The Rotary Valve Engine I
if you've stuck with me through this part, here is part two where I make the head, valves and accessories.
The Rotary Valve Engine II
Years ago I read about a company that made some rotary valve engines.  The book is long gone but I think I will do one to see how it comes out.

Go Back Home

11 August 2016:
With nothing better to do, I rooted around on one of my junk shelves (most of them are junk shelves!)  and found this neat crankshaft out of a Briggs & Stratton engine of some kind.  I wonder why it was thrown in the scrap bin because I can't find anything wrong with it and it appears to be nearly new, with just a little surface rust.

Since it is such a nice beefy crankshaft, it will make a good basis for The Rotary Valve Engine.

Stay tuned.  
12 August 2016:
I've been doing some CAD work to try to get an idea of how this is going to come together.  

So far with the CAD.
So far, I'm really not set on any particular design although I'm trending toward a hopper cooled horizontal engine.  If it's not a Diesel, it could be either rotary valve or sleeve valve with spark ignition.  Both types are something I haven't built yet.

The crankshaft measures out to have a stroke of 2.260 inches or 11.23 mm.  This doesn't look right but I've checked it several times and it just doesn't come out to an even number.

The rod pin diameter measures 1.499".  The short main diameter measures 1.378" and is 1.282" long.  The long main diameter is 1.624" and it is 2.8375" long.  The output shaft is 1" in diameter and is 3.125" long.  I guess the engine it came out of was around 15 or 20 HP.

Oh, yes - I'm not happy with how the CAD drawings come out here.  Since my .DWG to .JPG file converter  used up it's trial period and I don't want to pay the bucks to get the "real" version, I'll just have to live with scans of printer plots.
1 September 2016:
It's been a while but I have made some progress......... I think!

I've made the executive decision to give the engine a larger bore and give it rotary valves.  It's also magically turned into a tank (or radiator) cooled vertical engine.  The larger bore is to give room for the valves.  Here is a drawing of what I've got so far.  Please note that everything is subject to change.

Here it is as it stands at this moment.
In addation to everything else, I've decided to make the rod out of a solid hunk of aluminum that was donated to the cause.  The crankpin and wrist pin will bear directly on the rod.  Bronze bushings will be used for the mains.  There is a 1:1 bevel gear drive to convert the horizontal crankshaft rotation to vertical.  The shaft goes up to head level where it has a 12 pitch 18 tooth pinion that drives the two 36 tooth valve gears which will be machined into rotary valves, one for intake and the other for exhaust.  To seal the valves to the head, the hubs will be grooved for a piston ring seal in the head.  This will take care of compression gases.  On the top surface of the valves, a perfect seal is not required and I will allow for a few thousandths of clearance so they won't bind.

I think the most complicated part of the engine will be the valves.  Designing of the ports and the valves will be critical for decent valve timing and duration.

As you can see, I haven't done too much to the head yet because I haven't decided on what compression ratio to use but it will probably be around 6:1.  Performance is better with higher compression but valve leakage is worse.  There must be a happy medium somewhere.
3 September 2016:
I did some more CAD today and am ready to get away from the 'puter for a while and make some chips.   I've designed the engine to have a bore of 3.00" (76.2mm).  The crank has a stroke of 2.26" (57.44mm).  I calculate the displacement at 15.98 cubic inches (261.98cc).

Since the design is not finalized, I will work on some of the parts that won't be affected if changes need to be made to the rest of it.  

I have a slab of aluminum big enough to make the rod so I'll start on that tomorrow.  I've made one design change to the rod from earlier and that is to press a bushing in the small end.  This will allow me to make the wrist pin a press fit in the piston instead of having a floating pin.

 I think I've got the end mills to do the work but may have to wait on part of it until I get some new and sharp tooling.  We'll see.
4 September 2016:
I thought I was going to make the connecting rod today but when I went out and looked at the new pile of aluminum that was given to me, I found that the 1.125" thick piece I'd seen there had a couple of holes drilled in it right where I needed them not to be.  I had to add that material to my McMaster-Carr order.

