Atkinson frustrations

[Gordon]

Gordon,
I looked up the Acro lap on the KBC site. It states the lap will expand 15%. When they say a barrel lap is a 1 1/8, does that mean it expands from 1 1/8, or do they mean max expansion is 1 1/8? Not sure if I need a 1 1/16 or 1 1/8?

It is the nominal size so you need 1 1/8. One problem is that they have a minimum order.

I ordered cast iron on eBay to make a new cylinder and USPS just brought me an empty box with a hole in the side. I have some 2" square HRS so I will probably try to use that. I filed a claim but that is going to take a while.

 

[Ramoye]

Gordon,
I looked up the Acro lap on the KBC site. It states the lap will expand 15%. When they say a barrel lap is a 1 1/8, does that mean it expands from 1 1/8, or do they mean max expansion is 1 1/8? Not sure if I need a 1 1/16 or 1 1/8?

It is the nominal size so you need 1 1/8. One problem is that they have a minimum order.

I ordered cast iron on eBay to make a new cylinder and USPS just brought me an empty box with a hole in the side. I have some 2" square HRS so I will probably try to use that. I filed a claim but that is going to take a while.

Thanks Gordon.
Sorry about your cast iron order. Sounds like you have my luck.
Ray

 

[Chiptosser]

Guy's
A barrel lap will not expand at the end of the lap, it expands thru the center like a barrel shape.
Why not make your own laps to fit your bores?
Use brass, aluminum, copper or steel. Drill and tap for a tapered pipe plug, allen type works best.
Drill and tap deep enough to let it expand. Then cut, lengthwise an inch or more, you will have to experiment.
Now you have an adjustable lap that expands on the end. This is how injection mold laps work for ejector pins.
I have made many different sizes,over the years. You can start a little big and size it, to the grit of the lapping compound that you are using.
As different types of compounds act differently. Also, are you under cutting or recessing, at the end of the bore in a blind hole situation ?
You can resize these laps later for other projects.
Good Luck

 

[doc1955]

Guy's

Use brass, aluminum, copper or steel. Drill and tap for a tapered pipe plug, allen type works best.

I use wooden dowels or old broom handels turned to size then split end with band saw split into four sections then turn a wood screw into end to expand. When you make a lap you want to use a soft material you want the lapping compound to embed itself into the lap and not what you are lapping. I have used this method many times and works just fine.

 

[Chiptosser]

Yes, wood is good, hard maple, hickory something hard and straight grain. I like using phenolic material too, very durable.

 

[Gordon]

Still not having much luck with this thing. I made a new one piece cylinder from steel. Lapped it and made sure that the piston and rings were to correct size. Slightly better compression but when I turn it over with the electric motor it fires but will not run on it's own.

When it fires it fires with a loud explosion. I am thinking that I still am not getting a good fuel mix and the engine is flooding and the explosion is burning off the excess fuel. The needle valve is extremely fussy.
A very slight adjustment makes the difference between explosion and nothing. I tried making a new manifold to take a commercial aircraft carburetor but due to poor planning on my part the carburetor interferes with the exhaust valve. I am going to work on the carburetor and fuel mix. I may try propane even though I have not had any luck with propane in the past.

 

[Cogsy]

To test if it is fuel you could shut the fuel supply off, but make sure it can still get air, then tip a small amount of fuel into the spark plug hole, reinsert the plug and try and start it. It will definitely be flooded but as it clears the excess, if all else is correct, it will start up and run for a couple of seconds. I've seen motorcycle engines test run in this fashion without having a carb attached. I'm not sure how enough fuel is retained in the cylinder for long enough to keep the engine running so long but it does work. You want to make sure it can't get more fuel through the carb or it could stay in a flooded state and not fire at all, which won't help your diagnosis.
Remembering that old saying "90% of carburettor problems are electrical" it is a good way to rule out an electrical/timing problem.

 

[Gordon]

I am pretty sure that the ignition is OK. I started with an electronic ignition (S&S) and switched to my old faithful automotive known box of 6 volt battery, automotive coil and condenser and points. If I accidentally touch the plug it give me a good jolt and it has a good spark both with the plug removed and ignition wire to ground. I still think that the problem is compression but I will try your suggestion of fuel in the spark plug hole again.

