earlwb

Cool, thanks for the info. So it is a OK plug then.
I'll update the picture post above.

iskandar taib

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HOLY COW!!! There's some here for sale, and photos, too:

http://pages.treasuredantiques.com/1...923941090.html

There's even a photo of the sheet of paper that came with them.

Iskandar

Sport_Pilot

I think 1 1/2" is too large and 1930 too early to be a model engine plug. Mr. Brown had built his first hand made version in December of 1930 and he hand built the spark plug as well. He sold a hand full of engines in 1933 and 34 and most people could not buy one till 1935 or so.

ZAGNUT

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it wouldn't be much larger than this: http://sparkplugs.morrisonandmarvin.com/v.php which was patterned after the champion plug.

also, being offered as souvenirs they may not have been made for models at all but just as a demonstration of how awesome AC was at the time......modelers discovered them and the rest is history. being those are from '33-'34 it sounds right to me.

earlwb

Those are a pretty neat find for sure. I remember someone telling a story about a small model engine company that was first starting out. One of their engineers or designers happened to see those at the World's Fair and he used up all his money buying as many of those as possible and borrowed money from his family members to buy more of the spark plugs too. A while later they started selling a model engine that used those spark plugs. If I remember correctly, I think they had a vending machine and you purchased them from the machine similar to buying large ball chewing gum out of one. The spark plugs actually worked too. But they were being sold more as a novelty though. But AC apparently made and sold the little spark plugs up until WWII got into full swing. I am thinking it was for Brown engines maybe at the time.

Those AC plugs are likely 1.5 inches long but were a 3/8x24 thread size.

iskandar taib

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The World's Fair in Chicago was actually in 1933-34, so it's about right in terms of the time frame. Zagnut, please read the story I posted - it's paraphrased from a Model Aviation column, wish I could locate it again. These plugs were being sold out of a gumball machine outside the GM pavilion, and were indeed made and sold as souvenirs, but as the piece of paper says, fully functional. Imagine being involved in making (inventing!) model engines and having to make your own spark plugs using mica insulators - finding a gumball machine full of these would be like coming across manna from heaven.

Yeah, 1 1/2" is a little big for today's engines, but there wasn't anything smaller back then, and they would have worked. 3/8" would be right.

Iskandar

ZAGNUT

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yeah, i read it, was trying to convince sport pilot that those were indeed the same plugs mentioned in the story.

interesting that this was pretty much the same time frame that porcelain insulators and the means to seal them in a one piece plug were developed..

Sport_Pilot

A year too early.Brown sold somethinglike 70 engines from 1933 to 34, then 5000 in 35. You could not buy a Brown in a hobby store till 35.I think Brown made his own plug on the earlier 33 to 34 engines, it had a mica insulator. The plug was about 3/4 inch tall, I have seen larger plugs installed in pictures. Not sure of the thread size. I thought most were either 5/16 or 1/4.

ZAGNUT

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i would highly doubt that Brown was the only guy developing a model engine at the time, he was just first to market.

Sport_Pilot

Well perhaps they were used in a larger engine that came out later. I say larger because that plug would look really odd on an engine the size of the Brown. Perhaps one of the .60 or .90 engines back then,

earlwb

Well the first Browns were .60 size.  But yeah there were some O&R engines, Forster,  OK engines and so on too. They actually made some .29 engines that used that size spark plug too.  But it wouldn't be unreasonable to see someone getting the spark plugs and then making a engine to use them for  the next year.

iskandar taib

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Yeah, the Brown Jr. was a .60. Engines back then also used to be taller (longer stroke, perhaps, or longer conrod) so the plug wouldn't have looked out of place.

I think I'll have to hunt for the article again - there were names mentioned, I can't recall who it was who cleaned out the gumball machine. Don't think it was Bill Brown, but it might've been.

Iskandar

ZAGNUT

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the little NGK CM-6 which just about the same size as those AC plugs looks right at home on this .60:

Sport_Pilot

I rhought the first Brown's were .45?

