venturi so the moving air does not create a vacuum with which to suck in fuel through the orifice. The air just knocks fuel off the needle and orifice in hopes it will be vapourized into the air stream. I blew some air through the finished carb and it actually pushed fuel back out the fuel delivery hose.
SO I made an adapter for a spare carb I have for my Howell V4 / V8 engine. That carb makes a spray of fuel as nice as a spray gun when you blow air through it and it is small and has a throttle.
Still no luck getting the engine to run.
Then after observing the motion of things again in my CAD program I had a revelation.
If the engine does not fire, then when the right piston goes through it's power stroke where the gasses are supposed to be expanding, instead (because it didn't fire) there is a huge vacuum created in the cylinder. More than the amount of volume compressed because the right piston moves very quickly to the right.
I always wondered why there seemed to be a pretty strong vacuum on the carburetor - much more than could be explained by the fairly short and relatively slow intake stroke.
What I think is happening is that the strong vacuum created in the cylinder by not firing is pulling fuel/air in through the carb when the intake port is uncovered. The vacuum is relieved but the fake charge is quickly pushed out the exhaust when the left piston follows along in the exhaust stroke.
I think this was pretty obvious when I looked at the intake valve popping open. It had a huge excursion - almost the full 0.1" limit of the spring. I would have expected it to barely open being self regulating.
So I think there is a fundamental problem with having two atmospheric valves especially on this engine.

So you might ask why doesn't a normal (four stroke) engine have a problem with vacuum in the cylinder when it does not fire. On a four stroke engine with cam actuated valves, the vacuum in the cylinder cannot open the intake valve so the vacuum persists until the the exhaust valve opens.
On a two stroke engine if it does not fire then the vacuum might help bring in the new charge or at least the fuel is coming is anyway by it's normal action of pressurized crankcase. And it's the compression stroke that follows. With this engine the intake stroke follows and it is being messed up by the missed power / exhaust stroke.

Gordon I believe you observed fuel dripping out your exhaust port. This may explain that. i.e the fuel is being sucked in and immediately blown out the exhaust port. I have a similar problem.
I think you've been lucky that the intake stroke actually pulled in some new charge or there was enough left around after the failed exhaust stroke to get it to run.

I'll admit that if it does fire i.e. you somehow stumble on the exact mixture then in may be self sustaining. But I think the first time it misfires it's doomed to failure unless conditions are just right for it to survive the screwed up mixture.

Let me know if you think I'm missing something. My brain hurts.

You might need to have a look at the video I posted a few posts back that explains the motion of the pistons to see what I'm guessing is the problem. Keeping in mind the action of a misfire condition.

I'm going to have to do some thinking about this before I go any further. I'm not going to do any more work on it without a clear direction. Maybe some sort of mechanically actuated intake valve??

Comments welcome.


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## teeleevs (Apr 29, 2020)

dsage said:


> I've been busy trying a few things. All of them failures. I tried a slightly modified version of the book carburetor. Conclusion - complete junk. I should have used the time to build the one Gordon presented a few posts back. The book carb doesn't have a venturi so the moving air does not create a vacuum with which to suck in fuel through the orifice. The air just knocks fuel off the needle and orifice in hopes it will be vapourized into the air stream. I blew some air through the finished carb and it actually pushed fuel back out the fuel delivery hose.
> SO I made an adapter for a spare carb I have for my Howell V4 / V8 engine. That carb makes a spray of fuel as nice as a spray gun when you blow air through it and it is small and has a throttle.
> Still no luck getting the engine to run.
> Then after observing the motion of things again in my CAD program I had a revelation.
> ...


Silly question but are you trying to run it the wrong way?


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## dsage (Apr 29, 2020)

Good question. And you had me worried for a minute. 
But I went back to the book and I am turning it the way it says to. (flywheel clockwise looking at the motion works).
That said, some two strokes - namely my old full sized marine engine -will run in the reverse direction just fine. (And this engine is as much a two stroke as a four stroke).
SO I went back and analyzed the motion works when turned backward and it seems it goes through reasonable motions but on the power stroke when turned backwards the pistons are moving more together down the cylinder rather than one moving fast to absorb the rapid expansion of gasses.
You have tweaked my interest in what might happen if I turn it "backward" though. I'll try flipping it by hand tomorrow but to give it a good try I'll have to make a new one-way bearing starter for my drill. I have a spare bearing. I'll see what happens.
Thanks for asking.