What I did do was modify the crankshaft for the miter gear.

Boring out the end of the crank.
  The crank with the stub shaft and the gear.                                                   The gear hanging off to show the pressed in stub shaft. 

 I found that turning the end of the crankshaft to 0.625", the diameter of the gear hub went right into the bore and it became so thin that you could see through it.  In other words, I messed-up in not measuring that hole.

The fix was fairly straightforward, though.  What I did was to cut off what was left of the area of the crank that was going to be the gear shaft.  Then I bored out the end of the crankshaft to 0.650" about 0.750" deep which gave plenty of engagement for the pin that I made to press fit into this bore.  The other end of the pin was turned to 0.625" to fit the gear.  a drop of Loktite and a loving squeeze in the press and it was done.

The diameter (0.875") that was turned between the gear pin and the main bearing journal is simply clearance for the mating miter gear.
7 September 2016:
Surprise!  The engine has now morphed into an air cooled version!  I did this to save some money on materials and make it simpler to fabricate and build.  The fins (at this time) will be made of 0.125" thick steel and lightly pressed onto the malleable iron bore.  Eventually, a cooling fan will be added.  It will probably be throttle governed, the governor mounted above the head of the engine, directly driven from the sideshaft.

Here's a side view of the air cooled version.
More CAD has been done and I have the engine sized to give a compression ratio of about 6:1, which should give moderate performance with lower stress on the valves.

It took a lot of brain scratching to come up with the valve/port dimensions but I think I have something I can work with.  Valve timing has the exhaust duration at 200 degrees, opening at 162.5 degrees BBDC and closing at 2.5 degrees ATDC.  The intake duration is 180 degrees, opening at 2.5 degrees BTDC and closing at 2.5 degrees BBDC.  Getting this exact timing will be difficult but with care and the machinery I have, I should be able to get to within 5 degrees of these numbers.

I will try to describe the valve and port arrangement.

Top view of head and disc valves.
The valves will be made from a couple of 12 pitch 36 tooth gears, driven by a 18 tooth pinion which is driven by a 1:1 miter gear drive from the crankshaft via a sideshaft.  The illustration above shows the valves positioned so the exhaust is at the end of overlap and the intake valve is opening.  The ports in the head are surrounding their descriptions.

Figuring out how to machine the ports took a half day but I think I can do it with my mill, rotary table and time.

Intake port machining plan.
The machining will be done in four operations.  The center mark is the center of the milling table and the parts are referred to it.  Referring to the left hand side of the drawing above, first, a 3/16 hole is drilled as shown.  Then, using a 1/4" end mill, the hole is enlarged.  Then, the rotary table is rotated 9.74 degrees in both directions to form the minor diameter of the port.

The table is moved back to zero and as shown in the next drawing, the Y axis is shifted to 1.0" from center and another 3/16" hole is drilled followed by the end mill.  The table is then rotated 15.33 degrees in both directions to form the major diameter of the port.

To finish the ports, in the third and fourth drawingsd, the radial cuts are made.  This requires rotating the table in each direction for the whole opening angle of the valve and offseting the workpiece by the diameter of the tool to make the cuts to the dimensions shown to make the sides of the port exactly radial.
Exhaust port machining plan.
To machine the exhaust ports, the same procedure is used with the exception of the rotation angles.  I think this will work.

Because I've lost my source of water jet cutting, I think I will be buying aluminum plate for the deck, crankcase sides and base.  The cutting and machining is easier working with aluminum and it should be plenty strong.   
10 September 2016:
Over the last couple of days, materials have been arriving.  Here's most of what I'll need to build the engine.

