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The primary pulse is positive, so the diode won't conduct. The flyback diode is built into the part. If the diode were in parallel with the coil however, you'd be right. I like your choice of the output transistor. I discovered those IGBTs designed for logic level ignition coil drive after...

EDIT: This circuit has been revised and improved. See post #11. For my Farm Boy build, I wanted to wind my own ignition coil and build my own ignition circuit. I searched around for suitable circuits, but found virtually all unacceptable. They usually had one or more of the following...

OK, per another member's suggestion, I remade the center section making sure there wasn't a chamfer in the drip tube hole. In addition, I made it slightly longer. While I still don't get drip, drip, drip, the oil now gets attacted to the bottom of the lubricator and I can see it's working. I...

I'll be there as a spectator... John

My digital camera broke and I haven't been able to take progress pictures until today; my tax refund came and I was bale to purchase a new camera. Since my last post to the "First Farm Boy Parts" thread, I've made many more parts and started to dry fit everything... The hardware I used is...

Tung oil would be an excellent choice as would be a good oil based polyurethane. Poly is about as tough as it gets before you start getting into two part coatings. A two part automotive urethane enamel is about a resistant a coating as they come but is likely overkill... But, if you're...

Glacern Machine Tools offers a more affordable equivalent to the Kurt vise... I have one and love it... John

For my Farm Boy build, I made the cylinder drip lubricator per the print. It does work, but I don't get a nice steady drip, drip, drip. The first drip comes out normally, subsequent oil no longer forms a drip but clings to the side of the drip tube and moves upward... The oil then flows down...

And finally (enough work for today), fitting the bearings to the connecting rod, and the whole schmiel to the crankshaft. Here is a closeup of the split bearings, the connecting rod installed, and a "Houston, we have a problem"... Looks like I didn't cut the radius in the back of the frame...

Next up was to make the split bearing for the big end of the rod. Didn't take any pictures of the actual machining but it went something like this: Slit a piece of bearing bronze lengthwise down the middle. Then, glue them back together with CA glue. Next was turning them round to the...

And a momentus moment: a dry fit up of the frame parts, the cylinder sleeve, piston and connecting rod, water hopper and crankshaft... John

Here is the completed water hopper: John

Here's the water hopper. I didn't take any pictures of the water hopper machining itself, but here are some shots of the water hopper funnel being turned. The circular boss sticking out is a separate piece shunk fit into the hopper after the water tank was bored out... John

Thanks Gus! What I have learned about crankshaft making is this: Choice of material is very important. Residual stresses in the metal are your worst enemy. Hot rolled is best. That said, even with the stressproff 1144 I used, the crank still warped during machining; although it wasn't too...

What about hardware store available rottenstone mixed with oil? John

Thanks for the kind words Graham. To answer your question: It's a combination of optical illusion and the fact that the big end is indeed narrower than the journal. There's a flanged, split bearing that has yet to be machined that "takes up the slack". In other words, the big end bearing...

And here's the connecting rod with wrist pin bushing installed... John

Thanks for all the good words! I just finished the crankshaft. It was a challenge to make. Even though I made it from 1144 StressProof, I had a lot of problems with warping. During turning of the main shafts, I removed it from the center and found it running out... A lot! Like 30+ thou...

A reasonable circuit. But, your coil is wired "upside down." The return side of the HV should NOT be connected to the collector of the transistor... I like the way you've AC coupled the Hall sensor so the battery doesn't get drianed or the coil burned out if the crankshaft is left in the...

Thanks for all the good words so far! Since my last post I've: 1) Made the cylinder liner, piston, wrist pin and wrist pin bushing. 2) Completed the cylinder head. Many springs were wound before I got two I was happy with. 3) Machined the front and rear frame halves. John