PS> I'll have to change the spark timing as well. Luckily I made that easy enough to do.


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## dsage (Apr 30, 2020)

teeleevs said:


> Silly question but are you trying to run it the wrong way?



teeleevs:

I will get to trying turning it backwards.
BUT

Back in post #98 Awake posted:


awake said:


> Dave, I found myself thinking about the video you posted above, early this morning when I woke up for my nightly OMB* call. Not sure why that was what popped into my head, but as I pondered it, I got to wondering about the way the spark plug is exposed just before it fires, and the fact that it is a very narrow space between the pistons that is acting as the combustion chamber. Is it possible that the mixture does not have a chance to come into adequate contact with the spark? This may be a complete red herring, but just in case ...
> 
> *OMB = old man's bladder.



SO I woke up this morning thinking about this and I think there might be something to it. Especially since I Have no firing at all.
At least it's something I have to consider. I'm not sure how to address it though.
To explain what Awake was trying to point out is that In order to get the compression up I ended up with only 1/16" between the pistons at TDC. Compounding the issue is that the spark plug is off to the side of the cylinder and not even in the combustion "chamber" (there really isn't one).
ALSO  I had to reduce the spark plug size to 1/4-20 from the 10mm original plug because of it's new location and it's sitting on a boss not much bigger than the plug. So there is even less volume of charge being collected at the tip of the plug.
This is compounded again by the fact that when the left piston goes to the right the spark plug is literally "hanging out in free air" behind the piston. So my thinking is that if anything, there is fresh air trapped around the spark plug not combustible charge when the pistons come together briefly in front of the plug again. At a minimum it will not be what's between the pistons. Then there is the issue of if the combustion will propagate between the pistons.
The latter issue is somewhat taken care of by the multi-spark ignition (another contributor suggestion) because the spark is now still firing when the piston gap increases as they move apart and are well down the cylinder.
SO I don't really know if this is the real issue but it's something I need to look at. I don't really know how to solve it considering the current configuration of the moving parts.
On the original design there was a huge space between the pistons at TDC becasue there was almost no compression. This might be why the original works to some degree.

I'll have to think on it some more.
Some more suggestions are welcome.
Thanks

The spark plug is off to the side of the cylinder. The gap between the pistons is only about 1/16"








The spark plug is in free air at the end of the power / exhaust stroke. Both pistons are at the right.


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## stragenmitsuko (Apr 30, 2020)

Yes the position of the spark plug is at a far from ideal location .
Just thinking out loud , what if something like a couple of tig needles would be inserted from opposite sides of the cilinder meeting each other in the middle .
That would put the spark where it should be . 

Hope you nail it , would be a shame to make such a beautifull design go to waste .


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## Gordon (Apr 30, 2020)

I think that you are correct on your vacuum theory if there is no firing. Unburned fuel keeps accumulating until it is super flooded. 

I tried running the engine in reverse and that did not work. It had better compression in reverse rotation but it did not fire. 

I did find that the engine seemed to fire better when the timing was very retarded. Perhaps 15° ATDC. It would not run but it fired more consistently. That may be because of your theory of vacuum on the return stroke which dilutes the mix from the unburned gasses as the chamber becomes larger the mix air/fuel gets closer to a combustible mix. I also wondered about the "fresh" air trapped in the spark plug boss. I shortened up the boss to minimize the dead air space. My spark plug boss is threaded into the main cylinder so I could play round with that. 

Like everything else I tried nothing seems to make any appreciable difference. Mostly the engine looks cute as a shelf elf. 

Gordon


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## dsage (Apr 30, 2020)

stragenmitsuko"
The rods in the cylinder is a thought except that (unlike a normal engine) both pistons move down the cylinder so the left piston would clip the rod(s) off. Thanks for thinking about the problem though.

I had thought for about a nano second that the spark plug could go in the bottom of the left piston with a hole in the piston top for the electrode to peak out. But then the spark plug would have to ride along up and down the cylinder with the piston. (Plus there is no room inside the piston because of the con rod.). Lots of silly thoughts come to mind when you're grasping at straws.  