 

[doc1955]

To me it sounds like your timing is either way to early or to late. Usually ends up with an extra loud report. I would guess to early. Have you changed the timing around a little and see. I haven't built this engine but I would guess you want it to fire a few degrees before top dead center.

 

[Gordon]

I have tried playing around with the timing. One big problem is that there is a very short time when the combustion chamber is actually open to ignition. The left hand piston goes over to the left and uncovers the 3/16 dia hole between the spark plug and the combustion chamber and just a few degrees of rotation later the right hand piston completes it cycle and both pistons begin the return exhaust stroke to the right. There is only about 15 to 20 degrees of rotation where the combustion chamber is actually open to the spark plug. Too advanced and the left hand piston is still blocking the chamber and too late and the left hand piston is on the exhaust stroke and again covering the 3/16 dia hole.

 

[Ramoye]

I have tried playing around with the timing. One big problem is that there is a very short time when the combustion chamber is actually open to ignition. The left hand piston goes over to the left and uncovers the 3/16 dia hole between the spark plug and the combustion chamber and just a few degrees of rotation later the right hand piston completes it cycle and both pistons begin the return exhaust stroke to the right. There is only about 15 to 20 degrees of rotation where the combustion chamber is actually open to the spark plug. Too advanced and the left hand piston is still blocking the chamber and too late and the left hand piston is on the exhaust stroke and again covering the 3/16 dia hole.

Gordon,
Any luck with your engine? I am almost finished with my new cylinder, just need to machine some cooling fins. The ARCO lap tool worked great. Measuring 1.125/1.124 at every point I checked. Still have not drilled the 3/16 holes into the bore yet. I do not trust the hole location as stated in the book.

Was looking at my old cylinder this morning. When turning counterclockwise, seems like everything is good (alignment wise). Got good compression at the spark plug. Ran it some backwards and got faint firing. This engine is a puzzle!

Sorry to hear your new cylinder did not help much, I may have the same experience when I try my new cylinder. I will need to make new pistons and get new rings (I can buy 1.125 instead of having to make them like I did before). Ray

 

[Gordon]

Ray:Not much more progress. I have been kind of sidetracked with a funeral and some fall yard maintenance etc. For some reason the engine only seems to fire when it is flooded. I think that it is only firing maybe every other cycle and when it fires it does so quite violently. It drains the gas tank (1 1/2" dia x 3" long) in 15 to 20 minutes so it is going through a lot of fuel. When it fires it is actually spraying a gasoline mist back through the carburetor throat. I will have to do some more playing around with stronger and weaker springs and also relap the valve seat. If I close off the needle valve so I get less fuel it does not fire at all. It seems to come closer to running with the timing set after TDC. Before TDC does not seem to work as well. I am quite sure that the problem is in carburation. It is not vaporizing properly.In have been using my proven automotive type ignition with 6 volt battery, auto coil, auto condenser and auto points which I have used successfully on other engines.

Hopefully I can do some more playing around with it tomorrow.

Gordon

 

[Ramoye]

Ray:Not much more progress. I have been kind of sidetracked with a funeral and some fall yard maintenance etc. For some reason the engine only seems to fire when it is flooded. I think that it is only firing maybe every other cycle and when it fires it does so quite violently. It drains the gas tank (1 1/2" dia x 3" long) in 15 to 20 minutes so it is going through a lot of fuel. When it fires it is actually spraying a gasoline mist back through the carburetor throat. I will have to do some more playing around with stronger and weaker springs and also relap the valve seat. If I close off the needle valve so I get less fuel it does not fire at all. It seems to come closer to running with the timing set after TDC. Before TDC does not seem to work as well. I am quite sure that the problem is in carburation. It is not vaporizing properly.In have been using my proven automotive type ignition with 6 volt battery, auto coil, auto condenser and auto points which I have used successfully on other engines.

Hopefully I can do some more playing around with it tomorrow.

