# Another Atkinson Differential build



## Ken Brunskill (May 4, 2020)

This thread via the suggestion of Dave Sage;

I bought a set of Atkinson Differential plans from Dave Perralt, and proceeded to draw them up in Solidworks, for two reasons, the primary reason was to learn the Solidworks program, the second was to understand the design, and do a check of the plans. I will say that his design was very good, I found only one error, which I pointed out and was thanked for catching that. I have built other models from plans and found his to be the best I've encountered.

Being a Tool Designer and Mechanical Manufacturing Engineer, I probably am a bit picky - hats off to Dave Perralt! Having read Dave Sage's thread, and seeing all the problem he and others have had with designs & their errors, as well as not getting their model to operate, I am hoping that this model will not be in the same category. Mr Perrault has an operating model built from this design, I hope I can have another.

So with that said here goes in somewhat chronological  order: (Have not been taking a lot of photos, or following HMEM all that faithfully - actually don't care to spend much time surfing or posting - will try to do better if people are interested.)

The photo 'Christmas Present from Son.jpg Was some what of a joke for our nurse son, who has zero idea of what is involved in making anything, I said "watch this space'".
The photo 'Base-Frame-Flywheel-Cylinder.jpg ' was the 2nd photo to him, It shows the Base, Vertical Frame & Purchased Fly Wheel.
The photo 'Machining Left Arm.jpg ' is the set up for machining the Left Arm, yep no CAD-CAM equipment in this old mans shop.
The photo 'Mid April Progress.jpg' was take mid April to show my kids and friends what I am doing to stave off 'Cabin Fever'
The photo 'Partially complete Atkinson Differential.jpg"  was for the record to show our son and family what that block of Cast Iron i.e., Christmas Present has become.

I am now awaiting some Aluminum Round and Brass Hex Bar stock, so I can fabricate the pistons, and Hex screws, one of my friends at the BAEM is going to provide the ignition components. In the meantime I'll build the gas and water tanks. Then hopefully this Covid-19 will allow me to visit my friend in his Sr Living's nice wood shop to make the box to house this whole thing. 

St that's where it stands at the moment.


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## Gordon (May 4, 2020)

As one of the folks who have spent far too much time trying to get one of these to run I hope that at some point we can figure our why some of these engines run and others do not even come close. Different designs seem to have only minor differences.


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## Ken Brunskill (May 4, 2020)

Gordon said:


> As one of the folks who have spent far too much time trying to get one of these to run I hope that at some point we can figure our why some of these engines run and others do not even come close. Different designs seem to have only minor differences.


Maybe it will be worthwhile to analyze the volume, compression, and pressure holding capability of the various designs. (Just food for thought.)


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## stragenmitsuko (May 5, 2020)

Great another atkinson thread . 
I'm following along . 
Hope all problems will be solved .

pat


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## Ken Brunskill (May 10, 2020)

At his point I am ready to make the pistons and rings, made the 1st Pump Piston, Atkinson Differential's have two (2) a Pump & a Power piston. The plans I have are from Dave Perralt, his plans were created from his working engine, with two (2)  so anyone else but me would just follow that. 
But no; I have to question whether the compression might be improved from his  two .062" T X .050" W rings  (remember this is working), by using three (3) .031" T X .045" W rings. The three rings would in theory produce 25% less friction by my calculations. However the ring gap increases three fold (DUH, three gaps vs two), maybe laying it out like this serves to provide the answer, still worth putting it out to the collective wisdom and experience of others.
Then again maybe four rings, two. .031' rings in the same .062" ring groove, that seems to cancel out or reduce the affect of the gap issues.

Regardless of which way, the rings need to be made, I've heard from our club president that some have successfully made their rings with the Trimble method while others have had success with making them oversize cutting the gap, heat treating, then squeezing down on a mandrel and finish machining them to size. Need to understand that a bit better, I think I can visualize that process but want to see photos of the fixturing before start to make sure I fully understand that process.
So would appreciate any and all comments and photos of fixtures.


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## Peter Twissell (May 11, 2020)

Hi Ken,

I don't understand why three rings would have more leakage through the ring gaps. The gaps are in series - any leakage would have to pass through the first gap, then find its way round to the second and if you have three rings, then find its way round the third gap.
Two rings in one groove can eliminate leakage through the ring gaps, provided you can stop the rings from rotating and aligning the gaps - possibly with pins like 2 strokes use.
In general, more rings should result in less leakage, as the pressure across each ring is reduced.


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## Ken Brunskill (May 11, 2020)

Thanks Peter, your comment makes perfect sense to this old man, I guess I was not thinking enough.


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## Ken Brunskill (May 11, 2020)

Peter Twissell said:


> Hi Ken,
> 
> I don't understand why three rings would have more leakage through the ring gaps. The gaps are in series - any leakage would have to pass through the first gap, then find its way round to the second and if you have three rings, then find its way round the third gap.
> Two rings in one groove can eliminate leakage through the ring gaps, provided you can stop the rings from rotating and aligning the gaps - possibly with pins like 2 strokes use.
> In general, more rings should result in less leakage, as the pressure across each ring is reduced.


Further thought on this is; seems that if initially placed 180 deg. apart the two rings in one groove would take quite awhile to become aligned, then with two set's the chance of both sets becoming aligned would be even more unlikely, could happen though. Think since I am in the mood, I'll try both and measure the compression as well as the decompression time (Anyone ever done this? Any suggestions on how?)


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## Peter Twissell (May 12, 2020)

Piston rings can rotate faster than you might think. Observation link shows up to 1rpm at 1000 engine rpm.
You might need to be quick with your compression measurements!
Sod's law (Murphy's law, law of universal cussedness) clearly states that the gaps will align (because you don't want them to).


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## Ken Brunskill (May 12, 2020)

Peter Twissell said:


> Piston rings can rotate faster than you might think. Observation link shows up to 1rpm at 1000 engine rpm.
> You might need to be quick with your compression measurements!
> Sod's law (Murphy's law, law of universal cussedness) clearly states that the gaps will align (because you don't want them to).


Very well acquainted with Murphy! Seems to be ever present in my shop, the smaller the object that hits the floor the further and more difficult to retrieve.


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## Ken Brunskill (May 17, 2020)

Followed some of the Ring Creation threads, great resource! Thought the idea of turning the OD 1st, then cutting the Thickness +.002" & depth .010" deeper than the finished ID, was a good idea, worked like a champ, just as described.
Now to bring the ring blanks to the desired Thickness. Then cut the ring gap (Bought a .006" X 2" Slitting saw for this [only $13].) 
As mentioned earlier, Going to try (1) ring/groove & (2) rings in (1) groove, thats why there are so many ring blanks of differing witdths, being turned.


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## Ken Brunskill (May 29, 2020)

Thought I'd post pictures of the simple method used to deburr the rings (they were turned to final size for the OD, .030" under size for the ID, width cut with narrow parting tool .010" deeper than final ID, finally bored to final ID. 
Photo is a Dremel stone and one of the rings being deburred. Took but a minute or two for each ring.


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## Ken Brunskill (Jun 2, 2020)

Getting close to completion of the engine, finishing the pistons, installing the rings, expecting to have all that accomplished by weeks end. Have all the electronics except the Spark Plug (It's in route). Now for the fuel and coolant system, then a stand/box.


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## ALEX1952 (Jun 3, 2020)

it is quite common to put a pin in the gap of the ring to stop rotation, of course this has to be allowed for when "gapping" the ring, it also makes it more of a pig to fit the ring.


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## Ken Brunskill (Jun 3, 2020)

Alex, thanks for that thought, these are pretty small pistons, so the pins would be super tiny.
Next task is to final polish the ring gap to acheive final OD, install the rings the final assembly - should be finished assembling the engine tomorrow.


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## Tim Wescott (Jun 9, 2020)

Goodness gracious those are itty bitty pistons!


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## stragenmitsuko (Jun 10, 2020)

Yes indeed , what dimensions are those pistons ? 

Pat


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## Ken Brunskill (Jun 10, 2020)

Pistons are .750" Diameter. The photo posted on 6/2/20 is 1st photo of the engine partially assembled. Right now awaiting delivery of hex Stainless to make the screws to hold the Intake/Exhaust Valve Manifold (The Brass part in front.)


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## Tim Wescott (Jun 10, 2020)

Ken Brunskill said:


> Pistons are .750" Diameter.



My eyes deceived me -- 3/4" isn't too bad.  Somehow I thought the were 3/8 or smaller.


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## dsage (Jun 11, 2020)

Ken:
As you look at the front of the engine and the oscillating arms, which piston (left or right) has the chamfers on it?


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## Gordon (Jun 11, 2020)

Ken Brunskill said:


> Pistons are .750" Diameter. The photo posted on 6/2/20 is 1st photo of the engine partially assembled. Right now awaiting delivery of hex Stainless to make the screws to hold the Intake/Exhaust Valve Manifold (The Brass part in front.)


I am confused. The Gingery design and the Pendergast design both have 1 1/8" dia pistons. Does yours have 3/4" dia pistons? That certainly makes a different design.


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## stragenmitsuko (Jun 11, 2020)

The pendergast design is even bigger . 1.25" od on the pistons .


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## Gordon (Jun 11, 2020)

In looking again at his design I find that  he offers a kit with a 10" flywheel and plans for one with a 4" flywheel. If we cannot get the larger one to run I cannot imagine the problems with one half that size.


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## Tim Wescott (Jun 11, 2020)

So, it looks like this is going from the patent drawing -- could that be why these things don't work well?

I don't know about the late 19th century, but in the late 20th century the point of a patent drawing was to get a patent, while making it as hard as possible for someone to duplicate.


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## dsage (Jun 11, 2020)

Probably is the reason. But somewhere I ran across a link where someone took the patent drawings and built one based on them.  He had to  "wing it" in a few places becasue not everything was specified. The article had a picture of it completed and he "said" it ran after a bit of frustration BUT there was no video proof.
Same thing for the Gingery version. There IS a Youtube video of it running but the book says it might be VERY difficult to get running and that a few pieces might have to be re-made to tweak it into submission. No very re-assuring to be sure.

Not to be too confused - I think Ken is building the one from Dave Perralt that apparently DOES run. It has some very strange valve actuating mechanism on the front so it's very different than the Gingery and maybe the Pendergast -(sorry sp?) for sure.

Perhaps Ken can post a larger picture of the front of the engine. ( i.e. take the picture in a higher resolution say 3mb in file size and paste it into the next post. (rather than the thumbnails presented thus far).


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## Steamchick (Jun 12, 2020)

Hi, just picked up on this thread... from my experience (engine design and testing with Nissan in the UK) rotating rings is really the way that wear creates the "perfect circles" of rings and bores during running-in. The finest of spiral grooves from machining in bores and ring surfaces is "worn flat" by lapping, but not completely polished. The  lapping or honing causes much finer grooves in the flatted peaks of the machining. All the valleys are oil reservoirs to prevent pick-up and siezing. But the finest peaks from honing / lapping are polished by rings running past bore surfaces, but the ring rotation helps ensure the high spots find each other and lap away, hence the rings and bore must become perfect circles.. Ring stops used on 2-strokes are a necessary evil to prevent ring ends from fouling cylinder ports after some rotation. Avoid on cylinders without side ports, if not part of the original design. Don't worry about ring gap alignment, it happens on your car's engine frequently, without significant trouble. The oil consumption change when a 3-ring piston in the car engine aligns the gaps is measurable on the dynamometer test kit (blow-by and exhaust gas monitoring and analysis). Manufacturers factor in this natural oil consumption in the service intervals, so I suggest you do the same on your model. When rings align, oil passes through the gaps, this causes gases to be withheld.. so excessive blow-by doesn't become a problem on the full sized engines. Maybe models have exactly the same effect?
Please add more expert comment, I love to learn!
Cheers!


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## Ken Brunskill (Jun 13, 2020)

At the suggestion of Both Dave Sage & Dave Perreault I created a utube video: (My 1st - sorry for the amateurish narration)

Filename
4th Shot Atkinson operation.MOV


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## Hettinger (Jun 14, 2020)

I see your going with two separate rings vs. the paired single ring. I was hoping you were going with paired ring. Did you go with heat treated ring or ( my preference) all machine ring? Congratulations on your progress and excellent work. Bob


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## Gordon (Jun 14, 2020)

Ken Brunskill said:


> At the suggestion of Both Dave Sage & Dave Perreault I created a utube video: (My 1st - sorry for the amateurish narration)
> 
> Filename
> 4th Shot Atkinson operation.MOV



Thanks for that. That engine valve configuration is a completely different setup than the Gingery or even the original patent drawings. With a mechanical valve actuator it stands a chance of working.


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## dsage (Jun 14, 2020)

Yeah
In fact I'll bet it does. I believe the designer has displayed it running at Cabin Fever.


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## stragenmitsuko (Jun 14, 2020)

Now I understand what the function is of that extra central connecting rod .
It actuates the valves .
Wonder if this can be added somehow to the other designs out there
thx for the vid .


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## Ken Brunskill (Jun 14, 2020)

Hettinger said:


> I see your going with two separate rings vs. the paired single ring. I was hoping you were going with paired ring. Did you go with heat treated ring or ( my preference) all machine ring? Congratulations on your progress and excellent work. Bob


Bob, based on the  comments of steamchick, have decided to go with (2) rings in one groove for the pump piston where there are no ports, and (1) ring per groove in the power piston.
As for the method of making rings, I made them both ways, the Trimble method, less fixturing and machining time, and the unheatreated way. Then used a Chattilion force gage to measure the force it takes to close the gap, either way it came to 1.3 lbs.


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## Gordon (Jun 14, 2020)

Just found this. Delete if the link is not permitted.


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## stragenmitsuko (Jun 14, 2020)

That is what  ken is building if I'm not mistaking . 
The piece of copper on the right seems to be a coolant tank .


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## Gordon (Jun 14, 2020)

Since Dave Perreault seems to offer both a larger kit with a 10" flywheel and plans for this smaller engine with a 4' flywheel I wonder if the larger model uses the same valve setup. I have not been able to find much information on his designs or kits. Anyone familiar with his offerings?

Gordon


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## Ken Brunskill (Jun 14, 2020)

Gordon & Strangenmitsuko:

Yes, I am building Dave Perreault's design. I would heartily endorse it, as the price is reasonable, and so far I have only encountered one error which he concurred. Mine should be up & running soon. I do fly fish also and need to get ready for a 4 day trip. By the way the RH cylinder is the coolant tank, I am adding a pump and cone screen, so the engine is doing something, not because I think it is needed, just because . . .


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## dsage (Jun 15, 2020)

Ken:
Do you have a link to a website or email for Dave Perreault so as to purchase the plans for his engine?


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## Ken Brunskill (Jun 15, 2020)

dsage said:


> Ken:
> Do you have a link to a website or email for Dave Perreault so as to purchase the plans for his engine?


Dave, I had copied him in an email to you a few days ago. For some reason my cpu is not loading my email server, I need to het that resolved, when done I will send you his contact details.


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## propclock (Jun 15, 2020)

Very interesting results on the 2 ring methods = spring factor . Good luck with the fish.


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## Gordon (Jun 15, 2020)

This is the email address he posted on Model Engine Maker in February. Let us know if you get any more information on what he has available and prices.

[email protected]


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## dsage (Jun 15, 2020)

Ken:
If you come up with anything different than Gordon posted above - in so far as how he'd like to be contacted for purchases post it here. Otherwise..... I guess we're good.


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## dsage (Jun 16, 2020)

That email should work.
He seems hesitant to post here (IMHO) to promote his work.
I have been emailing him.

Gordon:
Not to hijack this thread. Dave Perreault apparently researched the original patents for the differential and figured it out and built one. He used to (maybe still does) offer castings for it. Have a look here.


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## Gordon (Jun 16, 2020)

dsage said:


> That email should work.
> He seems hesitant to post here (IMHO) to promote his work.
> I have been emailing him.
> 
> ...



I have seen the video and agree that whatever he did he has a working model. 

In looking through my stuff on my computer I found that I had a copy of a purchase contract from him which I apparently got back in 2017. At that time he was offering the castings for $450 which was a show special with $100 discount. Not to downplay his efforts or expertise but that is more than I am in a position to pay. I am retired so I have more time than money. I would be interested in a set of his drawings but quite honestly mostly to see what he has made different than anything I have been trying to do.

I have thought about trying to play around on cad with his mechanical valve idea which he uses on his Mini. Not sure that I want to spend that much time on more Atkinson Differential design which I have already spent too much time on. At this point I have moved on to other more productive endeavors. 

The patent drawings and application are reprinted in the Gingery book but like all patent information that is to obtain a patent without giving away too much design information.

Gordon


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## dsage (Jun 16, 2020)

All valid points. I agree.
I consider the sliding valve addition as not true to the original design. (certainly not looks wise) which is what I was going for. So I won't be going there. Also it's too much work to add it now.
Having said that I don't like to have an engine that doesn't run sitting on the shelf so I might eventually end up with some sort of modification to "fix it" and hopefully not be too far from the original appearance

Enough said here in Ken's thread. We should continue in your or my thread.

On that note I think Ken will have success with the Dave P. design. It looks solid.


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## Ken Brunskill (Jun 16, 2020)

Dave & Gordon, near as I know there are not any castings available for the Perreault Mini-A design, it would be easy task for those of you with CAM milling capabilities, and a fun conventional machining task for rest of us  (Hey, isn't why we enjoy this pursuit.) By the way I made some of the part twice, not being pleased with the 1st parts. I paid $35 for the set of plans last year and as I've said before think they are well done.


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## dsage (Jun 16, 2020)

Your right, There aren't any castings for the Mini.
BUT Dave was at one time (maybe still) supplying castings with drawings ($500+) for the original large patent designed engine. I'm not sure if he would supply ONLY drawings for the original.
And yes the mini would be easy enough to make from the drawings. But I'd rather keep closer to the original design.

Continue on Sir. We want to see it run


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## Richard Hed (Jun 17, 2020)

I was just watching a vid on Diesel engines and I thot maybe someone might like to see this:



It's not about minis but it is interesting.


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## Ken Brunskill (Jun 21, 2020)

Mentioned a few posts back that I was going with (2) rings in (1) groove for the Pump piston only, well . . . . . I am finding out how fragile .025" thick rings are, see photo. Good thing I made extra's. The remainder are safely installed in the cylinder now! After that experience, feel that those thin rings would likely have been an issue crossing the .187" dia port holes that come in at an angle (making them obround in the bore).


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## Gordon (Jun 24, 2020)

I just received the plans for this from Dave Perreault. I have not had a chance to look too closely yet but the instructions say that you have to run it for 4 or 5 hours with an electric motor to get the rings seated properly.I am not too sure that I want to get into another engine which takes a lot of fussy tweaking.


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## Ken Brunskill (Jun 24, 2020)

I am just at that stage now, so very soon (next week, as  I am an ardent fly fisherman, and there is particular hatch going on in a N. Calif. Lake, so . . . . . ), I will be doing that and then start the process of getting it to run, I have a good feeling as using Solidworks 3D modeling I can observe the interactions of the valve, etc.


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## stragenmitsuko (Jun 24, 2020)

There are thougts against using an E motor to run in the rings . 
The pressure of the combustion should seat and wear in the rings . 
Offcourse if there's no combustion possible due to ring leakage .... 

I've also been told by a professional engine rebuilder that changing rings 
without honing the clinder is pointless . The "rough" spiral surface left by the honing 
works as an abrasive and wears in the rings . Altough it sounds logical , don't know if this is true . 
I've changed rings on countless occasions without honing and never had bad results .

Let's hope you have a runner . 

@Gordon , is that the full size or the mini plans you've got .


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## Gordon (Jun 24, 2020)

stragenmitsuko said:


> There are thougts against using an E motor to run in the rings .
> The pressure of the combustion should seat and wear in the rings .
> Offcourse if there's no combustion possible due to ring leakage ....
> 
> ...


It is the small one like in this thread. I am a little bit disjointed because the lines are light grey and hard to see with my old eyes. The dimensions are dark but the main part line are very light. I suspect that he made the drawing with the lines some color and then printed in greyscale. That is what my cad drawings look like so I either print in color or all lines to black.


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## dsage (Jun 25, 2020)

Gordon said:


> I just received the plans for this from Dave Perreault. I have not had a chance to look too closely yet but the instructions say that you have to run it for 4 or 5 hours with an electric motor to get the rings seated properly.I am not too sure that I want to get into another engine which takes a lot of fussy tweaking.



Oh no. Shades of Gingery. I hope it isn't so. Also disappointing on the poor quality of the drawings. I hate that.
 I guess Ken did the right thing redrawing them.


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## Gordon (Jun 25, 2020)

dsage said:


> Oh no. Shades of Gingery. I hope it isn't so. Also disappointing on the poor quality of the drawings. I hate that.
> I guess Ken did the right thing redrawing them.


I assume that the drawings are accurate. Ken redrew them and found only one minor error. The problem is the quality of the printing. Due to the lines being greyscale they are hard to read. If I do make one of these I will also probably redraw them in cad but I frequently do that with my projects.


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## dsage (Jun 25, 2020)

Yes. Redraw is standard with me. But the running in with an electric motor worries me (as was the case for the Gingery - page 111). Gingery said Twelve days of running in before it got to running on on it's own. Crazy.


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## Ken Brunskill (Jun 26, 2020)

Well, I fabricated all the parts as Dave P. had designed them, assembled everything less the rings and all operated smoothly, then observed a fair amount of stiffness with the spanking new rings installed, so the thought expressed by strangemitsku might turn out to be true. (BTW, Fishing was OK lastnight, catching not so much). Will be doing some E motor run in starting Monday, with the suggestions and comments here, think I'll try to power it on its own after each hr. of E motor breaking in. Will keep posting as progressing.


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## Ken Brunskill (Jun 27, 2020)

Regarding the light feature lines, my bet it is because Mr. Perreault did not desire them to be xerox copied, I tried that and those light lines do not copy or scan worth a darn. Wise on his part, IMHO.


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## Ken Brunskill (Jun 28, 2020)

Slightly different topic, maybe worth a individual post? Anyone come up with a method and/or device for measuring compression of one of our model engines? I.E. measuring via the 1/4-32 thread hole? I am sure I can come up with something, but why reinvent this 'wheel'?


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## dsage (Jun 28, 2020)

I made an adapter from 1/4-32 to whatever is on the end of the hose of a standard compression gauge. I added an o-ring above the threads so you don't have to crank down on it and possibly damage the head of the engine (since there generally aren't many threads).
Works fine.


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## Ken Brunskill (Jun 28, 2020)

dsage said:


> I made an adapter from 1/4-32 to whatever is on the end of the hose of a standard compression gauge. I added an o-ring above the threads so you don't have to crank down on it and possibly damage the head of the engine (since there generally aren't many threads).
> Works fine.


A picture would be a great addition to your 'elegant' solution. Elegant IMHO, is simple, efficient & effective.


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## dsage (Jun 28, 2020)

The o-rings are green. One to seal the adapter to the hose end and one to seal the adapter into the model cylinder head.
The black o-ring does nothing in this application . It's for the original seal to a standard plug hole. Bronze because it's what I had around and the original end was brass.


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## Ken Brunskill (Jun 29, 2020)

Elegant! Thanks Dave.


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## Ken Brunskill (Jul 11, 2020)

Ken Brunskill said:


> Well, I fabricated all the parts as Dave P. had designed them, assembled everything less the rings and all operated smoothly, then observed a fair amount of stiffness with the spanking new rings installed, so the thought expressed by strangemitsku might turn out to be true. (BTW, Fishing was OK lastnight, catching not so much). Will be doing some E motor run in starting Monday, with the suggestions and comments here, think I'll try to power it on its own after each hr. of E motor breaking in. Will keep posting as progressing.