Gordon:
Thanks for giving me more insight into your engine and what you've tried. I did notice in my animation that it might have more of an intake stroke running backwards (i.e. more compression). Interesting that you noted that. Did you also change the timing? to go along with that. Because it would then be on the wrong side of TDC.
But I think the biggest killer of the backward running idea is that the pistons are more or less moving together down the cylinder and if it does fire I think the pressure and the mechanism might actually stop the engine.

It's also good to know that (if you are running the normal compression) that yours does not fire reliably with more gap between the pistons at TDC (where mine has almost none). This tells me that it could still be a mixture thing because when yours it at TDC with the large(r) gap the spark should be able to get to the mixture. I have somewhat accomplished a work around for this with the multi-spark. But that just leads to ignition when there is less compression so it's counter productive.
The mis-fire leading to vacuum is certainly going to mess things up.
I had a thought of an electrically controlled intake valve that is locked out until the real intake stroke starts (BDC). Then the vacuum can be released out the exhaust valve when it opens. Then unlock the intake and let it work normally.

I had thought about the spark plug and it's distance from the pistons when I made the boss. The tip of the plug is just flush inside the cylinder before I added the copper gasket. So it's still about as close as I dare make it. (My cylinder walls are very thin so I couldn't screw it into the wall itself?

All food for thought.
Thanks for participating.


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## awake (Apr 30, 2020)

dsage said:


> So my thinking is that if anything, there is fresh air trapped around the spark plug not combustible charge when the pistons come together briefly in front of the plug again. At a minimum it will not be what's between the pistons. Then there is the issue of if the combustion will propagate between the pistons.



Yes, this is what I was thinking, but you've said it much better / clearer than I did.

Here's a thought, FWIW - what if you clipped the corner of one or both pistons, so that there is a bit more of a chamber at TDC? Particularly if you cut off a corner from the left-hand piston, it would expose the plug sooner, perhaps allowing some swirl to occur at the plug - ?

Not that I actually know what I'm talking about ... !


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## dsage (Apr 30, 2020)

awake said:


> Not that I actually know what I'm talking about ... !



No, actually that's a good suggestion. I just wish I cold get it to at least respond a bit first. I'm surprised that it does not fire at all especially with the multi-spark is firing from just before TDC to well beyond when there should be mixture moving around. Even though the compression is going down. I think there's a nasty combination of things going on.

And for the doubters that think I don't have a spark. (a logical thought).
I put my spark tester (gap) in the circuit and there is lots of spark. i.e it's jumping a gap in series outside the plug much larger than the plug gap on it's way to the plug.
And no it's not sparking to ground outside the plug. I looked at it in the dark.

I'm going to ponder a bit on simple things to try before I get carried away modifying any parts.

Thanks for the suggestions.


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## Cogsy (Apr 30, 2020)

I forget what engine it was, but I once built an engine that for some reason had the end of the plug down a fairly deep 'hole' in the combustion chamber. I was concerned that even if the plug got enough of a charge to fire once then it would be surrounded by exhaust gases and it wouldn't fire again. It turned out to run just fine though, which suggests to me that your plug probably isn't trapping fresh air around it's electrode (I think that's what you're thinking). It looks like an interesting engine and I hope you get it sorted.


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## teeleevs (May 1, 2020)

dsage said:


> stragenmitsuko"
> The rods in the cylinder is a thought except that (unlike a normal engine) both pistons move down the cylinder so the left piston would clip the rod(s) off. Thanks for thinking about the problem though.
> 
> I had thought for about a nano second that the spark plug could go in the bottom of the left piston with a hole in the piston top for the electrode to peak out. But then the spark plug would have to ride along up and down the cylinder with the piston. (Plus there is no room inside the piston because of the con rod.). Lots of silly thoughts come to mind when you're grasping at straws.
> ...


I'm thinking that the spark plug should be in its own little combustion chamber so there is a rush of mixture into the chamber as the piston uncovers the hole. Just a thought from my Diesel experience.


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## dsage (May 1, 2020)

teeleevs said:


> I'm thinking that the spark plug should be in its own little combustion chamber so there is a rush of mixture into the chamber as the piston uncovers the hole. Just a thought from my Diesel experience.


