Miniture spark plugs

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Robert Simons

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Hi everyone..
Am greatful to be a member of this site. I hope to learn a lot from you all.🙂.
My name is Robert. And for some time, have tinkered on my small lathe, making tooling, and some engineering projects..
The aim was to enhance my skills along the way, in readiness to build a few miniture engines.
But as always, when building from scratch, one finds it difficult to know where to start.
So I thought, start with what .aye the hardest parts first. In this case, sparkplugs.

Now have seen some different ways of constructing in miniture, but here is my question......

Q. Can my plug bodies be made of brass?

Reason is, I have plenty, and it's easy to work with?
Your thoughts fellow members???





In this case, sparkplugs
 

GailInNM

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While my prefered material is leaded steel, I have seen brass used without problems by others, and as Minh Thanh said he has done it. Be sure to use a soft copper washer on the plug to make a good seal with the head.

Your next material problem may be the insulator material. Most US A constructors use Corian as it is common here, but it is not easily available in other parts of the world. I discussed this a little bit in post #44 of this thread.


A search for spark plug on this forum will yield a lot of other different techniques used by others.

I suggest that you make a few extra so you have a spare plus an extra or two for your next engine.
 

Robert Simons

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While my prefered material is leaded steel, I have seen brass used without problems by others, and as Minh Thanh said he has done it. Be sure to use a soft copper washer on the plug to make a good seal with the head.

Your next material problem may be the insulator material. Most US A constructors use Corian as it is common here, but it is not easily available in other parts of the world. I discussed this a little bit in post #44 of this thread.


A search for spark plug on this forum will yield a lot of other different techniques used by others.

I suggest that you make a few extra so you have a spare plus an extra or two for your next engine.
Thank you..
My plugs are around an 1'long. 1/4×32 thread.
Bodies are just 1/2 inch in total.
Have made 14 bodies while the lathe was set up. So yes spares.
Tungsten rod 1.6mm for the centre.
The material of choice for the insulator is nylon.
Can't think what they call it. But can machine it down to a 2.5mm diameter with no problems, using a centering rod, drilled in to the material at the start, and placing that into the tailstock.
Araldite, or some other 3 pack glue to hold it all in place. That is the hope.....!!🙂
 

gadabout

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Robert, hi!
Whereabouts are you ? I’m in Hobart!
regards
Mark
 

gadabout

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Was up that way the week before last, we’ll probably St Mary’s was the closest I got
cheers
Mark
 

simonbirt

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I use mild steel for the body, brass for the electrode and PTFE for the insulator. The Insulator is held in place by swaging as obviously you can’t glue it. They work fine. Like others I made a batch so I have a few spare.
 

Robert Simons

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I use mild steel for the body, brass for the electrode and PTFE for the insulator. The Insulator is held in place by swaging as obviously you can’t glue it. They work fine. Like others I made a batch so I have a few spare.
Thanks. As I am making the body from brass, swaging might be difficult.
Am going to try JB weld to hold the PTFE insulator in place, and see how it goes. Have heard others trying this with success.
 

simonbirt

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PTFE does not glue with anything, including JB Weld, the plug bodies are easy to machine from FCMS. If anybody is interested I’ll upload the drawings and photos.
 

rutzen

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I made the body on my spark plug from Corian [worktop stuff]. You can stick it with superglue and seems to hold fine.
 

DaveJones

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the plug bodies are easy to machine from FCMS. If anybody is interested I’ll upload the drawings and photos.
Absolutely interested in your drawings and photos.
What is FCMS?
I'm just about to start building a Windsong .099 spark ignition engine from R Schroeder castings and intend to make the spark plug myself.
 

Steamchick

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Hi,
Just a couple of observations, that may or may not be correct. (I have never done this, but have worked with Champion on spark plug "tuning" for production car engines). I hope some of this is useful?
The ceramic insulators in "production" engines do a few jobs.
  1. They support the central electrode.
  2. They get hot at the sparkey end, which burns-off carbon deposits (at over 600 degrees C?) so the insulator stays clean to prevent flash-over down the surface of the insulator. ((This means the spark does NOT occur across the electrode gap - which is needed for the engine to run properly).
  3. They cool the electrode, as the spark (at 5000 degrees C) and combustion gas (at 900 degrees C), are also trying to burn the central electrode away and make the gap bigger....
  4. Therefore the ceramic material, shape and electrical resistance of the ceramic are carefully selected to get the best compromise of all the conflicting requirements.
The wrong ceramic will:
  1. crack or break, so the ceramic particles get dragged up and down the cylinder walls, and bounced around to form grinding paste inside the engine.
  2. allow too much pollution to collect on the surface and then the sparks will flash-over and the engine will mis-fire or stop.
  3. will not keep the electrode cool enough, so it burns away too rapidly.
The wrong shape will:
Cause the ceramic or electrode to fail as above.

But you are trying different materials, in engines (like hit-and miss) that run quite differently from "regular production" engines. More comments below:
  • Nylon probably won't handle the temperature and pressure.... as the electrodes can get near red-hot. (Nylon burns well below this!). Also burning Nylon will create carbon - which conducts electricity and causes the plug to fail to spark in the right place...
  • PTFE sounds good, providing you don't get to 350 degrees C - when the PTFE gives of flourine ions which combine to make some of the most corrosive stuff imaginable! Hydoflouric acid, and more complex stuff! - This may be OK as ejected from the engine in tiny quantities with exhaust gas.... but may cause a sore throat if you breath ANY of the gas.... or burned lungs if in the Great War when it was one of the gases experienced in trench warfare... PTFE does not melt. It ablates. (Goes directly from solid to gas). Used for space-craft tiles to protect hot surfaces from burning-up when they re-enter the atmosphere - by sacrificial ablation and insulation, and on non-stick cooking utensils as it doesn't change below ablation temperature (This is >100 degrees higher than burnt food temperature!).
  • I like the idea of Tungsten electrodes, but a bit of copper wire can be OK, or stainless steel wire, - even mild steel... which can save a dollar or two. Avoid brass that will create zinc oxide compounds that are abrasive and will pollute the surface of the insulator inside the engine, and encourage flash-over, so the spark won't be where you intend...
  • A colleague uses the domestic fuse bodies to make his ceramic insulators. They already have a hole for the central electrode, which he seals using silicon sealer or fire-brick cement, or car exhaust assembly paste.... They can be machined: at high speed, with very fine cuts using very hard and sharp tools... (I know no more). But they can explode if you get it wrong when machining (WEAR EYE PROTECTION AND USE MACHINE GUARDS! - You can lose an eye, or need a surgeon to remove ceramic particles from within an eyeball, or flesh.). Again he bonds to steel bodies with car exhaust sealer, or other. (Silicon sealer won't take the pressure at this joint). The plug is baked before use... Swaging the body to secure a flange of the insulator is standard practice. Look at a bought spark-plug to see the standard design. It works.
But enjoy your developments, and tell us all what works and what doesn't.
Cheers,
K2
 

Willyb

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Hi simonbirt

Yes I would be interested in your drawings and photos.

Cheers
Willy
 

simonbirt

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The drawings are in the other thread, we seem to have two on the go. Let me know if you need any help with them, these are Beta drawings and instructions, very happy for any errors or observations to be pointed out.
 

simonbirt

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Now we have proved that spark plugs made in the home shop work in practice, we just need to prove they work in theory?

Simon
 
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