Atkinson frustrations

[Gordon]

Another thought on the propane. If you find it works and your happy with it you will need to build a "demand" regulator because, as I think more about it, propane will free flow out of your carb air intake when the engine is not running. A demand regulator will supply propane only when the engine "sucks" air in (like it does for gasoline from a tank below the carb).
So to test the engine on propane initially you should probably turn the engine over and then slowly supply the propane with the needle until it runs and shut the propane off at the tank to stop the engine.

I have tried propane in the past but never got good results. I even built a demand regulator but still could not get it to work. It may be time to give it another try. Nothing else seems to work.

 

[Gordon]

Ray
You may have something. I have not really tried pressure after moving back to the right but it seems like that may be true. It would also explain why I am only able to get it to fire with the timing retarded so that it fires after the piston is beyond TDC. I will have to play around with that.
Gordon

 

[Ramoye]

Another thought on the propane. If you find it works and your happy with it you will need to build a "demand" regulator because, as I think more about it, propane will free flow out of your carb air intake when the engine is not running. A demand regulator will supply propane only when the engine "sucks" air in (like it does for gasoline from a tank below the carb).
So to test the engine on propane initially you should probably turn the engine over and then slowly supply the propane with the needle until it runs and shut the propane off at the tank to stop the engine.

Hi Dave,

I have thought some about using propane, but not quite ready to give up on using gasoline.

Wow Dave, that Parcell and Weed engine you built is beautiful! Great job on it! My engine is starting to look like it has been through WW2.

Thanks for the ideas.

Ray

 

[Ramoye]

Ray
You may have something. I have not really tried pressure after moving back to the right but it seems like that may be true. It would also explain why I am only able to get it to fire with the timing retarded so that it fires after the piston is beyond TDC. I will have to play around with that.
Gordon

Hi Gordon,

Another thing that might cause some leakage on the far left, is when it was lapped the edges got a little more material taken off, but I do not recall measurements being that different, plus, it seems the rings are springy enough to compensate for it. I still suspect a side load on the piston at that far left location. I may make another eccentric shaft for the left oscillating arm to move the pivot point down some to test my theory. My engine is really starting to have a lot of adjustments.

Let me know what you find?

Thanks Gordon.

Ray

 

[Ramoye]

Ray
You may have something. I have not really tried pressure after moving back to the right but it seems like that may be true. It would also explain why I am only able to get it to fire with the timing retarded so that it fires after the piston is beyond TDC. I will have to play around with that.
Gordon

Hi Gordon,

How are things progressing?

I changed things up some on my end. I went with a 1 1/2 link arm on the left, and a 1 7/16 link arm on the right. I am still using the eccentric crank pin to adjust the right piston location relative to the left piston (have a gap of around 1/16 inch when the pistons come together).

I took some time to build a stand for the motor. I also changed to a 12V ignition system, as well as adding a 4 1/2 fan and duct to cool the cylinder. I got two great runs today of 9 minutes each. Not sure why it quit, but it could be due to thermal issues and/or carb. I have no throttle, so the engine was running really hard and fast uncontrolled (increasing the heat output). I am still waiting to receive the new chainsaw carb. The chainsaw carb. has an idle and fast needle for adjustment, as well as a butterfly valve for throttle control. I hope the new carb. will give me better fuel management.

Ray

 

[Gordon]

I have not made much progress. I have been doing some other things, mostly to get a break from this source of frustration. I have made a new intake manifold which provides more support for the valve. I think that the intake valve is hanging up and not closing properly. I have only had a few very short runs where the engine ran on its own. Not sure if a stronger spring would make a difference. I will be getting back to the engine again in a couple of days. I have been working on VFD drives on my lathe, mill and drill press. Another set of frustrations but at least different.

 

[Ramoye]

I have not made much progress. I have been doing some other things, mostly to get a break from this source of frustration. I have made a new intake manifold which provides more support for the valve. I think that the intake valve is hanging up and not closing properly. I have only had a few very short runs where the engine ran on its own. Not sure if a stronger spring would make a difference. I will be getting back to the engine again in a couple of days. I have been working on VFD drives on my lathe, mill and drill press. Another set of frustrations but at least different.

Hi Gordon,

I know what you mean about the frustration. Been a challenge.