Yes, that's a thought. Compression is a real problem on this engine and anything that increases the combustion chamber volume would lower the compression. Also I'm trying to solve the problem without doing any major work on the engine. An added combustion chamber would mean work on the cylinder etc. etc. (it never ends.).
Also I think my multi-spark ignition being fired for along period when the pistons open up is sort of like a huge combustion chamber. Somewhere in there I figure it should fire.
It's all guess work at this point. But I'll keep your suggestion in mind. Thanks

I have something I'm going to try soon to eliminate the vacuum issue on a mis-fire (I hope). I'm pretty sure it is one of the issues I need to eliminate if I'm going to move forward.
I did a lot of flywheel twisting today starting from various positions and have proven that there is a pretty serious vacuum on the carb being created on what is supposed to be the power stroke during a mis-fire condition. IT's many time greater than the proper intake stroke vacuum. And all that fuel / air is pushed straight out the exhaust a few degrees of flywheel rotation later.
I need to do some work around the house so I won't be working on it so often.
Later.


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## teeleevs (May 2, 2020)

dsage said:


> Yes, that's a thought. Compression is a real problem on this engine and anything that increases the combustion chamber volume would lower the compression. Also I'm trying to solve the problem without doing any major work on the engine. An added combustion chamber would mean work on the cylinder etc. etc. (it never ends.).
> Also I think my multi-spark ignition being fired for along period when the pistons open up is sort of like a huge combustion chamber. Somewhere in there I figure it should fire.
> It's all guess work at this point. But I'll keep your suggestion in mind. Thanks
> 
> ...


I fear that the combustion chamber will remain filled with spent gasses with no way of it scavenging, so the spark plug would have to be near the cylinder so the mixture would rush past it to repressure the chamber.


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## dsage (May 2, 2020)

I understand your concern and it could be an issue at some point. I can cross that bridge when I get there.
But you gotta burn something first to get trapped spent gasses. And we're not there yet. No pop yet.
On the exhaust stroke there is even more tight clearance between the pistons - also round about 1/16" so I think all the gasses will be getting out ok when there are any.
The vacuum in the cylinder on what's supposed to be the exhaust stroke (when it doesn't fire) is real. I hooked up an open ended hose with fuel in it to the carb and opened the needle valve and the throttle. When I spin it over by hand just in the area of the exhaust stroke it makes a huge suction and the fluid comes right up the tube to the carb. All that charge would be going right out the exhaust an instant later when the exhaust port is uncovered.
The real intake stroke an instant later seems normal and barely moves the fluid.
I suspect the real intake charge has to be getting messed up.

I'm working on something pretty complicated to try to get rid of the problem but it's going to take some time.
I'll try this first. Hopefully it results in a normal charge that fires. I'll write down your concern.
Thanks for the feedback.


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## Ken Brunskill (May 3, 2020)

Dave, 

I am building Dave Perallt's design of an Atkinson Differential, at this time have machined all the parts except the pistons and rings, did a trial fit (see photo), during this trial fit discovered I was short some bearings, which arrived yesterday. Our mutual friend Paul D. suggested you contact me, and got me reacquainted with the HMEM posts, and I thank you for reaching out to me.
Having read all the posts, and your progress, the one thing that I see as a potential and worth some thought is, on the Perrault design the POWER piston (3/4" Dia.) has  three (3) 1/8" x 45 deg angles at the top of the piston, one centered in line with the Con-Rod, the other two at 20 deg from the one on center, the spark plug is at 20 deg., which would put the upper most 20 deg. chamfer of the piston in line with the Spark Plug,  with the other two below it to align with the exhaust port. This appears to square with the comments & observations in earlier threads. I'd like to share the details with you but do not want to run afoul of copyright issues.


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## dsage (May 3, 2020)

Nice looking work. Seems to be a fair bit different.
I see no reason you can't take a picture of the finished piston you made (if possible) and post it here.
A picture is worth a thousand words. But no drawings please.

Gordon:
Is this the engine design that you have combined with the Gingery to arrive at what you have?
Comments?


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## Gordon (May 3, 2020)

dsage said:


> Nice looking work. Seems to be a fair bit different.
> I see no reason you can't take a picture of the finished piston you made (if possible) and post it here.
> A picture is worth a thousand words. But no drawings please.
> 
> ...


That is different than the design I partially used. The design i partially followed was by Brooks Pendergast. I also would like to see the piston design. It sounds like it is completely different than either engine we have. See post #21 for a picture of mine.


