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thanks all, I'll borrow the retract design. Seems perfect. Model engine carbs aren't air tight valves, they're actually pretty leaky. They also don't close down perfectly, they stay open a bit for idle (not really a valve). They're also about as expensive as buying a whole new model engine...

I made one of those carbs to use on another engine (same displacement). I discovered I could get a lot more RPM out of the engine by increasing the carb throat to 7.5mm but then became picky about needing muffler pressure in the fuel tank. You may want to try a few different sizes if it's an...

Sounds like exactly what I want except it seems to be a check valve.

that's a great idea! How do they use o-rings to keep the rotating part sealing the input from the output? Do you have any pictures that would help?

yeah, I've got an adjustable height tool post and that's how I do it when I'm matching tapers. Do the outside as normal, then remove the tool insert a boring bar upside down, and crank the height up till it's on center, and do the inside taper. I usually just use my normal boring bar holder and...

the problem with silicone is it breaks down in the presence of petroleum fuels. I like the idea of the 3 sheets! I suppose a disc between 2 sheets with a slot in it would work too, just turn the disc. The trouble with either of those is making it air tight.

Of course it works this way. Wrack my brain for a few days, come up empty. Post the question to the forums, the ideas start flooding in. I think maybe something like a needle valve, a conical needle going into an accurate hole, pushed in by the servo instead of with threads.

I need to make some type of valve to hold small air pressure (less than 5 psi) and be operable by a standard size RC servo. Having serious trouble coming up with ideas that aren’t high drag. I could use a cam-lock type clamp on a piece of tubing, but I dislike crimping the tubing, it kind of...

matching inside and outside tapers! Set the compound, cut your outside taper on part A with the regular way. Flip the tool upside down, leave the compound the same, bore the matching inside taper of part B on the back side. Part A will be a perfect angle to fit part B. This not only matches the...

actually now that I think about it, why not use the actual real cylinder, and clamp it in with a fake cylinder head with a big hole in it? that way any distortion from clamping forces gets honed out.

yesh that's hard on the fingers! I'd previously been making a fake cylinder that slides over it (not the full length just the top 1/4 or so) and a fake cylinder head to clamp the rim out of some 1.5" square bar. This time I just lapped when the cylinder was in the boring setup, then did...

good stuff...I like that hone design a lot better than mine. Do you hold it by hand or in the tailstock?

Great idea! How critical is that hole since the restriction is the needle further up the fuel line? My next closest drill size I have is 0.045" (1.1mm)

I was running a really sweetly running RC gas engine the other day that I've got hanging on my favorite model airplane. Did a great flight, landed, killed the engine with my ignition cut switch on the transmitter, checked the battery, topped up the fuel, and went to restart it. Flipped my arm...

fantastic! I can't wait to get started! Gotta order some steel for the liner. I have a pile of 6061 kicking around, would that be good enough for the block? I've started with the carb, since I need a carb for another commercial engine I'm making a liner for at the moment and carbs had scared...

oh, I don't think anyone's mentioned yet, but for the first little bit, purchased stuff might be the way to go, since with feeds and speeds on unknown materials, the wisdom comes after you need it. If you know what you have, you can just look it up.

that's right! the one copier I took apart had some really, really nice shafts in them. Machined beautifully too!

nevermind on the magazine number, I looked on the first post and it's right on the cover! I wonder if they'll ship one to Canada... Does that one issue have everything you need articles and drawings wise to build it?

That thing is gorgeous! I've been looking for a good "from scratch" glow engine to build since I've done all these worn out glow engine re-lines and I've convinced myself I can make a liner/piston fit properly. I don't subscribe to the magazine, is there somewhere I can buy the plans? Or, what...

I go through piles and piles of 1/2" bar making odds and ends and tools and holders and things. Find the largest thing that will fit through your headstock, buy a couple of feet of it (cheap aluminum or something that's relatively easy on you), turn till you're moderately uncomfortable with the...