I had a four and five minute run today, then no luck. Backfiring keeping it from running longer, it seems, not sure why. I think it may be carb. issue. Still waiting for the new carb. At least when it runs it runs hard, too hard, which may be causing a heating problem too.

You may want to make an eccentric crank link so you can adjust the gap between the cylinders. That seemed to be the key for getting my engine to run. I have a 1/16 gap between cylinders, 1 1/2 left link arm, 1 7/16 right link arm. Left piston sticks out of left end of cylinder about 1/32 (when all the way to the left) and right piston is inside the right end of the cylinder about 1/16 (when all the way to the right). Port locations, pistons, and piston rods are per Gingery's book.

Ray

 

[Gordon]

Hi Gordon,

I know what you mean about the frustration. Been a challenge.

I had a four and five minute run today, then no luck. Backfiring keeping it from running longer, it seems, not sure why. I think it may be carb. issue. Still waiting for the new carb. At least when it runs it runs hard, too hard, which may be causing a heating problem too.

You may want to make an eccentric crank link so you can adjust the gap between the cylinders. That seemed to be the key for getting my engine to run. I have a 1/16 gap between cylinders, 1 1/2 left link arm, 1 7/16 right link arm. Left piston sticks out of left end of cylinder about 1/32 (when all the way to the left) and right piston is inside the right end of the cylinder about 1/16 (when all the way to the right). Port locations, pistons, and piston rods are per Gingery's book.

Ray

Ray: I am sure that the problem is poor vaporization of the fuel. I am not sure if it is a result of compression or carburation. I think it is some of both. The fact that you get it running by squirting oil in the cylinder points to a compression problem. The engine seems to be firing way too hard. When it is firing it is burning off fuel in excess of what it can use. Therefore it runs for short periods of time until there is just more fuel in the cylinder than it can burn off in one cycle and once it is flooded it stops running. I have played around with both a vapor carburetor and propane but I have not had much luck with either of them. I have also done some experimenting with different carbs with smaller jets and other throat size. I will be getting back on the engine in a few days.

 

[Ramoye]

Ray: I am sure that the problem is poor vaporization of the fuel. I am not sure if it is a result of compression or carburation. I think it is some of both. The fact that you get it running by squirting oil in the cylinder points to a compression problem. The engine seems to be firing way too hard. When it is firing it is burning off fuel in excess of what it can use. Therefore it runs for short periods of time until there is just more fuel in the cylinder than it can burn off in one cycle and once it is flooded it stops running. I have played around with both a vapor carburetor and propane but I have not had much luck with either of them. I have also done some experimenting with different carbs with smaller jets and other throat size. I will be getting back on the engine in a few days.

Gordon,

I agree with you on poor vaporization of the fuel. Today I adjusted the gap between the pistons wider. It resulted in a 7 minute run at a slower rpm (and richer carb. setting). This rpm seems about right, it was running way too fast before. It still quit after the 7 minute run, which may be attributed to fuel build up (causing flooding). Seems to be a correlation between piston gap and rpm. I may have some piston/cylinder leakage, but it seems to have enough compression to run.

I will be glad to get the chainsaw carb. in. Curious to see how it will work.

I ran out of time to experiment with it more today. Will try playing with the piston gap some more tomorrow.

Thanks Gordon.

Ray

 

[Gordon]

Got around to doing a little more experimenting on the engine yesterday. Still not much progress but I did discover that if I held the intake valve open while turning over with the electric motor the engine fires or backfires every stroke. There seems to be a fine line between a strong enough valve spring and too weak. Too strong and it will not fire and too weak and it spits back through the carburetor. It looks like there may be an ideal match between intake and exhaust valve spring match. I have tried several different carburetors and they all work some times. They seem to be close and then they will not run at all. Then suddenly they seem to work again for a short time.

 

[Ramoye]

Got around to doing a little more experimenting on the engine yesterday. Still not much progress but I did discover that if I held the intake valve open while turning over with the electric motor the engine fires or backfires every stroke. There seems to be a fine line between a strong enough valve spring and too weak. Too strong and it will not fire and too weak and it spits back through the carburetor. It looks like there may be an ideal match between intake and exhaust valve spring match. I have tried several different carburetors and they all work some times. They seem to be close and then they will not run at all. Then suddenly they seem to work again for a short time.

Gordon,

Might can try to put shim washers under the spring to incrementally increase the spring force? I also have noticed too weak of a spring causes carb. spitting. Maybe temperature is affecting the spring force (I would hope it is not that sensitive).