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## dsage (May 3, 2020)

Thanks Gordon:
So yet another one lurks out there 
Ken contacted me by email with some details.
I think it would be safe to post a piece of one of his CAD drawings of the piston.
He posted above a description of the angles involved. I'm hesitant to implement that change until I really have no other choice. Compression is a precious commodity on this engine and it looks like it would steal quite a bit.
His engine must be considerably better in that respect.
Perhaps I should have started with those plans.
Looks like what Teeleevs is suggesting.


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## Ken Brunskill (May 3, 2020)

Gave this design some more thought, and thought that a bit of a description and/or explanation might help one to understand what my opinion is of this design.
1. the upper angle coincides or is perpendicular to the *Spark Plug *hole & *Intake Port*.
2. The small center angle is essentially a path for the exhaust to reach the *Exhaust Port*.
3. The lower angle coincides or is perpendicular to the *Exhaust Port*.

Dave rightfully is concerned that such a large 'relief' might negatively affect to compression, so on my build I'll start small and increase in 25% increments (looks as if I'll need to fabricate a holding fixture to accomplish that.) Dave suggested I start a thread on my build, will follow  up on that, not nearly as well as he has done, so be patient with this old man.


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## bluejets (May 4, 2020)

dsage said:


> Compression is a precious commodity on this engine and it looks like it would steal quite a bit.



There is a way to overcome this by using methanol fuel with castor (castrol M) as a lubricant mix and varying amounts of nitromethane.
There is also available, commercial mix at any hobby shop which uses synthetic oils.
The nitro is substituted for the equal amount of methanol in the mix.
On ignition, the nitro releases oxygen a bit like supercharging only with fuel.
With the rc aircraft engines, a 10% nitro mix usually cleans up idle and transition etc. and desensitizes the needle setting, all without any compression setting alterations.
By some quirk of nature, increases of 10% seem to have the most noticeable effect however, once at the 20% mark and above, normally compression lowering is required.
I have used it in volumes of up to 60% on the small cox engines but for others, 20% was the limit.
Thought it might help to mention.
Just one drawback is , burning causes acid release so necessary to use after run oil or simply flush out the internals after using it.
Can't imagine you'll be using bucketfuls so cost would be irrelevant.


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## dsage (May 29, 2020)

I'm back. Sorry it took so long but I had to prove / disprove my observation of a vacuum being in the cylinder when the engine does not fire. I decided to make a very elaborate intake valve arrangement consisting of the standard poppet valve followed by a sliding piston valve (not sure of the correct term).
It turned out to be one of those things that you draw and figure it's fine and then realize it won't work so you make a change. Eventually when it looks good you end up with something possibly way more complicated than it needs to be. So please don't comment  "you should have done it  this way". It's what I ended up with after a lot of changes.
Unfortunately I had to throw some electronics at it.
The theory was I'd needed to keep the poppet valve because it will seal properly when there is pressure in the cylinder under normal operation. The problem to solve was how to relieve the vacuum in the cylinder (that will open the poppet valve) but don't let it pull air through the carb. Then, when the proper intake cycle begins, enable that proper vacuum to the carb. That's where the piston valve comes in. It's solenoid operated and it's set up like a directional valve. It vents the cylinder vacuum when the poppet opens but through the use of a couple of hall sensors that detect the proper intake timing it closes the vent and opens up the passage to the carb.

The picture below is the solenoid I pulled from by parts bin. You can see it is fastened to the top of the water jacket and pulls  the piston that is inside the valve block. At rest the piston is in vent mode. Behind that you can see the standard poppet valve that leads to the cylinder.







Below is a CAD drawing looking from the top of the valve block with the piston in vent mode.  The vent hole is the small one in the piston valve and body facing you. The vacuum will come up through the poppet valve  and will pull air in through the vent  instead of the carb.







The next image is from the carb input side also when in vent mode. The passage to the carb is blocked by the piston valve. Vacuum comes in through the poppet valve (green) and air is pulled in though the vent on top (not the carb).








Looking from the top again, the next picture shows the piston valve when the solenoid pulls in. The vent is blocked off and there is a direct path to the carburetor (up in this picture).







From the carb side you can see there is a direct path through the block past hole in the the piston valve where you can see the valve stem of the poppet valve.








