Mini-jet sparkplug needed

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ss540chevelle
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Mini-jet sparkplug needed

Post by ss540chevelle » Thu Feb 16, 2017 10:41 pm

I've had a Mini-Jet pulse jet lying on a shelf for years and would like to fire it up but it's missing the spark plug. Any info would be appreciated. I'm hoping it uses an RC 4 cycle gas engine plug.
Thanks
Gary

Mark
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Re: Mini-jet sparkplug needed

Post by Mark » Fri Feb 17, 2017 4:47 pm

Looks like a Champion V-3 1/4 32 thread spark plug.
download/file.php?id=2662

http://sparkplugs.morrisonandmarvin.com/v3.php

"The Rimfire V plug for example, replaces the old Champion V plugs used in the early days, the VR2, replaces the old VR2, V3 replaces the old V3, etc."
http://sparkplugs.morrisonandmarvin.com/main2.php

It looks like if you widened the hole slightly you could use the common inexpensive CM-6 plug.
http://www.homemodelenginemachinist.com ... 1342622159

There're people that used to start up the Dyna-jet with a flame at the tail end of the jet I read in a magazine article and I've started a few of my homemade jets that way. I think the very old article mentioned the poorer modelers who couldn't afford the ignition system ....

The original V-3 plug
http://www.antiquemodeler.org/sam_new/p ... 0plugs.pdf
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ss540chevelle
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Re: Mini-jet sparkplug needed

Post by ss540chevelle » Sun Feb 19, 2017 1:47 am

Mark
Thanks for all the info. I have one more question. What is the 'air' connection that is just above the 'fuel' connection?
Gary

Mark
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Re: Mini-jet sparkplug needed

Post by Mark » Sun Feb 19, 2017 2:09 pm

Here's what someone wrote. "The streamline thing on the side of the Minijet is the inlet for the fuel and a compressed air outlet to pressurize the fuel tank."
You can see a little hole bottom left where they are bleeding pressure from the combustion chamber in the first photo. I can't really say positively how it is arranged, whether there's a valve in the fuel pressure line or if it works pneumatically but a member wrote this. "If you look at the lower left corner of the pyramid closest to the air outlet there is a small bleeder hole. There is no valve, so I'll have to find out if it will pressurize the fuel tank when my new valves are done."
download/file.php?id=2656
download/file.php?id=2663

Some tidbits from Jerry, but I wouldn't toy with the reeds unless there's something majorly wrong with them - don't fix what's not broken.
"The Minijet was made by a group of G. M. Gianinni employees led by a John Kloth and first sold in 1946. As you have found, flipping over used reeds is not a good idea because they seldom seat properly. If you make new ones from blue spring steel, I would suggest that you orient the grain of the steel such that it runs from the hold-down strap toward the tip. (Use the same thickness as the originals.) This will reduce the tendency for the metal to fatigue and break across the grain. Mark's suggestion that you "lap" the surface of the pyramidal seats to a very smooth finish is good. Otherwise, the reeds can chip during operation and have too short lives."
Finally, best starting and running is most probable when the reeds are very slightly and carefully curved so that their tips stand open about 1 mm. The curves MUST be smooth so that there are no gaps under them when they are closed by combustion pressures. Be prepared to "fiddle" with the needle valve setting for starting and be sure to not let the Minijet (or any other valved pulsejet,) run lean after starting. Otherwise, the valves will burn out very quickly."
Good luck. dynajetjerry
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ss540chevelle
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Re: Mini-jet sparkplug needed

Post by ss540chevelle » Sun Feb 19, 2017 4:36 pm

Looks like I now have all the information that I'll need.
Thanks guys!
Gary

Mark
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Re: Mini-jet sparkplug needed

Post by Mark » Tue Feb 21, 2017 3:12 pm

I can't figure out what that dead end channel is that's between the needle valve fuel line and the fuel pressure line. In the sketch of it, the photo doesn't show the complete plumbing. I wonder how that middle channel functions?
download/file.php?id=2663
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Re: Mini-jet sparkplug needed

Post by Mark » Thu Feb 23, 2017 1:49 pm

Mark wrote:I can't figure out what that dead end channel is that's between the needle valve fuel line and the fuel pressure line. In the sketch of it, the photo doesn't show the complete plumbing. I wonder how that middle channel functions?
download/file.php?id=2663
The only thing I can imagine is that the bulbous middle dead end channel is some sort of air hammer pressure arrestor.
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