Shop built sparkplugs for model engines

[stevehuckss396]

There has to be more to it than that. I have had the same plugs in my Peewee since first start 2010. No electrode erosion of any kind. They still work very well. My theory is that the gap is huge and the voltage has to build up to a very high voltage to jump the gap damaging the electrode. Another theory is, if an automotive coil (old school) is being used it may be delivering way more energy (Joules) than the little CDI coil which is all volts and no amps. Or theory number 3, Both!

 

[johwen]

Hi Brian,
I make my own spark Plugs very simple to make see attached sketch. No fancy materials needed Body 3/8 inch hex length to suit engine 4mm ceramic tube with 2mm bore. Nice square ends, protrude though the end of body .020 inches for spark gap. Centre electrode mild steel turned down to 2mm from 5mm OD rod. Length to suit length of insulator. Insulator length say .750" above body. When inserted into insulator and Loctite in place you will end up with a full circle .020" gap. Make a brass terminal nut to suit. These plugs work extremely well for me, easy to clean and gap is permanent and look scale in the engine.
See attached sketch, I made a mistake and said 5/16" hex when it should have been 3/8" John

 

[rutzen]

Hi, I made the spark plug for my Rumely tractor, I used Corian for the insulator and I used nickel silver 1/16 rod for the electrode and there is no sign of any erosion so far. I seem to remember from way back that conducting the heat away from the central electrode is more important than the hardness of the material. I just happened to have the nickel silver, I would have used brass otherwise. It's easy to solder the connection the top as well.

 

[awake]

I'm wondering if hardness of the material is a red herring. EDM (spark erosion) seems to work equally well regardless of soft or hard material ... right?

 

[almega]

johwen - I am curious as to where you are able to purchase your ceramic tubing.

 

[johwen]

You will find several listed on EBAY try your local area it is used in High temperature insulation in many areas such as oven manufacturers.

I was lucky here in Melbourne Australia to be able to buy same from a manufacturer about 6 kilometers from where I live. he even cut them to length for me.

So do a search on the net you will find some one who can help. Johwen

 

[Bentwings]

Hi Brian,
I make my own spark Plugs very simple to make see attached sketch. No fancy materials needed Body 3/8 inch hex length to suit engine 4mm ceramic tube with 2mm bore. Nice square ends, protrude though the end of body .020 inches for spark gap. Centre electrode mild steel turned down to 2mm from 5mm OD rod. Length to suit length of insulator. Insulator length say .750" above body. When inserted into insulator and Loctite in place you will end up with a full circle .020" gap. Make a brass terminal nut to suit. These plugs work extremely well for me, easy to clean and gap is permanent and look scale in the engine.
See attached sketch, I made a mistake and said 5/16" hex when it should have been 3/8" John

Very innovative actually I think model spark plugs are available I think they us 1/4 32 to I don’t ave the supplier name handy most modern two and fou strokes now use automotive standard plus even my model plane engines use standard over the counter plugs

 

[almega]

I am thinking it is an interesting challenge to build your own spark plugs but with them available at $5.99 each, why bother. That would be like making your own nuts and bolts. Check out this link.

https://www.rcgfusa.com/product/stinger-spark-plug/

 

[Vietti]

Or go to your auto parts store and pay $4 +/-. Google them, good deals on ebay too.

 

[Ghosty]

I am thinking it is an interesting challenge to build your own spark plugs but with them available at $5.99 each, why bother. That would be like making your own nuts and bolts. Check out this link.

https://www.rcgfusa.com/product/stinger-spark-plug/

They are M10x1 threaded plug, no good for 1/4" plug application

 

[stevehuckss396]

"I am thinking it is an interesting challenge to build your own spark plugs but with them available at $5.99 each, why bother. That would be like making your own nuts and bolts. Check out this link."


Because I dont have a single engine that that giant spark plug will fit in. I don't think any of the sparkplug makers care much about making #8-40 plugs. Either I make them or I don't have them. If you find 8-40 plugs for sale, send me that link.

 

[almega]

Because I dont have a single engine that that giant spark plug will fit in. I don't think any of the sparkplug makers care much about making #8-40 plugs. Either I make them or I don't have them. If you find 8-40 plugs for sale, send me that link

Best I could find was 10-40 plugs here: World Famous Rimfire Spark Plugs Distributed by Roland Morrison

BTW, this link started with Brian making a 5/16 plug so perhaps in your instance it would be necessary to make your own 8-40 plugs.

 

[Brian Rupnow]

I think that Steve Huck makes and sells great sparkplugs. I have ran into some weird issues with ignition on this engine I am currently playing with, but it is certainly no bad reflection on Steve's sparkplugs. I'm having some health issues right now, so I'm not forging ahead with this engine as I generally do.---Brian

 

[stevehuckss396]

"BTW, this link started with Brian making a 5/16 plug so perhaps in your instance it would be necessary to make your own 8-40 plugs."