Obviously the trick to operating the solenoid at the right time is to time it with the motion of the pistons. This turned out to be fairly easy by adding a rotating magnet plate to the crank shaft and a couple of hall sensors on a stationary plate. The first hall sensor triggers a simple 555 timer (cheap) that activates a mosfet to turn on the solenoid. The second hall sensor resets the timer and de-activates the solenoid. The timer function is not really required. The chip is used as a cheap flip fop. But I took advantage of the timer function to turn off the solenoid if it gets triggered but not reset (depending on where the engine stops) after about a half second.

The picture below is the surface mount board I made for the timer / driver fastened to the frame. Building that was not without problems. WOrked fine on the bench but when installed the buzz coil ignition was triggering it so I had to tack on a few extra components to filter the noise. That's why the extra stuff scabbed onto the board.
The nice thing about all this crap I have added is it can be removed with no signs it was there.







SO.... does the engine run now - NOPE.
But this addition does prove my observation of the vacuum in the cylinder when it does not fire.
Was it the source of the problem? Apparently it wasn't the only problem but IMHO one that could have been a source of mixture issues. So it was worth eliminating it before moving on to other issues.
This modification does function as expected. I can feel a vacuum on the vent port on what should be the exhaust stroke and then the vacuum on the carb seems about the same as before when the solenoid switches to intake mode. The exhaust valve also works because there is a (normal) brief period of compression in the cylinder after the vacuum is vented and the intake port is covered while the piston finishes a few degrees of motion to finish the exhaust stroke.

So what's the next step?
As some have suggested I might add a chamfer on the side of the pistons to make a sort of combustion chamber.
I also seem to have lost  a bit of compression (wear perhaps due to minimal lubrication). So I may make new pistons with the chamfer and with O-rings if I can find some of a suitable size This way I can put the current pistons back in if required.

BUT. This won't happen any time soon. It's summer and there are a lot of things that need attention outside the shop.

LATER - (much later)


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## dsage (Jun 16, 2020)

Although not the Gingery Design - apparently it can be made to work. Dave Perreault researched the original patents and managed to get one to work. Apparently very finicky. So maybe there's hope for me / us yet.


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## Gordon (Jun 16, 2020)

dsage said:


> Although not the Gingery Design - apparently it can be made to work. Dave Perreault researched the original patents and managed to get one to work. Apparently very finicky. So maybe there's hope for me / us yet.



An interesting point: I just looked at the original patent drawings again which are available on the web:






						Patent Public Search | USPTO
					






					pdfpiw.uspto.gov
				




The original design seems to have a mechanical actuator on the intake valve. I am not sure whether it actually controlled the intake or if it was intended to be a governor. I will have to take another look at that when I get a chance. I keep saying that I am not going to get sucked back into this thing but things keep coming up which renews my interest.

Gordon


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## dsage (Jun 16, 2020)

Yeah. Me too. Interesting.
I've been doing some drawings for new pistons with the chamfers to get more combustion space and O-rings. I've noted recently that I've lost a lot of the original compression I had. But strangely I can build a good vacuum. Not sure what's going on with the that. I'm not sure if the O-rings will last though because the rings pass over the ports in the cylinder and they will probably wear them out.
I'm grasping at straws really.
It's not real clear in the video what's going on with the intake valve on his supposed copy of the patent engine.
I'll ask him.
I'll also have a look myself at the patent drawings. Most times they are sorely short of information and possibly mis-leading info (purposely).

Back at it sooner than I wanted to be I guess.


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## dsage (Jun 16, 2020)

I got a pretty quick email answer from Dave P.

_The 10" flywheel Atkinson Differential engine has atmospheric valves on both intake and exhaust.
The mini Atkinson Differential engine has mechanical intake and exhaust.
Being so small, I found the need to come up with a different valving approach.... So that is when I decided to design my own valve arrangement.
Using atmospheric valves on this engine would make it very hard to build.... This slide valve simplified that whole section._

He didn't specifically say the patent replica engine but I guess that's the only 10" flywheel engine.
It's all very confusing with so many versions out there.


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## dsage (Jul 22, 2020)

I came across these engines on Youtube (again) and thought I hadn't seen them before. Turns out I had and I even contacted him via the comments on the first video (which you can read). Seems they are from the Gingery plans (with some embellishments). He says he figured it out first by building a wood model. Not sure if he stumbled on the solution to it's problems of if he's a more careful builder than I am. Anyway the results speak for themselves I guess.
I guess I've probably posted all this before. Sorry.




and another from the same Youtube page


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## Ken Brunskill (Jul 23, 2020)

Dave,
I am considering and of the opinion that O Rings for the Pump Piston will likely increase the compression, however multiple posts here in HMEM, indicate/suggest O Rings are not suitable when there are cross holes involved, seems logical to me. Will be trying that on my Mini Atkinson, I am of the belief that it will benifit yours for Compression as well as Vacuum.