OK that was a pre production engine. The Brown production was a .60. But a much longer stroke and smaller bore than a modern two stroke .60.

Sport_Pilot

The cylineder from fin to fin is probably over 2". If so it would be about right maybe a bit smaller than the AC. But it would look odd on the smaller Brown.

iskandar taib

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Hmm! Some actual photos here:

http://www.craftsmanshipmuseum.com/BrownJr.htm

Yup, those plugs look HUGE in relation to the engine. Very interesting read - lots of ups and downs. Apparently Bill (IV) started building engines while in high school, later his father (Bill Brown III) got involved, found financing and started up the Junior Motors company to make the engines.

I was under the impression, before reading this article, that mica-insulator plugs were crude things - I imagined a stack of mica washers separating the electrode from the plug body/ground. In actuality, this is how plugs - in particular, aero plugs - were made in the 1920s and 30s. You can't actually see the mica on the outside, it's buried within the body of the plug. Here's some photos:





Article abstract about inadequacies of mica-insulated aero plugs (from 1940!):

http://papers.sae.org/400145/

Iskandar

iskandar taib

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Just spent the day analyzing plug filaments. I had a bunch of data before, but I just got a shipment of plugs from the US, including quite a few car and turbo plugs. Sort of curious to see if car plugs were very different from airplane plugs, actual run tests will probably take place over the next couple weekends. I've got turbo head buttons for my Foras and Profis, and my OS .15LAs will serve to test the regular 1/4" car plugs. Yeah. I'm not interested in idle, so I really don't expect too much in the way of dissapointment.

So far, it looks car plug elements use the same alloys as airplane plugs. Hot plugs are typically Pt + Rh, cold plugs Pt + Ir or Pt + Rh + Ir. This cuts across both aero plugs and car plugs - hot car plugs use the same element alloys as hot aero plugs, cold car plugs use the same element alloys as cold aero plugs. The similarities are particularly striking within a brand. This does not mean they're identical, of course, there are other things that control heat rating other than alloy. For instance I'm also taking measurements of wire diameter, cavity diameter and coil diameter. To do a really thorough job I'll need to section the plugs, but I'm not going to go that far just yet.

The only truly weird plug I found so far was this one:



I had absolutely no idea this existed. The element is also very weird - very large diameter spiral, large diameter wire, and only ONE turn in the spiral (which is consequently very steep). The analysis gave 94.5% Pt and 5.5% W. Al Kelly told me about early pre-RC racing plugs containing W, but this is the first one I've ever come across - and I've looked at Rossis, McCoys, OPSs, STs, etc.

Iskandar

ZAGNUT

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maybe the tungsten would add strength at elevated temps?

ZAGNUT

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and on the world's fair story: just read somewhere that the commercial champion and AC 3/8" plugs came out in '36 and that Ohlsson had been working on an engine from around '34.

iskandar taib

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Yup, that's what Al said. The drawback was it made the plug colder. It's not used any more, as far as I can tell, I've been trying to find old CL racing plugs from the 50s and 60s to see if I could find any that used tungsten, this is the only one I've found so far.

Iskandar

iskandar taib

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Here's a possible use for that plug:

http://www.modelairplanenews-digital.../?pg=118#pg118

No, I don't mean the Enya engine being reviewed. In the article, Clarence Lee mentions that the B-24 and B-17 had a APU on board - which was a glow-ignited gasoline engine!! This predates model glow engines by a few years. This one does seem a little small, though - perhaps there were other small, gasoline engines - lawn mowers, etc. that used them. Also, I used to think automotive/truck diesel glow plugs were a recent thing. Nope.. if you're checking out patents you'll find some for these from the early 20th century. Some of them were probably as crude as these - modern ones tend to be ceramic on the outside with a filament sealed inside.

Iskandar

iskandar taib

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Wow.. one for sale with the packaging!

http://www.ebay.com/itm/350832949921

Iskandar

earlwb

iskandar taib,  That is a pretty neat find there.