OK, ran into an issue doing the E-Motor run-in, as mentioned here the stiffness has caused the pivot pins (which were a light press fit in the 'ARMS'),  and being catilevered enough to cause binding, (I think caused by the stiffness) which after 10 min. of relatively low speed worked one of the the pins out of it's 'ARM'. Analyzing options & fix to this. My suggestion to anyone thinking about building to this design, make the components out of steel vs. aluminum.
I know my holes were dead straight/square and to size, feel the angular pressure in soft material (6061 Aluminum) is a major factor. The mechanism operated smoothly until I installed the rings, which were built to Dwight Giles methodology.


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## dsage (Jul 11, 2020)

By chance did you fit a ring into the cylinder (without the piston) to ensure you have enough ring end-gap?
And also that there is enough space behind the rings in the piston groove?

Of course if either of those is not sufficient you probably wouldn't have got the piston into the cylinder. 
What are the ring dimensions? Did you use two thin rings per piston ring groove as you once said you were going to do. Or just wide one?


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## stragenmitsuko (Jul 12, 2020)

The pins are a press fit in the arms and they pivot in the frame  ?
I thought it would be the other way around .

How about pressing / bolting / loctiteing the pins in the frame .
I would thread them , add a small shoulder and loctite them in place .
And th use an extended bronze bushing in the arms wich could also be bolted or locktited to the arm .


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## Ken Brunskill (Jul 12, 2020)

dsage said:


> By chance did you fit a ring into the cylinder (without the piston) to ensure you have enough ring end-gap?
> And also that there is enough space behind the rings in the piston groove?
> 
> Of course if either of those is not sufficient you probably wouldn't have got the piston into the cylinder.
> What are the ring dimensions? Did you use two thin rings per piston ring groove as you once said you were going to do. Or just wide one?


Dave, made a dummy cylinder exactly the same I.D. as the cylinder (.750"), made sure I had .001"-.002" end gap, rings on the Power Piston are .050" wide (1/groove), Pump Piston rings had same end gap, but since there are no side ports, just a cylindrical surface I'd gone with (2 rings/groove) as my 1st try. Did a relatively fair measurmemt of the load required to get the rings to close, near as I could measure they were consistent, and about as expected, the .025" wide rings came in about 1/2 of their .050" wide cousins. The angular load on the ARM pins in aluminum, & related losening, has set me back a bit, before I remake the ARM'S I am going to try cross through pins - as perpindicular to the implied load as I can make them. Might just be a simple enough solution.


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## Ken Brunskill (Jul 13, 2020)

stragenmitsuko said:


> The pins are a press fit in the arms and they pivot in the frame  ?
> I thought it would be the other way around .
> 
> How about pressing / bolting / loctiteing the pins in the frame .
> ...


Like your suggestion 'strangemitsuko', the ARM's piviot on bearings, that are mated to posts in the FRAME, they are secure there being a light press fit to a shoulder and tightened to that shoulder from the far side of the frame, a good design there! The culprit pin is a 3/16" diameter pin press fit into the 1/4" thick ARM. So I think I will invest in a 7/32 -32 Tap & Die (Sure that will come in handy in the future - or that will be my explanation to my lady ) then do as you suggest including the loctite, since this particular pin requires a 3/8" Dia. spacer I'll use that as the shoulder.
I'll make drawings of the new pins and have them available for anyone interested in building this model.


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## stragenmitsuko (Jul 14, 2020)

Ken Brunskill said:


> (Sure that will come in handy in the future - or that will be my explanation to my lady )



Now that sounds familiar


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## Ken Brunskill (Jul 21, 2020)

stragenmitsuko said:


> Now that sounds familiar


Ended up making the 7/32-32 Tap, will post a picture and details if anyone is interested.


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## jquevedo (Jul 22, 2020)

Ken:
I made a small change in the design of same engine, made the arms a one piece element, started from a 0.500 thick Al plate and machined all critical dimensions ( holes) then machiend profile and top surface to allow for the two ARM and Small ARM pieces to be made as one piece, then made the groove/space for the piston arm to be inserted, the pin that will hold the arm to piston Arm is a 0.125 in with external retaining rings.
Engine has very good compression, no binding and seems like it should run..
Working on ignition and water and fuel tanks now.


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## jquevedo (Jul 22, 2020)

sorry forgot the side view


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## stragenmitsuko (Jul 22, 2020)

Ken Brunskill said:


> Ended up making the 7/32-32 Tap, will post a picture and details if anyone is interested.


Please do , I'm always interested how others approach this . 

@jquevedo
what are the two brass pipes for on the side view ? 
Coolant maybe


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## jquevedo (Jul 22, 2020)

Coolant entry and exit, they connect to a water tank and fill a void pocket behind the main cylinder body, thermal circulation is expected to happen, top one is hot / exit and is at a 30 degree angle


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## Ken Brunskill (Jul 22, 2020)

jquevedo said:


> Ken:
> I made a small change in the design of same engine, made the arms a one piece element, started from a 0.500 thick Al plate and machined all critical dimensions ( holes) then machiend profile and top surface to allow for the two ARM and Small ARM pieces to be made as one piece, then made the groove/space for the piston arm to be inserted, the pin that will hold the arm to piston Arm is a 0.125 in with external retaining rings.
> Engine has very good compression, no binding and seems like it should run..
> Working on ignition and water and fuel tanks now.


Very nice looking work, you are to be congratulated! 
I have stripped the paint from mine, and am tumbling them in just plain gravel, to provide a matt finish. Then back to understanding the compression issue.


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## Ken Brunskill (Jul 22, 2020)

stragenmitsuko said:


> Please do , I'm always interested how others approach this .
> 
> @jquevedo
> what are the two brass pipes for on the side view ?
> Coolant maybe


Here is a photo of the tap, I used (3) .024 wires for making the tap, carefully making sure to maintain ZERO on the cross feed and note the reading on the compound, then made the screw thread of the mating part imediately afterward, ended up with a Class 1 fit. The chip relief was milled with a . 125" Ball End Mill deep enough to achieve a flat face or .030" for this 32 TPI thread. Then the tricky part was back to the lathe to pick up the thread (done with dykem, 10X Optivisor) and just barely remove the dykem & burrs from milling the thread relief.


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## Ken Brunskill (Aug 29, 2020)

dsage said:


> Ken:
> As you look at the front of the engine and the oscillating arms, which piston (left or right) has the chamfers on it?


Dave, Looked for my reply without success, do think I replied via email. Belatedly, realizing others may be equally interested. So, in the Perrault design the Power Piston (on the LH side, from the front) has the chamfers.


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## Ken Brunskill (Aug 29, 2020)

An update, way back I mentioned that I was going with (2) rings/groove, which I did only for the PUMP piston, well that did not work out so well, I ended up with an unmeasurable compression, as in it did not even budge the needle on the gage. Next I modified that piston to accomodate some .070" cross section O-Rings, that while knowing it would not be suitable long term (the O-ring crosses the sparkplug hole, and would not hold up.) This resulted in acheiving a 20 psi jump in compression, so a remake of the PUMP piston, and full width rings are being made.


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## jquevedo (Aug 30, 2020)

Ken:
I've been experiencing compression issues as well, first tried the 1 ring per grove at 0.035 thickness, at start compression was over 20-25  psi before breakin-in, then it went down to less than 5 psi.

Cleaned and re honed cylinder, made new pistons with very close fitting and rings, this time 1 per grove at recommended 0.062 in thickness. Compression was above 20 psi but quickly went down to around 10 psi, seems like the challenge here is balancing friction vs compression.

Have made rings using Trimble method ( heated to 1100 F),  forming and machining (turning on a mandrel to final size after parting ) as described by Tom Schwartz in Model engine builder, as well as a combination of both methods. 
So far the best rings I think I have been able to make are  using BOTH methods. Trimble heat treatment to 1100 F with final sizing using methods and machining as described in Schwartz approach. While compression is low arlound 10-12 psi, engine kind of start, sputters but refuse to run for considerable time, close inspection of rings shows they have not seated all the way around, some more time on assisted cranking may be needed hoping the rings will eventually seat all the way around.

Start attempts are better when engine is cold (i.e. overnight)  and when the spark is closer to TDC..

Best regards.
Jaime


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## Steamchick (Aug 30, 2020)

Just a point on combustion... Of course many old timers will remember flooding carburettors.... and using a manual choke - all necessary on a cold engine - or one with lower compression at start when the slow cranking speed allows much more blow-by (time) past the ring grooves and end gaps. (Modern engines with computer controlled fuel injection simply don't have "human applied" choke or other fuel enrichment! Younger folk (e.g. my daughter) simply don't know what the choke is for! - last seen on her Ford Fiesta in the 1980s. 
Often a drop of oil helps cold starting as is closes some of the gap around the top, bottom and inside of the rings, as well as surface roughness of the bore, (Although microscopic gas dynamics define the machining grooves in the bore as microscopic labyrinth seals, so "aerodynamically" they develop a back-pressure to resist gas flow.). So running-in the rings in a bore will help develop compression, but ideally this should be done by idling the engine or running on a light load, so that the bore is heated (and heating distortion partly compensated) and therefore the rings will bed-in "more truly circular" and the bore likewise. But stop periodically and check for high spots - as these are where any engine will seize. Hand cranking the engine (especially with a torque wrench - gauge type - will enable monitoring of running-in. When the torque isn't reducing (from an initial hand wind) then the running-in is OK from an initial point of view and examination of high and low spot witness marking is the best monitor, until you get a good fit.
The reason you need more fuel at low compression at start is simply that the cold engine causes some fuel "spray" to condense, and therefore the mixture is effectively leaner than when hot and running - when the compression at firing will be naturally higher du to adiabatic heating of the intake charge - which doesn't happen at low speed cranking. That is more or less isothermal compression. But Models exacerbate the starting problem, as a 1 thou ring gap of a 500cc cylinder lets through a smaller fraction of the intake charge (proportionately) than the same 1 thou ring gap of a 5cc engine.
On ring size and fitting, I assume you are closely following drawings for fit of the ring width and inside diameter sizes and tolerances, as also the ring groove width and bottom diameter tolerances. These are critical to minimise the gas leakage past the rings and WILL NOT change with running-in. Often this is where rings don't work well, even when properly bedded-in to the bore. Blow-by gas goes around the back of the ring to get past the ring-groove quite effectively. On Manufactured engines, the piston groove width and depth tolerances are very closely controlled, and rings are ground to 1/10th thou in. tolerances for thickness, so they JUST don't seize in the piston ring-grooves. Also, most of the pressure of the ring on the bore comes from gas blowing past the top surface of the ring to the back of the ring on the compression and firing strokes, so the actual "static" ring pressure should be "just enough" to make the initial sealing contact of ring to bore.
Sorry if I'm teaching Grandma to play Rachmaninov again.... But I can also talk about being Brahms and Liszt! (She was a concert pianist anyway).
K


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## Steamchick (Aug 31, 2020)

Peter Twissell said:


> Piston rings can rotate faster than you might think. Observation link shows up to 1rpm at 1000 engine rpm.
> You might need to be quick with your compression measurements!
> Sod's law (Murphy's law, law of universal cussedness) clearly states that the gaps will align (because you don't want them to).


Just comments for interest? => When engine testing at the NIS### factory where I worked, the oil consumption had periodic spikes where the 3 rings on any piston aligned during long term testing. And on 4 cylinder engines this happens 4 times more often than a single cylinder. It was monitored on 200 hour durability tests, as on "your car" you don't want to be topping-up the oil every week! 
But the rotating ring syndrom is necessary for the "perfect circle" of a ring to fit the same circle of the bore. As the ring pressure is constant for most of the ring, but changes close to the cut ends, the radial variation of pressure (hence wear) needs the rotation to maintain longevity of the ring to bore seal by the rotation causing uniform wear around the bore.
 2-strokes with pegged rings have much shorter lives....
K


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## Ken Brunskill (Aug 31, 2020)

jquevedo said:


> Ken:
> I've been experiencing compression issues as well, first tried the 1 ring per grove at 0.035 thickness, at start compression was over 20-25  psi before breakin-in, then it went down to less than 5 psi.
> 
> Cleaned and re honed cylinder, made new pistons with very close fitting and rings, this time 1 per grove at recommended 0.062 in thickness. Compression was above 20 psi but quickly went down to around 10 psi, seems like the challenge here is balancing friction vs compression.
> ...


Jaime, 
Are you building the Perrault design as well? If so please post some pictures.


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## Ken Brunskill (Aug 31, 2020)

Steamchick said:


> Just comments for interest? => When engine testing at the NIS### factory where I worked, the oil consumption had periodic spikes where the 3 rings on any piston aligned during long term testing. And on 4 cylinder engines this happens 4 times more often than a single cylinder. It was monitored on 200 hour durability tests, as on "your car" you don't want to be topping-up the oil every week!
> But the rotating ring syndrom is necessary for the "perfect circle" of a ring to fit the same circle of the bore. As the ring pressure is constant for most of the ring, but changes close to the cut ends, the radial variation of pressure (hence wear) needs the rotation to maintain longevity of the ring to bore seal by the rotation causing uniform wear around the bore.
> 2-strokes with pegged rings have much shorter lives....
> K


K, thank you for the very informative treatise on ring performance. While an experienced tool maker and engineer, this is my 1st internal combustion engine build proving that 'old dog can learn (want to anyway) new tricks. Wished may father and brothers were still with us, all good mechanics they would have enjoyed all this enormously.


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## jquevedo (Aug 31, 2020)

Ken:

I have built the Mini A from Dav Perrault design, it is such a nice engine that it was a pleasure building the pieces and assembling the engine, running it, another story, ring making and ring setting is a challenge, that is the main reason I built this engine, difficulty to get something this precise to run.
The issues are mainly related to having two pistons with 2 rings each running in a single cylinder and that cylinder happens to have open ports for fuel intake, exhaust as well as spark plug.
So all the things learned in the past building engines, radial, V8, 4 flat 4 aero engines etc have proven to be very helpful.

I managed to get some decent runs yesterday, but today engine will barely kick a couple of sparks, who knows, maybe rings have rotated and aligned again causing lose of compression..

here are some pictures from the engine as built, flywheel is a new one built to see if I can increase momentum to keep the engine running for a bit longer.


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## Ken Brunskill (Aug 31, 2020)

jquevedo said:


> Ken:
> 
> I have built the Mini A from Dav Perrault design, it is such a nice engine that it was a pleasure building the pieces and assembling the engine, running it, another story, ring making and ring setting is a challenge, that is the main reason I built this engine, difficulty to get something this precise to run.
> The issues are mainly related to having two pistons with 2 rings each running in a single cylinder and that cylinder happens to have open ports for fuel intake, exhaust as well as spark plug.
> ...


Very nice indeed! See you too went with the one piece Arm's. Good idea in my opinion.


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## Steamchick (Sep 1, 2020)

Flywheel inertia is significant in getting engines to start. There needs to be enough "stored energy" (Rotational inertia) from a single firing to get the engine through 3 strokes to the next ignition, with all the valve/cam losses, and compression Adiabatic losses (back-pressure effectively), and still have enough energy to get over the firing compression with enough inertia so there is adequate speed to trigger the combustion before TDC without the pressure rise from combustion "fighting back" and giving a kick-back. Hence also the need to a good retard mechanism on the ignition for starting. Pre-1960s single motorcycles had retard mechanisms (not the riders, though I suspect a few?) that gave a spark AT TDC for starting. In fact my 500cc Matchless had a manual Advance retard lever (and exhaust valve lifter to position the engine for kick-starting) that when set for the correct full advance condition had enough travel that fully retarded was after TDC. Easy to start! Really only you need a TDC starting ignition point, then advance to idle position when running. Modern electric start engines don't start when you "just" crank enough to get over TDC.... Old hand cranked engines would do that. Almost self-start on the ignition when you got over TDC.... but needed some speed for the ignition Magneto (Who remembers them?) Not necessary with battery powered ignition though. However, modern engines need to achieve at least some speed for the hall effect sensor to define the TDC of the crank to be able to determine the next ignition point, usually by rotating at least 80rpm or more. So a duff battery that gives you slow cranking on a modern electronically controlled, fuel injected car can develop a no-start condition with a very slow crank because the Hall effect sensor doesn't trigger.
On top of that, especially when cold, the cranking speed needs to be high enough to warm the fuel-air charge with some rapid (adiabatic) compression to assist the ignition. A very slow speed - also from an "inadequate" rotational inertia (stored energy) from the flywheel after 1 firing can mean that the adiabatic heating doesn't happen enough for the second firing, with the cold metal causing condensation of fuel on the metal walls of the cylinder, etc. Note that as the air-fuel mix is drawn into the cylinder, the air is expanding into a lower pressure chamber of the inlet stroke, so is adiabatically cooling and the fuel mist will form larger droplets that need more ignition energy (spark) to ignite, or maybe they are too big so need a flame from other smaller droplets igniting. These larger droplets will wet the walls of the intake and cylinder so the mixture is weakened form the planned mixture ratio, so again ignition becomes harder to achieve. Hot engines actually give some heat to the intake mixture and when running achieve an equilibrium, thus fuel mix is stabilised. Hot cylinder walls, etc. do the rest, and with normal running the higher speed of compression ensure the adiabatic heating of the mixture during compression - and reduced time for blow-by-leakage - ensure the fuel-air charge is OK for ignition when the spark fires. 
So: a more massive (actually a higher rotational inertia) flywheel is a good thing for starting! (It can also help stabilise Idle running, when hot and ignition is more advanced, and fuel-air mix is normalised.).
Hope my waffle isn't too complicated and some are able to understand infernal combustion engines a bit better. Any experts can always correct my knowledge, which isn't perfect..., and I would hate to teach people the wrong information.
Enjoy!
K


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## stragenmitsuko (Sep 1, 2020)

love it when people are willing to share their knowledge


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## Steamchick (Sep 1, 2020)

But I have more rubbish in my brain than knowledge... Too few are interested in the knowledge, well, that applies to the rubbish as well.
Ken


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## stragenmitsuko (Sep 1, 2020)

Still , there will be far more with nothing at all in their brains ...;


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## Ken Brunskill (Sep 1, 2020)

Steamchick said:


> Flywheel inertia is significant in getting engines to start. There needs to be enough "stored energy" (Rotational inertia) from a single firing to get the engine through 3 strokes to the next ignition, with all the valve/cam losses, and compression Adiabatic losses (back-pressure effectively), and still have enough energy to get over the firing compression with enough inertia so there is adequate speed to trigger the combustion before TDC without the pressure rise from combustion "fighting back" and giving a kick-back. Hence also the need to a good retard mechanism on the ignition for starting. Pre-1960s single motorcycles had retard mechanisms (not the riders, though I suspect a few?) that gave a spark AT TDC for starting. In fact my 500cc Matchless had a manual Advance retard lever (and exhaust valve lifter to position the engine for kick-starting) that when set for the correct full advance condition had enough travel that fully retarded was after TDC. Easy to start! Really only you need a TDC starting ignition point, then advance to idle position when running. Modern electric start engines don't start when you "just" crank enough to get over TDC.... Old hand cranked engines would do that. Almost self-start on the ignition when you got over TDC.... but needed some speed for the ignition Magneto (Who remembers them?) Not necessary with battery powered ignition though. However, modern engines need to achieve at least some speed for the hall effect sensor to define the TDC of the crank to be able to determine the next ignition point, usually by rotating at least 80rpm or more. So a duff battery that gives you slow cranking on a modern electronically controlled, fuel injected car can develop a no-start condition with a very slow crank because the Hall effect sensor doesn't trigger.
> On top of that, especially when cold, the cranking speed needs to be high enough to warm the fuel-air charge with some rapid (adiabatic) compression to assist the ignition. A very slow speed - also from an "inadequate" rotational inertia (stored energy) from the flywheel after 1 firing can mean that the adiabatic heating doesn't happen enough for the second firing, with the cold metal causing condensation of fuel on the metal walls of the cylinder, etc. Note that as the air-fuel mix is drawn into the cylinder, the air is expanding into a lower pressure chamber of the inlet stroke, so is adiabatically cooling and the fuel mist will form larger droplets that need more ignition energy (spark) to ignite, or maybe they are too big so need a flame from other smaller droplets igniting. These larger droplets will wet the walls of the intake and cylinder so the mixture is weakened form the planned mixture ratio, so again ignition becomes harder to achieve. Hot engines actually give some heat to the intake mixture and when running achieve an equilibrium, thus fuel mix is stabilised. Hot cylinder walls, etc. do the rest, and with normal running the higher speed of compression ensure the adiabatic heating of the mixture during compression - and reduced time for blow-by-leakage - ensure the fuel-air charge is OK for ignition when the spark fires.
> So: a more massive (actually a higher rotational inertia) flywheel is a good thing for starting! (It can also help stabilise Idle running, when hot and ignition is more advanced, and fuel-air mix is normalised.).
> Hope my waffle isn't too complicated and some are able to understand infernal combustion engines a bit better. Any experts can always correct my knowledge, which isn't perfect..., and I would hate to teach people the wrong information.
> ...


Very informative, thank you. Your comments give rise to more thoughts to trying butane as a fuel, for this engine. Curious as to what the thoughts are on that.


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## Ken Brunskill (Sep 1, 2020)

Ken Brunskill said:


> K, thank you for the very informative treatise on ring performance. While an experienced tool maker and engineer, this is my 1st internal combustion engine build proving that 'old dog can learn (want to anyway) new tricks. Wished may father and brothers were still with us, all good mechanics they would have enjoyed all this enormously.


Think that will be the last time I post from my phone  . (may instead of my) is the kind of dumb errors that creep into the the sentence's.


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## jquevedo (Sep 1, 2020)

Propane gas is cleaner to run so they say, for me it stinks worst than regular gas, does not provide lubrication to engine parts and in engines like this which depend on the gas/oil mix for lubrication, I think it would need an oiling device to work.


Wont work all the theory here but engine lacking of compression will benefit from higher power fuels like MAPP gas /Propane, RC alcohol nitro mix but there are ways to get around the low compression issue.

I removed pistons yesterday to find that rings have indeed rotated to the point where the gap in both rings are aligned.
In the pump piston, the two ring gaps aligned with the spark plug hole, in the case of the power piston the rings have aligned with the intake port..

Did some work yesterday in the rings and cleaning the engine inside, and today I have managed to ge4t three very decent runs using  Coleman fuel mixed with a bit of synthetic 2 stroke oil.
I'm using a slightly larger diameter flywheel (0.250 over original design) but with all other dimensions per drawings, therefore increasing the momentum more than the mass.
Will work an idea on a new set of pistons and rings  and see if that helps to solve the problem of low compression.
JQ


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## stragenmitsuko (Sep 1, 2020)

Propane/butane will have the advantage that it's already a gas , not an atomised or vaporised liquid . 
So all problems of running lean when cold , fuel condensing , wet spark plugs etc will be gone .
A needle valve in the  intake from a small torch fi will be all you need to experiment .  

No lubrication whatsoever so indeed some oil will have to be added .  
After all  this is basicly a two stroke engine , altough it has 4 strokes .

Ignition will need abt 1500 volts more compared to regular fuel because an air / propane mixture is 
harder to ionise .

Air fuel ratio is 15.5-ish  instead of the 14.7 we all know and love


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## Richard Hed (Sep 2, 2020)

Steamchick said:


> But I have more rubbish in my brain than knowledge... Too few are interested in the knowledge, well, that applies to the rubbish as well.
> Ken


Tell me the rubbish then.


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## Cogsy (Sep 2, 2020)

Steamchick said:


> However, modern engines need to achieve at least some speed for the hall effect sensor to define the TDC of the crank to be able to determine the next ignition point, usually by rotating at least 80rpm or more. So a duff battery that gives you slow cranking on a modern electronically controlled, fuel injected car can develop a no-start condition with a very slow crank because the Hall effect sensor doesn't trigger.



Hall effect sensors work on magnetic flux magnitude and not the variation of the magnetic flux so they should work even at virtually zero rpm in theory. Anecdotally, I have had hall effect model ignitions fire at very low crank speeds when trying to manually determine ignition timing. At a guess, I would assume a low battery that gives a slow cranking speed is simply not producing enough current to energise the ignition system and simultaneously turn the engine over rather than the hall sensor not triggering.


