Shop built sparkplugs for model engines

[Jasonb]

Yes the body of the plug would be better off drilled through say 1/8" and the 3/16" hole stopped just short of breaking through which combined with the 1/16" electrode would mean a 30thou gap.

Adjust the 1/8" hole to get the desired gap eg if you want 25thou then use a #33 or 2.9mm drill

 

[Rocket Man]

WHY build your own spark plug they come in 100s of, sizes, shapes, lengths, threads. You can make adaptors so any spark plugs will screw into any engine. I buy 1" long sparks plugs from O'Riley auto parts they cost $3 each. I thought this photo would show the 1" spark plug but its on the back side. I don't remember part number, I have to walk out to the shop to see what the # is. Spark plugs also come in smaller sizes 3/4" long and 1/2" long.

 

[Carbuilder]

WHY build your own spark plug they come in 100s of, sizes, shapes, lengths, threads.

Seems like kind of a strange thing to say on a forum like this. Why make anything when you can buy it? I do it for the challenge. If you just want a part to get a job done, then fine. But the satisfaction of designing and making something that didn't exist before you made it.....as the ads say....priceless!

 

[Rocket Man]

Seems like kind of a strange thing to say on a forum like this. Why make anything when you can buy it? I do it for the challenge. If you just want a part to get a job done, then fine. But the satisfaction of designing and making something that didn't exist before you made it.....as the ads say....priceless!

Do you also mine your own iron ore, cast & forge your own metal, make your own, nuts, bolts, screws and make your own paint. I build engines too but I buy several things I need, nuts, bolts, screws, set screws, metal, belts, piston rings, pins, roller bearings, O'Rings, pipes, spark plugs, gasket material, valves, springs, paint, oil, grease. I design my own engines I don't build kits. I never would have guessed people make every single part they need. I worked as Design Engineer for many years in factories we built special machines but never made parts we could buy like, electric motors, gear boxes, bolts, flat washers, nuts, chain, V belts, sprockets, gears, hydraulic pumps, radiators, rubber hoses, electric wire, wire connectors, electric boxes, fuses, switches, relays, etc. I know what you mean the satisfaction of designing & building something. For each his own. Have FUN. I almost forgot to mention fire clay works good in spark plugs don't add more than 3% water mix very well then hammer it to compact it very tight in the hole with home made tools.

 

[Brian Rupnow]

Something you should know---I'm not Mister sparkplug. Like I said, the last one I built was about 13 years ago. I'm sure that the arcing on the outside of the sparkplug was because of the relatively huge 1/16" gap at the business end. I didn't know it was going to do that, or I would have made the sparkplug 1/2" longer. See--now I know something that I didn't know before. Before I do anything more, I will pull out the sparkplug I made and put the one I purchased in instead. I'm sure it will work fine. If it does or doesn't I will let you know.-------I spent today making new cabinets for tooling. It was very nice not being Mr. Machinist for a day.

 

[Brian Rupnow]

The tip of my new sparkplug electrode is almost totally eaten away by what I assume is spark erosion. Does a tungsten electrode resist spark erosion better than steel?

 

[stevehuckss396]

Pull the gap back to about .020 to .025 inches. A gap that is too large will stress the s#!* out of the ignition system. The coil has to work way too hard to jump the gap. Excessive volts means excessive energy that is not needed to ignite the fuel. That creates stress on the coil, plugs, and the CDI or points.

The Gap on my V8 is only .012 inch and works just fine. 1/16 inch is just way too much.

 

[Brian Rupnow]

Steve--I'm in the process of a redesign to my sparkplug right now, and the new design reduces the spark gap to 0.030" I ask about tungsten withstanding spark erosion because I have 1/16" tungsten electrodes for my tig welder that I can use..

 

[stevehuckss396]

If you get the gap down to 20 to 25 there will be way less wasted energy and the music wire will be sufficient. Be much easier on the coil too.

 

[Brian Rupnow]

Okay---still in design phase here. Will set up for a 0.025" gap.

 

[Brian Rupnow]

Perhaps the large gap of 1/16" accounted for the rapid spark erosion of the center electrode.

 

[trackmaggot]

If you decide to investigate Tungsten electrodes, you may be interested in micro torch electrodes. You can get them in .5, 1.0 and 1.5mm diameters. They are 66mm (2.6 inches) in length, and come in packs of 15 for 45USD.
Link below for reference

https://sunstonewelders.com/orion-micro-tig-welding-electrodes

 

[gilbycoath]

i have not made a spark plug, I have under construction a Westbury Seagull.
So my suggestion maybe out of order. but I have a collection of Nichrome wire for the plugs, my idea of what might be a good material.
Haven't seen it mentioned before

 

[TonyM]

Nichrome has high resistivity and is used for heating elements, Whether it is enough to make a difference between that and tungsten or carbon steel in a small spark plug I do not know.

 

[Jasonb]

Brian, I have used tig electrodes for spark plugs and the contacts on ignitors and no signs of errosion

Plug gap was smaller than your 1/16" but if you make the body like I showed it won't be a problem as you can set the gap by the hole dia at the end.

 

[Steamchick]

The tip of my new sparkplug electrode is almost totally eaten away by what I assume is spark erosion. Does a tungsten electrode resist spark erosion better than steel?

Yes!
But if simple points ignition, try reversing the polarity? Or take an old car spark-plug and use the core electrode and side electrode as the material to make your own. (BE VERY CAREFUL when breaking off the ceramic! Wear proper eye protection!) Often these are odd alloys?
Nichrome is OK as the resistance won't affect the spark.
K2

 

[Jasonb]

I'd rather change the electrode than the polarity, Your spark plug body has a lot more work invested in it than a length of music wire and being a lower carbon steel than the wire will probably erode even faster.

 

[Steamchick]

Hi Jason, not knowing much about spark erosion, why does more carbon (easy to burn off in a spark!) make the iron molecules erode slower (or quicker?).
I can cope with a more massive molecule - like tungsten - needing more arc energy to erode a molecule, but iron is iron, carbon is carbon, and I know it changes the crystalline structure to change the mix, but I am without knowledge of the arc resistance of steels.
K2

 

[Jasonb]

Just an assumption that the unhardened body of the plug would likely be eroded quicker than the hardened electrode, even if it were no slower I'd still not want to have the body get eroded by swapping polarity as it would have taken a lot more time to machine than just cutting the electrode.

 

[Steamchick]

Fair comment Jason. But sometimes life is a compromise. The tiny bit of central electrode may be too small for sensible running lifetimes, but the body metal may be tens of times more, and thus more durable. But that only works if the polarity reversal makes a difference!
K2