Author Topic: A Robinson from rejects.  (Read 71965 times)

Offline RayW

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Re: A Robinson from rejects.
« Reply #345 on: May 07, 2018, 05:28:22 PM »
Thanks for the suggestion Graham. Sorry to sound stupid, but do you mean to blank off the burner or to do what you suggested with the burner burning?

Jason, the Magnum sounds like a much more sensible suggestion than playing with engines in this heat!

Ray
Ray

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #346 on: May 07, 2018, 06:37:38 PM »
Thanks for the suggestion Graham. Sorry to sound stupid, but do you mean to blank off the burner or to do what you suggested with the burner burning?

Jason, the Magnum sounds like a much more sensible suggestion than playing with engines in this heat!

Ray

Hi Ray.

No, not stupid, I should've mentioned to blank off the burner.

You might find that there's less gas entering than you thought, I'm suggesting a starting from the off position and waiting to see the Blue flame appear. If it's Yellow from the start then there's way too much, ideally what you're looking for is nothing then a small Blue flame then moving to Yellow.

Cheers Graham.

Offline RayW

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Re: A Robinson from rejects.
« Reply #347 on: May 12, 2018, 12:43:27 PM »
Thought I would check how well the inlet valve is sealing before trying Graham's suggestion. Removed the whole inlet valve block and connected to the gas supply, having first blanked off the burner connection. As I suspected, even with the valve appearing to be seated flat against the inlet block, gas is escaping from under the valve head, meaning that gas would be flowing continuously into the cylinder all the time that the needle valve was open.
Tried re-facing the valve and lapping it against the valve block, but even holding the valve down by hand as hard as I can, I cannot get it to seal completely.
I have been thinking about the design of the inlet valve itself and am toying with the idea of trying a modified design to see if that cures the problem. My thought is that part of the problem with the current valve is that it is trying to seal over a fairly large flat area which contains numerous holes including the gas jet. If I made a slightly larger valve and recessed most of the face by a very small amount leaving a narrow raised rim, would that be easier to lap in and achieve a seal? Admittedly, this would allow a very small amount of gas to be held under the valve head until it opened but would that be a problem?
I would be interested what others think of my idea.
Ray

Offline Jasonb

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Re: A Robinson from rejects.
« Reply #348 on: May 12, 2018, 01:29:21 PM »
You may get gas leaking out through the inlet holes as there will be nothing between them and the gas hole, watch your eyebrows.

May work if you milled a "C" shape to recess all the surface around the air holes but left the area around the gas hole flush with your sealing surface

Offline ettingtonliam

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Re: A Robinson from rejects.
« Reply #349 on: May 12, 2018, 01:36:53 PM »
With an inlet valve that seats perfectly, the force trying to lift it off its seat is the combined area of the holes times the gas pressure. If you made a  wider valve and recessed the area containing the holes, the force trying to lift it off its seat is the area of the recess times the gas pressure, which will be much larger.
On the other hand I could be talking rubbish.

When I built my Stuart 600 gas engine, getting the valves to seat properly was one of the most difficult jobs

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #350 on: May 12, 2018, 02:42:36 PM »
Well....

Even the originals leak!!

I wouldn't be too concerned at this point Ray. Once you've tamed the beast and found its " spot " that weepage won't be a problem.

A question..

Do you have good compression? ie, does the flywheel bounce back against compression? Ideally the flywheel will oscillate back and forth at least twice.

If yes then I'd try the " burning candle " test to see if there's too much gas entering.

Now there's some metals that won't work as an ignition tube, Cuprous being one of them. Iron was extensively used along with ceramic. These days we've got Stainless Steel, the best. Did you follow the dimensions from the drawing? One eighth of an inch internal diameter. This might need either opening or closing depending on your developed compression pressure.

I'd be inclined to blank off the supply to your burner and with the engine firmly anchored try using your favourite gas torch on the tube, get it good and hot then try starting it. You can then see where the
" sweet spot " is. If it's low down, open the diameter by 1/64" if it's high up reduce the diameter by 1/64".

Good luck Ray, we're all agog, cheers Graham.

Offline RayW

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Re: A Robinson from rejects.
« Reply #351 on: May 13, 2018, 05:29:09 PM »
Thanks all for your responses. As Jason pointed out, my idea of a recessed valve face would not work as it would not seal off either the gas jet or air inlet holes. Think I must have been having a senior moment when I came up with that idea!