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## jquevedo (Sep 2, 2020)

Hall effect sensors in practice are as good as contact points, reed switches etc, they sense the magnetic flux and send a signal.
The delayed spark issue surfaces when the ignition system has functions like advanced spark control, the ignition system (not the hall sensor) needs time to determine when the spark needs to occur, been it the first spark and the subsequent ones based on some key factors like engine temperature and engine rpm's.
I have been working ignition systems for full size engines including Bosch systems for Ferrari cars and it is amazing how simple and reliable they are. Have done good progress with Micro/Mega squirt to handle model  EFI injectors. Need some work in smaller sensors.

For slow running engines, I prefer basic systems with no advance spark control.. for 9 or 8 cylinder radials or any of the high speed engines I use ignitions with advanced spark based on engine RPM's.


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## Ken Brunskill (Sep 2, 2020)

jquevedo said:


> Propane gas is cleaner to run so they say, for me it stinks worst than regular gas, does not provide lubrication to engine parts and in engines like this which depend on the gas/oil mix for lubrication, I think it would need an oiling device to work.
> 
> 
> Wont work all the theory here but engine lacking of compression will benefit from higher power fuels like MAPP gas /Propane, RC alcohol nitro mix but there are ways to get around the low compression issue.
> ...


Wonderful, congratulations!  Very encouraging, my new rings are in the HT furnace as I write this, a new Pump Piston is in the works.

Nice that others are contributing informative commentary. Appreciate the discourse on Propane, Mapp gas, Butane, warrants a trial, possibly some collaboration to speed up revealing the results. Of course 1st having an operating engine.


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## Ken Brunskill (Sep 2, 2020)

jquevedo said:


> Propane gas is cleaner to run so they say, for me it stinks worst than regular gas, does not provide lubrication to engine parts and in engines like this which depend on the gas/oil mix for lubrication, I think it would need an oiling device to work.
> 
> 
> Wont work all the theory here but engine lacking of compression will benefit from higher power fuels like MAPP gas /Propane, RC alcohol nitro mix but there are ways to get around the low compression issue.
> ...


JQ, curious to know if you measured the 'Ring Gap' at the 'Bore' diameter, if so what was it?  As mentioned new rings were in the works, thought I'd share photos  1st is the Fixture - it has a .041" pin to establish the gap.
 2nd is the HT Fixture simple Cast Iron Nipple  two caps, the wood piece is to consume the oxygen, works splendidly-all that remains is a piece of charcoal.
 3rd is the HT Fixture in the oven at 1400 F according to the analog temp meter. 
All now cooling off in the oven - remove tomorrow when I finish the Pump Piston.

Regarding the use of some sort of gas, if anyone is interested I can provide the dimension for placing the 'oiler' hole such that it would be between the rings when the piston is at the bottom of the stroke (being that I redrew all the parts in Solidworks, it is not very hard to do a measurement), my thought is to make it a #4-40 at most, therefore able to be plugged with a set screw. Believe an oiler with a  very small thru hole to be sufficient, anyone have thoughts on that?


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## Steamchick (Sep 3, 2020)

Thanks for info about Hall effect devices. I got my 80 rpm min info from a company paper when I worked for a car company. So maybe there was some other reason they said 80 rpm min cranking speed so the ignition trigger would fire? Possibly software, for fuel injection? So no point firing sparks before fuel is introduced? I simply don't remember any more. I was dealing with starter motors, not ignition systems.
K


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## bdolin (Sep 3, 2020)

Steamchick said:


> Thanks for info about Hall effect devices. I got my 80 rpm min info from a company paper when I worked for a car company. So maybe there was some other reason they said 80 rpm min cranking speed so the ignition trigger would fire? Possibly software, for fuel injection? So no point firing sparks before fuel is introduced? I simply don't remember any more. I was dealing with starter motors, not ignition systems.
> K
> [/QUOTE


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## bdolin (Sep 3, 2020)

I still have my Matchless G80 CS witn manual spark advance and magneto. My knee still hurts from trying to kick it over at full advance!


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## Gordon (Sep 3, 2020)

Ken Brunskill said:


> JQ, curious to know if you measured the 'Ring Gap' at the 'Bore' diameter, if so what was it?  As mentioned new rings were in the works, thought I'd share photos  1st is the Fixture - it has a .041" pin to establish the gap.
> 2nd is the HT Fixture simple Cast Iron Nipple  two caps, the wood piece is to consume the oxygen, works splendidly-all that remains is a piece of charcoal.
> 3rd is the HT Fixture in the oven at 1400 F according to the analog temp meter.
> All now cooling off in the oven - remove tomorrow when I finish the Pump Piston.
> ...


I have been making rings using the same Trimbrel method except that I have read several times the the temp should be 1100° and I have been using Brownell anti scaling compound which seems to work well.


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## Steamchick (Sep 4, 2020)

Lesson learned I hope! I assume you have manual advance? - Retard?
K


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## bdolin (Sep 4, 2020)

Steamchick said:


> Lesson learned I hope! I assume you have manual advance? - Retard?
> K


Yes, lever on the handlebars. Compression release lever. Torque enough to move mountains or climb trees (dont ask!)


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## Steamchick (Sep 4, 2020)

I remember it well... Good for may-be over 85-90MPH? But not on the UK's 70 mpH limited roads! A superb bike!
Have fun.


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## jquevedo (Sep 4, 2020)

Ken Brunskill said:


> JQ, curious to know if you measured the 'Ring Gap' at the 'Bore' diameter, if so what was it?  As mentioned new rings were in the works, thought I'd share photos  1st is the Fixture - it has a .041" pin to establish the gap.
> 2nd is the HT Fixture simple Cast Iron Nipple  two caps, the wood piece is to consume the oxygen, works splendidly-all that remains is a piece of charcoal.
> 3rd is the HT Fixture in the oven at 1400 F according to the analog temp meter.
> All now cooling off in the oven - remove tomorrow when I finish the Pump Piston.
> ...



Ken:
Cylinder bore is 0.7490 in.
I made rings at 0.062 thick, inner diameter was as close as practically possible to 0.7490 - 0.80 in.
ring gap measured in bore as little as possible, just enough space for me to get the ring in the bore, I thin in practical measurable space of less than 0.004 in with a feeler gauge in a small bore is hard to get real accurate.
I use a very thin slit saw to split the rings.
I made the rings as the usual Trimble process with a lower OVEN temp 1100 F there are many discussions here and some other forums regarding the issues of softer rings created at 1400 F, not sure about this but i have always done mine at 1100.
Outside ring diameter was 0.010 in over desired finished diameter, then placed inside cylinder to adjust end gap, then machined in a custom made arbor for final diameter turning.

Engine ran OK for some time however not enough to call it a RUNNER, so I'M making new pistons and rings.
Will re-hone cylinder with one of those hones that look like bottle brushes, which are great for softening CROSS HOLES since they tend to round the sharp edges in this case the spark plug and ports.
Will make the pistons from Al 4032 (High Silica Aluminium), will use the same ring thickness but will make the piston grooves for rings LESS deep, I usually leave about 0.0010 - 0.0020 in smaller piston diameter than ring inner diameter, this allows easier insertion of pistons etc. This time I will go as close to ring inner diameter as practical.


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## Steamchick (Sep 4, 2020)

Hi there jq.. Just a few odd comments. 
I hope not to confuse you, but maybe add a bit of knowledge that will help you set-up the rings for correct machining "to size"?
First - having made a ring - slightly over-size - and slit it, you then need to clamp it in a fixture - compressed to the circle to get the gap you require in service. I assume you do not have a lazer to cut a 0.001" ring gap!
ALSO: IF I remember correctly from 50 years ago...The ring gap when installed should be about 0.004" per 1" of bore. - so you really want to achieve 0.0007 to 0.0008" ring gap when installed. So find some material that is the size of the ring gap you want when installed, cut a piece of that material that you can insert in the ring, and clamp it with a circular clamp (A piston-ring clamp, a hose clamp or piece of tin-plate and mole grips, or whatever you have to compress the ring without breaking it). THEN: When closed onto the finished ring gap insert (a piece of aluminuim foil, cigarette paper or whatever you find that is a suitable thickness) only THEN introduce the ring into your fixture for the finish machining of the diameter the few fractions of a thou less than bore size. (Linishing the last fraction of a thou so there are no machining marks on the ring). 
THUS you will have made the ring with the required gap WHEN IN THE BORE. and as it was compressed from your ring made with a larger gap, the ring radial pressure will be a function of the difference between the gap as cut and the gap as installed.
Ring manufacture is a very complicated process in plants like Hepworth and Grandage - where I visited in Sunderland 30 years ago - as they were still making cast iron rings the only way that worked properly (after 75 years of ring manufacture). I was amazed at all the fixturing needed to get the metal from a cast circle to a machined circle - then reduced after slitting to get the periphery required as a perfect circle the size of the bore, with correct ring gap and radial pressure as installed. This was followed by re-boring the inside (in a sized cylinder fixture, so again the ring was in an "as installed" condition) to get the correct ID for the piston ring groove - minimal back clearance. Finally, the machined rings were in yet another fixture to be ground on the flat faces to get the exact thickness - to match the ring groove width.
I can't remember the clearances, but here are some dimensions from my Moto Guzzi works manual:
Bore: 74mm nominal:  Actual:74.008 - 74.014mm
Piston OD: 74mm nominal: Actual 73.982 - 73.988

I'll let you work out the clearances in thousandths of inches so you can appreciate the small tolerances and clearances involved in MASS PRODUCTION of these parts. But these dimensions are for Aluminium pistons in chromed Aluminium cylinders, so no differential expansion required. These dimensions in a cast iron cylinder would seize. - But I'm sure you can find such dims and tolerances for an engine of your materials.

But for rings on pistons, the side clearances should be sensible (the Guzzi has cast iron rings in the aluminium piston).
Ring groove width in piston: to ring thickness - difference - 0.030 ~0.062mm. 
Piston groove width: 1.52 ~1.54mm; Ring thickness: 1.478 ~1.49mm.
The fact you are 1/4 of the size doesn't matter as this dimension does not scale. (To the best of my knowledge).

ALSO: Ring gap (installed in cylinder) 0.25~0.45mm
Of course, your piston & bore are 1/4 of this size so the ring gaps will also be 1/4 of these gaps. But please check these dims for an engine of equivalent material to your engine - as the Guzzi's aluminium cylinder means these are following different differential expansions to you engine. (Al cylinder +cast iron rings + al piston) is not equal to (cat iron cylinder + cast iron ring + al piston). Hope this is clear?
I do not have dimensions for ring ID as installed, versus piston groove diameter. But understand in principle that this clearance between the CLOSED ring ID to piston groove diameter is only slightly larger than the side clearance. (0.030~0.062mm). My engine is assembled in the bike so I can't measure these for you... But I'm sure you'll find appropriate dimensions so you can get a better understanding of real mass production engines versus yours?
I hope this helps, but I'm not a piston & ring designer, just worked with some.
If anyone can correct this info, I'll be glad of your help/advice? (It's 30 years since I was doing that job, the memory isn't perfect!).
K


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## peterl95124 (Sep 4, 2020)

Ken, Jamie, since you guys live in the Bay Area I'd really like to see your Atkinson engines at a BAEM meeting some time (like after a vaccine is available and we re-start having meetings). Both the Atkinson Cycle and the Atkinson Differential engines are now on my bucket list.
Pete, still working on the Merlin the Cirrus and the Duesy, Lawrence.


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## jquevedo (Sep 4, 2020)

K:

Thanks for the measurements, will try to make some correlation and hopefully make some sense on what tolerances are suitable for this engine.
As you mentioned, the key in manufacturing these rings after splitting has been the manufacturing of the machining mandrel and compression collar as well as the little piece that keeps the ring at that compressed state ( hopefully as close as to as installed measurements as possible) and then the very light machining of each individual ring.
You spend so much time and effort calculating the right measurements of the machining / holding tools and then you have to make sure your mandrel is accurate and centered as close to TRUE center as possible, then machining is not more than three seconds in the lathe, close to less than 3 seconds of polishing..

To tell you the truth, I have been using most of the tolerances that I use while building engines before, most of them in the 1 inch bore size and it worked fine for smaller engines like the Mastiff..

One major issue I have been facing is ring rotation, and the subsequent realignment of the ring gaps in the cross drilled holes ( ports or spark plug) and then the ring edges (closer to the gap) will wear off faster than the rest of the ring at this point the ring does not rotate any more but the ring stops sealing properly and the compression drops.

This is why my idea of producing a shallower ring groove to provide some drag in the ring to reduce the rotation. I know this is not best practice, we need ring rotation to make perfect circles on cylinder and rings to have a long life engine.
I understand this is more like the 2 stroke engines where a pin locates the ring and prevents the rotation, the only problem is how to practically do the same in a bore that is barely 0.750 in and rings which are 0.062 wide and about 0.040 thick..

Right now I have to finish replacing axles and bearings in one of those old Mercedes Benz Gwagen which is a nice distraction, having to make some tools to remove old bearings and install oil / grease seals..


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## jquevedo (Sep 4, 2020)

peterl95124 said:


> Ken, Jamie, since you guys live in the Bay Area I'd really like to see your Atkinson engines at a BAEM meeting some time (like after a vaccine is available and we re-start having meetings). Both the Atkinson Cycle and the Atkinson Differential engines are now on my bucket list.
> Pete, still working on the Merlin the Cirrus and the Duesy, Lawrence.


Peter, built an Atkinson Cycle engine which is a solid runner..idels at a very nice low speed and start with a couple of pulls on the flywheel..
The design is based in a couple of builders, Jan Ridders from the Netherlands and Frank Kurtz( sadly left us many years ago) but he made some very creative designs which inspired the design.


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## peterl95124 (Sep 4, 2020)

FYI, for a ring to seal it needs to be not only a perfect fit in the cylinder but also a perfect fit against the sides of the groove in the piston, IE the sides of the ring need to be perfectly smooth and the sides of the groove in the piston need to be perfectly smooth. Its easy to polish the sides of a ring to a mirror finish with a holder and 2000 grit wet-or-dry paper, but the groove in the piston is another matter, I always do this groove with a carbide tool and lots of tap-magic as a cutting fluid. Examination with a 10x magnifier should show a smooth machined surface, otherwise scrap and start over...


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## Steamchick (Sep 5, 2020)

Lots of good information on this thread. I'm really enjoying reading! Thanks guys!
jq: You mention that you are going to reduce the clearance at the bak of the ring by making pistons with slightly larger diameter at the bottom of the ring groove. Well, I like your idea, but please be aware of how much the piston will expand, compared to the rings and (presumably cast-iron?) bore? The bore may only expand from room temp to 80 ~120 degrees C.... but the piston can get 100~150 degrees C hotter: And then the coefficient of expansion of the aluminium is so much greater than the cast iron, I think you may get to the point of seizure when you get a hot piston? (without exact dims I haven't done the sums). So please do the sums or post a picture of all the finished dims of the piston, rings and bore and we'll do the sums and let you know.
Peter, Text book perfect comments! Thanks.


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## Steamchick (Sep 5, 2020)

On ring rotation... 
As rings rotate, the end appears to be passing a port from your explanation. This is categorically a "No-no!" in my experience of engines. The radial pressure from and "endless" ring is constant, but the radial pressure of an end of a ring is higher (as far as I remember from 30 years ago - probably I'll find out from Google someday) and when it finds a port - as uncontrolled rings in a 2-stoke port - it will expand into the port. This will eventually cause a breakage and severe wear of the bore as the edge of the ring rubs on the edge of the port when it transfers from port to cylinder wall above or below the port. LOTS of extra heat will be generated, as the ring and bore machine each other. The expanded ring end will prevent further rotation to get past the port - as you mention - so the only solution (as on 2-strokes) is to peg the ring, where the ends are "mid-way" between ports. (On 2 strokes with transfer ports on 2 sides, and an extra transfer port opposite the exhaust port which is between the 2 main transfer ports, the pegs will be positioned between transfer port far away from the exhaust port.). As the ring gap is only 3~4 thou in in your case, a peg of that size isn't practical, but if you have (E.G.) a 0.030" peg, you can make the ring gap 0.033" wide when rings are fitted in the bore - which actually may make life easier? In fact, a peg the same size as the ring groove width is probably the best, with ring gap adjusted accordingly. Use brass for the peg and be sure it is below the surface of the piston, but only by a couple of thou.
Hope this is of some assistance?
K


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## jquevedo (Sep 5, 2020)

K thanks for your comments, the issue as you described was, wear in ports area of the cylinder most likely caused by ring rotation and alignment to ports, some additional wear was maybe caused by metal residue in the middle section of the cylinder, causing the cylinder to have more wear where the rings rub that at the two ends. 
Re-machined cylinder to new diameter and made pistons to fit with new dimensions and reduced ring groove depth, will use your idea of making a 0.0062 in pin and insert it where the ring end gap should be in relation to ports (power piston) and spark plug ( pump piston).
Thanks for the advise..
JQ


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## Steamchick (Sep 5, 2020)

Hope it is a step forward anyhow.
Cheers!
K


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## Ken Brunskill (Sep 5, 2020)

JQ, K & Peter, 

Wonderful reasoning and information flow going on here! Heretofore I'd not been a follower of any online or web-based stuff of any description, yet I am finding that following this site most interesting and informative, akin to 'measuring twice cutting once!   I was about to head out to the shop and finish up the rings for the Pump Piston, now with the information JQ has just provided I'm of the mind to do the pin concept as that just makes good logical sense! Will give it some  serious consideration.

As to bringing the engine to BAEM meeting, will do! The next meeting is Sept 19th, since it is outdoors, maintaining a good social distance is easy, although not everyone wears a mask it is easy to maintain a safe distance and still participate.  JQ where are you in the Bay Area, I am in Fremont.
Ken


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## jquevedo (Sep 5, 2020)

Ken:

I used to attend some of the BAEM meetings when worked allowed it, my work was mostly international long term travel so I was pure luck if I was home and the meeting was scheduled.

Now I reside in Monterey near Carmel so the trip has gotten way too long specially when they moved the meetings up North from Palo Alto.
I also spend significant time in Baja CA Sur, near San Jose del Cabo where I have built my simple beach house, and sadly there is no Work shop there.
JQ


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## peterl95124 (Sep 5, 2020)

don't know how true this is but concerning ring groove depth in the piston, I've been advised that the ring should not be able to bottom out in the groove as the piston moves side to side in the cylinder, gas pressure needs to get behind the ring to create ring-to-cylinder sealing force.  my guess is there needs to be as much depth clearance as there is side clearance, rule-of-thumb is at least 0.001" per inch of bore. also differential thermal expansion of the piston compared cast iron ring will increase the side clearance but decrease the depth clearance so depth should be even larger.


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## Ken Brunskill (Sep 6, 2020)

jquevedo said:


> Ken:
> 
> I used to attend some of the BAEM meetings when worked allowed it, my work was mostly international long term travel so I was pure luck if I was home and the meeting was scheduled.
> 
> ...


JQ,

To bad, would have been neat to have two of these show up at a BAEM meeting. With your place in San Jose del DCabo, do you fly fish? If so that would be an amazing coincidence, as that is my other significant avocation. I've not tried the message component of this site, has anyone? Is it 100% separate from these postings (presume so)?


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## awake (Sep 6, 2020)

jquevedo said:


> Peter, built an Atkinson Cycle engine which is a solid runner..idels at a very nice low speed and start with a couple of pulls on the flywheel..
> The design is based in a couple of builders, Jan Ridders from the Netherlands and Frank Kurtz( sadly left us many years ago) but he made some very creative designs which inspired the design.



From the pictures, this looks like the other Atkinson design, not the differential - very different animals, from what I understand (which may not be much!)


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## Ken Brunskill (Sep 7, 2020)

K, You have inspired me to make a new set of Pistons and Rings utilizing the 'Pinned' concept. Once the weather here has dropped (It is in the 100 F range at present) I will venture back out to my shop and make the fixtures shown in the two attachments. Your review and comments are encouraged, as I'd not thought about taking this path before you mentioned it.
In the meantime, I'll forge on with Dave Perrault's design, to see if I can get as far as JQ has. (Won't run it much as I suspect I'd damage the cylinder walls, I'll be satisfied if I get compression, and a "pop" for now.


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## Steamchick (Sep 8, 2020)

Ken, you are welcome to my knowledge. Just keep a big bucket of salt handy for those moments when you take my comments "with a pinch"! It can take me ages you Figure out when I was wrong -Often for the simplest mistake - so as usual, check, check again, doubt the result and check a different way before using my knowledge!
K


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## Ken Brunskill (Sep 8, 2020)

A few weeks back there was mention of sharing detail/data, so in that vein here is some on my Atkinson Differential (Lets refer to them as just (AD). Anyway my AD build has the following:
Bore is .749" 
Rings are .050" wide by .041" thick made via the HT Method (Trimble) with .0015" gap (At least a .001"feeler Gage passes but not a .002" when in a .749" ID Ring.
Compression was negligible on 1st try when I had (2) .025" wide rings in one slot on the PUMP piston, but achieved 20 PSI when I re machined it and put in .070" Cross section O'Rings (hand cranking with no run in of any sort). 
Did a measurement of the max & min distances of the piston faces and determined that when the pistons are furthest apart the volume is .18 cu", at closest the volume is .047 cu" calculates to 3.83:1 compression ratio. (Measurements via Solidworks 3D model). Will do a compression test after every hr for 3 hrs to see if there is any change, since the O rings will be crossing the spark plug hole I anticipate a loss - will report findings.
Supposed to be cooler today so hope to get out in the shop, if it gets over 90 F, out there, that will put a stop to the efforts!


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## Ken Brunskill (Sep 12, 2020)

Steamchick said:


> Ken, you are welcome to my knowledge. Just keep a big bucket of salt handy for those moments when you take my comments "with a pinch"! It can take me ages you Figure out when I was wrong -Often for the simplest mistake - so as usual, check, check again, doubt the result and check a different way before using my knowledge!
> K


K,

Looking for your expertise, please offer your opinion on sizing the rings for this little engine.
My bore is .749" Dia.
My rings were made to .7515" OD with .041" Wall, and are .051" wide. I have just lapped (.400 grit sandpaper) the gap to be .003" when in a .749" ID Ring. There is just barely a hint of light on the periphery.
Rereading your post of Sept. 4th, I interpret that your recommendation is for .002" (.052 mm) total clearance for the width, and .004" (.104 mm) between the ID of the ring (closed) and the OD of the Ring Groove.
Cheers, Ken


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## dsage (Sep 12, 2020)

Ken if I read and you type correctly above I think you missed the first step in the Trimble method of making rings.
If your bore is 0.749 then the rings should also be 0.749 +/- zero  OD i.e exactly the same as the cylinder bore. (to the best of your abilities) before they are split and heat treated for their end gap.
To split them I usually place one section of the circumference over a piece of #22 wire on a flat surface and press down with two thumbs close to the wire to snap the ring. That will give you a zero gap.
Optionally you can saw the gap but for a 1" piston that would require a 1thou saw blade. Never seen one.
After the heat treating I hold the snapped section  securely over the edge of the table and put a piece of fine sand paper in the gap and carefully work the paper up and down to create the gap. Periodically put the ring squarely  in the bore and check with a feeler gauge to get the required end gap. Rinse and repeat with the sandpaper to your end gap specification.
If you are seeing light around the circumference while in the bore, stop. The ring is no good.
While the ring is in the cylinder I make a cardboard mask to put over the inside diameter of the ring to block light. Shine a light from the top of the cylinder and look carefully up from below  around the circumference. There should be no light visible except through the end gap.
My 2cents on the subject. Of course there are a hundred opinions on the same thing. I'm sure you'll see them all.


