Valve timing

[Gordon]

Well if you must hang on small details, yes, but just as difficult to set up.(which, as you can see was successful)...that being the point afterall.
As far as I am aware there are very few, if any, successful "differential" engines that will actually run anyhow (well known).
Pos in that they have crap model design and buggerall compression along with spark plug being located incorrectly.

Photos of the crankcase required are not yet forthcoming so we may have to write to NASA or the FBI and get clearance as it appears to be a big secret

Between computer problems and medical appointments I have not been very active in the engine department. Not sure what the crankshaft view proves.

 

[Steamchick]

Sorry, I had picked-up on a comment about difficulties of getting smoth running in horizontally opposed twins using a single crank. (Original question?). Not related to your Atkinson differential at all.
The Atkinson differential (correct me if I am wrong?) uses 2 pistons - one for intake and exhaust , the other for compression and firng. Valve timing is important so it blows then sucks when the right port is open. Compression is really just a way of defining how big the bang can be.These engines must be very free running, and all infernal combustion engines can be sensitive to mixture and ignition timing. As long as you can feel "good" compression on the crank then that should be ok.
Hope this is of some use?
K2

 

[Gordon]

Sorry, I had picked-up on a comment about difficulties of getting smoth running in horizontally opposed twins using a single crank. (Original question?). Not related to your Atkinson differential at all.
The Atkinson differential (correct me if I am wrong?) uses 2 pistons - one for intake and exhaust , the other for compression and firng. Valve timing is important so it blows then sucks when the right port is open. Compression is really just a way of defining how big the bang can be.These engines must be very free running, and all infernal combustion engines can be sensitive to mixture and ignition timing. As long as you can feel "good" compression on the crank then that should be ok.
Hope this is of some use?
K2

The biggest problem with the Atkinson Differential is that the two pistons are both traveling to the left during the compression stroke. The the two pistons travel at a different rate so that when the LH piston reaches TDC the RH piston is about 3/4 through the stroke so it makes compression only in about the last 1/4 of the stroke. I also built an Atkinson Cycle and I found that kind of fussy but much easier to get running. Bluejets was saying that the two Atkinson designs were the same. In my opinion they are not.

 

[stevehuckss396]

Hello Gordon. Do both cylinders fire at the same time? From the picture it appears like both intake valves open at the same time.

 

[Gordon]

Hello Gordon. Do both cylinders fire at the same time? From the picture it appears like both intake valves open at the same time.

No. They fire 180° apart. I have not been back on this engine again until just about an hour ago. I have adjust the exhaust to open later to give less overlap and advanced the ignition. Getting a few 15 second runs at lower RPM. Time to quit for the day. It will still be here tomorrow morning.

I apologize for not getting back to folks. Sometimes "the other life" gets in the way.

 

[Richard Hed]

The biggest problem with the Atkinson Differential is that the two pistons are both traveling to the left during the compression stroke. The the two pistons travel at a different rate so that when the LH piston reaches TDC the RH piston is about 3/4 through the stroke so it makes compression only in about the last 1/4 of the stroke. I also built an Atkinson Cycle and I found that kind of fussy but much easier to get running. Bluejets was saying that the two Atkinson designs were the same. In my opinion they are not.

It's well known they work differently

 

[Arild]

I have a question which I should know the answer to but I am not doing well. I am building a horizontal twin IC engine. My thinking is that the two cylinders should fire 180° apart. I have both cylinder set up for exhaust to open 40° BBDC and close 20° ATDC. Intake open 15° BTDC and close 45° ABDC with the other cylinder 180° after the first. I have good compression but I cannot get the engine to actually run or even fire well. The cylinders get warm but no actual firing. The engine turns over but the two cylinders seem to be fighting each other. The engine actually acts like it is backfiring. I have tried different ignition positions but I am not even close to having the engine running. Any idea what I am missing?

Does the pistons share the same crankpin? (It will be a very shaky engine then!). On a "boxer engine" where the pistons goes opposite way, the valves share the same cam lobes...

 

[Jeffro]

Your picture shows a 180 deg crank which means BOTH pistons are at TDC at the same time.

180 deg firing is not possible.

Both cylinders firing at the same time is possible and would be fun to watch.

360 deg firing the more likely set up.

 

[Steamchick]

Ever watched a BMW boxer shake from side to side on idle? - Ok when at speed on the road though...
My Guzzi Vee-twin does that as well...
K2

 

[kuhncw]

Hello Gordon,

Looking at your crank, both pistons are at TDC at the same time, then BDC 180 crank degrees later which I believe would make the engine fire 360 crank degrees apart. If both cylinders were side by side, with your crank, the pistons would move opposite each other and the cylinders would fire 180 crank degrees apart. Your pistons are moving opposite to each other, but the opposed cylinder configuration makes the difference.

Model Engine Builder Magazine published a build article for the Upshur Horizontal Twin. The crank configuration is like yours. The distributor has the contacts 180 cam degrees apart to fire the engine 360 crank degrees apart.

You are getting some short runs, but the engine may be running on one cylinder. I had that happen while debugging my Titan twin cylinder (Doug Kelley"s design). The cylinders are side by side, pistons travel together, and it fires 360 crank degrees apart, I just looked at the cam in my Titan. The lobes are roughly 180 cam degrees apart. If, with this cam, my cylinders were horizontally opposed like yours, both my inlet valves would be open at the same time. I'd have to rotate the lobes so both inlet lobes were in sync. The same for the exhaust lobes.

I think reorienting your cam lobes will make your engine run.

This is my 2 cents worth based on looking at your photos and the Upshur article in Model Engine Builder. I'm sure you'll get your engine sorted out.
It should be a good runner.

Regards,

Chuck

 

[Gordon]

Apologies to all. My cylinders were out of phase by 180° so that they were both in the intake/compression/firing position at the same time. I went through the sequence so many times thinking that the position was correct that I missed the obvious. I will keep working on it. Presently lost compression for some reason but that is another problem which I do know how to analyze. Thanks to all.

 

[Charles Lamont]

It is not directly relevant to your problem, but why do the brass guides finish so far away from the camshaft?