Gordon

Could be carb problems. Always bothered me that the carb spits gas (weak spring force on the valve seemed to make it spit vs. a stronger spring, but too strong a spring could impact fuel getting in the cylinder). Makes me wonder if it is not getting enough gas until it cycles several revolutions? Seems spring tension is super sensitive (might make an adjustable spring by using thin washers under the spring).

I had to take a few days off to rebuild part of my deck, and yard work. Hope to get some more time to work on the engine. About ready to order rings and make new pistons. Ray

 

[bluejets]

This is the engine with opposing pistons in one cylinder. It has been a challenge to get it to run! I have tried everything I can think of. Decided to make a new cylinder from stock 1.125 inch I.D. No boring and brazing, which I hope will make a better cylinder. Will need to make new pistons, piston rods, and rings.

Machinist friend of mine, George Punter, took a look at this particular engine here a couple of years back.
Someone here had the same problems as you are having.
He suspected a design flaw and what he did was redraw the plans into (at the time) Pro Desktop where one can interlock parts and "see" a skeleton view of everything working, revolving etc. etc.
His final conclusion was, as drawn, the engine could never work as the location of the spark plug was completely wrong for correct operation.
He was starting to redesign but other more important stuff cropped up.

I don't think he went any further after that but I will ask him and post back his exact results or if he intends to finish the remake.
We have both built the other type Atkinson engine with good results.

cheers Jorgo

 

[Gordon]

Jorgo
I would certainly be interested in your friends take on the design. I am also convinced that the actual firing area is just too limited. I have built over twenty engines and I have never had as much problem as I am having with this engine. I have not really figured out why this engine will not at least run even intermittently. I have remade the cylinder three times. I have made three sets of pistons and at least five sets of rings. The last set of parts was made with careful attention to correct tolerances. The cylinder was carefully lapped. The pistons were made to closely fit in the cylinder. The rings were made for a close fit. I have tried to find any leakage points. I have tried at least four different carburetors.

I am almost to the point of just setting the engine on the shelf and working on something else at least for a while but I hate to just give up. Also there are more of these engines made by others which seem to work.

Gordon

 

[WOB]

I suspect your rings as well. The variable sealing you describe is not right.

.002" is really too much side clearance for the rings. You should be shooting for .0005 to .001" max. The upper and lower outside corners of the rings have to be burr free and preferably have a tiny 45 deg. bevel maybe .001"-.002" wide. Looking at them under 10X magnification will surprise you. The ring surface against the cylinder wall should be finished very smoothly. I finish up with 600 grit SC paper before slicing them off the parent tube and end up with a near mirror finish. The top and bottom surfaces that face the ring groove walls should likewise be very smooth. I cut mine off about .002" wider than the ring groove and finish them to size by hand on a 600 grit diamond bench stone after heat treating. Then I bevel the outside corners as described above. This method give precise control of ring thickness and gives very smooth surfaces to support the oil seal between groove and ring. Your existing groove depth is not a problem IMHO. A good way to judge ring fit is to put a finished ring into a clean cylinder ( no piston) squarely and hold the cylinder up to a bright light. The ring circumference should be light tight. If light shows anywhere over the length of the piston stroke, the bore is not uniform and you need to make a new cylinder.

WOB

 

[Ramoye]

Machinist friend of mine, George Punter, took a look at this particular engine here a couple of years back.
Someone here had the same problems as you are having.
He suspected a design flaw and what he did was redraw the plans into (at the time) Pro Desktop where one can interlock parts and "see" a skeleton view of everything working, revolving etc. etc.
His final conclusion was, as drawn, the engine could never work as the location of the spark plug was completely wrong for correct operation.
He was starting to redesign but other more important stuff cropped up.

I don't think he went any further after that but I will ask him and post back his exact results or if he intends to finish the remake.
We have both built the other type Atkinson engine with good results.

cheers Jorgo

I have suspected the hole location for the bore penetrations are off. On the last cylinder, I had to slot the exhaust hole because the pistons did not align with the hole. I also slotted the intake hole because I read that another builder had to do that to get it to run (he stated that the intake hole needs to be open 90 degrees of rotation). By slotting my intake hole, it did improve things, but not enough for the engine to run on its on power more than kicking over a few times (had no more room to slot before infringing on the intake valve body mount hole, but thought about opening up the hole larger than the 3/16). I am making a new one piece cylinder (no brazing or boring required). This is an intriguing engine, but a real mystery to me.

