Atkinson frustrations

[dsage]

As far as adding to the top of the left piston and changing the connecting rod I think the same thing could be accomplished by just making a longer LH connecting rod. The goal is to move the LH piston to the right and just making the connecting rod longer does that unless that causes some interference some other place. As far as slotting the intake I think that you may have something there. You are starting the compression stroke with a smaller initial volume so that you are able to compress the smaller volume with a shorter stroke. What you are doing is creating a shorter stroke. Getting fuel into the chamber is not the problem. Getting the fuel to a state where it is compressed enough to create a combustible mix is the goal. I have played around a little bit with my drawings but I still have not found the sweet spot. As you have found a relatively small change makes a big difference. I found that just the amount of play in the various connecting points can change things.

You are correct and that particular solution to do both (add to the piston and to the connecting rod) was just one of the many places I ended up with good compression. Noticing that effect, I actually tried transferring all of what I added to the piston to the conrod instead and vise versa in increments.
The whole thing is a repetitive trial and error and that's just were I ended up with one of dozens of trials.
Then I started thinking about someone modifying an existing engine and decided that just adding to the piston would be a simple(er) fix. BUT it appears from my experimentation the best solution is not to add just to the conrod because the piston movement is not linear so the effect of adding to the rod isn't linear either (even though it pretty linear as the piston gets to the center of it's travel). So I did end up with a balance. But there was very little added to the piston top. (note I again haven't given values). Of course either of those changes can cause piston clash at the right end so..... Over and over you go.
I think we might be on the same page with the intake port. Although I don't understand your explanation we're probably saying the same thing. From watching the model I can see that there is a point in the movement of the pistons together to the left where the gap between them is maximum - therefore trapping the maximum mixture. Slotting the intake port to the proper point allows the mixture to "flow" onto that gap before it is trapped. The more you trap and compress into a fixed volume on the left end is by definition better compression.

I have been intentionally vague with any dimensions because the more I read the book the more IMHO I've concluded it's a piece of crap. Many confusing dimensions and dimension s that don't jive from one place in the book to another and very poor and vague descriptions of assembly.
Case in point is pages 83 through 87 where they basically suggest just slapping the cylinder assembly onto the front of the engine and fiddling with it's position until the movements just "work properly" giving several thing to look for. Anyone that knows how finicky the movement is knows that is not a proper suggestion. They even suggest that new connecting links might be required to make the movement work properly.
IMHO this is completely un-acceptable as any other set of drawings I've used ASSUME you have made everything as per the plans and that it WILL work if they give the the proper dimension for assembly and they do so.
SO it's for this reason I've concluded that anyone with an existing engine should NOT take any of my advice because I can't guarantee how your particular engine is currently assembled. Moving almost anything a few thou changes the whole operation.
So I think I've decided to build it according to my drawings but that will take some time. Don't expect results any time soon.
I might consider a build log here when I start.
But who knows I might fail too.

BTW have you tried propane or a vapor carb?? I ask because watching the movement with respect to the intake slot some of the movement is just shuttling of the pistons with very little relative movement and so the actual vacuum produced may be very low. So low that the intake valve may not work. I'm thinking propane under a very slight pressure - just enough to be cut off by the valve spring and no more, may go in better under low vacuum. Also a carb generally does not work well with low vacuum so the liquid fuel will not be vaporized. A vapor carb might be better.
Food for thought.

 

[Gordon]

You are correct and that particular solution to do both (add to the piston and to the connecting rod) was just one of the many places I ended up with good compression. Noticing that effect, I actually tried transferring all of what I added to the piston to the conrod instead and vise versa in increments.
The whole thing is a repetitive trial and error and that's just were I ended up with one of dozens of trials.
Then I started thinking about someone modifying an existing engine and decided that just adding to the piston would be a simple(er) fix. BUT it appears from my experimentation the best solution is not to add just to the conrod because the piston movement is not linear so the effect of adding to the rod isn't linear either (even though it pretty linear as the piston gets to the center of it's travel). So I did end up with a balance. But there was very little added to the piston top. (note I again haven't given values). Of course either of those changes can cause piston clash at the right end so..... Over and over you go.
I think we might be on the same page with the intake port. Although I don't understand your explanation we're probably saying the same thing. From watching the model I can see that there is a point in the movement of the pistons together to the left where the gap between them is maximum - therefore trapping the maximum mixture. Slotting the intake port to the proper point allows the mixture to "flow" onto that gap before it is trapped. The more you trap and compress into a fixed volume on the left end is by definition better compression.