Yes I know. I made the original purchased plug for him. I'm not too sure you can find a 5/16 plug either. He also had call for an extended length plug a few months back. It's easy to say just buy one but finding something that works for your design can sometimes be impossible. I guess the point is that he made one because he couldn't just buy one. The idea that he should just buy one when they are only 6 bucks made me laugh. He had to make what didn't exist. That's why you make one.

 

[almega]

Brian - I hope you are able to get past the health issues soon. It's not fun to be down and out.

stevehuckss396 - Not trying to be contentious here and certainly no animosity toward anyone. Given the limitations of products available in the sizes we are working with, I understand the need sometimes to make our own widgets or sometimes we just want to take on the challenge to make something that may be available. This whole discussion has been instructional for me as I was not aware such small spark plugs could be purchased at the outset. Now that I am aware they are available at such modest prices, I doubt I would make one and I will design the head(s) of my engines to accommodate what I am able to purchase. That is just my chosen path, not a path that I am proposing anyone else follow if they want to go another way. As I have learned on this forum, there are many ways to approach any problem that arises. Peace to all.

 

[johwen]

"I am thinking it is an interesting challenge to build your own spark plugs but with them available at $5.99 each, why bother. That would be like making your own nuts and bolts. Check out this link."


Because I dont have a single engine that that giant spark plug will fit in. I don't think any of the sparkplug makers care much about making #8-40 plugs. Either I make them or I don't have them. If you find 8-40 plugs for sale, send me that link.

Hi Steve,
Model engineering is all about making stuff. Some guys make the tooling to make the stuff making spark plug is a synch. With the materials at hand takes me around an hour. all it takes is about an hour and 90% of the time is turning the body and centre electrode the Loctite together and you've created something yourself. johwen

 

[stevehuckss396]

For me it's mostly necessity. I build small and that means having to make stuff that isn't available. Piston rings is another thing. I make them because 5/8 inch rings just aren't out there. I have even made nuts and screws because what I needed wasn't available and I wasn't willing to compromise. Believe it or not it happens.

 

[simonbirt]

Has anybody experience of using home made spark plugs with Corian or PTFE insulators in high revving engines? The reason I ask is I made some a while back with PTFE which has a slightly higher temperature tolerance than Corian. These work fine in my Farm Boy, in fact it is still running on the original plug. Hit and miss engines run cool. I am now building a 4 cylinder Seal which may be a more demanding application, PTFE doesn’t melt as such, it vaporises at arround 360 deg C or 620 F. Corian I believe has a lower melting point. I imagine it is the cylinder head temperature that is important as the combustion temperature is transient and obviously much higher than the melting point of most of the materials we use to contain It.

By the way, the drawings for my plugs are on another Spark Plug thread. The PTFE insulator is held in by swaging, which works well.

 

[mayhugh1]

There has to be more to it than that. I have had the same plugs in my Peewee since first start 2010. No electrode erosion of any kind. They still work very well. My theory is that the gap is huge and the voltage has to build up to a very high voltage to jump the gap damaging the electrode. Another theory is, if an automotive coil (old school) is being used it may be delivering way more energy (Joules) than the little CDI coil which is all volts and no amps. Or theory number 3, Both!

Something to keep in mind with a points-type or simple transistor ignition is that energy is being built in the coil during dwell - that's the time the points are closed or the transistor is ON. In a multi-cylinder engine the dwell is necessarily limited to tens of crankshaft degrees since the coil has to service other plugs. The resistance in series with the coil is often minimized in order to get enough current through the coil to build enough energy in the time allotted for each plug.

In a single or dual cylinder engine, the dwell is huge. The points spend most of their time closed, and if an automotive coil with insufficient series resistance is being used, the energy built is much more than needed in a model engine. When the points open, and all this energy is dumped into a single cylinder model engine plug, you're going to greatly shorten the life of the plug. If you also run a really wide plug gap, that excess energy will show up as some terrifically high voltages during compression that can result in a rash of arc-over problems that a typical plug isn't designed to handle. (i.e. it doesn't have a 3 inch long insulator).

The solution for a single cylinder model engine isn't to design a beefier plug or to use exotic metal electrodes. The solution is use a coil designed for model engines, or reduce the coil voltage, or add resistance in series with the coil, or to use a capacitive discharge ignition that works independent of dwell.

When testing a model engine ignition by firing a plug in open air you're looking for a thin blue spark - not a fat yellow-red flame. A flame is telling you that something is burning. - Terry

 

[Bentwings]

I am thinking it is an interesting challenge to build your own spark plugs but with them available at $5.99 each, why bother. That would be like making your own nuts and bolts. Check out this link.

https://www.rcgfusa.com/product/stinger-spark-plug/

ha ha I like that yes there are small model spark plugs. I thing most builders are going to automotive plugs as they are readily available . All my Rc engines have them I haven’t used a small model spark plug in years. I know room is usually the issue but if you want to make them and they work fine just another project
Byron