Rotary Valve Engine

[Jasonb]

If you are happy to have the air come in from the bottom of the head and exit the top then the halve is quite simple to make as it only requires a flat to be machined into it. You can see here how the inlet opens to the cylinder just after the piston passes TDC and then just as it passes BDC the exhaust opens to let the air out. It is moving a bit far and covering the holes at mid piston position  so a reduction in that 9mm or shortening the valve lever will soon sort that out. The red area is where the valve has been milled away.

Best viewed on Youtube at full screen size

 <a href="https://www.youtube.com/watch?v=X429Dnl88Io" target="_blank">http://www.youtube.com/watch?v=X429Dnl88Io</a>

[PaulR]

If you are happy to have the air come in from the bottom of the head and exit the top then the halve is quite simple to make as it only requires a flat to be machined into it. You can see here how the inlet opens to the cylinder just after the piston passes TDC and then just as it passes BDC the exhaust opens to let the air out. It is moving a bit far and covering the holes at mid piston position  so a reduction in that 9mm or shortening the valve lever will soon sort that out. The red area is where the valve has been milled away.
<a href="https://www.youtube.com/watch?v=X429Dnl88Io" target="_blank">http://www.youtube.com/watch?v=X429Dnl88Io</a>

Thanks for taking the time to make the video. Yes, the valve lever travel is way more than 90 degrees in my image, I need to sort that! I was thinking of keeping the engine as low as practical so I could either make some sort of right angled inlet to fit at the bottom (so the supply comes in from behind) or a simpler fitting on top. I see what you mean about the valve, it's much simpler in your arrangement rather than having two flats and a longitudinal hole.

[PaulR]

Right, I think I'm finally getting there. The valve pin is 90 degrees ahead of the crank pin which has been moved out to 8mm. The valve lever arm has been changed to 13mm which gives pretty much spot on 90 degrees of travel but doesn't take up too much vertical space. The arc of travel is also equidistant about a perpendicular to the cylinder axis. I think it's time to get the saw out! 

[Jasonb]

You could put the air into the top and just let it blow out the bottom.  An alternative would be to drill in from the back end to meet the vertical holes which could be plugged top and bottom.

If you also had the valve lever at the top that would keep the height down and hang your flywheel off the side of whatever you mount the engine onto.

That extra spigot on the end of the cylinder can be loctited into a suitable hole in a block to support the cylinder.

This is it with the crank throw taken back up to 8mm, the "eccentric pin" positioned 8mm from the crankshaft axis not 9mm which does not block the passages. Air in from the top. Valve arm still the same 10mm. Steam holes in the head all 2mm. Flat on the valve 1.7mm deep by what width you fancy 3-4mm will do.

Right that's your weekend homework, expect it handed in Monday morning

[PaulR]

Yes, air coming in at the back and plugging the drilled holes works for me. When I put in the figures you give the valve rotation will be a bit more than 90 deg so that will give a little lap??

[Jasonb]

Yes there is a point at either end of the piston movement where both passages will be closed for a short time. Altering the depth of the notch in the valve will increase or reduce the lap. If you make the valve arm movable on the valve then you can set it so the exhaust is open a bit longer than the inlet which is quite common on single acting engines.

A few critical sizes as mentioned in my previous post

[PaulR]

Yes there is a point at either end of the piston movement where both passages will be closed for a short time. Altering the depth of the notch in the valve will increase or reduce the lap. If you make the valve arm movable on the valve then you can set it so the exhaust is open a bit longer than the inlet which is quite common on single acting engines.

A few critical sizes as mentioned in my previous post

Perfect, thanks for all the help 

[PaulR]

Made a start on the cylinder with the nubbin on the front and drilled a 6mm through hole.

Now, according to https://www.rdgtools.co.uk/product/6mm-shank-boring-bar-ccmt-06/ this 6mm bar I have will bore a minimum 8mm hole (the size I want) - does that mean the minimum it will fit into is an 8mm hole or will it fit something a tad smaller  The only drill bit I've got  between 6 and 8mm is the recommended hole size for reaming (7.8mm). Not sure whether to use this and try to bore the last 0.2mm with the bar (if it'll fit) or just follow it with the 8mm reamer (which seems to have worked fine in the past).

Think I'll use that drill and see if the bar fits, if not I'll use the reamer (or drill it out to 8mm, bore a big bigger and increase the piston size  )

[Jasonb]

I think it will be a tight fit even down a 7.8mm hole. Insert and/or holder is likely to rub and get deflected so you won't get a parallel bore.

Given what you have ream or take it out to say 10mm bore

Did you add the extra length to the 30mm cylinder for the spigot?

[PaulR]

Did you add the extra length to the 30mm cylinder for the spigot?

I did BUT didn't take account of the throw being increased from 6mm to 8mm I'll go back to the drawing and either shorten the piston or remake the part.

[Jasonb]

it would still work with the 6mm throw. I took it back up to 8mm to make use of the full cylinder length.

[PaulR]

it would still work with the 6mm throw. I took it back up to 8mm to make use of the full cylinder length.

That increases the rotation of the valve by maybe 5 or 10 degrees (eyeballing it) compared to 8mm throw which I guess would have a marginal effect on the depth of the valve flat?

[Jasonb]

It should not change much if the 8mm from crank ctr line of the eccentric pin stays the same and the overall engine length remains the same.

Keep the valve flat the same so that it has a bit of lap.

[PaulR]

I have the crank-axle to valve distance at 90mm (the same as the valve rod) which makes the piston conrod 63.25 so a bit longer than in your drawing. The arc of the valve lever is about the same ~95-100 degrees. I'm going to stick with the long piston (16mm) and go back to the 6mm throw so as not to waste the part!

[PaulR]

Drilled and reamed the bore and the fit and finish is fine. Next got the valve block to size then turned the 1mm spigot - so much back and forth with the handles I had to stop a few times to remember which one I was supposed to be turning next  Next I set the block sideways, using the spigot to resist any movement along the lathe axis when drilling. Drilled and reamed to 6mm for the valve and all seems good. Here's the cylinder and valve block assembled with 6mm and 8mm rods inserted to check alignment - looks good. Next will be steam passages and holes for screws to fasten these two parts together.