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## Steamchick (Sep 13, 2020)

dsage - I agree with everything you say, except my experience is for the ring to be machined to the exact bore size when compressed to give the correct radial pressure ( and clamped between 2 collars to hold it at the correct compression when machining). At Hepworth and Grandage works in Sunderland - making cast iron rings - it was interesting to see a mandrel filled with a hundred or so rings, for final machining to bore diameter.
First the rings were cast - 6 around a central metal feeder - then broken into single pieces. Horizontal grinders set the ring thickness and they were clamped together to form a cylinder for machining the bore.  Then the OD was machined after fitting on a different mandrel - a sliding fit for the bore. Also while held on this mandrel, the rings were split with a slitting saw.  These rings were then fitted into a Bore-sized cylinder and clamped together on yet another mandrel. Then the finished bore size machined. So when released the rings had the correct amount of spring deflection for the required ring radial pressure to resist compression. Finally, rings were installed on a mandrel that was on a weird motion in a bore with very fine grinding paste to shape the barrel-shape required on the rings. On a model, the "running-in" should put the barrel honing onto the rings - providing you DON'T use molybdenum in the oil.
I don't know the Trimble method, but I hope that helps?
Ken


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## Steamchick (Sep 13, 2020)

Ken Brunskill said:


> K,
> 
> Looking for your expertise, please offer your opinion on sizing the rings for this little engine.
> My bore is .749" Dia.
> ...


Hi Ken, Let me try and understand your sizes. 

Ring OD 0.7515" to fit a bore 0.749" dia. gives 0.0025" "compression" of the ring when fitted. Sound Ok without consulting calcs for radial pressure... but I guess you are working to someone's proven design?
Ring groove width: I guess you have 0.053" wide for your rings of 0.051" thick - That is a fine bit of machining! = OK. - as that is where most of the blow-by gas passes the piston.
Back-gap (behind a closed ring) of 0.004" for a diameter 0.749" bore less the ring width of 0.041" (x 2) gives a ring groove diameter of 0.659" by my calculations. This should be Ok as the object is not to seize the ring radially, and permit some float for the piston to move (align with the various forces) within the bore. It accommodates more than potential "mis-alignment" of bore and piston line (perpendicularity of the crank line and bore), as the barrel shaped piston skirt allows a tiny rotation of the piston about the gudgeon pin, as the the piston oscillates between "suction" and "Compression" strokes..  
 Hope this helps?
Ken


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## dsage (Sep 13, 2020)

Steamchick:
Not sure which side of the fence you're on. Make them over size and leave them as is - or make them over size and turn them on a mandrel after to size. Your two post are in conflict.

Certainly making them oversize and leaving them as-is they will NOT be round when jammed into a cylinder (even with an appropriate gap to get them to fit). The bore and ring are not the same circumference. SO that method is out.

The Trimble method does specify turning the last thou off on a mandrel but I've never had any luck being able to reliably turn a thou or so off the diameter after the fact on my lathe. There is more than a thou run-out in my lathe chuck and I assume most hobby lathes. So you end up with a ring with a non-round shape even though it might measure the right diameter here and there. This may work in a factory setting though as you point out. Not for me.

SO I turn them right from the get-go to the exact diameter and sometimes even polish them to get the last tenths.
Then the proper amount of expansion at the gap (Trimble specifies it) and the heat treating gives them their radial pressure. When they are inserted in the cylinder they will be round again and the exact diameter because they started out that way.

Certainly NOT leaving them oversized and making them fit with the gap. Which is what Ken's post was implying he was doing.

Again just my 2 cents for what has worked for me.


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## Steamchick (Sep 13, 2020)

Sorry, probably mixed things up a bit, accidentally. 
First you machine over-size to the required "spring" plus a couple of thou. Then compress in a bore that is the size for the correct amount of ring compression (actually they called it "spring tension" at H & G from what I remember?) and hold clamped axially (at the correct ring-gap) and machine to the BORE size while compressed. (That "couple of thou"). This means the COMPRESSED ring in the bore has a "perfect circle" and correct cylinder wall pressure. Perhaps this is just impossible for the rings as small as you are making? The smallest production process I saw was about 2" diameter. - But I was a visitor, not working there, so may be wrong with the process I remember? Also, I have no hard data of sizes etc. - which were their "secret" to get the required finished parameters and sizes.
I don't know the Trimble method. Is this a way of machining to size, then softening, expanding and hardening to give some ring to cylinder wall pressure? - This sounds like a heat treatment that could possibly distort the shape of the ring from the "perfect circle" that was the target at H & G. But they were dealing in cast iron rings that would not be heat treated. They did make steel wire rings as well, that were heat treated - but this was a time for soaking them in burning Ammonia gas at a very dull red heat to nitride the surface. Actually the steel ring shape came off a clever winder that gave the ring "tension" that was uniform when in the bore. Which meant it wasn't a perfect circle unloaded, as the end effect of the element of the ring close to an end was to give a different wall pressure when compared to a "middle" element that is supported by elements either side with the same wall pressure. There must be a mathematical paper on this somewhere, that is better than my imperfect memory from 35 years ago.
Sorry about confusion.
K


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## dsage (Sep 13, 2020)

Steamchick said:


> Sorry, probably mixed things up a bit, accidentally.
> First you machine over-size to the required "spring" plus a couple of thou. Then compress in a bore that is the size for the correct amount of ring compression (actually they called it "spring tension" at H & G from what I remember?) and hold clamped axially (at the correct ring-gap) and machine to the BORE size while compressed. (That "couple of thou"). This means the COMPRESSED ring in the bore has a "perfect circle" and correct cylinder wall pressure. Perhaps this is just impossible for the rings as small as you are making? The smallest production process I saw was about 2" diameter. - But I was a visitor, not working there, so may be wrong with the process I remember? Also, I have no hard data of sizes etc. - which were their "secret" to get the required finished parameters and sizes.
> I don't know the Trimble method. Is this a way of machining to size, then softening, expanding and hardening to give some ring to cylinder wall pressure? - This sounds like a heat treatment that could possibly distort the shape of the ring from the "perfect circle" that was the target at H & G. But they were dealing in cast iron rings that would not be heat treated. They did make steel wire rings as well, that were heat treated - but this was a time for soaking them in burning Ammonia gas at a very dull red heat to nitride the surface. Actually the steel ring shape came off a clever winder that gave the ring "tension" that was uniform when in the bore. Which meant it wasn't a perfect circle unloaded, as the end effect of the element of the ring close to an end was to give a different wall pressure when compared to a "middle" element that is supported by elements either side with the same wall pressure. There must be a mathematical paper on this somewhere, that is better than my imperfect memory from 35 years ago.
> Sorry about confusion.
> K


It's nice to hear the way they make them in industry. I've always wondered. I'm sure it could be duplicated by many model engineers. I've just followed the Trimble method for cast iron rings. He did a lot of research on the subject and came up with it. Of course it's probably not perfect but easy enough to accomplish except the skiming off a thou (for me).
  As for the heat treating it's NOT done at high temp. The rings are heated only to dull red visible in a dark room. I guess that's maybe 1200 F or so (the way I do it anyway). Pretty low compared to "heat treating". Not even hot enough to create surface oxidization to any great extent (in my experience anyway). It think it's more of a stress relief of the stresses put in by opening the gap a prescribed amount. Then when they cool they are fixed in that position and the tension comes again when they are put in the cylinder.
Many rings are stacked in a jig and clamped. So I've never had them distort. They lay flat on a surface plate for lapping to exact thickness.
You should look up the procedure. It shouldn't be hard to find.


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## dsage (Sep 13, 2020)

I guess we've sufficiently confused Ken now


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## Ken Brunskill (Sep 13, 2020)

dsage said:


> I guess we've sufficiently confused Ken now


Dave & Ken, enjoying the discourse and really appreciate the collective knowledge being shared here. Actually even though an octogenarian, I am not being confused in the least bit. 55 years ago, I was lucky enough to have gone through a Tool & Die Apprenticeship at two companies, at one of which I had to spend 6 months in the HT department, followed by another 1 1/2 years where we as apprentices had to heat treat our  own work. Provided a great background for most of the rest of my career (Mechanical Manufacturing Engineer and sometimes Mechanical Design Engineer). Of course none of which had anything to do with gas engines. Having always worked in the SF bay area my experience was in audio visual, computers, & computer peripherals.


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## dsage (Sep 13, 2020)

I meant confused as to the number of choices you have to ponder to make the rings.


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## Ken Brunskill (Sep 13, 2020)

dsage said:


> I meant confused as to the number of choices you have to ponder to make the rings.


 Not even that!  I am even contemplating an overlap gap. Hey, after all it is a hobby right?


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## Steamchick (Sep 13, 2020)

I suspect that when you get the fine clearances of rings in grooves, and no light around the ring to bore, you'll  have Ok compression. Even if the straight gap is a thou or 2 big.
K


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## Ken Brunskill (Sep 14, 2020)

Steamchick said:


> I suspect that when you get the fine clearances of rings in grooves, and no light around the ring to bore, you'll  have Ok compression. Even if the straight gap is a thou or 2 big.
> K


Made the Rings .003" under the Piston Ring Groove, width, assured that the Dia. of the Ring Groove was .003-.004" less than the Ring ID when in the Gap Checking/Setting ring. Installed the rings on the piston, and installed these in the engine, compression is the same as I had with the O-Rings (approx 20 psi.  ,Feeling positive, thinking I might have success. Now to proceed with the Fuel & Water Tank.


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## Steamchick (Sep 14, 2020)

Sounds good, but with all puddings, the proof is a satisfied full tum!
K


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## dsage (Sep 15, 2020)

Ken before you move on.
Squirt a bit of fuel in it and see if you get a pop. Don't forget the oil mix.


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## Ken Brunskill (Sep 15, 2020)

Thanks for that bit of advice Dave, trying to have it provide a 'Pop" before Saturdays BAEM meeting.


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## Tim Wescott (Sep 16, 2020)

A detailed description of the Trimble method.  I haven't made rings, so I can only pass it on 'cuz I read the article and remembered how to search it out: How To Make Piston Rings


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## Ken Brunskill (Sep 16, 2020)

Steamchick said:


> I suspect that when you get the fine clearances of rings in grooves, and no light around the ring to bore, you'll  have Ok compression. Even if the straight gap is a thou or 2 big.
> K


K,

Pursuant to the thought of split gap (overlap) or pinned rings:
1. Thinking about the split gap, or more correctly stated 'overlap', I am inclined to this over the pinned concept.
    a) Seems that the overlap would provide a better seal, the logical question would be sizing the split. (Bottom view of the sketch.)
    b) Theoretically this, it would appear provide the better seal of the (3) concepts.
    c) Now to understand what the sizes should be, my thoughts are to have the overlap be such that the ring end up .000" to .0005" of width.
    d) The length of the overlap will need to be such that each side can be cut with the ring expanded to almost breaking, trial & error I suppose.
    e) The gap at both ends (each end),I suspect would be the same as for the traditional method (for a 1" ring .002").
2. The center concept appears to me to be the least likely to provide a good seal, as the gap is tangential to any pin size considered.
3. The upper most concept, seems as good as the traditional technique, while stopping ring rotation.


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## jquevedo (Sep 16, 2020)

Ken:

I've had good luck stopping ring rotation by controlling the amount of clearance between piston groove and ring.
I've done my set of rings using trimble method, then machining them in a very accurate and well centered spigot with the right dimensions based on the ring and bore and ran my engine for several hours to the point of having some pops but no sustained run, so I opened the pistons to replace rings and they were in the same location where they were installed..both pistons had decent be in of rings but compression was low (1round 10-12 PSI) I think we need to achieve over 20 PSI's to get a decent pop..
Funny thing is most times I start with 20 plus PSI and then trying to bed in the rings, compression goes down to almost 5 PSI and then slowly start to come back up when the bed in the cylinder.
At this point in time, I think the need for pinned rings is not necessary. Good rings and controlling the ring groov gap to ring to be under 0.005 in would be sufficient to stop the rotation, my rings are 0.062 thick once polished on the sides and the groove in the piston is 0.063 in.

Kind regards


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## Steamchick (Sep 17, 2020)

Hi Ken,. I last saw overlap piston rings back in the early 1960s. (I think IJ fvounde tghe typingh probledm - my kedboard ijs ghooszeded! - Takes a lot of correction.).
The ring-gap blow-by area is 3thou (ish) by ring radial thickness. The leak area passing the top and back of the ring is maybe 2thou x circumference.... so the gap leakage is small compared to ring and groove clearance. Or so I was taught ... Hence modern engines use simple gaps, not overlap. Yamaha use the simple pin to stop rotation. (They are quite expert at this).
But I am not the expert - I just worked with many...
K


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## Steamchick (Sep 17, 2020)

Try a bit of oil in the fuel? 50:1? That helps the bore to ring seal - when bores are still relatively rough.


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## Steamchick (Sep 17, 2020)

How To Make Piston Rings
		

.
All sounds OK for models, although it differs a bit from my "full-sized" industrial experience - except for the Cold Forming bit.
]But at H & GH I witnessed the barrel honing of rings -  essentially pre-running-in.
K


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## dsage (Sep 17, 2020)

Sorry I get thickness and width confused as it depends on how your looking at the ring. And I forget the convention.
I consider thickness the vertical height of the ring looking as installed from the side of the piston. Sorry if it's opposite to convention.
With that in mind:
On one hand it would seem a good idea to make the ring thickness and piston groove have almost no side clearance since an aluminum piston is going to "grow" faster than the ring is going to get thicker so the groove will bet wider an the clearance will increase as the engine heats up. (I think).
On the other hand there is a need for some clearance (they say) go gas pressure can get around behind the ring and make it expand and seal against the cylinder bore. Not sure which is correct for a model engine.
I'd be tempted to forget the overlapped ring ends and try almost no side clearance because - as mentioned by others - there is a lot more leakage by area around the ring than there will ever be through a small end gap.
I'd also keep the end gap to an absolute minimum because an aluminum cylinder is going to expand and the ring end gap will increase. Then again the ring might get hotter faster than the cylinder. Again - Not sure.
I'm not sure why this Atkinson engine has so much trouble. I've certainly had no trouble with any of my other engines. Sometimes I think we're overlooking something. Certainly the intake and exhaust ports are problematic and having two pistons to seal at the same time is double trouble.
I've never made a two stroke engine and this engine is more of a two stroke than anything. Maybe a change in thinking is required.
I've stopped work on mine when I discovered the issue with vacuum in the cylinder when it failed to fire. Hence my elaborate solenoid valves (which didn't help).

I've been holding off further work on my engine until I see the results here. I hope you don't mind being the guinea pig Ken   

I've been following a guy on Youtube. A channel called "2stroke stuffing".  The guy is a genious. He's building his own two stroke 50cc engine 30 horsepower (he figures) from scratch to put in a salt flat racer. The engine starts with conventional reed valves etc. but turns into strictly a tuned resonant system when running at speed. He just got it to run and idle. You have to watch the early videos to watch the progress. Quite motivational.


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## Steamchick (Sep 17, 2020)

dsage: There are many who know a lot more than I do, but my training told me the Axial clearance really needs to be at a minimum. The gas pressure will get behind the ring - so no-one need ever worry about that. The gas pressure forces the ring "down" on the compression stroke, thus giving max area for gas to get past the ring to the inner annular gap. So 0.001" axial clearance is adequate. Assuming the piston crown gets to 400deg.C, (it won't) work out the expansion of the inner diameter of the ring groove and make sure there is a thou or 2 clearance for the ID of a fully compressed ring,. so it doesn't seize. That should be OK for ring gap.
OK?
K


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## Ken Brunskill (Sep 17, 2020)

Dave, Jamie & K; Truly have enjoyed this discourse and the friendly manner of it. I sincerely hope none of us ever feel as if it taking up too much of our time!
Cheers, and stay safe.


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## Steamchick (Sep 17, 2020)

Probably more hours of debate than making bits. But that's why we contribute to the thread. We enjoy the debate and sharing of ideas.
Thanks.
K


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## jquevedo (Sep 17, 2020)

Positive feedback instead of someone trying to make us think certain way goes a long way. Thanks to the inputs provided ideas are formed, some are practical and some are not but all of them deserve consideration..
Debate is needed to challenge old ideas or approaches and to create new ones.


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## Ken Brunskill (Sep 26, 2020)

So far no luck getting a Pop, not discouraged yet, I've just finished assembly, connected the ignition parts, and mixed the fuel. Next step is to build a cranking device so I can continuously crank the engine at a modest RPM while slowly fiddling with Carburetor settings. Of course stopping every few tries to change the spark timing and start the process over again. Any suggestions are appreciated.

After reading and following the other  Atkinson Differential threads, another thing has crossed my mind; may be it would be worthwhile to measure the vacuum created at the fuel intake. Any thoughts? Any suggestions of sources for a vacuum gage? Suspect that it will be low vacuum as the compression is in the 10-20 PSI range.


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## Steamchick (Sep 26, 2020)

Just a clue on intake vacuum.... 
I have a pair of vacuum gauges "for cars" - actually good for anything. They work fine for constant vacuum carburettors, but on my slide carb Moto Guzzi V50 they bounce from 0 ~ 4 or 5 "inches of mercury below atmospheric" and if the throttle slides are lifted they just flutter off the stops. (N.B. Full-ish Vacuum is about 30 inches of mercury below atmospheric, for those unfamiliar with "Grand-dad's measurements").
I guess on a model there will be almost nothing to show on a gauge. 
BUT you can try a water column? - Easily made with a clear plastic tube fixed to a plank as a U-shape and HALF filled with water. When vacuum (partial) is applied to one end, with the other open to atmospheric pressure, you can measure "inches water gauge" by the difference of the water levels.
For "hardly any suck" these are great! - see what your lungs can do, and have fun with the kids (OK if they drink the water). The gas man has one for checking the gas pressure supplied to your boiler or gas fire, or maybe the modern ones have digital gauges by now?
K


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## jquevedo (Sep 26, 2020)

Ken:
My experience so far: 
Be patient, it will take a while to get the engine to show any signs of life..Low compression, 4 ringsw one cylinder you know the story.
I started with 20 PSI compression and it went down to almost 5-7, then slowly building up again, to almost 25 PSI..
I have been cranking mine for days, short periods, maybe 10-15 minutes at a time.
I have placed the spark setting very close to TDC to avoid kick back in the engine while running in, once the engine showed signs of life, I adjusted spark time to 5 degrees before TDC.
No need to fiddle with gas/air settings for a while..be patient, I used 1/2 to fully open air and 3/4 turn on gas.
Once you get some different noise in the engine and depending on the oil/gas mix you may see some smoke off the exhaust, then it may be time to start trying the air/gas adjustments
Once you start hearing some pops you can also add some oil drops in the carburetor and see if that increase compression and allows you to better tune your engine, one thing you can monitor is cylinder temperature, when the fuel explosion is happening, you will have a steady increase in temperature in the engine..
This is the second cylinder I'm using, first one material was not the best choice, this one is Mehanite and it is taken way longer to get to the point of getting some pops from the engine..
Been two days of short periods of running in to get some pops and finally engine has shown some signs of life..
I have been running the engine at lower rpm's 400 - 600 during the "wear in" period but Dav Perrault thinks it was too slow, 650-750 seems to be a better spot once you are getting some engine pops to do the adjustments.
You may notice some blow by from the rings this will reduce over time and should mostly disappear just before you get engine pops, pump piston is easier to tell when this happens, Power piston is a different story, the intake port gets exposed inside the cylinder, when the piston moves all the way to the right and you get some fuel dripping in the skirt of the piston, which then get flung out the cylinder.. and looking like ring blow by.

Patience is the key, if you get frustrated /impatient, stop go and take a walk and come back to it later, check plug batteries for ignition, fuel etc..
if you prefer give me a ring and we can chat in more detail..

Jaime


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## dsage (Sep 26, 2020)

If you read my thread to the end you will see I was investigating the vacuum issue. I found when the engine does NOT fire there is a vacuum in the cylinder when the pistons move back apart (due to some loss in the original compression). This vacuum is exposed to the carburetor when the piston move farther down the cylinder and sucks fuel in before the actual intake stroke comes and also just before the exhaust valve opens. I found that fuel is sucked in and immediately spat out the exhaust port. I suspect that problem also plays havoc with the real intake stroke that happens later. Gordon also confirmed that his engine seemed to have a lot of fuel coming out the exhaust. The last few posts in my thread show an elaborate valving arrangement with solenoid I tried to relieve that false vacuum from reaching the carb. Of course none it works but it did prove the vacuum in the cylinder issue.
May I suggest putting a bit of fuel right in the cylinder through the spark plug hole. Replace the plug and give it a spin. If things are conducive to starting the engine should at least pop once (or more).


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## jquevedo (Sep 26, 2020)

I will check on the vacuum issue you experienced in your engine design, just need to find how to hook a gas (LPG) electronic device to the intake port or carburetor to see if I have any back blow form the intake.

So far this does not seem to be an issue, engine has a sliding valve which may help to reduce the issue.
My problem with the initial cylinder, intake and exhaust port size was wrong and cast iron material wear inside faster than the rings. My first cylinder got the engine running for short periods I assume the small size in the intake ports was starving the engine, then too much cranking and new set of rings wore the cylinder.


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## dsage (Sep 26, 2020)

I think A couple of people were typing at the same time. So messages might be a bit out of sync.
Following on SteamChicks idea of a vacuum gauge. I did at one point put a column of fuel on the carb fuel line. This is where I notice a suction on the carb before the actual intake stroke as described in detail above. This led to the development of the wacky solenoid valve arrangement to eliminate the issue. Which it did. The only vacuum on the carb was then only due to the intake stroke.

For those following along wondering what's going on  - this engine is NOT your typical engine being that it is opposed pistons. So it's probably not exactly accurate to think about it like a typical 4-stroke. Nor is it helpful to compare experiences with a 4-stroke engine break in. Other than in very broad terms. This differential action  engine is particularly troublesome.
It might be more useful to think of it like a 2-stroke as far as the intake stroke is concerned. But vacuum in the cylinder due to a misfire is probably not as disruptive on a 2-stroke due to the porting. I'm not a 2-stroke expert.

Jquevedo: Is your engine an Atkinson differential as well. Sorry I haven't been following along to well.


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## dsage (Sep 26, 2020)

Duplicate message.


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## peterl95124 (Sep 26, 2020)

Ken,  really appreciated seeing your Atkinson Differential at the BAEM meeting, awesome work.

Question, does the intake happen because the the compression piston has created a vacuum in the cylinder so that when the intake port is uncovered the intake is drawn into the cylinder ?  if so then then maybe the ring should have more tension against the cylinder wall than in a conventional 4-cycle ?  just idle thoughts, ignore if not relevant !

Peter.


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## Ken Brunskill (Sep 26, 2020)

Steamchick said:


> Just a clue on intake vacuum....
> I have a pair of vacuum gauges "for cars" - actually good for anything. They work fine for constant vacuum carburettors, but on my slide carb Moto Guzzi V50 they bounce from 0 ~ 4 or 5 "inches of mercury below atmospheric" and if the throttle slides are lifted they just flutter off the stops. (N.B. Full-ish Vacuum is about 30 inches of mercury below atmospheric, for those unfamiliar with "Grand-dad's measurements").
> I guess on a model there will be almost nothing to show on a gauge.
> BUT you can try a water column? - Easily made with a clear plastic tube fixed to a plank as a U-shape and HALF filled with water. When vacuum (partial) is applied to one end, with the other open to atmospheric pressure, you can measure "inches water gauge" by the difference of the water levels.
> ...


OK this is where I slap myself on the forehead, I certainly know about the U-Tube and water, but did I think about that? NO  !


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## Ken Brunskill (Sep 26, 2020)

peterl95124 said:


> Ken,  really appreciated seeing your Atkinson Differential at the BAEM meeting, awesome work.
> 
> Question, does the intake happen because the the compression piston has created a vacuum in the cylinder so that when the intake port is uncovered the intake is drawn into the cylinder ?  if so then then maybe the ring should have more tension against the cylinder wall than in a conventional 4-cycle ?  just idle thoughts, ignore if not relevant !
> 
> Peter.