I have been intentionally vague with any dimensions because the more I read the book the more IMHO I've concluded it's a piece of crap. Many confusing dimensions and dimension s that don't jive from one place in the book to another and very poor and vague descriptions of assembly.
Case in point is pages 83 through 87 where they basically suggest just slapping the cylinder assembly onto the front of the engine and fiddling with it's position until the movements just "work properly" giving several thing to look for. Anyone that knows how finicky the movement is knows that is not a proper suggestion. They even suggest that new connecting links might be required to make the movement work properly.
IMHO this is completely un-acceptable as any other set of drawings I've used ASSUME you have made everything as per the plans and that it WILL work if they give the the proper dimension for assembly and they do so.
SO it's for this reason I've concluded that anyone with an existing engine should NOT take any of my advice because I can't guarantee how your particular engine is currently assembled. Moving almost anything a few thou changes the whole operation.
So I think I've decided to build it according to my drawings but that will take some time. Don't expect results any time soon.
I might consider a build log here when I start.
But who knows I might fail too.

BTW have you tried propane or a vapor carb?? I ask because watching the movement with respect to the intake slot some of the movement is just shuttling of the pistons with very little relative movement and so the actual vacuum produced may be very low. So low that the intake valve may not work. I'm thinking propane under a very slight pressure - just enough to be cut off by the valve spring and no more, may go in better under low vacuum. Also a carb generally does not work well with low vacuum so the liquid fuel will not be vaporized. A vapor carb might be better.
Food for thought.

I am at a little disadvantage here because I actually ended up building the engine using the Pendergast plans. I started with the Gingery plans and had very poor results so I ended up using the other plans. That may or may not have been a good decision. I did a lot of playing around with drawings with various linkages and various connecting rods. I also did a lot of making experimental parts with just different centers w/o actual bearing points. That is something like making the upper linkage from 1/4 x 1/2 steel bar with centers slightly longer and slightly shorter just to see what cheapened. I soon discovered that actual parts did not give the same results as the drawing would suggest.

As far as carburation. I did try both a vapor carb and a propane carb but i did not have very good luck. Getting fuel into the cylinder is not a problem. It is easy to get fuel dripping out of the exhaust because it is not vaporizing and burning properly.

I have been using 2 D cad for a long time and I can do things with that. I even started to play around with Fusion 360 but I was not sure that I wanted to spend the time that it would require to learn it properly. As someone said folks who are familiar with 2 D are at a disadvantage because 3 D is an entirely different concept.

 

[dsage]

As far as carburation. I did try both a vapor carb and a propane carb but i did not have very good luck. Getting fuel into the cylinder is not a problem. It is easy to get fuel dripping out of the exhaust because it is not vaporizing and burning properly.

I have been using 2 D cad for a long time and I can do things with that. I even started to play around with Fusion 360 but I was not sure that I wanted to spend the time that it would require to learn it properly. As someone said folks who are familiar with 2 D are at a disadvantage because 3 D is an entirely different concept.

Your example is why I don't recommend changing anything unless you are at wits end and just want to try something that sounds like it might help.
I'm sure I'll run into issues as well if / when I build it. I've used the 3D modelling enough to trust it completely as long as I have the parts modeled correctly. I've found many mistakes in drawings I've received. That's why I always re-do flat drawing in 3D CAD before I make chips. You can instantly tell when things don't fit and the program can point out interference's.
SO I'm pretty sure if I build it according to what I have now I'll be off to a good start.
Yes I used ACAD to do flat drawings for years and almost nothing transferred to the 3D process. It was very frustrating to learn but after about a year I gained enough ability be dangerous now I'm by no means "good" at it and just follow what processes I've figured out even if they might not be the best methods.
You also have to do it frequently to remember (at least I do) and so I model a lot of things - even simple blocks with holes in them to keep fresh.
We'll see what happens I guess.

