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There's a question in here... But first some background info... My old lathe chuck has jaws that were slightly bell mouthed and resulted in inconsistent chucking. I was able to correct them fairly well by loading the jaws with a shop made fixture then running them through with a carbide boring...

Thanks Phil! It is indeed a bar stock engine. The engine was designed by J.E. Howell and plans are sold by his son Allen. http://www.model-engine-plans.com/ A video of it running can be found here: http://www.youtube.com/watch?v=DoI33CuWYsU John

It's almost done! I made the fuel tank today which has an integral check valve. All that's left to do is to make a buzz box look-alike to hold the ignition circuit, add a battery pack, and to take it all part for painting. John

UK source for 2N4124 http://www.digikey.co.uk/product-search/en/discrete-semiconductor-products/transistors-bjt-single/1376376?k=2n4124 John

We've got a winner! The Corian insulator with a slightly increased gap (0.030) and a shorter insulator to allow for more electrode protrusion... Engine runs as good, if not better, with this plug than it does with the Rimfire VR2L. John

Hi Jack, Now that's what I call a pretty spark plug! Nice work! I really like the rebuildable design. It's remeniscent of very early spark plugs from the turn of the century. Is the body brass or does it just look that way in the photo? Cheers! John

Be careful specifying the 2N3904 as a replacement for the 2N4124... It'll likely work, but the circuit wasn't designed for that unit. The 2N4124 has much higher DC current gain (Hfe or Beta) than the 2N3904, especially operating at a switch. When a transistor is operated as a switch (i.e...

I've tried several different Hall sensors with this circuit and all worked reasonably well. The clear winner for performance and reliability is the OH090U from Optek. Those things are absolutely bullet proof. Not being one to follow my own advice, I was grounding my engine with just a...

Thanks fore the vote of confidence on the Corian. I like the looks of the swage but it does have one major drawback... It basically means I need to make a new spark plug body every time I change something. It's hard to undo the swage without damaging the body. I figure using just epoxy...

Admittedly I contributed to the failure. I was running the engine under load with 10% glow fuel. I was trying to have the engine hit on almost every stroke to see how the plug would hold up. Parenthetically, I was really surprised how much power the Farm Boy makes! All in all, the Farm Boy is a...

I made the first plug from Corian last night. I like the Corian much better. It machines easier and is much more rigid. It also allows the insulator to be glued into the spark plug body. It is a bit brittle, but machines easily with sharp tools. I didn't take any pictures... Sorry. I do...

Thanks Bill, As far as run time, it's hard to say. Maybe an hour or two before the engine became hard to start. The open circuit voltage is still OK but the spark became weak and the engine flooded very easily. John

Beautiful engine! Thanks for sharing... John

Found some white off cuts on ebay. Enough for many plugs! Thanks again! John

Beautiful spark plugs, Steve! Where did you get the Corian? I'm a purist, so I'd want white... I'll give it a try if I can source some... Thanks! John

Well, back to the drawing board. Spark plug v1.00 still works but the engine was getting hard to start, then it blew the top terminal an electrode right out of the insulator. The tip of the insulator looks like it melted. I guess it's time to try Corian. The Teflon is SO soft... Any other...

I just completed a JE Howell Farm Boy. It's been running off a 6V supply generated from 4 AA cells. After those batteries called it quits, I've been using a battery charger. So, what's a good battery technology to use? I'd like it to be small and easy to hide. Also, easily rechargeable. The...

And last but not least, the drawings.... Enjoy! John

Swage the insulator into the body. This was done with a suitable and dull lathe bit. The lathe was turned by hand in reverse while pressure was put on the tool to roll the body over the insulator. The completed spark plug (except for the top nut) Installed in the Farm Boy A...

Start making the insulator from Teflon Screw in the terminal. Per the drawing, there is a small groove cut into the thread on the terminal using a Dremel cut-off wheel. This allows the threads in the insulator to be formed using the terminal. The insulator will cold flow into the groove and...