Peter,
The vacuum occurs while the 'Pump' piston is moving away from the 'Power' piston. They are moving in the same direction, the travel of the (2) pistons vary in speed, see the video I made of the 3D Solidworks Model posted on Page 2 of this thread June 13th. (Please excuse the amateurish narration.)


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## Ken Brunskill (Sep 26, 2020)

peterl95124 said:


> Ken,  really appreciated seeing your Atkinson Differential at the BAEM meeting, awesome work.
> 
> Question, does the intake happen because the the compression piston has created a vacuum in the cylinder so that when the intake port is uncovered the intake is drawn into the cylinder ?  if so then then maybe the ring should have more tension against the cylinder wall than in a conventional 4-cycle ?  just idle thoughts, ignore if not relevant !
> 
> Peter.


Peter, thank you for the complement on the engine, I'd not done that level of machining since the 1960's, it was fun! Sure can see why folks are enamored with the CNC machines. But us old handle crankers are still around, slower though!


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## Ken Brunskill (Sep 26, 2020)

jquevedo said:


> Ken:
> 
> I've had good luck stopping ring rotation by controlling the amount of clearance between piston groove and ring.
> I've done my set of rings using trimble method, then machining them in a very accurate and well centered spigot with the right dimensions based on the ring and bore and ran my engine for several hours to the point of having some pops but no sustained run, so I opened the pistons to replace rings and they were in the same location where they were installed..both pistons had decent be in of rings but compression was low (1round 10-12 PSI) I think we need to achieve over 20 PSI's to get a decent pop..
> ...


Well ,I have the blanks ready to make new rings using the 'No Heat Treat method'. Where the rings are over size to begin with, compressed to cylinder Dia. for machining both ID and OD at a preset end gap. Will go to this step if don't get a POP, and the vacuum and compression indicate the need.


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## peterl95124 (Sep 26, 2020)

Ken, no matter what method you use to make your rings you can always fix them the way I did, put some extra fine lapping compound in the cylinder and slide the pistons with rings up and down in it, disassemble and use an ultra-sonic cleaner to be sure to get all the grit out of everything, reassemble, first pop. (works better with pinned rings so you can rotate a bit while lapping up and down, but I didn't and it still worked for me) Pete.


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## Ken Brunskill (Sep 27, 2020)

peterl95124 said:


> Ken, no matter what method you use to make your rings you can always fix them the way I did, put some extra fine lapping compound in the cylinder and slide the pistons with rings up and down in it, disassemble and use an ultra-sonic cleaner to be sure to get all the grit out of everything, reassemble, first pop. (works better with pinned rings so you can rotate a bit while lapping up and down, but I didn't and it still worked for me) Pete.



Thanks for that suggestion Pete, this is getting as interesting as the build itself  . I hope that others are enjoying these exchanges.


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## Steamchick (Sep 28, 2020)

That lapping is what they did in the Hepworth and Grandage factory - last operation before washing, packing and selling their rings.... They called it "barrelling": perhaps as the cylinders they made for the purpose were the "barrels", or because the rings had a microscopic "barrel" profile afterwards? I can't remember...
K


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## Steamchick (Sep 28, 2020)

Try toothpaste for the finest lapping compound you probably have ready access to. (It is used for polishing diamonds as well). Toothpaste also makes good tapping lubricant, especially for Aluminium.
Or "Brasso".... or T-cut car body-paint polish.
K


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## Steamchick (Sep 28, 2020)

There's nothing like a bit of hand-cranking for satisfaction. Having always been an Engineer - designing and preparing stuff for others to make - I seriously enjoy doing the calcs, then making the stuff myself that proves my calcs are good. So personally I avoid CAD, CNC, digital readouts, digital micrometers and verniers, etc. and much prefer the slide-rule, paper and pencil, drawing board, etc. and the micrometer with real marks, or vernier caliper with a vernier scale. AND a good file and hacksaw! I just love the tools and skills, both mental and physical. It is a hobby, not a business, isn't it? Something so we can play and make things as we did as kids?
But for the "technophobes" - enjoy the CAD and CNC digital world....
Just remember the artisan skills that have a natural beauty in "hand-made", rather than the modern "Machine made". Sometimes the imperfections give the object "personality", or "character"?
Enjoy life! - It's the only one we know we experience.
K


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## Gordon (Sep 28, 2020)

Ken Brunskill said:


> Thanks for that suggestion Pete, this is getting as interesting as the build itself  . I hope that others are enjoying these exchanges.


The discussion is indeed interesting but unfortunately much of the discussion is relevant to this engine but a lot of the suggestions apply to a standard two stroke or four stroke design and the Atkinson Differential is in a completely category. Talk of compression, vacuum and ring seating etc. are almost impossible to test with this design. After spending far too much time trying to get one of these to run it is obvious to me that the design in intriguing but is not really a practical design. A very minor change makes the difference between running and not running. I seriously doubt that the design could actually be used to power anything.


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## johwen (Sep 28, 2020)

Here's a tip i use with Piston Rings. I use the Trimble method, but what I do is half the width of the ring and place two rings in the groove with the gap set at 180 degrees apart a couple of strokes in the bore and they seal very well. Give it a try as if you follow the Trimble method they work and seal very well. Cheers.

John


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## Steamchick (Sep 30, 2020)

Has anyone plotted the "pressure graph" and tried to determine theoretical efficiency of this cycle? - From what you are saying, there is some intriguing geometry and motion, but the "engineering" of the gas cycle is in question?
Before I start from scratch - never having done this before on an infernal Otto or Carnot cycle.... - or steam for that matter - I am sure some of the Engineers out there have done so and some may have the software to make it easy?
For a High Voltage circuit breaker (back in the 1980s) I designed a new configuration of linkage to non-linearise the mechanical advantage (inverse of velocity ratio) to re-engineer the motor-to-contacts ratios so that the motor did about 3/4 of it's work while the contacts did 40% of their motion, then in the last 1/4 of the motor's stroke the contacts were decelerated to rest over the last 60% of their motion. I worked with a Doctor of Mathematics who evolved a computer programme so I could "tweak  - iteratively - the parameters between various chambers of the motor so achieve a 2-stage deceleration that enabled the circuit breaker to become an off-load interrupter, by increasing the number of cycles from 500 to 5000, before mechanical servicing was required. The computer programme was eventually turned "inside-out" so instead of my numerous iterations to optimise loads from the gas flow and pressures inside the motor, I input the required motion result and the programme did the iterations - working backwards - to a solution for the various orifi that gave the motor its required force variation through the stroke. - But I take no credit for the maths and computing! - I think this can now be done on a spreadsheet.... but Desktop computers were still at the Amstrad 64kB capacity.... or HP 500kB capacity... ! - An "Apple" was a piece of fruit... Some younger people cannot imagine how we put a dozen men on the moon 10 years before we had computers!
Is there someone out there who can do the Maths for this Atkinson differential engine? - I have no plans, but will "have a go" if no-one else is bothered, and wants to send me the plans?
It sounds like a problem yet to be solved? (Non-linear Geometry and varying volume gas chambers). I.E. following Ken's suggestion of 16th Feb? - (Maybe I have missed a pressure/volume analysis somewhere in the thread?)
Ken Br. - maybe you can send a geometric plan of the linkage with dimensions of arms and pivot locations, - a pdf will do - and I'll get on my drawing board. (No CAD here! - I was born when we used pencils and slide rules (Mechanical logarithm calculators). "Computers" were the girls NASA used to do the calculations and "Compute" the trajectory of rockets! - Strangely, I enjoy the mental challenge of using my brain to work things out....
Ken


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## Steamchick (Sep 30, 2020)

STUPID me... Some of it has been done  - Atkinson cycle - Wikipedia. Just a matter of using my computer as a reference book!


			https://upload.wikimedia.org/wikipedia/commons/c/cb/Atkinson_Opposed_Piston_Engine.gif
		

By MichaelFrey - Own work, CC BY-SA 3.0, File:Atkinson Opposed Piston Engine.gif - Wikimedia Commons
But it doesn't show valve timing?
Also:




 By Richard Rusnák (Rios) - Own work, Public Domain, File:T cycle AtkinsonMiller.png - Wikimedia Commons
The ideal Atkinson cycle consists of:


1–2 Isentropic, or reversible, adiabatic compression
2–3 Isochoric heating (Qp)
3–4 Isobaric heating (Qp')
4–5 Isentropic expansion
5–6 Isochoric cooling (Qo)
6–1 Isobaric cooling (Qo')


A few curious comments in WIKIPEDIA... suggest that the apparent efficiency increase of Atkinson cycles, have been achieved now due to modern design and manufacturing of "conventional" Carnot cycle engines... Is this an example of Darwin's laws of natural selection? - We make the cheapest things that sell best? - And scrap the rest?
I wonder if the limitations of this engine were simply the Capital cost? - or perhaps the huge energy required to accelerate and decelerate the large levers of the main linkage? - This all requires large bearings (for durability) and substantial beams for fatigue resistance. The substantial beams in themselves are major inertias driven by the pistons and crankshaft so the bearing losses will be larger than in a "simple" crank-to-con-rod-to piston configuration. The extra cost of these, plus the structure, possibly were impractical compared to the fuel savings, for a buyer's budget?
But all credit to Atkinson as the British Gas Engine company did make a lot of the Cycle and Utilite engines...
Reading Wiki, I wonder if much of the running problem enjoyed by Ken B is due to valve losses, rather than piston losses? - Something I have experienced on both model Steam engines and full sized motorcycle and car engines. Perhaps the piston seal can be proven as the culprit by a single wrap of PTFE tape around a piston ring (Top one?), then check for a significantly improved compression? That trick worked for me on a worn single acting oscillating steam engine. It confirmed the oscillating face-joint spring force was too low, then when I fixed that it proved the pistons were leaking too badly and needed new rings. But as a trick it only works for a few strokes.
K


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## dsage (Sep 30, 2020)

Steamchick:
All interesting Ponderings.
But were you researching the Atkinson "Cycle" engine or the one we are discussing here which is the Atkinson "DIFFERENTIAL" engine? Two very different beasts.
The differential engine we are talking about has two pistons in the same cylinder  which for the most part work against each other.
I built the Atkinson cycle engine and it works fine. Not exactly efficient IMHO but it at least runs.
As for some Engineer that has studied it. I would assume Atkinson did. Unless it has been a scam since the beginning. If it weren't for the fact that there are a couple I've seen running I wouldn't believe it could run based on the workings I've observed in the one I'm building. 
BTW the version Ken is building is a bit of a cheat from the original design. It has some extra valve gear that may make it better.


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## dsage (Sep 30, 2020)

Further to above the differential engine is also on Wikipedia. If you look at the link below and go partway down the you'll see an animation of the differential version. Kens has some extra valve gear. Fill your boots plotting the pressure graph  I'd be interested in you results.









						Atkinson cycle - Wikipedia
					






					en.wikipedia.org


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## Steamchick (Sep 30, 2020)

The Wiki article covered all 3 of Atkinson's patented engines.












See Wikipedia for credits.


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## dsage (Sep 30, 2020)

Cool. I didn't read past the animation mentioned above. Looks like in the third attempt he abandoned the wacky mechanisms in favor of what looks like a two stroke.
So if you have what you need to analyze the differential version I'd be interested to know if it is theoretically able to run. 
Practically it doesn't seem so.


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## Ken Brunskill (Sep 30, 2020)

Gordon said:


> The discussion is indeed interesting but unfortunately much of the discussion is relevant to this engine but a lot of the suggestions apply to a standard two stroke or four stroke design and the Atkinson Differential is in a completely category. Talk of compression, vacuum and ring seating etc. are almost impossible to test with this design. After spending far too much time trying to get one of these to run it is obvious to me that the design in intriguing but is not really a practical design. A very minor change makes the difference between running and not running. I seriously doubt that the design could actually be used to power anything.


Gordon,
True enough about this thread 'Another Atkinson Differential Build' being relevant to the Atkinson Differential, curious of why one would consider it "unfortunate", after all it is specifically about this design.

No offence intended, just a thought. For me, and I hope others, the post have provided some delightful exchanges, all friendly and very informative. 

I'd exchanged a few email's with dsage, and started this thread at his suggestion. Based on his contributions, I'd venture to say he is enjoying the exchanges as well.


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## Ken Brunskill (Sep 30, 2020)

Steamchick said:


> STUPID me... Some of it has been done  - Atkinson cycle - Wikipedia. Just a matter of using my computer as a reference book!
> 
> 
> https://upload.wikimedia.org/wikipedia/commons/c/cb/Atkinson_Opposed_Piston_Engine.gif
> ...


K, I will contact the originator of the plans I have for the 'Mini A' Atkinson Differential to obtain permission to share those specifications for this purpose, I respect his proprietary rights and would not want to offend him, his plans are well done and reasonably priced.


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## Gordon (Sep 30, 2020)

Ken Brunskill said:


> Gordon,
> True enough about this thread 'Another Atkinson Differential Build' being relevant to the Atkinson Differential, curious of why one would consider it "unfortunate", after all it is specifically about this design.
> 
> No offence intended, just a thought. For me, and I hope others, the post have provided some delightful exchanges, all friendly and very informative.
> ...


Yes. Unfortunate was not really the proper choice of words. My point was the some of the discussion was relevant to a standard engine design but not the differential design. Some of the points relevant to measuring compression, vacuum, stroke etc. on a standard engine are difficult or almost impossible to obtain in an engine where the intake stroke is just a fraction of an inch and the compression stroke is dependent on one piston moving faster than the other. Some of the suggestions in this and other discussions show that it was not obvious that this design is unique. 

I also got into an offline discussion in an earlier thread with Ray and we certainly did end up batting a lot of ideas around but never came to any firm conclusions.

There. I think I just dug a deeper hole for obscurification. Sorry if I offended anyone. That was certainly not my intention. You are certainly correct that many of these discussion can be very interesting and useful.


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## dsage (Sep 30, 2020)

Ken:
I enjoy the general discussion. It's all good. But sometimes I wonder if it's getting off topic so I try to be sure we are all talking about the same thing. I get confused.
I am waiting for what to try on my engine next. You are my guinea pig 
The pressure is on you Ken 
All in good fun.

In the end it is your thread so I should just step aside and let it take it's course as you see fit. 
Thanks all.


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## Steamchick (Oct 2, 2020)

Although I worked as an Engineer for 45 years, it wasn't studying combustion cycles. Does anyone on the thread understand the "Atkinson cycle" - as shown in the "Pressure/Stroke" diagram? As I do not have a drawing of valve gear - just Wiki sketches of crank to piston linkages - and I am learning from your best info in this thread. - Dsage: Yes, you are correct - the diagram shows the Atkinson Cycle, but as it shows an engine "cycle" it could be related to any configuration of engine that creates the particular "cycle". In Innocence, I read it that the "Atkinson differential engine" is one configuration (probably an early configuration?), followed by the "Atkinson Cycle engine", and latterly the "Atkinson Utilite engine"...? - All of which emulate the "Atkinson cycle" for combustion.
To be able to determine the thermodynamic cycle for an engine needs some knowledge of the valve and ignition timing, as well as the configuration of piston motion - versus shaft rotation, or other datum. As I wasn't planning to "buy the book", I wonder if any of you kind folk have that information in a simple diagram or table? - My interest is purely intellectual, as I am not planning to make a version of any of these engines. I only have experience of "mid-to-late 20th century conventional" engines, and their components, so am curious about some earlier designs.
Ta,
K


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## Tim Wescott (Oct 2, 2020)

No diagram, but I can verbally describe it:

The Atkinson cycle is designed around the notion that what makes an engine efficient is the expansion ratio, not the compression ratio per se.  As it was conceived at a time when compression ratios were, necessarily, low to avoid knocking, it solves the problem of low compression ratio & high expansion ratio by having a differential action -- the intake & compression strokes are short, followed by long combustion & exhaust strokes, then repeat.

It's basically the Otto cycle, but with different strokes (for different folks?).  

My thermodynamics isn't strong enough, but because the expansion stroke is larger than the intake stroke, it ought to be releasing exhaust that's cooler than could be achieved in a fixed-stroke Otto cycle engine.  I suppose that in theory, with a whole lot of expansion, the exhaust valve could open at zero pressure differential, or you could even have the thing pull a vacuum at the end of the expansion stroke -- presumably you could have a vacuum _and_ a cylinder filled with rarified air that's cooler than atmospheric pressure, although then you'd be losing efficiency to pumping losses, not gaining it.

I think, though, that the real reason for the Atkinson Differential Engine was to dodge Otto's patents.


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## Ken Brunskill (Oct 2, 2020)

dsage said:


> Ken:
> I enjoy the general discussion. It's all good. But sometimes I wonder if it's getting off topic so I try to be sure we are all talking about the same thing. I get confused.
> I am waiting for what to try on my engine next. You are my guinea pig
> The pressure is on you Ken
> ...


Ha Ha, Hopefully we can keep the subject related to the Atkinson Differential. 

Yet,  to that end I feel the discussion regarding 'RINGS' to be pertinent as the compression (or if you prefer 'expansion ratio'), may be much more critical on this specific design vs. that of even the single piston Atkinson Cycle engine.

Keep the pressure on, I need it!! All too often I get sidetracked.


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## Ken Brunskill (Oct 2, 2020)

Steamchick said:


> Although I worked as an Engineer for 45 years, it wasn't studying combustion cycles. Does anyone on the thread understand the "Atkinson cycle" - as shown in the "Pressure/Stroke" diagram? As I do not have a drawing of valve gear - just Wiki sketches of crank to piston linkages - and I am learning from your best info in this thread. - Dsage: Yes, you are correct - the diagram shows the Atkinson Cycle, but as it shows an engine "cycle" it could be related to any configuration of engine that creates the particular "cycle". In Innocence, I read it that the "Atkinson differential engine" is one configuration (probably an early configuration?), followed by the "Atkinson Cycle engine", and latterly the "Atkinson Utilite engine"...? - All of which emulate the "Atkinson cycle" for combustion.
> To be able to determine the thermodynamic cycle for an engine needs some knowledge of the valve and ignition timing, as well as the configuration of piston motion - versus shaft rotation, or other datum. As I wasn't planning to "buy the book", I wonder if any of you kind folk have that information in a simple diagram or table? - My interest is purely intellectual, as I am not planning to make a version of any of these engines. I only have experience of "mid-to-late 20th century conventional" engines, and their components, so am curious about some earlier designs.
> Ta,
> K


K,
Await word from the originator of the Mini A Atkinson Differential. I am confident he will respond in the affirmative. Everyone should note that, going forward, any information shared in this regard will apply to the Mini A specifically, conceptually it may or may not be applied to other designs of the Atkinson Differential concept.

However the best I can do at the moment is refer you to the video I posted on this thread (Refer to page 2, June 13) it is my amateurish narration of the operation, I think it covers the operation. Bear in mind that the major difference between this engine (Mini A) and the Gingery-Pendergast engine is the valve operation. The Mini A, deviates from the  original patent design in that it's designer D. Perreault, brilliantly designed a '_Piston Valve_' for the intake and exhaust eliminating the 'atmospheric valves' of the 'Gingery-Pendergast engines'. The timing of this valve is very sensitive to it's operation, I have completed my engine, and have yet to get a 'POP'.

Jquevedo & I are both building a Mini A, he has been far more diligent that I have and reports getting some 'POPS', so he is closer to success. Wish us luck!

Cheers,
Ken


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## Ken Brunskill (Oct 3, 2020)

Luckily I have convinced D Perreault (Originator of the Mini A differential design) to review this thread, he has agreed to share a schematic of the mechanics involved. With this our friend Steamchick might be able to generate a pressure diagram of the 'Mini A' design of the Atkinson Differential, this does not mean by any stretch that it will make it easier to get this engine to operate, as I found out today getting the valve timing is very sensitive.

I have created the schematic and passed it onto DP for review, hopefully together we will be able to share it soon.


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## Steamchick (Oct 4, 2020)

Thanks, I'll try my best, when the data is available. But maybe you simply have a assembly drawing of the major linkages with the relevant overall dimensions? And similar for the valves/timing?
Then I'll have a go at working it out (I use pencil and paper, with a smidgen of brain, not CAD).
K


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## Ken Brunskill (Oct 4, 2020)

Steamchick said:


> Thanks, I'll try my best, when the data is available. But maybe you simply have a assembly drawing of the major linkages with the relevant overall dimensions? And similar for the valves/timing?
> Then I'll have a go at working it out (I use pencil and paper, with a smidgen of brain, not CAD).
> K


I have communicated with the designer of this engine, unfortunately, we could not come up with a way to share the information with out divulging the crucial construction dimensions. I know this would have been interesting to some, I hope that everyone recognizes & respects the proprietary rights involved here. 

While these Atkinson Differential engines are  arguably the most interesting to watch run with all the motion, the plans for this engine are very reasonably priced and this is a fun build, one in which if done well, is worthy of a prominent place on your display shelf. I'll post a photo of mine when I have it mounted its base.


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## Steamchick (Oct 4, 2020)

I'm currently using a spreadsheet to develop calculations for the pressure of gas and air in a pipe burner, as the gas flows past the orifi of the burner tube.... "WHY?" - because I don't know how to do it but want to make a better model burner than all the "luck, chance, and trial and tribulation" offerings I have ever seen. It seems like a bit of Engineering that I should be able to do (in retirement, as there are no dead-lines, just "death" at some hopefully distant date). As I have never studied Bernoulli's equations I am getting a bit confusticated... so I need a simply geometric problem to distract me, and clear my brain. So the Atkinson volume/pressure diagram sounds simple - after struggling with Bernoulli!
Am I stupid?
Tell me to "stop" - please, someone?
Enjoy modelling!
Ken


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## Steamchick (Oct 4, 2020)

Hi Ken B and Gordon.
I have just watched Ken B's early video on how the engine works - much as I deduced from Wiki and a bit of scalp scratching, but Ken explains the valve action and timing - which I didn't know. That's really good. Now the video Gordon found has shown a working engine! - Great! - Thanks guys!
With some dimensions, I'll have a go at the pressure diagram. 
Cheers.
K


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## Steamchick (Oct 5, 2020)

Ken's Cad creation has all I need to approximate the pressure per rotation diagram.
Now I'll have a go. and let you know after a winter of hibernation! (Deep thought?).
K


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## Steamchick (Oct 5, 2020)

I'm currently using a spreadsheet to develop calculations for the pressure of gas and air in a pipe burner, as the gas flows past the orifi of the burner tube.... "WHY?" - because I don't know how to do it but want to make a better model burner than all the "luck, chance, and trial and tribulation" offerings I have ever seen. It seems like a bit of Engineering that I should be able to do (in retirement, as there are no dead-lines, just "death" at some hopefully distant date). As I have never studied Bernoulli's equations I am getting a bit confusticated... so I need a simply geometric problem to distract me, and clear my brain. So the Atkinson volume/pressure diagram sounds simple - after struggling with Bernoulli!
Am I stupid?
Tell me to "stop" - please, someone?
Enjoy modelling!
Ken


Ken Brunskill said:


> At the suggestion of Both Dave Sage & Dave Perreault I created a utube video: (My 1st - sorry for the amateurish narration)
> 
> Filename
> 4th Shot Atkinson operation.MOV



Ken, this video is very clear. Commentary excellent. Don't hide your light under a bushel...
I just wish I could do the CAD....
K


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## Steamchick (Oct 5, 2020)

Tim Wescott said:


> No diagram, but I can verbally describe it:
> 
> The Atkinson cycle is designed around the notion that what makes an engine efficient is the expansion ratio, not the compression ratio per se.  As it was conceived at a time when compression ratios were, necessarily, low to avoid knocking, it solves the problem of low compression ratio & high expansion ratio by having a differential action -- the intake & compression strokes are short, followed by long combustion & exhaust strokes, then repeat.
> 
> ...


