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Spark Plugs

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Spark Plugs

Unread postAuthor: Lockednloaded » Sun Sep 12, 2010 12:02 am

I Am in the building stage if a medium sized hybrid, and I only lack one major component. I still need a spark plug capable of handling 10x mixtures. I don't know if I should use a real car or lawnmower spark plug, or just make one myself. The port that is left for the spark plug is a 3/4" threaded opening. I have appropriate reducers to get it down to 1/4" or 1/2", so I think an epoxy spark plug inside one of a bushing would work, but it may be troublesome. I'd like to have as small a gap as possible since I'm using a BBQ ignitor.

sorry, but in conclusion:
What threads do lawnmower/car sparkplugs have?
Will a lawnmower/car sparkplug be able to arch at 10x
How well would the electrodes of an epoxy spark plug be held in place?
How small should the gap be with piezo-electric ignition?
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Unread postAuthor: ilovefire » Sun Sep 12, 2010 12:09 am

well not sure about the rest but if you want 10x then you will want a spark gap less the .5mm if your using a piezo
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Unread postAuthor: Technician1002 » Sun Sep 12, 2010 12:18 am

Note that regular combustion engines have compression ratios in the range of the mix you mention. Spark plugs work fine with a proper ignition coil. High octane fuel is used in high compression cars to prevent knocking.

High compression is considered in the 10-13:1 ratios. Normal low compression for pumped gas uses 10:1 or less. A typical compression is about 8:1.

http://en.wikipedia.org/wiki/Compression_ratio#Petrol.2Fgasoline_engine
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Unread postAuthor: MrCrowley » Sun Sep 12, 2010 3:38 am

I use spark plugs at 10x mixes and if I recall correctly I had to force-thread it in to a 3/8" fitting and then JB-Welded it to be safe. You can get them with NPT threads, I have no idea where or how you can tell. I've been looking for some recently and they all just list their thread diameters in millimeters but not whether they're NPT (or BSP for that matter).

I just use the cheap ones by the way, not sure how much better the expensive ones are. SpudBlaster15 uses them with an electric BBQ igniter I believe though I use a stungun myself.
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Unread postAuthor: Hubb » Sun Sep 12, 2010 4:20 am

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Re: Spark Plugs

Unread postAuthor: Heimo » Sun Sep 12, 2010 5:03 am

Lockednloaded wrote:What threads do lawnmower/car sparkplugs have?
Will a lawnmower/car sparkplug be able to arch at 10x
How well would the electrodes of an epoxy spark plug be held in place?
How small should the gap be with piezo-electric ignition?


1 the car spark plug I have in fromt of me now (champion N9YC) got a M14 x 1.25 thread on it, it is a non standard thread so obtaining a tap for it is a little more difficult that obtaining a normal tap go to specialty tool store...

2 I am pretty sure it would since the gap on this plug is smaller than 0.5mm

3 I don't know but I am going to find out soon since I made one a few days ago for a small hybrid I am building
Image

4 According to JSR it should be smaller than 0.5mm the gap on the above one I made is 0.26mm
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Unread postAuthor: Crna Legija » Sun Sep 12, 2010 6:12 am

the suzuki dr 250(not sure what year spark plug has 1/8'' nptf threads which would mach any normal 1/8'' inch threads
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Unread postAuthor: whoa044 » Sat Sep 25, 2010 9:43 am

Please don't modify the threading on anything -_-
If you want 10x mixtures, what would happen if you screw up?

I was hoping I'd get to post a little earlier, but here it goes:
You can find spark plug to NPT adapters here. From there, I'm sure you could use a bushing if you need a larger size than 1/2 inch or 3/4.

I was looking everywhere for NPT threaded spark plugs. The only ones I found were antiques. Then, one unrelated search later, I found spark plug adapters. These have to be the greatest invention for spud ignition systems :P
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Unread postAuthor: Crna Legija » Sat Sep 25, 2010 10:24 am

theirs no need to mod them, its already 1/8'' NPTF( the F is for fuel) which are a little tight on standard NPT taped hole.
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Unread postAuthor: whoa044 » Sun Sep 26, 2010 9:27 am

That's if you use suzuki dr 250 spark plugs.
You can find adapters for 14mm spark plugs, if you don't want too many bushings to go from a 1/8 inch spark plug.
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Unread postAuthor: Lockednloaded » Sun Sep 26, 2010 10:42 am

I made an epoxy spark plug inside a 3/4"-1/2" bushing with coat hangers, the hybrid is on hold though, I'm going to a friends ranch so I need something big and loud
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Unread postAuthor: dewey-1 » Sun Sep 26, 2010 2:05 pm

-_- wrote:theirs no need to mod them, its already 1/8'' NPTF( the F is for fuel) which are a little tight on standard NPT taped hole.


10mm x 1.0 mm is not 1/8 NPTF!
"Close to" is not "it is already".
See drawing.

NGK plugs Suzuki DR-250 is 10mm x 1.0 thread size
Here are the spark plug thread diameters and pitch.

M10 x 1.00
M12 x 1.25
M14 x 1.25
M18 x 1.50

See link for spark plug taps.
http://tools.sjdiscounttools.com/spark- ... t-American
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10mm x 1.0mm vs 1/8 NPTF
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