Author Topic: Senft "Poppin" engine  (Read 24510 times)

Offline Jasonb

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Re: Senft "Poppin" engine
« Reply #105 on: March 23, 2018, 01:45:26 PM »
You will more likely find 26 or 24 gauge wire as 25g (0.020") is not a common size. Model aircraft shop is a good place to look or just google 24g piano wire

Offline NickG

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Senft "Poppin" engine
« Reply #106 on: March 23, 2018, 03:38:33 PM »
Yes it follows it, that is the intention, but Only a very light spring stiffness is needed. I might try mine without spring to see if it works!

My bases were similar to Bills. Make sure the burner is a tight fit so it doesn’t vibrate loose, it’s good to be able to swing the flame away from or towards the port to adjust speed. If directly behind the port mine picks up too much speed and blows the flame out!

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Offline Admiral_dk

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Re: Senft "Poppin" engine
« Reply #107 on: March 23, 2018, 07:44:13 PM »
Quote
Where do I get a piece of 0.020" diameter spring wire? I'm thinking guitar string---maybe?

It is a standard guitar string size and all guitar strings are made from the absolutely best Swedish steel available.
There's actually only one factory in the Whole World WHO makes steel in a good enough quality for instruments, so ALL brands of string are made from huge coils of that steel from that Swedish factory.

Offline Doc

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Re: Senft "Poppin" engine
« Reply #108 on: March 23, 2018, 08:33:40 PM »
I made springs for my little blazers I used .011 dia wire I have more than I'll use in 5 life times if you want I could post you some.

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #109 on: March 23, 2018, 10:19:24 PM »
I worked in my office across town today, and managed to score a piece of .002" shim stock for the valve and a piece of 0.026" spring wire that should get the job done. Thanks for the offer Doc.

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #110 on: March 23, 2018, 11:06:55 PM »
There is definitely a degree of "Hinky" to the valve mechanism on this engine. I have hidden one flywheel here to show the "hinkiness" a little better. The angular relationship between the lever with the roller on it and the small 1/16" diameter rod holding the 0.002" thick valve is adjustable.  When the roller is fully "on the cam", the 1/16" diameter rod should be positioned so that the .002' thick valve just covers the hole in the cylinder head and overlaps the edge by about 0.015".--It doesn't in this picture--That was just me placing the 1/16" rod in a perfectly horizontal position when the roller was up on the cam. As you can see, the valve doesn't come close to covering the hole. I can sort out what the angle SHOULD be tomorrow. Then after establishing the correct angle, I have to establish exactly WHEN this event should take place in the cycle of the piston moving in the cylinder. Dr. Senft states that ideally, "Choose a direction of rotation and initially position the cam/flywheel on the crankshaft so that the valve closes the port when the piston has completed about 85% of it's outward motion, that is about 45 degrees before outer dead center."-I've never had so much fun with my clothes on!!

Offline b.lindsey

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Re: Senft "Poppin" engine
« Reply #111 on: March 23, 2018, 11:48:04 PM »
Brian, it is tricky and hard to find, but there is one timing setting that will allow the engine to run either forward or reverse. So if you run out of things to do you can try to find that exact setting. I will say it is usually best to optimize it for one direction or the other as it will run better that way.

Bill

Offline Alyn Foundry

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Re: Senft "Poppin" engine
« Reply #112 on: March 24, 2018, 12:12:41 PM »
Hi Brian.

Bill is correct, there's a very fine line between direction of running. On one of mine if you get the flame
" just right " it'll rock back and forth without actually rotating at all!

In " clock speak " most of mine see the port shutting with the crankpin at 20 past the hour.

Good luck, I'm beginning to realise why I " shelved " Nattie 18 years ago!

Cheers Graham.

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #113 on: March 24, 2018, 01:32:32 PM »
Dr. Senft covers that in the instruction sheet.He says that although the timing if set at 45 degrees is "optimum" for good running in one direction, if you go to 50 degrees advance it will run either direction, but not quite as well.

Offline NickG

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Re: Senft "Poppin" engine
« Reply #114 on: March 24, 2018, 03:47:46 PM »
When you think about the ridders internal valve engine, the timing is exactly the same whichever direction it is run in. It isn’t optimum, the speed at which the valve closes cannot be changed as it can with a cam profile, it is the same speed as the piston - so all of those things are probably part of that engine’s shortcomings.


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Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #115 on: March 24, 2018, 04:06:49 PM »
I arose from my warm and comfy bed this morning and decided that this would be the day to build a proper engine base and start on a burner. Everything worked, everything fit, and now I'm off to a nearby coffee shop for some lunch. Goodwife has taken #2 son to #1 daughters house in Orangeville to repair a garage door, and I am left to amuse myself for the day. After lunch I will decide whether to finish the burner or set it aside and see if I can start the engine on a "borrowed burner" from another project.

Offline NickG

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Senft "Poppin" engine
« Reply #116 on: March 24, 2018, 05:13:00 PM »
Finish it!! ... although I borrowed a burner on my first one though!


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Offline 90LX_Notch

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Re: Senft "Poppin" engine
« Reply #117 on: March 24, 2018, 05:19:35 PM »
Maybe I'm missing something Brian; but your drawing shows the roller on the base circle of the cam.  The lobe pushes the roller/arm downward causing the flapper valve to rapidly close the port off; thus, causing the hot gas charge to rapidly cool, sucking the piston back to tdc.  The valve actually snaps closed on this engine; it doesn't slide across the port.   It follows the radial path of the rod.  Think of a fly swatter.  Also,
the power stroke occurs from bdc. 

-Bob
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My Engine Videos on YouTube-
http://www.youtube.com/user/Notch90usa/videos

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #118 on: March 24, 2018, 06:15:51 PM »
No argument 90LX  I realize that the .002" valve swings away on an arc following the arc of the rod it is supported on. That drawing was just me messing around to see where I actually could put things.---Brian

Offline NickG

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Re: Senft "Poppin" engine
« Reply #119 on: March 24, 2018, 08:00:21 PM »
I can’t remember what thickness I used
For the valve, but I think it was thicker than that as the stuff creases really easily. Thinner works better in a way but have to be careful not to damage it or it won’t seal.


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