Yes Tim, I think you are right - from what I have read - Atkinson did try and overcome the restrictions of the Otto patent by deriving a "more efficient cycle". Which I think it probably is.... but life isn't always like that and the "more power per bang" usually wins initially, before the accountants decide we need "maximum output per dollar of fuel cost"... Hence a hundred years or more before people (Toyota?) seriously looked at the efficiencies of Atkinson's cycle(s). - Excepting the British Gas Engine versions of course, using his later engine arrangements. 
Just an aside: I had a college mate who ended up working on using hydraulic actuated poppet valves on regular car engines... so the intake could be restricted when appropriate, and the exhaust timing radically altered between idle, low throttle and high throttle positions - all to improve the efficiency of the engine (Following the 1970's oil crisis!). - But hydraulic operation like that needed microprocessors/engine management computers of the type that were not invented until a decade or 2 later... Yet now we have the search for even higher efficiencies, even to having a steam generator in the exhaust - recovering heat energy - and powering an alternator by a reciprocating or turbine steam engine... (Just downstream of the catalyst there is a relatively high temperature gas stream suitable for a heat recovery boiler to generate adequate steam pressure, quantity and superheat).
K


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## Ken Brunskill (Oct 5, 2020)

Steamchick said:


> I'm currently using a spreadsheet to develop calculations for the pressure of gas and air in a pipe burner, as the gas flows past the orifi of the burner tube.... "WHY?" - because I don't know how to do it but want to make a better model burner than all the "luck, chance, and trial and tribulation" offerings I have ever seen. It seems like a bit of Engineering that I should be able to do (in retirement, as there are no dead-lines, just "death" at some hopefully distant date). As I have never studied Bernoulli's equations I am getting a bit confusticated... so I need a simply geometric problem to distract me, and clear my brain. So the Atkinson volume/pressure diagram sounds simple - after struggling with Bernoulli!
> Am I stupid?
> Tell me to "stop" - please, someone?
> Enjoy modelling!
> ...


Thank you for the compliment.
Ken B


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## Ken Brunskill (Oct 5, 2020)

Steamchick said:


> Ken's Cad creation has all I need to approximate the pressure per rotation diagram.
> Now I'll have a go. and let you know after a winter of hibernation! (Deep thought?).
> K


I suspect that the distance ratios, would provide reasonable results. Maybe drawing it up 10X to model it?
Keep up the good thoughts, since your efforts will specifically applicable to the Atkinson Differential, I feel that anything you come up with will be a contribution to the overall body of knowledge. 
For us handle crankers that have an engine 'almost operating', I hope it provides some insight, leading to helping ease the frustrations faced with getting one of these model engines to operate.
Ken B


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## Gordon (Oct 6, 2020)

Ken Brunskill said:


> I suspect that the distance ratios, would provide reasonable results. Maybe drawing it up 10X to model it?
> Keep up the good thoughts, since your efforts will specifically applicable to the Atkinson Differential, I feel that anything you come up with will be a contribution to the overall body of knowledge.
> For us handle crankers that have an engine 'almost operating', I hope it provides some insight, leading to helping ease the frustrations faced with getting one of these model engines to operate.
> Ken B


Actually I would like to see an analysis of the larger Gingery differential. The mini uses a mechanically operated valve which makes it a different operation. The Gingery more closely follows the original Atkinson design which has atmospheric valves. I have built the larger engine although I did not strictly follow the Gingery design and I have been able to get it to kind of sort of run for very limited cycles. There are a few videos showing the larger engine running but there are a lot more engines setting on the shelf because the builder could not get a consistent run. I think that the secret is in the motion created by the pivot arm lever ratio and the pivot point.

Actually the Perrault video is the only running mini engine I have seen. There may be others which I have not seen.

Note: I do not want to hijack this thread or turn it into another extended discussion on the Gingery/Atkinson original. There are other threads on that already.

Gordon


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## dsage (Oct 6, 2020)

Gordon et. al.
I posted this video on my thread of the Gingery engine. As Gordon says it is more like the original.
So SteamChick you can ponder this one as well. Not much difference really except for the lack of the sliding valve on Kens and it has check valves in the ports instead.
I also brought to attention that when the engine DOES NOT FIRE you can see that there will be a vacuum created in the cylinder when the right side piston moves back in what should be the power stroke. This vacuum creates a false intake vacuum and IMHO it floods the cylinder. Some of that flooding is evident in the fuel dripping out the exhaust port when the exhaust port is uncovered. I think this gets the whole mixture messed up on the next compression stroke. I believe Gordon has had similar results but apparently Gordons' engine runs to a certain extent. I can't get mine  to pop even once.
Just more facts to chew on.


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## Steamchick (Oct 8, 2020)

Hi all,
Before I start to study other variants, I need to commit some hours to the first one - Ken's CAD of a slide-valve arrangement.
My first idle musings on the chamber volumes and timing that I have measured from the video (Not precise, but adequate for now):
The intake is miniscule compared to the size of the engine. Really like trying to run 1/0th power for all the friction involved in the linkages - as well as pumping losses. But some people make flea-powered Stirling engines very successfully. There are 2 concerns with this "lack" of intake volume.
The power is proportional to the size of chemical (fuel and air) charge. As some will leak-away during the pumping action, there is less for "firing". Also less for "pre-heating" the charge to get it to firing conditions by the compression stroke. - This is also speed related and this is intended to be a slow engine. 
Charge suction and cut-off need very good sealing. I note the "valve" piston does this after the slide valve has closed, but I suspect the slide-valve may also have a leakage that contributes to the effectiveness of the engine, as if the exhaust side leaks it will suck-back some exhaust to corrupt the mixture instead of drawing-in fresh charge?
The ignition point is not well defined, but I assume at TDC of the power piston? with maybe a little advance? - Actually, I need to study the motion a bit more, as the full compression "TDC" of the combustion chamber may not be precisely at TDC of an individual piston. 
- Is there any way of producing a table from the CAD where the piston positions can be plotted per 3 degrees of crank rotation?
In another post I recall that you determined a 3 or 4 bar compression? As I cannot deduce the cylinder volume at MAX COMPRESSION and INTAKE VALVE CLOSURE I can only deduce there is considerable volume of piston machined-away for the valve porting? And FLAT topped pistons would instantly improve the compression rather than domed pistons.
Dsage: Just viewed your video, and maybe you can use the CAD to make a table of piston position ve. crank angle - I think 3 degree steps should be adequate - with crank-angles when the valves open and close? - Much better than my "quick and crude" extracts from measuring screen prints!
More musings later.
Now to the spreadsheet calcs... Catch you later!
K


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## Steamchick (Oct 8, 2020)

A first attempt... just a picture of my representation of Chamber Volume versus Pressure. 
The peak pressure is just after ignition.... I have assumed "No losses", but "guestimated" a chamber volume at max compression based on 4 bar attainable pressure, and to simplify things uses a 2cm diameter bore. The peak pressure after firing is just a number to make a picture.
2 things: As Atkinson intended, the Pressure-combustion cycle (Top loop) is very large compared to the intake cycle, (bottom loop). Thus the limited charge will do a lot of work efficiently in expanding to ~25% of it's original "fired" pressure before the exhaust is released. Of course, as Otto and Carnot both knew, the compression ratio is "almost everything" and modern petrol engines running at 10:1 compression ratio are twice as efficient as the numerical model I have used.
I haven't plotted curved lines - just for speed to get something of interest here.





Hope this is interesting to some?
More when I have done some tarting-up.
Ken


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## dsage (Oct 8, 2020)

If Ken desires, he should be able to give you your measurements at 3deg intervals. He has the cad drawings. It would be a lot of work rotating and measuring though.
He should at least give you the piston diameter and also the distance between the pistons at compression and at the point the intake valve closes so you know how much volume of intake is trapped in the cylinder. That will give you the compression ratio (more or less).
None of that is proprietary information.
Since you have chosen to analyze Kens engine I wont confuse the issue with the Gingery (my) numbers. The engines are pretty similar except for the slide valve.
I presume your conclusion will be that either engine is pretty sketchy in terms of it's ability to run. Because that's the result in practice.
Looks good so far.
Soldier on man


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## Gordon (Oct 8, 2020)

I pretty much came to the conclusion that the main problem was that due to the marginal operation the problem was that engine did not fire consistently in the final ignition position. This means that now the raw fuel is still in the chamber when it returns, without power, to the exhaust/intake position. At that point there is not enough pressure to completely exhaust the chamber and then it immediately adds more fuel to the already too rich mixture. After a couple of cycles you have raw fuel dripping out of the exhaust. If you are fortunate enough to fire the engine keeps running until it misses a couple of cycles. Unfortunately  due to the very marginal operation this happens on a regular basis. The engine is far too dependent on a perfect set of circumstance like correct carburetor setting, adequate compression, proper timing and apparently the correct phase of the moon and alignment of the planets.

Gordon


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## Steamchick (Oct 8, 2020)

Hi Guys!
I hope my musings - as attached - will give you something to ponder? (Hope you can open the file!).
I may easily be wrong with my observations and ideas, but it may give you some new insight to get your engines running?
I realise that changing valve timing and/or porting is no small task.... but it is just my humble idea.
I'm not offended it it is all trash.
Enjoy?
K


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## Ken Brunskill (Oct 9, 2020)

dsage said:


> Gordon et. al.
> I posted this video on my thread of the Gingery engine. As Gordon says it is more like the original.
> So SteamChick you can ponder this one as well. Not much difference really except for the lack of the sliding valve on Kens and it has check valves in the ports instead.
> I also brought to attention that when the engine DOES NOT FIRE you can see that there will be a vacuum created in the cylinder when the right side piston moves back in what should be the power stroke. This vacuum creates a false intake vacuum and IMHO it floods the cylinder. Some of that flooding is evident in the fuel dripping out the exhaust port when the exhaust port is uncovered. I think this gets the whole mixture messed up on the next compression stroke. I believe Gordon has had similar results but apparently Gordons' engine runs to a certain extent. I can't get mine  to pop even once.
> Just more facts to chew on.



Nicely done video Dave, very good explanation.
Cheers, Ken


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## Gordon (Oct 9, 2020)

I never got the engine to run for more than about two minutes. At this point it is on the shelf and I have "borrowed" some parts like carburetor and ignition module. The engine seems to run best if timing is ATDC. The carburetor adjustment is super sensitive. 1/64 turn on the needle makes the difference between running and not running.  As the engine heats up the carburetor has to be readjusted. I have tried several different throttle body sizes for the carburetor but nothing works well. As many of you know once you get most engines to run a minor adjustment in fuel mix or ignition timing makes the engine run better but does not necessarily make the engine not run. 

As I said. Phase of the moon and plane alignment.


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## peterl95124 (Oct 9, 2020)

observations regarding Dave's (dsage) recent video post

1) I'm assuming both intake and exhaust have at least one-way-valves if not cam operated valves,
 otherwise both intake and exhaust are open during the intake stroke

2) the ports on the cylinder look minuscule compared to for example a typical "model RC airplane engine" whose ports form a ring around the cylinder that is perhaps 50% open for an old engine and probably 75% open for a Schnuerle ported engine

so my scientific-wild-assed-guess is that these engines need massively widened cylinder cut outs for the ports, although I acknowledge that the wide ports on RC engines are for high RPM and power which isn't the goal with an Atkinson, but still I think the carburetor should be the smallest cross section to the flow and everything else should be much larger

also, since this is a low RPM and small displacement engine getting the carburetor to work properly is most likely problematic, switching to propane to eliminate carburetor "draw" problems has been done by many modelers and seems to work well.

just my 1.414-cents,
Peter


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## Ken Brunskill (Oct 9, 2020)

Steamchick said:


> A first attempt... just a picture of my representation of Chamber Volume versus Pressure.
> The peak pressure is just after ignition.... I have assumed "No losses", but "guestimated" a chamber volume at max compression based on 4 bar attainable pressure, and to simplify things uses a 2cm diameter bore. The peak pressure after firing is just a number to make a picture.
> 2 things: As Atkinson intended, the Pressure-combustion cycle (Top loop) is very large compared to the intake cycle, (bottom loop). Thus the limited charge will do a lot of work efficiently in expanding to ~25% of it's original "fired" pressure before the exhaust is released. Of course, as Otto and Carnot both knew, the compression ratio is "almost everything" and modern petrol engines running at 10:1 compression ratio are twice as efficient as the numerical model I have used.
> I haven't plotted curved lines - just for speed to get something of interest here.
> ...


Steamchick, et al;

Being that I am an novice at Solidworks, I need to get advice from their forum on how I can get the 3 deg. step increments you ask for. So silence from me on this topic for a bit, is expected. Then there is actually doing it , as I am still trying to get my engine to provide signs of life.

I think there are a few members of our club following this thread, hopefully it will spur some more interest and construction of a model of this engine, knowing machinists as I do, we are prone to think outside the box, which in this case may well bring some fresh ideas to light, ha, some might even work.

Ken B


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## Ken Brunskill (Oct 9, 2020)

Gordon said:


> I never got the engine to run for more than about two minutes. At this point it is on the shelf and I have "borrowed" some parts like carburetor and ignition module. The engine seems to run best if timing is ATDC. The carburetor adjustment is super sensitive. 1/64 turn on the needle makes the difference between running and not running.  As the engine heats up the carburetor has to be readjusted. I have tried several different throttle body sizes for the carburetor but nothing works well. As many of you know once you get most engines to run a minor adjustment in fuel mix or ignition timing makes the engine run better but does not necessarily make the engine not run.
> 
> As I said. Phase of the moon and plane alignment.


Gordon,
I know that you have a different variation (Gingery I think) from the Perreault design that jquevedo & I are building, but the 1/64 turn on the needle indicate to me that you have a different taper on your needle than I have, could you elaborate on that? On this aspect I doubt that model design makes much of a difference (piston diameter might be a factor so please. provide that as well.)

Ken B


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## Gordon (Oct 10, 2020)

My engine is roughly following a design by Brooks Pendergrast. Not an exact copy but I used most of his locations for the pivot points and length of lever ratio on the pivot arms. The piston is 1 1/8 dia. The needle on the carburetor is a #18 darner needle.

Attached is a layout of the action. That will probably just make everything more confusing.


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## Ken Brunskill (Oct 10, 2020)

peterl95124 said:


> observations regarding Dave's (dsage) recent video post
> 
> 1) I'm assuming both intake and exhaust have at least one-way-valves if not cam operated valves,
> otherwise both intake and exhaust are open during the intake stroke
> ...


To say, I am a step ahead on that would be an exaggeration, maybe 1 #9 foots worth, I am constructing fittings to try both propane and mapp gas.  This inspired by dsage's comment on having "fuel dripping out of the exhaust port" (last Tuesday). Hope to have that done by next weekend.


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## Ken Brunskill (Oct 10, 2020)

steamchick et al;

Met today with a mechanic friend we discussed the issues regarding the Atkinson Differential, he is going to allow me to use some of his sophisticated analysis tools in his shop, and intriguing tool is a 'Smoke Tester' where smoke gets blown into the Spark Plug hole. Will post pictures of that test, in theory this may be a simple enough of a device we 'handy men' can make a home made unit for ourselves.

Steamchick: I sent you an message separate from this thread, we need to work out the details of the data in the Excel spread sheet. I have learned what to do to get the model to stop at 3 deg. increments, & have started collecting the data, but don't want to go any further until we are in sync on the spreadsheet content.


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## jquevedo (Oct 10, 2020)

Steamchick said:


> Hi Guys!
> I hope my musings - as attached - will give you something to ponder? (Hope you can open the file!).
> I may easily be wrong with my observations and ideas, but it may give you some new insight to get your engines running?
> I realise that changing valve timing and/or porting is no small task.... but it is just my humble idea.
> ...


Ken:

Excellent study, diagrams and insight on what may be the key to get the engine to run..

I have put my best effort in cylinder construction and finish, the same goes for the rings, using the best rings produced from the batch for the the engine, after many hours of trying to get the engine to break in rings and cylinders and then reduce the drag from pistons and rings I have made some progress but remain having trouble getting the engine to run, some pops but not enough to make the engine run..

I share your thoughts regarding timing been one of the key issues, specially in low compression engines, when you have more compression, it usually hides some of the imperfections on timing and allows you to run an engine even when lean/slightly flooded.
In this case, the timing of the engine, should be as close to specifications as possible.

Will use the power piston as the one to determine TDC..

I have checked some of the basic specifications for Atkinson engines . This numbers are for not the atmospheric model but the model with mechanical valves, this engine with a sliding valve should belong to the same group.

Intake valve opening at 0 Deg Closing at 70 Deg, compression cycle 70 deg - 220 deg Spark at 140 Deg. Exhaust valve opening 220 - 335 Deg.
I will check the timing of the engine against the numbers you came with in your Diagram and see how they look..

I'm traveling so may take some time to get back to my shop but thanks so much for taking the time to create all these diagrams and calculations, I think we need to address this engine a bit more scientifically to see how can we improve the engine running..

Kind regards

Jaime


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## Steamchick (Oct 11, 2020)

Hi Ken,
I have sent an email this afternoon (Been away from the desk for a while). 
Thanks gents for the encouragement. - I hope with Ken's new data I can get a more accurate picture of what is happening. But I realise that sometimes it is labour intensive and time consuming getting a lot of data out of computers, for "numb-nuts" like me to play with, unless you are an IT geek.
Jaime, I think your engine may be a bit different from Ken's? - I also think you started the crank zero at 180 degrees from where Ken's video started. - But good stuff! - I'll see if I can make a picture using your data? 
Just give me a little time to get the grey stuff working (A lot of booze last night has left me "cloudy" today).
Thanks guys!
K


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## jquevedo (Oct 11, 2020)

K..

Building same engine Perrault mini Atkinson with slding valve, just realized I was taking the TDC from the wrong piston yesterday based on your input. Need to consider the pistons on the RIGHT ( pumping Piston ?) instead of power piston to set the events.

Ken:
Some of the blow by- dripping fuel in the power piston is due to the geometry of the engine and the fact that the intake port gets uncovered when the power piston travels all the way to the RIGHT right before the Spark happens, this exposes the port to the piston skirt right below the rings, so gas drips from the intake port, I have not found any vaccum leaks, but funny thing is why does the sliding valve has to open the intake again at this point, well to move upward to get in position when the exhaust port will have to open.
BTW this fuel drip tends to get better after the engine has started bedding rings in cylinder. Not sure why.

I think an easier to control valve mechanism would be to separate intake and exhaust valves.
I have been toying with some ideas, need to make some designs ad dimensions based on engine capacity and then figure out if this is practical.

Cheers.

Jaime


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## Steamchick (Oct 11, 2020)

Just going through some of the latest discussions....
There is a comment about port sizes, versus carb choke sizes. My understanding: (any engine tuners with more precise theory or experience please teach us all something better.) - The carb choke is typically 80% - ish of the intake tract before - AND AFTER - the the carb, in order to get the pressure drop in the carb by increasing the air velocity - and thus draw-in the fuel charge (being petrol, etc.). Unless the choke of the tract increases back to original size after the carb it won't work as well. However, to increase the VELOCITY of the charge and get it past the valve (in the case of poppet valve ICEs), it is normal practice for the intake tract to smoothly and uniformly reduce in cross-sectional area to that of the valve-port CSA. This encourages turbulent mixing of the charge in the cylinder, because there will be some residual exhaust gas, and from the carburettor there will be inconsistency of charge (air and fuel) mixing.
HOWEVER - the porting of "conventional" 2-strokes is designed for the intake tract to feed the crankcase first - where mixing is good - then transfer to the cylinder (which is near full volume, albeit with exhaust port open creating some vacuum from the pressure wave in the exhaust) in a very short time (compared to 4-stroke engines). Thus the transfer port area from crankcase to cylinder is not so representative of the Atkinson, that takes the intake through the carb, past the intake valve directly into an expanding small volume cylinder. 

So my "theoretical" intake for the Atkinson would be something like Intake area "A", through carb of choke 0.8 x A, into the intake tract CSA = A, followed by intake tract reduction to a CSA of "valve/port" OPEN CSA... which may be of a similar magnitude to the Carb. choke CSA of 80% intake tract.
Does this make sense with the various Designers' drawings you have? The other problem - comparing current conventional engines with the Atkinson differential - is that the volume between the cylinder (port), when the intake valve is open, to the carburettor "jet" position, should be a small fraction of the volume of the cylinder when the valve opens. As the cylinder volume at valve opening is so small, it means the carburettor will need to be very close to the valve, which in turn will need to be very close to the cylinder port. This makes matching the physical shape of the intake to the theoretical shape very difficult. - So I recommend you follow the designer's idea very closely - assuming he made good working designs.
Further, if you are trying to make "suitable" carbs without a design, then you need to copy something like a small carb for an engine of only (say) 3cc engine, even through a 3/4" bore engine like Ken's has a larger displacement (>5cc compression).

I haven't made any "Gas" carburettors, only "wet fuel". So I don't know if any of this is relevant to Propane or MAPP gas. But I can throw in a "2-pennorth" for gas ignition. Butane and Propane are small "stable" molecules that need a lot of spark energy - and correct mixture - to make them fire. "Petrol", Acetylene, and coal-gas ignite very easily, as Hydrogen is free or loosely bound to the fuel molecule, so much less spark energy will work with these. - I think MAPP gas is also a mixture that will ignite using a lower energy ignition? So my comment is to make sure the ignition gives a really good spark - at the pressure within the combustion chamber. If you can make a "clear" spark plug (I have one for 14mm thread from an old "Colour-tune" kit) then you can see what the spark is like when you spin the engine. There are 2 aspects to a good spark: The voltage - you need 4 times the volts at 4:1 compression than in air to break down the molecules and make a spark, or 10 times the volts at 10:1... And the current in the spark. - conventionally, we talk about a "fat" spark - lots of current = lots of ignition energy, or a "weak" spark, where the spark just looks "thin", like a fine hair of spark. Weak sparks don't ignite fuel. No sparks means you need more volts, or a smaller spark gap. I'm sure most know this, but there may be something here for the innocent?

I hope some of this makes sense?
K


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## Steamchick (Oct 11, 2020)

Jaime, I think that for the valve operation, if you make independent levers from independent crank-pins you can drive the valves independently. ( Effectively the same logic for "twin-camshaft" engines as opposed to "single camshaft" engines.). It's just a matter of how authentic you want to be, or how much complexity you like to make. I like to make steam engines with a single eccentric to run one way only, rather than a pair of eccentrics to allow a reversing gear to reverse the engines. But I like to make engines to power generators, which tend to run just one way. (Making lots of levers doesn't excite me so much).
Enjoy!
K


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## Ken Brunskill (Oct 12, 2020)

Gordon said:


> My engine is roughly following a design by Brooks Pendergrast. Not an exact copy but I used most of his locations for the pivot points and length of lever ratio on the pivot arms. The piston is 1 1/8 dia. The needle on the carburetor is a #18 darner needle.
> 
> Attached is a layout of the action. That will probably just make everything more confusing.


Gordon,

A couple of questions:
Observing your comment ". . . roughly following a design by Brooks Pendergrast. Not an exact copy . . . "
And your pistons being 1.125" Dia. - .1372" apart at ignition, presume that to be TDC (Closest point).
D. Perreault pistons are   .750 Dia. - .1077" apart at ignition, presume that to be TDC (Closest point).

The DP design is 66.75% smaller diameter vs. the your version of the BP design.
The TDC are 78.49% smaller for the DP design vs. your version of the BP design.

So, the question is:
How much of a difference does this make.
Are both too large a combustion area, or too small? 
From your experience of getting yours to run at all is a sign that that ratio is on the right path.

Maybe Steamchick's analysis will shed some light on this, lets hope so!


