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Ahh -- for infernal combustion 2-strokes, the rule of thumb is to put half the reciprocating weight on the crank pin, and then balance the assembly. If you don't hit it exactly, you just remember that your motor can't be perfectly balanced anyway. (But aside from having a nifty counterweight...

Putting in the physics that Brian leaves out, and hopefully not confusing things too much: the moment of inertial is proportional to mass times radius squared, where radius is the distance of that mass from the center of the circle. After a whole lot of math (or cheating by looking at tables...

So, your method of machining eccentrics is always -- eccentric?

Gaah! I just mucked up my bearing block! I should have used blocks to keep the chuck from digging into the ends. Next one I'll do the mount ring first (when the ends are solid!) then bore it out and do the bearing holes. Which I have to get right again, after sweating bullets the first time...

After I did the above, I decided that I wanted the groove to fit entirely inside my 1/2" square bar. This entailed not just making the diameter smaller, but reworking my tool because it was not clearing the 0.44" OD of the trepan. But the test cut came out pretty good; I feel confident in...

How do you make the insides of those cross-head guides smooth enough that a cross-head will be happy sliding therein?

No scrapyards in your area? There's one just down the road from here that sells steel, copper, brass, and aluminum by the pound. Of course, it's often mystery metal (although I do have some 6061 from them that came marked). Granted, I haven't checked to see if they're still here given COVID.

You could make steel flywheel tires for shrink fit on aluminum wheels. Polish up the steel, heat it until it's a pretty color, drop the aluminum in and let it shrink. It should give some corrosion resistance while you're at it.

I'm really late to the party (actually I was looking for Twingle plans on the web and found this). What may not be apparent in the drawing is that a single, rocking connecting rod will bind if the attachment to crank and wrist pins is perfectly rigid. That's because the paths described by the...

Don't buy electronic components off of eBay (Sorry @doc1955) At least not common chips like the 555 -- you can get them cheaply from real mail-order suppliers. DigiKey, Mouser and Newark in the US, Farnell (I think) in the UK. Counterfeit chips are a thing, you can trust a distributor, and it...

If I were the same guy who came up with all the bitty parts in the Citroen DS suspension, or whoever it was at Bristol that decided that a 9-cylinder radial engine should all the complication of sleeve valves (all those gears!) instead of a couple of bump rings, roller lifters and tappets, I'd...

I feel like it's too late for this comment since you're already commencing work -- but if you put the valves on the bottom and the power cylinders on the top, you'll be driving the flywheels with the crankshaft without any major changes to the rest of the engine. (Well, aside from making it...

Y'know, everyone motivates themselves differently. But if I were in your shoes and started despairing that the thing would ever run, I think I'd try gasoline (or ether!) just to make sure that the rest of the engine is functioning correctly. Once I'd verified that the only salient problem is...

So, to solve a problem with figuring out how to hold the work in my Smithy in milling mode, I decided I'm going to trepan a slot in the bearing block, and make a matching dingus in the post. I've just trepanned something for the first time ever! And made a trepanning tool for the first time...

So, curiosity here since I seem to be in the company of folks with more glow expertise than I possess -- and possibly way more throttled glow engine experience, because I've been flying mostly control line for the last decade. I know that there's a mantra in the US at least "more nitro will...

Remember that if you skim the head and overshoot, you can always make head shims. I'm not sure where you fly or availability of fuel, but getting it working on 5% nitro, or even 0%, shouldn't be hard. Then, if you want to fly on higher nitro (or find you need to adjust the compression for the...

Hah! I put it in an electric skillet set to 350F (probably way hotter than necessary, and only as I write this do the words "temper" and "draw" zip through my brain), and it popped right out. Next time I won't get it so warm, if there even needs to be a next time.

I'm quite happy. I inherited a bunch of mechanical and electrical and electromechanical doodads from my Uncle, who passed away 30 years ago. In all the stuff is a little tube with some very sweet little bearings, 3/16" ID, 5/16" OD, and about 0.110" long. I'm going to use these to support the...

You could always go with a Kettering (points, condenser & coil)! That's pretty easy.

@Ramon You could use a wavy washer to spring-load the thing. Or maybe a really skinny Belleville washer. Even once you're past the need for it to be custom-made, I can see all sorts of difficulties with getting the material and temper right so that it stands up under heat cycling and...