Author Topic: A Robinson from rejects.  (Read 71923 times)

Offline Jasonb

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Re: A Robinson from rejects.
« Reply #330 on: April 05, 2018, 07:54:13 PM »
I thought the thread started with the one Graham is building so that makes 4 though he is a bit slow ;)

Jo has also got a set or two of X-type castings

Offline RayW

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Re: A Robinson from rejects.
« Reply #331 on: April 05, 2018, 07:58:44 PM »
I stand corrected Jason. How could I possibly have forgotten Graham's own engine! My apologies to him for the oversight. I didn't mention Jo as I didn't think she was actually building a Robinson at the moment, even though she has castings

Ray
Ray

Offline RayW

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Re: A Robinson from rejects.
« Reply #332 on: April 18, 2018, 07:38:42 PM »
I seem to have got sidetracked lately with other things and have not done much on the Robinson, but finally got the pipework finished and fired up the burner for the first time today. Initially only got a rather small weak flame, then realised that the gas bottle was probably getting low! With a new bottle, there was a really good fierce flame, which brought the tube up to red heat pretty rapidly, so I should be attempting a first start-up any day now. Watch this space!!

P.S. If you are reading this Graham, I hope that you are feeling better now.

Ray
Ray

Offline zeeprogrammer

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Re: A Robinson from rejects.
« Reply #333 on: April 18, 2018, 07:39:57 PM »
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline Ian j

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Re: A Robinson from rejects.
« Reply #334 on: April 18, 2018, 07:47:57 PM »
Neat gas arrangement Ray. Looking forward to seeing it running.

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #335 on: April 19, 2018, 12:57:52 PM »
Hi Ray.

Looking good!!  :ThumbsUp:

I'm still under the weather, thanks for asking, your first run will definitely cheer me up.

Cheers Graham.




Offline RayW

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Re: A Robinson from rejects.
« Reply #336 on: April 19, 2018, 03:52:21 PM »
Hi Graham,

Things did not exactly go according to plan today. First attempt to start once the hot tube was nice and red resulted in the engine erupting in flames as soon as the gas inlet valve was opened! Big panic as it was on the rubber covered floor of the workshop but luckily the wooden base that the engine is mounted on prevented flames reaching the floor.
Quickly turned off gas and allowed flames to go out. It became obvious that there were some leaks in my pipework, so dismantled every joint and re-sealed them all.
Took engine outside to try again and got a couple of chuffs, but still repeatedly burst into flame almost every time that I opened the gas inlet valve.The fire happens so fast that it is impossible to see where it originates. I re-tightened the nuts holding the inlet and exhaust valve blocks in case there was a leak there.
Final attempt resulted in no more flames, but no sign of any attempt to run.
I am wondering if a lot of oil has drained down into the cylinder head and is igniting when gas is admitted to the cylinder and is ignited by the hot tube. On the first occasion that it caught fire, flames were actually coming up past the piston at one point.
Any suggestions please?

Regards and get well soon,

Ray


Ray

Offline Ian j

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Re: A Robinson from rejects.
« Reply #337 on: April 19, 2018, 05:24:09 PM »
I think Jason mentioned that that type of needle valve wasn't very sensitive ie from no gas to load of gas.
My needle valve only requires approx 1/12 of a turn to deliver sufficient gas and that is with a number 3 burner jet (.15mm) between the outlet of the needle valve and the inlet valve chest.
« Last Edit: May 25, 2018, 11:17:33 PM by Ian j »

Offline Jasonb

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Re: A Robinson from rejects.
« Reply #338 on: April 19, 2018, 06:39:10 PM »
Yes mine was giving too much gas and would flare up from the exhaust which makes things exciting :o

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #339 on: April 19, 2018, 07:51:51 PM »
Hi Ray and All.

The gas control on your needle valve does seem rather ineffective but as I mentioned many pages back the inlet valve always leaks a little.

What is actually happening is the leaking gas is being ignited by the flame from the hot tube burner.

My only suggestion is to perhaps make a better needle that actually plugs up the hole more effectively and try to reduce further the gas input before the needle valve proper.

I will confess that my engine has flared up many times over the years too.

Cheers Graham.

Offline Ian j

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Re: A Robinson from rejects.
« Reply #340 on: April 19, 2018, 08:43:21 PM »
Before I connected the gas to mine I tested the pipe connections with compressed air connected and a brush with soapy water.

Offline RayW

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Re: A Robinson from rejects.
« Reply #341 on: April 20, 2018, 04:39:36 PM »
Thanks all for the feedback. It is reassuring to hear that the experts (Graham) engine also spontaneously combusts occasionally!
I did put a restrictor in the inlet pipe to the needle valve, but re-reading all your previous postings, I clearly made the hole much too big as I used a Number 60 drill bit, which is about 40 thou. Fortunately, I deliberately made this a removable screw-in restrictor, so no problem to replace it with another with a much smaller hole.
I have also had another look at the "needle" valve internals, and I think it would be quite easy to modify it if necessary. I will try the smaller restrictor first and see if that helps.
When I first assembled the pipework, I sealed every threaded joint with special Calor Gas sealant, so I had no reason at that stage to suspect any leaks, but when some became evident, I did use soapy water to find them Ian. Unfortunately, I do not have a source of compressed air so had to resort to blowing through the pipework by mouth while immersing it in water.
Ray

Offline RayW

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Re: A Robinson from rejects.
« Reply #342 on: May 07, 2018, 02:40:45 PM »
Tried the engine today with a modified restrictor before the needle valve. Reduced the bore from 40 thou to about 13 thou. Still tending to erupt in flames and no sign of any attempt to fire at the minute. Noticed slight bubbling from the inlet valve gasket so that is probably where the gas was leaking and igniting. Have resealed with silicone gasket sealant and will allow to cure overnight before trying again.
I will also try capping off the supply to the burner so that I can check exactly how much gas is getting to the cylinder and how well the needle valve is regulating the flow.

Ray
Ray

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #343 on: May 07, 2018, 04:04:04 PM »
Hi Ray.

Still reads like too much gas....

Try this, extend the exhaust a little from the valve chest using some metal pipe. Anchor the engine and with a candle flame burning under the exhaust outlet start trying to turn the engine through its cycles.

If too much gas is present the exhaust will ignite with a very Yellow flame, what you're looking for is a Blue flame. Blue indicates a near perfect mix of fuel to air. It's a simple and effective way of fine tuning the mixture of a gas engine.

Cheers Graham.

Offline Jasonb

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Re: A Robinson from rejects.
« Reply #344 on: May 07, 2018, 04:09:31 PM »
I have also had a little try with mine, now got a No3 jet (0.015mm) infront of the valve and using the 4 bar regulator. still don't seem to be getting a very hot tube and no signs of life. Gave up then as it was too hot in the shed to be turning over engines so decided to have a magnum.

<a href="https://www.youtube.com/watch?v=13PxqCo1QtM" target="_blank">http://www.youtube.com/watch?v=13PxqCo1QtM</a>
« Last Edit: May 07, 2018, 04:38:28 PM by Jasonb »

 

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