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## Steamchick (Oct 13, 2020)

Hope my light is a bright as you wish... but usually I am dimmer and duller than expectations!
Thanks for the confidence!
K


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## Gordon (Oct 13, 2020)

Ken Brunskill said:


> Gordon,
> 
> A couple of questions:
> Observing your comment ". . . roughly following a design by Brooks Pendergrast. Not an exact copy . . . "
> ...


I am not sure of anything in regard to making the engine run. The drawings/layouts which I attached were one of several I tried to determine what changing the pivot link (the link between the crank and the oscillating arm) would do to operation. I tried making the RH link shorter and the LH longer and vise versa. In some cases I actually made new links but nothing I did made any real appreciable difference. It has been at least a year since I have tried running the engine so I am a little older and a little fuzzy on the actual results once I made minor changes. The thing which seemed to make the biggest difference was making changes in the carburetor throat dia. I think that the carburetor changes mostly reflected the fact that fuel mix is critical and like I said in a previous post once you do not fire the mix keeps getting worse until it no longer will fire. With the low compression and the limited intake stroke everything becomes critical.

 I keep watching this thread in the hope that someone comes up with a magic bullet and determines something which makes this engine run. I am leaving for a few days so I am counting on the folks here to have an answer by the time I get back. 

Gordon


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## Steamchick (Oct 13, 2020)

Enjoy the break Gordon,
We are restricted to "local and essential travel only" - so no holiday breaks for us in the UK. So MAYBE we'll have an answer... but I doubt it very much. On paper one cannot absolutely decide things like ignition timing, carburation, etc. as those traditionally have always been fine-tuned on the test-bench/dynamometer. The study is called Engine Mapping, and takes in various loads, speeds, atmospheric pressures, fuel qualities, etc. - but the sum of knowledge here could do the same, if we had running engines, which we do not...
All I am striving to achieve with my study is a simple explanation of the combustion cycle of the engine, so the various modellers can appreciate better how the engine runs. (Or not). The usual attributes - like minimising friction and leaks, will of course always apply and are often critical in modelling. (The main reason I have some non-runners!). The subtleties of carburation, both for starting and running (seldom the same) are really a study of a "supposedly running" engine, with a lot of chance thrown-in.
An aside: I once spent 4 hours working on a friend's CZ motorcycle that he had acquired as a non-runner and had re-built the engine. Ignition timing and carburation were set "as the book", but the engine would not run despite all checks - including compression - seeming to be OK. We even pre-heated spark plugs, tried a few different grades of plug and changed the HT connections, - all showed good sparks but no ignition of the fuel. Finally we got it to start with a completely wrong spark plug set at a small gap, but it would not run for more than about a minute. He bought a new spark plug, and it started straight away, and ran for a couple of years before he sold it. It seems that it didn't like "Wrong grade" spark plugs as they had the wrong position of the spark gap in the cylinder, and the original spark plug - although it worked in my motorcycle (we even tried that!) that he bought new when he did the re-build would not work in his engine.... and we didn't know why.
So getting something like an Atkinson Differential to run is a REAL hard-task.
Actually, I suspect it will run with some compression, as long as the fuel air mixture is correct and ignition timing close to "right". But the fuel air mixture is probably the hardest to achieve...
An engine that pops or runs for more than a few sputters is very nearly there... so WELL DONE. so far...
K


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## Dave Perreault (Oct 17, 2020)

Hi, this is Dave Perreault..... Thank you for all the interesting conversation about my Mini A  Atkinson Differential engine.... I thought I would put a like to the engine running video.
Thanks Dave


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## Ken Brunskill (Oct 18, 2020)

Dave Perreault said:


> Hi, this is Dave Perreault..... Thank you for all the interesting conversation about my Mini A  Atkinson Differential engine.... I thought I would put a like to the engine running video.
> Thanks Dave



Dave P.,
Thanks for posting the video, shows that when everything is right, your design does produce a runner. I am finally at the stage, with all the ignition components in place, tomorrow I'll commence starting attempts, at getting mine to run. 

I have a spreadsheet where I have used Solidworks to take Piston-Piston & Pump Piston to Port measurments for every 3 Deg. of Flywheel rotation, unsure if every one here would be interested, will post if if there is enough interest. Alternatively, I'll post just the valve timing.


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## Ken Brunskill (Oct 18, 2020)

OK Folks, as mentioned earlier today, this is the valve event timing for Dave P.'s Mini A. Keep in mind these are nominal (perfect) dimensions and fabrication tolerances must be considered. Leaving this, strictly a start point.


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## Gordon (Oct 19, 2020)

Just to add another one of my wild theories which I came up with when I was working on the engine a year or so ago. Since ring sealing is dependent on gases getting behind the ring to force it against the cylinder wall the rings are not being forced against the cylinder wall when the LH piston is moving in the compression stroke. This theory is probably as valid as my theory about phase of the moon.

Gordon


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## Dave Perreault (Oct 19, 2020)

Hi guys.... This is a segment of an email conversation with Ken about getting the engine to run. Thought it might be of interest to someone.

From Dave Perreault

Getting the Mini A engine to run.

Fuel - In the plans I have provided some guidelines as to how to get the engine to run. You must provide oil in the fuel mixture as this engine does not have any other means of lubrication. The fuel mixture that I recommend is what I have found to be the best for this engine.

Electric motor assistance when first starting the engine.
- the Atkinson Differential engine is like no other engine I have built. It has so many variables to get it to run on its own that the use of an electric motor assistance on start-up is a big plus.
- mechanical timing
- valve timing 
- fuel mixing valve setting
- ignition timing
- ring seating
- etc.

Having the engine ready to run, ignition ready and lubricant fuel in the tank.
Turn the electric motor on and you can now concentrate on setting things while it is being rotated by the electric motor.
Keep adjusting things until you hear simple ignition of the engine. It will definitely be random but this is telling you that you are close. Make small adjustments to all the above settings to see if it starts to  get more regular.
At some point you will notice that it is firing at 90- 95% of the time. This is the point that you can now try to run the motor on its own.
If you can not get the engine to get to this point within a period of about 3 hours of adjustment than you must stop and evaluate everything to see if you have missed something.
YOU SHOULD SEE A STEADY POSITIVE PROGRESS IN GETTING THE ENGINE TO RUN DURING THIS TIME.... 

Note: No progress = something is not right. This engine will run if everything is right.

There is a reason why so many people can't get the Atkinson Differential engine to run.... It is not your typical internal combustion engine and it does require a different approach.

I have made several model 4 cycle gas engines.
I have designed, made and have 6 Atkinson engines that run well.

Atkinson engines are a special kind!

I hope this helps and if I can be of further assistance just let me know.

Regards
Thanks 
Dave


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## dsage (Oct 19, 2020)

(turning it with an electric motor) 

>>> "If you can not get the engine to get to this point within a period of* about 3 hours of adjustment *then you must stop and evaluate everything to see if you have missed something"

Well.
There you have it.


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## Dave Perreault (Oct 19, 2020)

dsage said:


> Steamchick:
> All interesting Ponderings.
> But were you researching the Atkinson "Cycle" engine or the one we are discussing here which is the Atkinson "DIFFERENTIAL" engine? Two very different beasts.
> The differential engine we are talking about has two pistons in the same cylinder  which for the most part work against each other.
> ...


 
Hi, the slide valve design on the Mini A is my approach to simplify the build as making an intake and exhaust valve for this scale would be very hard for the average home builders.
This is a half scale model of my 10" flywheel casting kit that I have available. The valves are .312 diameter so at half scale the valve diameter would be .156 diameter.
Hence the design of the slide valve on the Mini A. 
James Atkinson Differential engine.
Didn't use a spark plug used a hot wire.
Had a governor on it.
So yes the Mini A is different!
Cheating?


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## Ken Brunskill (Oct 19, 2020)

Gordon said:


> Just to add another one of my wild theories which I came up with when I was working on the engine a year or so ago. Since ring sealing is dependent on gases getting behind the ring to force it against the cylinder wall the rings are not being forced against the cylinder wall when the LH piston is moving in the compression stroke. This theory is probably as valid as my theory about phase of the moon.
> 
> Gordon


Good point!  Believe your analysis point's out and emphasizes the need for both the rings and pistons to have finely machined mating surfaces (fine a finish as possible), with dead square ring grooves with '0' ZERO radius at their bottom. Likely more critical in the Atkinson Differential than most engines. One of our (BAEM Club) very prolific builders has emphasized this very issue many times, I'll bet from experience!   This make me think that in addition, some experimentation with Ring pressure against the cylinder wall may prove useful.

Ken B


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## Dave Perreault (Oct 19, 2020)

Ken Brunskill said:


> Good point!  Believe your analysis point's out and emphasizes the need for both the rings and pistons to have finely machined mating surfaces (fine a finish as possible), with dead square ring grooves with '0' ZERO radius at their bottom. Likely more critical in the Atkinson Differential than most engines. One of our (BAEM Club) very prolific builders has emphasized this very issue many times, I'll bet from experience!   This make me think that in addition, some experimentation with Ring pressure against the cylinder wall may prove useful.
> 
> Ken B


 Hi Ken, ring pressure on cylinder wall is very critical.... It wants to be a free ring gap on the Mini A should be about .060 ( that is the gap when the ring is out in free air) 
And a ring gap of .001 when in the cylinder.
Too much ring pressure will increase the friction of the pistons traveling in the cylinder.


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## Steamchick (Oct 20, 2020)

Hi Gordon. From my experience of ring sealing - and maths - the radial force of ring on cylinder wall is not zero at zero pressure behind the ring, but is the natural radial force of the ring against the cylinder wall from the spring press re of the metal. Always assuming that the rings are made correctly so need some compression to be installed into the bore. 
However, you are perfectly correct in that there are moments when the ring is not held dynamically against either top or bottom surface of the ring groove, so there is a tiny leakage there. But as the pressure is quite low when that part of the cycle occurs, and it is for a relatively short time, the leakage is less significant. In production engines, ring thickness to ring groove width is a sliding fit I.E. microns of clearance, not thousandths of an inch. But I recognise that models (parts made on less precise machines without micron measurement!) may have a "thou or 2" of clearance. But I think leakage will be relatively small. (I haven't done calculations on this).
As there are videos of running engines, there are some OK conditions that work. But please strive to make the ring to groove clearance a minimum, within your capabilities.
I remember (40 or 50 years ago) cleaning pistons and rings (carefully) so the rings easily slid into the grooves all the way around, after I had cleaned off the hard carbon on the piston surface. The ring had to be a "neat" fit, just not tight enough to hold it in the groove when turned so gravity could make it fall out. E.g. When rings are on a piston, held with the axis horizontal, rotate the piston around its axis and the rings should naturally fall all the way 'in' to the upper part of the groove all the way around, without binding. But any more (excess) clearance should be avoided. Any tightness will cause the ring to "nip" when warming-up due to frictional heating of rings before the heat can flow into the piston, and the bore expand as it warms. This nip will cause wear, scuffing and possible early seizure. So rings must be free to move in the grooves. But as you indicate, any gap is leakage, however small.
Incidentally, as the gas in front of a ring has to turn 90 degrees 4 times to get to the inside and back out again, this also acts like a labyrinth seal, where there is a pressure drop of something like 20% at each 90 degree transition, acting as a resistance to the leakage gas.
Additionally, any oil on the bore that is swept-up by the ring also helps to block the leading edge (motion direction) of the ring. Some oil (a molecule thickness plus surface inclusions) stays on the bore and ring outer surface, and some is carried across the flat face to get behind the ring. Actually this also will reduce leakage at the lower pressures.
But a good theory! And I like your sketches. Keep up the good work - all ideas accepted.
K


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## Richard Hed (Oct 20, 2020)

Gordon said:


> Just to add another one of my wild theories which I came up with when I was working on the engine a year or so ago. Since ring sealing is dependent on gases getting behind the ring to force it against the cylinder wall the rings are not being forced against the cylinder wall when the LH piston is moving in the compression stroke. This theory is probably as valid as my theory about phase of the moon.
> 
> Gordon


Well what is your theory of the mooN?


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## Gordon (Oct 20, 2020)

When I was working on my engine, which was quite some time ago, I tried using O rings. As I remember I got the engine to fire pretty consistently while it was being turned by the electric motor but the O rings had too much friction to make the engine run on its own. The O rings did not last very long before they no longer worked. I now believe that was due to to the nipping of the ring as it passed the intake and exhaust holes in the cylinder. It is still my belief that adequate compression is the answer. 

With all of this conversation I am coming close to taking the engine back off the shelf and trying again. I keep hoping that someone comes up with some answers. Note: My engine is close to the original design and uses atmospheric valves instead of mechanically actuated valves. It is also larger with 1 1/8" bore as opposed to this one with 3/4" bore.

Gordon


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## Dave Perreault (Oct 20, 2020)

Hi guys, a few comments before someone quoted me as saying about getting the Mini A to run for the first time. "After turning it over with the electric motor for 3 hours if it doesn't run on it's own you need to stop and check everything as you missed something"
I want to make sure I get this across right.
By no means am I saying just to attach it to an electric motor and let it run by itself for 3 hours and expect the Mini A to run on its own. 
 This is what I expect the person who is trying to get the Mini A to run on its own to do during the 3 hour period.
Make sure the following has been set up as best as possible before attaching to the electric motor.
Mini A
- With the spark plug out the motor should rotate free. No additional friction.
- Slide valve adjustment made so it opens and closes the ports at proper timing
- Carb adjustment made to what you think is correct to start.
- Fuel mixture added to fuel tank
- Spark timing is set 
- A good working spark plug is installed

Once this is checked 
- Connect the engine by belt to the electric motor
- Start it up and it will most likely not be firing at all
- During the entire 3 hour period that I am suggesting to get the Mini A to run you are doing the following to get it to come alive.
- Adust fuel mix air/fuel
- Adjust spark timing
- Adjust slide valve timing
- Make sure the plug is not fouled ... As this can happen often when the engine does not have the right conditions.
- Stop every now and then and think!!!!

The electric motor assistance is not magic.... It is not going to make an out of tune motor run by no means. 
The use of the electric motor is one for purpose only.... To rotate the Mini A so you can THINK, ADJUST AND GET IT RUNNING.

My hat is off to anyone that can make an Atkinson Differential engine, fuel it up, give it a few good spins and it runs like a top!

I hope this clears up any confusion I may have caused on the use of the electric assist motor.

Regards Dave


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## Gordon (Oct 20, 2020)

Dave Perreault said:


> Hi guys, a few comments before someone quoted me as saying about getting the Mini A to run for the first time. "After turning it over with the electric motor for 3 hours if it doesn't run on it's own you need to stop and check everything as you missed something"
> I want to make sure I get this across right.
> By no means am I saying just to attach it to an electric motor and let it run by itself for 3 hours and expect the Mini A to run on its own.
> This is what I expect the person who is trying to get the Mini A to run on its own to do during the 3 hour period.
> ...


That is pretty close to what Gingery says in his book. He says between 30 and 40 hours run time with the electric motor before it will start and run on it's own. I suspect that most builders give up before they reach 30-40 hours of assisted run time.


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## Dave Perreault (Oct 20, 2020)

Gordon said:


> That is pretty close to what Gingery says in his book. He says between 30 and 40 hours run time with the electric motor before it will start and run on it's own. I suspect that most builders give up before they reach 30-40 hours of assisted run time.



Hi Gordon, in my experience 3 hours is a good amount of time and if you are not getting anywhere in the positive direction something is off and you need to scratch your head a little. IMHO


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## Dave Perreault (Oct 20, 2020)

I thought I would share this email that I sent to Ken. It is in reference to the Mini A and the piston locations at TDC and the distance between them.

Good morning Ken!

After thinking about this I believe this is the best way to give you this information. 

To start with.....
I want to make sure that everyone understands this.
- The Atkinson Differential engine has like 25 plus dimensions that make the mechanical part of this engine to work right! With that being said...... Every time a part is made and it is off just the smallest amount it effects the stroke of the engine. So these machining errors add and subtract to the total stroke.
Note: If any builder of this Mini A engine substituted bronze bushings for the bearings I specified that is a REAL PROBLEM. Here is why... If you rotate the engine you will notice that the right piston during the compression stroke is retreating to the right.... There are 6 bearing sets that that are in play during this right piston movement. With the ball bearings I have ZERO backlash. If you use bronze bushings Lord only know how much it would have and this backlash will subtract from the compression ratio in a bad way.

Ok, back to the piston to piston distance at top dead center.

On my running engine....
I took the plug out.. by the way make sure you are using a long reach plug.
- When the right piston is to far right the right piston top is aligned with the right side of the spark plug hole.
- When the left piston is to it's far right I have .055 on an inch between them.
See picture.

This is what I would suggest to do if you find that your Mini A piston to piston is different.

- I strongly suggest that once you put the pistons and rings in the engine and started to break them in that you DO NOT REMOVE THEM. I have found this to be a step backwards in ring seating.

- I would make new upper links and change the length of them accordingly to get the proper piston positions at TDC

You don't need to remove any other atms to do this with the exception of the slide valve linkage.




Side note:
A word about calculating displacement

Unlike our standard combustion engine displacement calculation on the Atkinson Differential engine has some added things to consider.
On the Mini A
- Chamfer on the piston
- Distance piston to piston TDC .055
- Spark plug hole 
- Inside the spark plug
- When are ALL ports sealed of by the rings...i.e. when does compression official start

Please feel free to share all this information with anyone you like. I don't care if you post it on the forum.


So Ken, I hope this helps!
And as always, feel free to ask more questions as needed.

Regards Dave


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## Ken Brunskill (Oct 20, 2020)

Wow folks, what a great conversation , this has been my 1st foray into the website world and I must say thanks to Dsage for urging me to begin this thread!
I have found it rewarding as well as informative. If you too are enjoying this thread - Thank Dsage.

Now for some technical information, Dave Perreault and I have been trading emails which caused me to figure out how to get the volume of the chamfered area of his POWER piston. Hope this helps anyone interested.


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## Ken Brunskill (Oct 20, 2020)

Dave Perreault said:


> I thought I would share this email that I sent to Ken. It is in reference to the Mini A and the piston locations at TDC and the distance between them.
> 
> Good morning Ken!
> 
> ...


Thanks for this post Dave!


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## Steamchick (Oct 20, 2020)

All good stuff. Just what I like about this thread - the people willing to share lots of good technical stuff.
Thankyou all!
K


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## Steamchick (Oct 20, 2020)

From my musings I think the engine could be improved by reducing the volume of the chamfers.... If these were simply 2 half-drilling in line with the port location - made by pre-drilling the piston before turning to size - then the gases could traverse the piston readily and the compressor would be higher. Would it help Dave P..?
 I'll do a sketch if interested?
K


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## Dave Perreault (Oct 20, 2020)

Steamchick said:


> From my musings I think the engine could be improved by reducing the volume of the chamfers.... If these were simply 2 half-drilling in line with the port location - made by pre-drilling the piston before turning to size - then the gases could traverse the piston readily and the compressor would be higher. Would it help Dave P..?
> I'll do a sketch if interested?
> K



While that will work ....
If you want more compression just move the the left piston further to the by .010

I would proceed with caution.... You may be giving yourself more work. My engine design does work with the chamfers as specified and the pistons at .055 apart from each other TDC.

If you have read my previous post....
You will notice that Colman Camp fuel is only like 50-55 octane and if the compression is too high you will get preignition! I usually try for 5:1 theoretical and end up with like 4:1 because of losses.

IMHO
Dave


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## Steamchick (Oct 20, 2020)

Thanks for that. I was looking at it from the perspective of higher efficiency (thermally) which should help it run for engines less perfect than yours. I have made a few flea-powered engines that I could not get to run, simply because my handiwork is not so perfect. And as an engineer I always want to improve things.... (most people translate "improve" to "interfere"!).
Thanks for your advice,
K


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## Gordon (Oct 21, 2020)

Did some drawing or diagram on this engine disappear on this discussion? I was sure that I remembered a drawing where it showed the pistons at TDC with .050 between them. I was a little bit confused, a common occurrence, and too busy right then to actually analyze it. Later I could not find it. Am I dreaming?

Gordon


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## Steamchick (Oct 22, 2020)

Just so anyone interested can see where I am at with my latest "picture" of the Atkinson's Differential chamber pressure versus volume.
This is a PROGRESS REPORT, not the final thing, so it will change as data is refined - and when I get to do a thorough check that all the correct factors of 10 have been applied in this peculiar Metric system that is reputed to be so easy... (Much easier to be out by tens of thousands than anything, as the numbers are either huge or incredibly tiny...).
I now have a numerical model, that I think gives a useful picture. Though the values shown are purely imaginary (from my head) as an illustration. - This avoids any complications of anyone using data and getting something drastically wrong.
Simply:

at the x-axis = 50, there is a vertical line representing ignition.
This expands (the pressure drop) to around x = 270-ish, when the exhaust valve opens and the gases exhaust, just before max volume.
The graph shows the bottom "loop" as the exhaust (to min volume) to intake phase (back to larger volume), followed by:
Compression to the ignition point (min volume).
The pressure is up and down the graph, whereas volume is smallest on the left and largest on the right. The area of the TOP loop expresses the power of the engine, and the area of the bottom loop is the power consumed by pumping gases in and out.... I think? - Any better explanation please?
I hope that makes sense?
The experts will appreciate the differences between this cycle and the Otto and Carnot cycles, so there may be some further "Thread" discussion of that - I hope? - as I want to learn a bit.
I'll be doing a lot of work to make a small presentation around this picture, so can accept useful suggestions if you wish to post anything.
Enjoy!
K


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## Tim Wescott (Oct 22, 2020)

I'm not enough of an s-spert to see a difference from the Otto cycle -- but thanks for doing the work!  Excel will allow you to label your axes, so that militant axis labeling zealots won't be poised to criticize you severely, and only stop at the last moment when they see that you described them in the text.


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## Steamchick (Oct 23, 2020)

Gordon said:


> When I was working on my engine, which was quite some time ago, I tried using O rings. As I remember I got the engine to fire pretty consistently while it was being turned by the electric motor but the O rings had too much friction to make the engine run on its own. The O rings did not last very long before they no longer worked. I now believe that was due to to the nipping of the ring as it passed the intake and exhaust holes in the cylinder. It is still my belief that adequate compression is the answer.
> 
> With all of this conversation I am coming close to taking the engine back off the shelf and trying again. I keep hoping that someone comes up with some answers. Note: My engine is close to the original design and uses atmospheric valves instead of mechanically actuated valves. It is also larger with 1 1/8" bore as opposed to this one with 3/4" bore.
> 
> Gordon


Hi Gordon,
As I am exploring the pressure cycle of the Atkinson Differential engine, I have been re-reading the thread, trying to extricate some extra glimmer of inspiration.... Your comment "the original design uses atmospheric valves instead of mechanically actuated valves" inspires a question or 2:
I imagine - as I have no drawings of engine - that the "chamfered" piston is actually performing the job of the valve timing by opening and closing ports to atmosphere - as appropriate to the pressure within the chamber? So I guess there is 

the exhaust port in the cylinder, which when exposed towards the end of the Power piston's stroke, but part-way down the stroke of the "valve" piston, permits the exhaust to vacate to atmosphere by the pressure differential between the cylinder and the atmosphere:
When the cylinder pressure has then dropped to atmospheric, the non-return "automatic" valve closes on the exhaust as the valve piston continues to travel and cause a negative (to atmospheric) pressure in the chamber:
Then when the valve piston traverses the intake port, the negative pressure causes the intake through the inlet "automatic" (non-return) valve.
As the pistons continue, the power piston creates more negative pressure to draw-in more air through the intake, until  the valve piston has traversed back up the bore to close the inlet valve.  
But as the pistons proceed, there is some small compression while the exhaust port is still exposed, thus allowing some mixture to vacate the cylinder via the exhaust auto-valve, before the valve piston closes the exhaust valve. - Could this be the cause of some "wet fuel" appearing in the exhaust?
Following closure of the exhaust valve by the transition of the valve piston, the ensuing compression can proceed to ignition firing expansion and the whole thing continues to cycle. 
Please correct any foibles or errors in my description? I hope to do a similar numerical model to develop the combustion pressure volume cycle of this design after I have a satisfactory version of the Perreault design of mini-A engine with slide valve.
If you are able to determine timings of all the events from your drawings/CAD of your engine, starting at "ignition" and at approx 3 degree intervals, then this will be a great help to me, but I realise there are hours of mindless work to do so, as the combustion chamber volume is a complex solution of off-set phased piston motions that are not necessarily sinusoidal, so if you are unable then don't loose sleep. I'll find another way.
Thanks,
K


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## Steamchick (Oct 23, 2020)

Tim Wescott said:


> I'm not enough of an s-spert to see a difference from the Otto cycle -- but thanks for doing the work!  Excel will allow you to label your axes, so that militant axis labeling zealots won't be poised to criticize you severely, and only stop at the last moment when they see that you described them in the text.


