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Hard firing

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Gordon

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I seem to have a problem with hard firing on several of the engines I have built. I look at You Tube videos and videos on this and other sites and many of them show the same engine firing with a gentle firing when my engines seem to fire with a loud explosion. I have tried advanced and retarded timing and various carburetors and carburetor settings.

I am not sure of what things I should be checking and what settings I should be changing to get a gentler combustion.

I have been working on an Atkinson Differential engine recently and I finally got it running but it is again firing hard. This engine is super fussy and it seems that any small adjustment makes the difference between running hard and not running at all.

It seems that after 20+ engines I should have this figured out but some of us take longer to learn I guess.

Any input?

Gordon
 

Brian Rupnow

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The most common cause of hard starting and hard firing is having the ignition timing too far advanced. If you back the timing off about 5 to 10 degrees, your engine won't have quite as much power, but should start easier and run with a gentler power stroke. I try to set my valve timing so that the valves begin to open about 20-30 degrees before the piston reaches top or bottom dead center. The compression ratio of the engine comes into play here as well. It seems that the optimum compression ratio for model 4 cycle engines falls between 4:1 and 7:1.
 

Gordon

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The most common cause of hard starting and hard firing is having the ignition timing too far advanced. If you back the timing off about 5 to 10 degrees, your engine won't have quite as much power, but should start easier and run with a gentler power stroke. I try to set my valve timing so that the valves begin to open about 20-30 degrees before the piston reaches top or bottom dead center. The compression ratio of the engine comes into play here as well. It seems that the optimum compression ratio for model 4 cycle engines falls between 4:1 and 7:1.
Thanks. In the present case (Atkinson) the valves are atmospheric so there is no adjusting them other than stronger or weaker springs. I have tried retarding the ignition but it seems that the only place that the engine will run at all is where it is now set at about TDC. As far as compression ratio it is anybodies guess because the compression stroke is just two opposing pistons moving in the same direction and compression is accomplished by one piston moving slightly faster than the other.

That being said there are several of these engines with You Tube videos where the builder has the engine running much gentler than anything I have been able to accomplish.

I have not been able to contact anyone who has actually built a successful engine. Every time I think I have discovered something which seems to make a difference it completely changes the next time I work on the engine.
 

mayhugh1

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It may not be hitting 'harder', just louder. The earlier the exhaust valve opens, the louder the exhaust note. If this is an annoyance, you might try modifying the cam to delay opening the exhaust valve another 5-10 degrees. - Terry
 

Gordon

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It may not be hitting 'harder', just louder. The earlier the exhaust valve opens, the louder the exhaust note. If this is an annoyance, you might try modifying the cam to delay opening the exhaust valve another 5-10 degrees. - Terry
Unfortunately there is no cam. Both intake and exhaust valves are opened by atmospheric or compression pressure. The only adjustment is how strong the spring is.
 

doc1955

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I agree with Terry your exhaust valve is opening to soon . This will really make a difference in the way the engine runs and the sound. There has to be an exhaust cam to open the exhaust valve the intake yes it can be the vacuum of the intake stroke but not the exhaust.
 

Mechanicboy

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exhaust valves are opened by atmospheric or compression pressure. ---> Really fault if it's 4 stroke engine/Atkinson engine .. hence you get engine never started. The exhaust valve is operated by cam on cam shaft i four stroke engine or crankshaft in the Atkinson engine.
 

stevehuckss396

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I have never heard of an exhaust valve atmospheric operational. What keeps it closed during combustion but open on an exhaust stroke? or is the combustion and exhaust stroke one in the same.
 

Gordon

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Well it does not have a cam shaft. The pressure on the exhaust stroke holds the intake valve closed and forces open the exhaust valve. Once it exhausts the opposing pistons return toward the compression stroke and the exhaust valve closes and the intake opens due to the vacuum.

https://en.wikipedia.org/wiki/Atkinson_cycle

It certainly is not a normal four cycle engine. It was designed to get around the patent for the Otto cycle so it completes the cycle in one revolution of the fly wheel. It runs (reluctantly) but certainly was never a successful design.
 

Gordon

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That is because that is an Atkinson Cycle engine which is different than the Atkinson Differential engine. I wanted to build the Differential because it is unique. It is also a very marginal design. It has proven to be a very frustrating project.
 

coulsea

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I also wonder about the trickery used in you tube videos. some people start their engines with one finger through the spokes of the flywheel, if my engine was that low on compression it would not run. cameras also pick up sound in strange ways, mine amplify the gear noise and reduce the exhaust noise. I wonder how many 'takes' are involved in these videos.
 

doc1955

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In an Atkinson Differential it is the position of the exhaust hole that controls the exhaust timing isn't it. Even though no cam there is a timing of the valve opening under pressure. I have the plans and did model most of it up in CAD but never got around to building it. Only way to delay the exhaust is to plug the hole and move it. I personally would leave it even if it is a little loud.
 

doc1955

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You should be able to quite it a little with the ignition timing. Here is a video that I attempt to show that with an odd's and end's engine.

 

Gordon

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I also wonder about the trickery used in you tube videos. some people start their engines with one finger through the spokes of the flywheel, if my engine was that low on compression it would not run. cameras also pick up sound in strange ways, mine amplify the gear noise and reduce the exhaust noise. I wonder how many 'takes' are involved in these videos.
I have often so wondered about the same thing. It is easier to get an engine to run for two minutes and then turn sound down than to get it to start and run consistently. The videos do not show the ten tries to get it to start.
 

doc1955

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Or this one it comes down to putting in the time to sort things out not trickery!

 

Mechanicboy

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Now, i understand, it's a Atkinson differntial engine you build,.. are the Ginger book well wrote to explain how to build and adjust the valves who works after pressure/vacuum instead cam shaft? Maybe some was build without be attention to follow the build instruction? There is very info in the Google..
 

deverett

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I have never heard of an exhaust valve atmospheric operational. What keeps it closed during combustion but open on an exhaust stroke? or is the combustion and exhaust stroke one in the same.
There is a two stroke design from the early 20th century, written up in Gas Engine Magazine 1972 and described by ETW in ME after being shown a model built in the US by a Mr Arthur P. Stone of Elfers, Fla.
Engineer's Emporium sell castings for this engine and they call it Pioneer.

Both the inlet and exhaust valves are atmospheric in this engine.

Dave
The Emerald Isle
 

Gordon

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Now, i understand, it's a Atkinson differntial engine you build,.. are the Ginger book well wrote to explain how to build and adjust the valves who works after pressure/vacuum instead cam shaft? Maybe some was build without be attention to follow the build instruction? There is very info in the Google..
The Gingery book is OK but the problem is that there is no way to adjust things like stroke or valve action other than making new parts or moving the cylinder assembly. At this point I have kind of a hybrid with ideas from the Gingery book and other modifications from other suggestions and experimenting.
 
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