 

[Gordon]

I am sure that given the motivation I could learn 3 D cad. The problem is that 95% of my drawing is for the model engines I am building. At 80 I probably am not going to be using a new cad program long enough to make it worth the effort to learn it. As you say it is also a use it or loose it thing. If I build two engines a year that is not enough to become proficient at using the program. I usually do redraw the plans which gives me a better understanding of the design and frequently catches mistakes in the original drawing. Frequently the original designer does not make the drawings in a way which I find easy to use. I don't care about the dimensioning rules I learned way back in high school. I want the dimensions to be how I am going to use them. If I have to get my calculator out to find out where I want to cut it is not done properly. A+B-C/2 may get me there but why not just put on the dimension I am going to use. Also as you have stated frequently the information is in a couple of different places and the different places do not agree. Another gripe I have with many drawings is the precision implied. This is especially true in cad where dimensions can be shown to four decimal places. .640625 implies a precision which may not be necessary. 5/8 +/- 1/16 may have been perfectly OK. I think that in many cases the original builder just started building and figured it out as he went along and made some rough sketches and calculations on the back of the envelope and when he was done someone else came along and made a drawing by measuring the final parts and may not have understood why and how things were done.

Enough soap box for one day. Sorry.

 

[dsage]

I am sure that given the motivation I could learn 3 D cad. The problem is that 95% of my drawing is for the model engines I am building. At 80 I probably am not going to be using a new cad program long enough to make it worth the effort to learn it. As you say it is also a use it or loose it thing. If I build two engines a year that is not enough to become proficient at using the program. I usually do redraw the plans which gives me a better ....

No problem with the soapbox. I agree with everything you said. I usually try to make everything to within a thou of the drawings (even if the dimensions are exaggerated from what's necessary). That way I don't have to worry about errors adding up (or thinking about where they may be adding up). I know the CAD package has it all fitting with what dimensions are there. I might as well build it to what it says. I generally do NOT have a 'good enough" attitude when making parts. Unless I've made a mistake and then I figure out if it's good enough to leave it like it is
I picked up some materials today.

 

[Gordon]

No problem with the soapbox. I agree with everything you said. I usually try to make everything to within a thou of the drawings (even if the dimensions are exaggerated from what's necessary). That way I don't have to worry about errors adding up (or thinking about where they may be adding up). I know the CAD package has it all fitting with what dimensions are there. I might as well build it to what it says. I generally do NOT have a 'good enough" attitude when making parts. Unless I've made a mistake and then I figure out if it's good enough to leave it like it is
I picked up some materials today.

I assume that you are using bar stock instead of making patterns and castings. I am really interested in seeing your build. Against my better judgment I spent a couple of hours playing around with Fusion 360. I may wise up by tomorrow and go back to my cave.

 

[dsage]

I assume that you are using bar stock instead of making patterns and castings. I am really interested in seeing your build. Against my better judgment I spent a couple of hours playing around with Fusion 360. I may wise up by tomorrow and go back to my cave.

Yes I use bar stock for the most part. I think I have one engine built from castings.
BUT I did build the other Atkinson. My friend has a small foundry and we cast a flywheel for it. There was another one that was a bit of a reject. Good thing I kept it because I think it's the same as the one required for this engine (Or at least the dimensions are close enough at first glance). With a bit of aluminum TIG welding I think I can fix it up and make it work.
I might start a build log here when I get to building it. I don't have a good camera. I could use my phone but getting the photos off of it is an extra step.
We'll see.

 

[propclock]

Dave the shop is calling you , too bad you will have to find an ignition
system for the new engine.
It is a nice and moderate temperature here.
just my 1.414 cents of motivation.

 

[dsage]

Dave the shop is calling you , too bad you will have to find an ignition
system for the new engine.
It is a nice and moderate temperature here.
just my 1.414 cents of motivation.

Yes. An ignition is going to be hard to find
It's a nice moderate temp here too (in the basement shop). A good place to be with a bit of occasional exercise shoveling snow.
It's all good.