Thanks Tim,
I'm making a few power-point slides to explain it with annotation of the graph. First I need to double check the picture - and make it a continuous loop at ignition. (End pressure should equal start pressure for continuous running. - This is the first cycle, where it has effectively started at atmospheric pressure, not at the end of the cycle just before ignition. - I said it was a draft "work-in-progress". - more like a "half-gale" than "draught" really!).
K


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## Steamchick (Oct 23, 2020)

Just so "we" have a starting point, I found this explanation relating to the Otto cycle. I think I'll use this as a guide to preparing my explanation of the Atkinson differential engine. And yes Tim you are right in that there is little difference from the Otto cycle to my picture of the Atkinson differential engine. The differences are in the detail of the amount of expansion, valve timings and a few subtleties that I have yet to study in detail. ( - like the position of the "cross-over" point between the exhaust curve and compression curve - is it relevant?). 

FYI:
*Actual and Ideal Otto Cycle*

*Comparison of Actual and Ideal Otto Cycles*


In this section it is shown an *ideal Otto cycle* in which there are a lot of *assumptions* differs from *actual Otto cycle*. The main differences between the actual and ideal Otto engine appear in the figure. In reality, the ideal cycle does not occur and there are many losses associated with each process. For an actual cycle, the shape of the pV diagram is similar to the ideal, but the area (work) enclosed by the pV diagram is always less than the ideal value. The ideal Otto cycle is based on the following assumptions:

*Closed cycle.* The largest difference between the two diagrams is the simplification of the intake and exhaust strokes in the ideal cycle. In the exhaust stroke, heat Qout is ejected to the environment, in a real engine, the gas leaves the engine and is replaced by a new mixture of air and fuel.
*Instantaneous heat addition* (isochoric heat addition). In real engines the heat addition is not instantaneous, therefore the peak pressure is not at TDC, but just after TDC.
*No heat transfer (adiabatic)*
Compression – The gas (fuel-air mixture) is compressed adiabatically from state 1 to state 2. In real engines, there are always some inefficiencies that reduce the thermal efficiency.
Expansion. The gas (fuel-air mixture) expands adiabatically from state 3 to state 4.

*Complete combustion* of fuel-air mixture.
*No pumping work*. Pumping work is the difference between the work done during exhaust stroke and the work done during intake stroke. In real cycles, there is a pressure difference between exhaust and inlet pressures.
*No blowdown loss*. Blowdown loss is caused by the early opening of exhaust valves. This results in a loss of work output during expansion stroke.
*No blow-by loss*. The blow-by loss is caused by the leakage of compressed gases through piston 
rings and other crevices.
*No frictional losses*.
These simplifying assumptions and losses lead to the fact that the enclosed area (work) of the pV diagram for an actual engine is significantly smaller than the size of the area (work) enclosed by the pV diagram of the ideal cycle. In other words, the ideal engine cycle will overestimate the net work and, if the engines run at the same speed, greater power produced by the actual engine by around 20%.

I must credit the authors for their explanation: https://www.nuclear-power.net/nucle...ycle-otto-engine/actual-and-ideal-otto-cycle/

I hope this is of interest? (and relevant?).
K


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## Gordon (Oct 23, 2020)

Steamchick said:


> Hi Gordon,
> As I am exploring the pressure cycle of the Atkinson Differential engine, I have been re-reading the thread, trying to extricate some extra glimmer of inspiration.... Your comment "the original design uses atmospheric valves instead of mechanically actuated valves" inspires a question or 2:
> I imagine - as I have no drawings of engine - that the "chamfered" piston is actually performing the job of the valve timing by opening and closing ports to atmosphere - as appropriate to the pressure within the chamber? So I guess there is
> 
> ...


That is basically correct. There is no bevel on either piston. If you look at my drawing on post #205 the intake is through the hole (port) on the top and the exhaust is through the hole in the side which is further to the right. The intake valve is held in position with a weak spring which opens when there is negative pressure in the chamber and the exhaust port is covered by the RH piston. The exhaust is held in position with a stronger spring which is opened by positive pressure in the chamber. The intake valve is mounted with the flat face of the valve facing the chamber so that pressure in the RH chamber holds the valve closed and the exhaust valve is mounted with the tapered face of the valve facing the chamber so that pressure in the RH chamber forces it open. The problem is that if there is no ignition in the left chamber there is very little pressure in the right hand chamber and the exhaust valve does not have enough pressure to open.

Since I do not have 3D cad it is not really practical to try to move in 3° increments. In my 2D cad each 3° increment basically becomes a new drawing. It is possible but extremely difficult.

I hope that I did not confuse you even more.

Gordon


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## Dave Perreault (Oct 23, 2020)

Gordon said:


> That is basically correct. There is no bevel on either piston. If you look at my drawing on post #205 the intake is through the hole (port) on the top and the exhaust is through the hole in the side which is further to the right. The intake valve is held in position with a weak spring which opens when there is negative pressure in the chamber and the exhaust port is covered by the RH piston. The exhaust is held in position with a stronger spring which is opened by positive pressure in the chamber. The intake valve is mounted with the flat face of the valve facing the chamber so that pressure in the RH chamber holds the valve closed and the exhaust valve is mounted with the tapered face of the valve facing the chamber so that pressure in the RH chamber forces it open. The problem is that if there is no ignition in the left chamber there is very little pressure in the right hand chamber and the exhaust valve does not have enough pressure to open.
> 
> Since I do not have 3D cad it is not really practical to try to move in 3° increments. In my 2D cad each 3° increment basically becomes a new drawing. It is possible but extremely difficult.
> 
> ...


Hello, all...
I have designed and built the Atkinson Differential engine with valves on my 10" flywheel engine and it uses 2 atmospheric valves on it.... For intake and exhaust.
The Mini A a half scale version of the Atkinson Differential engine that I have designed and built it does not use atmospheric valves. I designed a single slide valve mechanism that opens and closes the ports for proper timing.
Starting from ignition the slide valve is not in play all. Once the expanding gasses have reach the full stroke the exhaust port on the slide valve is opened and stays open until the completion of the exhaust stroke. The exhaust port is then closed and the intake port on the slide valve is opened. The intake port on the slide remains open while the intake stroke is almost completely finished. 
Compression starts and the cycle repeats.
That is a very simple explanation of the slide valve timing... There is some advance and lag designed in the slide valve to assure proper timing.
The intake, exhaust and spark plug  port holes only provide access to the cylinder chamber if that make sense. They obviously need to be in the correct spots.
The chamfers on the piston provide a lthe head space for ignition as well as provide a smoother transfer of gasses.
One has to think of these chamfers as similar to the otto engine head space.
You also have to consider that the cylinder ports only start to seal when the rings go past them.

I hope this helps a little in understanding how my slide valve timing works on the Mini A engine.

I have put many hours in getting this design concept to work. It does work!

A side note:
The atmospheric valve engines have valve charter as they do not open and close like mechanically operated ones do.

Regards Dave


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## Steamchick (Oct 24, 2020)

Gordon said:


> That is basically correct. There is no bevel on either piston. If you look at my drawing on post #205 the intake is through the hole (port) on the top and the exhaust is through the hole in the side which is further to the right. The intake valve is held in position with a weak spring which opens when there is negative pressure in the chamber and the exhaust port is covered by the RH piston. The exhaust is held in position with a stronger spring which is opened by positive pressure in the chamber. The intake valve is mounted with the flat face of the valve facing the chamber so that pressure in the RH chamber holds the valve closed and the exhaust valve is mounted with the tapered face of the valve facing the chamber so that pressure in the RH chamber forces it open. The problem is that if there is no ignition in the left chamber there is very little pressure in the right hand chamber and the exhaust valve does not have enough pressure to open.
> 
> Since I do not have 3D cad it is not really practical to try to move in 3° increments. In my 2D cad each 3° increment basically becomes a new drawing. It is possible but extremely difficult.
> 
> ...


Thanks Gordon.
Don't bother to do incremental measurements. I'll figure it out from other data. Thanks for the clear explanation of the "atmospheric" valves.
I understand and can model that when I get the Mini A done.
I'll catchg up with you when I have some more.
K


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## Steamchick (Oct 24, 2020)

Dave Perreault said:


> Hello, all...
> I have designed and built the Atkinson Differential engine with valves on my 10" flywheel engine and it uses 2 atmospheric valves on it.... For intake and exhaust.
> The Mini A a half scale version of the Atkinson Differential engine that I have designed and built it does not use atmospheric valves. I designed a single slide valve mechanism that opens and closes the ports for proper timing.
> Starting from ignition the slide valve is not in play all. Once the expanding gasses have reach the full stroke the exhaust port on the slide valve is opened and stays open until the completion of the exhaust stroke. The exhaust port is then closed and the intake port on the slide valve is opened. The intake port on the slide remains open while the intake stroke is almost completely finished.
> ...


Thanks Dave, That's what I have had fun modelling! - I'm glad to know my understanding matches your explanation.
Incidentally. I think you have done an excellent job adding the slide valve to the Mini A. From looking at my (crude - and slightly erroneous data) on my numerical model I can see exactly why the valve is timed as it is.
I don't know how you determined the timing - but it looks very good to me. I'm just beginning to understand some of the subtleties of this engine, by seeing how the chamber pressure changes.
K


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## Ken Brunskill (Oct 27, 2020)

Time for confession, I had taken the engine apart to some extent, seemed minor at the time, then I lost this part the 'CAM ARM', yes really, it went into Mr. Murphys storage! My shop is relatively clean, and as can be seen this is not really a tiny part, regardless I'd erroneously made it original  out of aluminum, so now I have to wait for the bearings to arrive before I can reassemble and start attempting to get the little guy running. Now that a new piece is made, want to bet the original shows up? At any rate the bass is a much better looking part.


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## Dave Perreault (Oct 27, 2020)

Ken Brunskill said:


> Time for confession, I had taken the engine apart to some extent, seemed minor at the time, then I lost this part the 'CAM ARM', yes really, it went into Mr. Murphys storage! My shop is relatively clean, and as can be seen this is not really a tiny part, regardless I'd erroneously made it original  out of aluminum, so now I have to wait for the bearings to arrive before I can reassemble and start attempting to get the little guy running. Now that a new piece is made, want to bet the original shows up? At any rate the bass is a much better looking part.



That is a bummer Ken!
Hope you find it soon!


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## Ken Brunskill (Oct 28, 2020)

Dave Perreault said:


> That is a bummer Ken!
> Hope you find it soon!


As mentioned, a new better looking brass part is finished, just awaiting bearings.

Now working on a pressure vacuum setup, anyone have experience with 'Schrader Valves' as check valves? I am thinking that an engine such as the Atkinson Differential, which produced both pressure and vacuum in one revolution needs to have two check valves so as not to introduce pressure to the vacuum gage (Damage?), or vacuum to the pressure gage (Again, Damage?). If this line of thinking is correct, seems it ought to work on any engine, with the added benefit of being able to observe the holding capacity (time). Somebody must have been down this road before . . . . . comments?


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## Sprocket (Oct 28, 2020)

I'm glad to hear that Mr. Murphy is as active in other places as he is here.....
But you got the chance to make a better part, so maybe he did you a favor!
Doug


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## Steamchick (Oct 28, 2020)

Ken Brunskill said:


> As mentioned, a new better looking brass part is finished, just awaiting bearings.
> 
> Now working on a pressure vacuum setup, anyone have experience with 'Schrader Valves' as check valves? I am thinking that an engine such as the Atkinson Differential, which produced both pressure and vacuum in one revolution needs to have two check valves so as not to introduce pressure to the vacuum gage (Damage?), or vacuum to the pressure gage (Again, Damage?). If this line of thinking is correct, seems it ought to work on any engine, with the added benefit of being able to observe the holding capacity (time). Somebody must have been down this road before . . . . . comments?


Schadenfreude valves are fine. My bought compression tester uses one, and my home-made tester the same. Vacuum gauges are just back to front pressure gauges, so should be OK as well.


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## Steamchick (Oct 28, 2020)

B or Schadenfreude  read Schr-ader.. sme,ll checker got me again!


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## Ken Brunskill (Oct 31, 2020)

Yesterday I took my Mini-A to a mechanic friend's shop for a smoke test, (Not to see if it burns up when powered up  ), he has a unit that introduces smoke under 1/2 PSI, the unit will indicate any leak down of pressure. Fortunately my Power Piston, valving and everything else are tight, unfortunately my Pump Piston leaks so that need a make over.  Anyone ever make their own 'Smoke Tester'? The unit he has cost him about $1,500 several years ago, he informed me it makes the smoke from baby oil, and can detect pin hole leaks.


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## Steamchick (Oct 31, 2020)

I'd forgotten this trick until you mentioned it. When I was a young lad, the boss used his lungs and a cigarette... but the health risks probably prohibit publication of this as safe practice!  But it was amazing to see smoke emerge through a leaking valve on a cylinder head, when he blew in the port. He did get a dirty ombishure on his face! Alternatively, I was taught to fill intake or exhaust ports with paraffin or other spirit and check for dampness showing on the combustion chamber side of the valves. Spirit  Doesn't work on pistons n rings.
You can make one cheaply from a bicycle pump, couple of non-return valves, some plastic pipe and a small bunch of cheap jos-sticks from the local oriental supermarket. The bicycle pump sucks-in smoke, then blows it into the cylinder through the spark-plug hole (make a simple adapter to affix the hose).
Or maybe I mis-understand the need for $1500?
Chefs use smokers for introducing smoke to food... could one of those be adapted? Just a smoke chamber bellows and pipe?
K2


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## Steamchick (Oct 31, 2020)

Found one called Waazus  portable smoke maker. Light some sawdust place in intake and turn on smaller blower and it blows smoke out of the pipe - for food or other use.
K


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## propclock (Nov 1, 2020)

I made one once with a NiChrome wire heating element submerged in
oil, baby oil? I forget. The hard part was the electrical feedthrough,
I had a panel mount BNC teflon insulated feed-through. The thing was made from an old pint paint can.  Worked fine but the food smoker sounds
like a better idea.  Hi Ken


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## Ken Brunskill (Nov 1, 2020)

Steamchick said:


> Found one called Waazus  portable smoke maker. Light some sawdust place in intake and turn on smaller blower and it blows smoke out of the pipe - for food or other use.
> K


Ken C,
Now that created some thought! Being that the Air Intake is really small, and the Spark Plug hole is 1/4", some external source as well as portability for use on other engines point my old brain toward an aquarium pump hooked up to some device with a canister where a drop of oil can be heated to create the smoke. Interesting how one project leads to another, then to another and so on.


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## Steamchick (Nov 2, 2020)

Instead of heating a drop of oil, I would simply have a jos-stick in a tube - the air drawn-in past the burning jos-stick will keep it burning and create quite a lot of nice smelling smoke... - Or you could buy "smoke matches"- as used by gas engineers to check the draught into domestic flues at gas fire and boiler installations? - or the humble cigarette? - Or maybe they are too expensive now? Or a teaspoon of smouldering sawdust? - It shouldn't be too hard to make a simple "burner and intake for the air-pump" for the sawdust to sit in - ingited and then the air drawn into the pump... a bit of aluminium foils should be useful?
K2


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## propclock (Nov 2, 2020)

An aquarium air pump and one of those vaping devices comes to mind. 
The vaping device has a potent battery and a heating element. 
Don't know what they cost, perhaps they actually have a useful purpose. ?


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## Steamchick (Nov 2, 2020)

Good idea! - but may cost more than a cigarette or jos-stick? - Burning vegetable matter with aromatic oils produces smoke particles of a range of sizes... I guess that a "vape" machine produces atomised droplets of oil? - or is it aerosol sized stuff? - No idea if it can detect leak holes.... But it may smell nice?
A candle with big wick - or oil lamp with the wick turned-up can make smoke - carbon particles. Just hard to collect the smoke and blow it into an engine?
K2


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## Ken Brunskill (Nov 2, 2020)

Steamchick said:


> Instead of heating a drop of oil, I would simply have a jos-stick in a tube - the air drawn-in past the burning jos-stick will keep it burning and create quite a lot of nice smelling smoke... - Or you could buy "smoke matches"- as used by gas engineers to check the draught into domestic flues at gas fire and boiler installations? - or the humble cigarette? - Or maybe they are too expensive now? Or a teaspoon of smouldering sawdust? - It shouldn't be too hard to make a simple "burner and intake for the air-pump" for the sawdust to sit in - ingited and then the air drawn into the pump... a bit of aluminium foils should be useful?
> K2


Thanks Ken C,

Had never heard of smoke matches, will try to source them.

Ken B


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## Ken Brunskill (Nov 2, 2020)

propclock said:


> An aquarium air pump and one of those vaping devices comes to mind.
> The vaping device has a potent battery and a heating element.
> Don't know what they cost, perhaps they actually have a useful purpose. ?


I had the same thought, wonder if they need the humidity & temperature, as would be in a human?


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## Ken Brunskill (Dec 18, 2020)

Well I have gotten sidetracked by designing and building a device for testing tensile strength of fly fishing leader material, will get back to work on this next week.

In the meantime I wish all a very Merry Christmas and best wishes for a healthier 2021, 2020 has been a bummer.


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## jquevedo (Dec 18, 2020)

Let's blame the pandemic, I have been sidetracked by family matters taking care of elder mom and have not been able to get back home to tackle the To-Do list on my Mini Artkinson either.
I will most likely be able to return to it mid January and we hope to make the planned changes then.
Have a nice holiday season and think about those you love even if you can not be with them.


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## Tim Wescott (Dec 18, 2020)

Yup.  The best 2020 meme I've seen so far is the claim that "2020 hindsight" isn't actually folk wisdom, but a warning from the future that we were all just unable to interpret.


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## Steamchick (Dec 19, 2020)

Sorry Tim, that went over my head. Easier to understand the Atkinson cycle for my brain! (Call me stupid - most people do!).
Ken & all, Good chatting with you in 2020 - I've actually had a good year - I have missed a lot of things with the Pandemic, but just the selfish "Modern Human things".  No-one I know has died - though hospitalised - and (maybe the Seasonal feeling?) there is hope for 2021 being better!
Don't be glum - HAVE FUN! - However and whoever you can share it with. 
As a child of the 1950s in the UK I have seen worse than 2020... - the family poverty etc. - but we didn't know we were poor (by today's standards) so if we could be so happy then, there is NOTHING stopping us being happy now. I know (now) that we were underfed as children, because that's all we could afford. We had hand-me-down clothes, (that was real re-cycling!) walked - as there was no cash for buses - dug veg from the garden, etc. 
And there were talks of the A-Bomb, end-of-the world with the H-Bomb, Russians invading Czechoslovakia, Hungary, and shipping missiles to Cuba... Air-raid practices, bomb-sites from WW2 as a reminder of history, and the occasional car accident killed someone (so few cars!). A smallpox outbreak (1962 I think?) Polio scares, we had measles, mumps, chicken pox and all, Ice on windows in the morning and choked on the fumes from the paraffin heater - we couldn't afford coal - but an hour of paraffin warmed us before we went to bed. And we'd "never had it so good!".
So Covid pandemic is just another brief chapter of life. Write it in the History books and move on - to the next model!
HOPING YOU ALL STAY WELL AND HAVE A HAPPY CHRISTMAS, and may all your castings be free from blow-holes in 2021!
K2.


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## Dave Perreault (Dec 19, 2020)

I was getting worried that you folks had some health issues going on! So glad to hear everyone is doing well!
Have a great Christmas and New Year
Dave Perreault and family


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## Ken Brunskill (Jan 9, 2021)

Getting back to the shop today ,can't blame the hiatus on Covid, as a fly fisherman I got interested in doing some tests on knot strength, I spent my time on building a test fixture - there learning that 'O' Rings do not work smoothly when used as hydraulic seal in a HDPE cylinder. Could be that the HDPE cylinder bore did not have the finish that a metal material would have produced. 
Interesting to observe that even a totally different & non engine avocation, bring up common issues.

Best to all for a healthy 2021.
Ken B


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## Richard Hed (Jan 9, 2021)

Ken Brunskill said:


> Getting back to the shop today ,can't blame the hiatus on Covid, as a fly fisherman I got interested in doing some tests on knot strength, I spent my time on building a test fixture - there learning that 'O' Rings do not work smoothly when used as hydraulic seal in a HDPE cylinder. Could be that the HDPE cylinder bore did not have the finish that a metal material would have produced.
> Interesting to observe that even a totally different & non engine avocation, bring up common issues.
> 
> Best to all for a healthy 2021.
> Ken B


so much to do, so little time


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## Ken Brunskill (Jan 17, 2021)

Steamchick said:


> Good idea! - but may cost more than a cigarette or jos-stick? - Burning vegetable matter with aromatic oils produces smoke particles of a range of sizes... I guess that a "vape" machine produces atomised droplets of oil? - or is it aerosol sized stuff? - No idea if it can detect leak holes.... But it may smell nice?
> A candle with big wick - or oil lamp with the wick turned-up can make smoke - carbon particles. Just hard to collect the smoke and blow it into an engine?
> K2


Well the ole noodle kept mulling this over, when I finally realized (remembered) that I have several old CPAP machines that have a chamber that heats water to make a vapor. So after a trip to a local store the sells sundry items, I bought some incense sticks, presume they are called jos-stick's in the UK, anyway after a few hrs of machining and a trip to the hardware I had the necessary hardware to connect the CPAP machine to my 1/4-32 Spark Plug thread.  An initial trial indicates that this will produce sufficient smoke , there is a small needle valve so the unit can be adjusted to barley push the smoke or increase to push more air than the (4) incense sticks produce, of course one could add more incense sticks. Now to make new rings for the PUMP piston and give this smoke tester a real test. Being early evening here in Calif. it was too late for a photo will do if anyone is interested. Oh, by the way I'd bought the CPAP machine from a garage sale for $35, when on a fishing trip - long story .


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## Ken Brunskill (Jan 20, 2021)

Ken Brunskill said:


> Well the ole noodle kept mulling this over, when I finally realized (remembered) that I have several old CPAP machines that have a chamber that heats water to make a vapor. So after a trip to a local store the sells sundry items, I bought some incense sticks, presume they are called jos-stick's in the UK, anyway after a few hrs of machining and a trip to the hardware I had the necessary hardware to connect the CPAP machine to my 1/4-32 Spark Plug thread.  An initial trial indicates that this will produce sufficient smoke , there is a small needle valve so the unit can be adjusted to barley push the smoke or increase to push more air than the (4) incense sticks produce, of course one could add more incense sticks. Now to make new rings for the PUMP piston and give this smoke tester a real test. Being early evening here in Calif. it was too late for a photo will do if anyone is interested. Oh, by the way I'd bought the CPAP machine from a garage sale for $35, when on a fishing trip - long story .


Finally, I the weather was perfect to get a photo of the CPAP Conversion to a Smoke Tester:
Simply used some modeling clay and as shown (4) Pieces of Incense Sticks, size to fit in the liquid container of the CPAP unit.
Adapted the 'Mask' End to a small commercially available Needle Valve, some 3/16" tubing and a quick disconnect to the spark plug thread fitting.
Cheers,
Ken B


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