Tried the candle test today, Graham, with interesting results. As Jason mentioned in a previous post, the big blunt "needle" in the valve provides very little control over the gas flow, being more or less on or off. As you will see from the video below, I did eventually manage to achieve a good fierce blue flame with the valve just about cracked open, but turning the handle even a fraction of a degree one way or the other resulted in either no flame or a flame thrower!

<a href="https://www.youtube.com/watch?v=KHnzh7-W_aA" target="_blank">http://www.youtube.com/watch?v=KHnzh7-W_aA</a>
« Last Edit: May 13, 2018, 10:15:14 PM by RayW »
Ray

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #352 on: May 13, 2018, 06:00:00 PM »
Hi Ray.

Yes, there were at least 3 places in your video where the mixture seemed to be just right. Near the end it became consistent.

The only suggestion I have is to perhaps make a replacement needle to try and get a better control over the supply.

Cheers Graham.

Offline ettingtonliam

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Re: A Robinson from rejects.
« Reply #353 on: May 13, 2018, 07:49:04 PM »
Sounds like you were working hard there, lots of heavy breathing!. When I was trying to get the Stuart to run, I rigged up a 1/4hp electric motor on a hinged plate, with a small rubber covered flat pulley on the motor shaft I arranged this at the flywheel end of the engine, with the weight of the motor pressing the pulley against the flywheel. This rotated the engine at about 200 rpm, so I could concentrate on getting the gas and ignition timing adjustments right. When it seemed to be running on its own, I swung the motor away.

Richard

Offline RayW

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Re: A Robinson from rejects.
« Reply #354 on: May 13, 2018, 07:57:05 PM »
Hi Graham,
Once I found the right setting the flame remained very consistent. The variations you see on the video were the result of me playing with the setting to optimise the flame. When I try to start the engine I will start with zero gas then open the valve by tiny amounts until it fires (hopefully). I will also look at the possibility of modifying the needle or, if not, finding an alternative valve.

Ray
Ray

Offline RayW

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Re: A Robinson from rejects.
« Reply #355 on: May 13, 2018, 08:00:53 PM »
Hi Richard,

I meant to apologise in my previous posting about the heavy breathing! It really wasn't that hard turning the flywheel.

Ray
Ray

Offline Ian j

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Re: A Robinson from rejects.
« Reply #356 on: May 13, 2018, 08:58:28 PM »
Ray.
I feel your frustration with the gas supply problems.
I'm reluctant to make a suggestion on a suitable needle valve but my engine now reliably starts and the speed varied with the set up I have. The needle valve I use is this item on ebay{-

"eBay item number:
253612197055"

Ian

PS. Making good progress with building the second engine from castings.(No.198)
« Last Edit: May 13, 2018, 09:03:19 PM by Ian j »

Offline RayW

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Re: A Robinson from rejects.
« Reply #357 on: May 15, 2018, 10:16:10 AM »
The beast awakes!
Had another try this morning and, with the tube glowing nicely and the needle valve barely cracked open, it fired and ran on about the second or third spin of the flywheel. The attached video is actually the second run, as I had not even got the camera set up the first time as it caught me completely by surprise when it started!
As was evident when I carried out the candle test, the tiniest change to the needle valve setting stopped it running, so I would still like to get a different valve to give me finer control over the gas supply. For now though, I am a happy chappy.
The run today was, of necessity, only short as the cooling system is not yet operational, the cylinder needing to be sealed to the base, which will be done when I strip the engine down for painting.
Thanks to you all, and in particular Graham, for your continuing support and encouragement along the way.

Ray

<a href="https://www.youtube.com/watch?v=x-0odv8w_a4" target="_blank">http://www.youtube.com/watch?v=x-0odv8w_a4</a>
Ray

Offline Jo

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Re: A Robinson from rejects.
« Reply #358 on: May 15, 2018, 10:22:53 AM »
 :whoohoo: :whoohoo: Well done Ray

I will have to go and see what Surus  has done with my X Type castings  :noidea:

Jo
Enjoyment is more important than achievement.

Offline Roger B

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Re: A Robinson from rejects.
« Reply #359 on: May 15, 2018, 10:32:51 AM »
Splendid  :praise2:  :praise2: Your persistance paid off  :ThumbsUp: Than needle valve is incredibly sensitive  ::)
Best regards

Roger

 

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