I am thinking of building a model on a flat board to better understand what is going on.

Gordon, I think I figured out why the compression is higher on the spark plug side when turning the engine backwards. The right piston is stationary while the left piston starts moving to the right, thus compressing the gas. Ray

 

[Gordon]

I have suspected the hole location for the bore penetrations are off. On the last cylinder, I had to slot the exhaust hole because the pistons did not align with the hole. I also slotted the intake hole because I read that another builder had to do that to get it to run (he stated that the intake hole needs to be open 90 degrees of rotation). By slotting my intake hole, it did improve things, but not enough for the engine to run on its on power more than kicking over a few times (had no more room to slot before infringing on the intake valve body mount hole, but thought about opening up the hole larger than the 3/16). I am making a new one piece cylinder (no brazing or boring required). This is an intriguing engine, but a real mystery to me.

I am thinking of building a model on a flat board to better understand what is going on.

Gordon, I think I figured out why the compression is higher on the spark plug side when turning the engine backwards. The right piston is stationary while the left piston starts moving to the right, thus compressing the gas. Ray

On the original patent drawings the upper links were adjustable and I have seen other models built with the adjustable links. I may give that a try. At this point I think that the rings are sealing quite well but the compression stroke is short and actually begins while the left piston is still retracting so it is not compressing the chamber at the beginning of the stroke.

I have thought about lengthening the holes into the bore but have been hesitant to do so since once it is done there is no going back. Without knowing what is causing the non running condition it is hard to make adjustments.

I find it strange the there are so few build logs on the various forums. There are several where a build was started but when it gets near the end the entries stop. I suspect that they are having the same problem we are having. There are several youtube videos where others have an engine running. On one video the poster said that he had 500 hours building and 500 hours getting it to run. Another said that it only would start after it was hot. I don't know how you get it hot without running it. Quite a few others have attempted this engine and some apparently have succeeded but I am reasonably sure that the ones who were successful have made some modifications. I wish we could find others who have completed it and find out what if anything they did to make it run. Running in with an electric motor may be part of the answer but I do not think that is the entire answer.

 

[dsage]

I started reading this thread today. I hope you guys figure it out. As with all my engine plans I redraw them in Alibre design before making chips. It helps me find errors and doing the drawings helps me understand the operation. I also get to animate it to be sure it "works" and makes sense.
I redrew these plans a couple of years ago and the animation showed some issues with piston timing. I ran into all the issues you have mentioned including the dimension that were either missing or did not jive with how it is supposed to go together. In CAD I also tried a lot of the changes you have mentioned and I couldn't get it to make any sense. So I put the plans aside. Having said that I have seen a few of the engines running at NAMES and Cabin Fever. I asked one gentleman if he had any issues. He said there were problems but he didn't recall what they were. Apparently he got it working.
EDIT:
I had a quick look at my book and I made a note on page 36 where it shows the layout of the left oscillating arm. I noted that the location of the hole at the tip if the arm (where it connects to the piston rod) is wrong based on the final machining on page 81. I'm not sure exactly what I meant by that. Perhaps there are incorrect dimensions called out or my the CAD model showed it did not go together properly as it was specified. That's the only notes I made but I seem to remember something else. Perhaps with the hole layout on the main plate??
Does this ring any bells??

Good luck.

 

[dsage]

BTW. I did a theoretical compression calculation from the operating volumes in my CAD drawing and I figure the compression of the engine is only 3.2:1
I might be wrong on that. But if I'm right it's going to be pretty iffy for the engine to run. Also it doesn't leave any room for leaks anywhere.
Let me know if I made a mistake.
You should be able to measure that with a pressure gauge in the spark plug hole while cranking it. Theoretically it should measure about 45lbs. Too low to be reliable IMHO.