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On your tool: it looks like you're using a fairly coarse grit on your grinder -- you may want to get a finer grit wheel if you want to invest in this (my grinder has a coarse and a fine wheel, all the time). Even so, the cutting edge should be sharp -- make sure that you've relieved it enough...

Or throw in the towel, use a 1:1 gear ratio, and put pen clickers in your lifters: Engineers Explain How Click Pens Work - Pen Vibe (And if the facetiousness irritates rather than amuses -- say so and I'll try to stop. It's just that you've gone and made exactly the kind of mistake that I...

So just put a bigger flywheel* on it, stick your nose in the air, and explain to people that it's a 4800 stroke engine. An external valve that swaps the exhaust with the intake when the cam is exactly 180 degrees out of what it should be might be a good idea, but then it'll be a 2400 stroke...

Welcome! So -- have you built any engines?

That seems like an awfully long valve duration for a slow engine. I'm +1 on the suggestion made by @dsage to look at commercial cams -- but to that I'd add that even a boring old stock cam in an automotive application is designed for some degree of extra time to give the valves time to do their...

Of course! The only discussion I've seen on this topic was for totally home-built engines, where the advise was to turn the taper on the crank and the prop driver with the same setup -- but that gives you no help when you're trying to make a part for an existing engine.

Brian, I suspect we have opposite aesthetic sensibilities here, but I'd leave that flywheel painted, and run the engine long enough so that the paint is just naturally worn off by the belt. Shiny metal surfaces that got that way by honest wear says "this is a hard-working machine" to me.

Vietti -- Balancing Small Engines by ET Westbury: Page 2 But no single-cylinder engine is going to be perfectly balanced; the best you can do is minimize the vibration. And some designers purposely under- or over-balance, depending on whether they want the engine vibration to be weighted (as...

Control line speed is alive and well in the US. These days it's more taking production engines and modifying them -- but the mods get pretty heavy.

I was wondering why no counterweights when I saw that shaft -- now I know. I assume you didn't want to start with an even bigger hunk of steel from which to machine the whole thing in one piece.

On the control line stunt forum, my location is given in lat/lon, with enough digits of precision that you can land a smart bomb on the toilet in my garage. I like checking Google Earth's maps from time to time, to see what the state of my field was when they took it -- there's a control line...

@Steamchick : it is utterly irrational, but if I built a model stationary engine, I'd feel bad if I didn't put it to some use where it would have the opportunity to deliver value until it wore out. Even if it was just some "hobby" value, like running the generator that runs a model train track...

@Steamchick : I know that glow plugs are 1/4-32, but I've been assuming they're NSF. Certainly, the 1/4-32 'merican tap that I bought makes perfectly good holes for glow plugs. @Cddeshon: I think you know this already, but you can get spark plugs with that same 1/4-32 thread. For these...

Sorry -- I didn't mean to say that you should go off and do a bunch of work just because I think it would be nifty, or that I think less of you for not attempting the theoretically-possible-but-ridiculous. I was just spinning off on an improbable tangent. For the scale you're working at, using...

That's actually what I was alluding to by the "without compressed oxygen" comment -- you may be able to scale down the flame ignition chamber, but only if you changed the chemistry of the gas jet inside of it.

OK. Interesting. Thanks.

Hey Brian -- you may have covered this already, but what are you doing for keepers on the valve stem ends? The ones that I've dealt with (old Toyotas and even older Chevys) were split cones that engaged with a shallow groove on the end of the valve stem. I can't see successfully scaling that...

Those are really cool engines, by the way. One of those is on the longer version of my "to-do" list. I figure that at the rate I'm going I should have the necessary skills when I'm about 150 years old. It's neat that you've dedicated the time to making it work in model form.

The fact that I can see that you obviously know what you're doing is having a war inside my head with your statement about flame ignition, and the behavior I've seen with those micro-mini welding torches that'll produce an oxy-acetylene flame just an inch long. Maybe it's trying to run things...

The rule is that the business end of the plug should be flush with the inner surface of the head. If it's proud by more than a thread or so it'll cause detonation, or at least mess up the combustion chamber geometry -- and there's usually not a lot of clearance in there anyway, especially if...