Engines > Your Own Design
Rotary Valve Engine
PaulR:
Following on from this thread https://www.modelenginemaker.com/index.php/topic,12120.0.html, I've drawn up fledgling plans for my next nutty project. This will be a single acting engine with a rotary valve controlling admission at the back and once again made from bar stock with just a lathe (so kept as simple as possible). The original 'scraps and solder' engine uses a side link set 90 degrees off the crank pin to control the valve but I figured this could be done using a second crank disk (or crank arm) and a straight side-link like a pair of coupled loco wheels, so long as the flats on the valve shaft are positioned perpendicularly to the valve crank pin (not sure I've explained that well but the 'plan' might help!). Air would exhaust via a hole on one of the flats on the valve and through a longitudinal hole.
Two things are bothering me slightly about this. Firstly, would the mechanism tend to lock up or would the flywheel inertia get it past the difficult bits? Secondly would it work ok without a crosshead guide? I've seen a few very small engines with this sort of arrangement and no guide which seem to work fine.
Comments and suggestions would be very welcome before I start creating scrap :Lol:
PS Sorry about the unconventional and very rough CAD, I haven't got time to learn to do it properly at the minute!
crueby:
A flywheel ought to get it past the dead spots till the next power stroke. :popcorn: :popcorn: :popcorn:
redhouseluv:
I must've missed the previous thread on this engine design, just read through it. I don't know if the mechanism will work, but it certainly looks like a interesting one.
I saw a mentioned making it with an eccentric first then substituting with the rotary valve once working, is that what you intend to do or are you going straight in.
N.B. your CAD is still considerably better than mine! :D
PaulR:
--- Quote from: redhouseluv on May 14, 2025, 09:39:39 PM ---I saw a mentioned making it with an eccentric first then substituting with the rotary valve once working, is that what you intend to do or are you going straight in.
--- End quote ---
I'm going for the rotary valve straight off. I've made a couple of engines with that type of valve in the past and they mostly worked ok. I was thinking about making this a two cylinder jobbie (probably straightforward) or a double acting single but that made my head hurt so I'll stick with the simplest arrangement first. :D
PaulR:
--- Quote from: crueby on May 14, 2025, 09:33:50 PM ---A flywheel ought to get it past the dead spots till the next power stroke. :popcorn: :popcorn: :popcorn:
--- End quote ---
Thanks Chris. I was also thinking an o-ring on the piston might help given that it's single acting, I need to read up on how to use them and whether the drag will offset any benefit.
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