Still waiting on the carb. to come from China. It was only six dollars, but beginning to wish I had spent a little more to get one sooner. I have about done all I can do for now until I get the new carb.

Thanks Gordon.
Ray

 

[Gordon]

See my post at:

https://www.homemodelenginemachinist.com/threads/compression.31308/page-2

 

[dsage]

Hi guys. Have you had any luck yet getting the engine running?
I stumbled on this video today on Youtube. He explains the motion. I haven't analyzed it yet. Maybe you can see some changes from what you built (and the book)?


There is another video here that has some good snap shots of the motion works as well.
As far as I got was to 3D modelling it and, like you have discovered, I can't see how it achieves any compression. I'd really like to build this engine.

 

[dsage]

I'm pretty sure I can see some issues with the motions.
I've had some discussion with one of the builders on You tube.
Sorry I have to link to the video again. But you can read the comments by me (Dave Sage) below the video.
Any thoughts??

 

[Gordon]

Never really got the engine running consistently for any length of time. If everything is perfect it will run but the next time it will not run even though nothing has changed. I finally decided that the design is just too marginal and I have too many other things to work on which are not as frustrating. That being said I am now working on my Snow Tandem to "improve" it and I am having similar problems. I get the engine running for a few minutes and then the next time I try it will not run. Maybe I need a less frustrating hobby.

 

[dsage]

Sticking with the Atkinson. May I suggest you look at the videos I linked and see if the motions are different from yours? Not withstanding that (I believe) you changed some of the linkage or positions. I'd really like to get to the bottom of the issues before I build it. Following along in the comments on the video may give you some clues. Thanks

As for the Snow. I suppose that should be a different thread but since you have similar problems perhaps there are common issues with the way you have constructed both engines. You mentioned compression issues for the Atkinson - possibly ring or valve related? Are those items up to snuff on the Snow?
I couldn't imagine improving that design. It's complicated enough as it is

 

[bluejets]

I gave some insight to at least one problem in the design of this engine back in #54 along with the fact that the compression ratio is very small to begin with so any machining imperfections will be a major impact on the final outcome.

 

[Bruce R.]

I’ve learned that coleman fuel doesn’t have a whole lot of octane, I put about a 3/4 tank of gas in my engines and using the little red straw, I fill them the rest of the way with 2+2 gumcutter, that stuff is kinda like race car fuel.

 

[Cogsy]

I’ve learned that coleman fuel doesn’t have a whole lot of octane, I put about a 3/4 tank of gas in my engines and using the little red straw, I fill them the rest of the way with 2+2 gumcutter, that stuff is kinda like race car fuel.

I've never heard of 2+2 gumcutter so I'm not sure what it is, but unless your engines are super high compression then octane is not likely to be your issue with the coleman fuel. Higher octane numbers simply mean the fuel can withstand higher compression before spontaneous combustion. As long as you're not getting pre-ignition ('pinging' or 'knocking') then you don't need a higher octane fuel and won't get any benefit (power, mileage, less emissions, cleaner burn, etc) from using higher rated fuel, it's just marketing from the fuel companies. This goes for any engine, so even with your car, if the owners manual says it will run on 91 then there's no point paying extra for 95 or 98 or whatever.

 

[dsage]

I gave some insight to at least one problem in the design of this engine back in #54 along with the fact that the compression ratio is very small to begin with so any machining imperfections will be a major impact on the final outcome.

I re-read your comments in #54 I have also drawn the engine as a 3D model. I haven't built it yet because I agree that from what I can see the design is very marginal. But the design is VERY critical as to positioning and dimensions of the components. A very SMALL change can make a HUGE difference in the motion. That's why I'm wondering if those that got it running (as per Youtube) unknowingly made minor changes OR they built it perfectly (i.e. didn't inadvertently make mistakes and throw it off).
I have rotated the crank in my 3D model exactly as shown in the one video and observed the positions and motions in between positions and from what I can see there is a big difference in motions that could result in much better compression and better intake strokes. I made those comments to the builder in the Youtube video. He admits that he made a wooden model first and played around with it to get it right (not his words). He says the book is correct but..... who knows.
Manipulating the 3D model is very tedious but that's what I might have to do to see what results in the "proper motion" or improves it.
It's one of those engines I'd really like to build but I don't want to waste my time.