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## jquevedo (Jul 23, 2020)

I made piston rings for mine from cast iron, old an trued Trimble method, they were made at 0.045 Inch thickness instead of the specified 0.062 inch, so far engine has very decent compression and suction from the carburetor.

I had some issue with the internal diameter of the rings, it was specified bigger than what my calculations gave.

Did not took much to make the rings sit well in the cylinder and make compression, ( no power assisted turning to set them was needed).
I may have been lucky, who knows we will see if it runs or just makes me place it on the shelf of failed projects.


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## dsage (Jul 24, 2020)

Ken:
I have been THINKING about this for a while but I've done nothing. I have abandoned the idea of O-rings for the reasons you mention i.e. I think they  will be torn up by the ports in the cylinder.
My recent thoughts will be to add a chamfer to the piston like you have to form a bit of a combustion chamber. I'm concerned that it will reduce the already low compression so I'll do some CAD measurements to optimize the size before doing anything.
Since I'm making new pistons I'll also make new rings, hone the cylinders and start again. I think I lost the original compression because I pulled the pistons out several times while messing around. This time I'll avoid removing them.
I could change my thoughts AGAIN before I find the motivation to make chips.


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## Ken Brunskill (Jul 24, 2020)

dsage said:


> Ken:
> I have been THINKING about this for a while but I've done nothing. I have abandoned the idea of O-rings for the reasons you mention i.e. I think they  will be torn up by the ports in the cylinder.
> My recent thoughts will be to add a chamfer to the piston like you have to form a bit of a combustion chamber. I'm concerned that it will reduce the already low compression so I'll do some CAD measurements to optimize the size before doing anything.
> Since I'm making new pistons I'll also make new rings, hone the cylinders and start again. I think I lost the original compression because I pulled the pistons out several times while messing around. This time I'll avoid removing them.
> I could change my thoughts AGAIN before I find the motivation to make chips.


Dave, I have decided to remake my pistons so I can try slightly wider/thicker rings, the original spec's were for .050" so I'll try increment of .010. Hey, this is a hobby after all.


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## dsage (Jan 23, 2021)

I finally found the enthusiasm to have another look at the Atkinson. I decided to connect a fuel tank pressure sensor to the intake port in place of the carb. I connected my scope and also triggered the scope from the ignition to get a TDC reverence. Attached you can see the waveform captured. The horizontal boxes on the screen divide the 360 degree full cycle of the Atkinson into 90 degree increments. You can ignore the vertical boxes they are for a four cylinder engine. You can also ignore the color of the boxes. Again they are for a 720 degree normal cycle. But they can rougly be labelled left to right Power, Exhaust, Intake, Compression.
The yellow waveform is the ignition trigger. The multi-sparks start on the hall sensor going low on my engine.
The green waveform is the vacuum at the intake port after the intake valve (where the carb would be).
As you can see - as expected - there is a huge vacuum pulse when the engine does not fire and the pistons travel down the cylinder to the intake end to the intake port where the valve opens. Then you can see the weaker official intake vacuum but it's not very strong and it appears to oscillate I think because it has trouble overcoming the valve spring pressure so the valve bounces and fades away as the stroke ends. The spring is about as weak as I can make it.
As I expected I can imagine the huge pulse would be sucking on the carburetor but immediately following that there would be a short period of pressure as the piston passes the intake port on the way to the exhaust port and the pressure would eject that fresh charge out the exhaust port. I think the real intake vacuum is not strong enough to bring in a suitable charge and that's why it won't fire.
If I could get it to fire then there would be pressure in the cylinder instead of that large vacuum. If the real intake vacuum could be improved it might make a good charge and allow it to fire. Sort of a catch 22 affair.
I don't have any solution to the problem. I'm just reporting more findings - for what they're worth.


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## dsage (Jan 24, 2021)

BTW. The above green vacuum waveform is flat on top (clipped) because I think the sensor was max'd out. It would have continued much higher further emphasizing the difference between it and the weak intake vacuum pulse.


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