Stuff to build the engine with.
There's going to be some serious whittling done on the two biggest rounds (the ductile cast iron for the head and cylinder).  In order to save time and energy and make the whole project easier, I will be using the 1/2" 6061 aluminum plate to make the engine frame and deck.  I hope to start with the chip making tomorrow.  I will build the engine up from the base to the head.
11 September 2016:
Today, I finally cut some metal.
Squaring-up the base.
Again, I've bitten off more than I can chew.  After getting all the materials, I find that the mill doesn't have the capacity to lay out the holes in the base in one set-up.  I could get half of them done then had to rotate the piece 180 degrees, locate on the center and start over on the other end of the part.  That's not too bad because all of the holes are mirror images of each other.

The base plate is now done.  Next up will be the ends.  I designed these parts to be exact duplicates of each other so I plan to lay them together and drill and bore all the holes at the same time.  There are also a bunch of holes in the edges of the material that will have to be done separately.

The base, sitting on temporary skids for assembly.
15 September 2016:
I got some stuff done today.  The crankcase parts are cut-out and sized and the side plates for the crankcase are partially finished.    

Crankcase parts are coming along.
These parts are just small enough to fit in the mill so it's easy to lay out the holes using the digital readout.  Tomorrow, I hope to have the crankcase parts done and do a test fit.
16 September 2016:
The crankcase is just about done.  All I've got to do is drill and tap the edge holes.

It's looking like a crankcase.
After the crankcase, it's on to the main bearings.  At that point, I can assemble the crankcase with the crankshaft in place.
17 September 2016:
The crankcase is all drilled, tapped and test fitted.

It went together!
I did discover something.  Aluminum plate like this is NOT flat!  This caused some of the fits to not be perfect although it did go together all right.  I may consider line boring the mains if they are out of alignment enough to matter.  Any misalignment should be less than about 0.002" in any direction though, so it might not matter.
18 September 2016:
One of the main bearing mounts is almost done.  This job turned out to be more time consuming than I estimated.  Starting with a 3-1/2" diameter hunk of 1018 steel, it took the better part of the day to turn and bore it on my dinky little lathe.
                         Turning the O.D.'s                                                                                 Boring the I.D.                                                   The semi finished part next to the semi finished crankshaft,
The flywheel end semi finished main bearing mount.
In the process of making the mount, I broke a couple of carbide inserts and broke the cog belt of the lathe.  Thankfully, I had a couple of spares because it had broken them in the past.  That little machine was not designed for such hard work.  In the future, I'll have to remember to just take more time and save the machine.

I have more to do to the crankshaft.  The flywheel end bearing journal still needs to be shortened by about a half inch.  The bushing has to be machined and pressed into the mount, the mounting holes need to be drilled and the oil hole needs to be drilled in the mount next to the crankshaft.  

I think I can use the lathe to run a line boring bar, mounting the engine crankcase upside down on the carriage and adding a small amount of shim to bring the center of the mains up to the center of the spindle.  A boring bar will be made using a piece of 1" shafting.  Line boring the mains will assure that any slight misalignment of the crankcase parts will not cause the mains to bind.  (Says here in the fine print!)
20 September 2016:
Both mains are finished and ready for line boring.  Tomorrow, I will attempt to make a boring bar and set the job up in the lathe.  The block looks like it is only a little low when mounted upside down on the carriage so I can shim it up and somehow clamp it down.
The gear end main bearing ready to mount.                                    Both main bearings in place for boring.  
I think I've lucked-into a cast iron tube of a dimension that I can make the cylinder from.  This will be a LOT easier than making it out of a solid round of cast iron.  Thanks to J.B. Castagnos for finding the piece in his junk pile and donating it to the cause.  It's going to show-up right on time for me to start whittling on it.
21 September 2016:
It's beginning to look like part of an engine now.  The mains are line bored and installed in the crankcase.
Aligning the axis of the crankshaft with the lathe.                                    Setting the Y axis centered on the bearings.                                                   line boring the bearings              

It's getting there.
If you check out the second and third photos above, you will see that I, at first, added a couple of 0.016" copper shims between the lathe carriage and the top plate of the engine.  This was just a little too much so I removed them and replaced them with a couple of 0.010" feeler gauge leaves, which was plenty close.  First, after bolting the crankcase to the carriage, I used an indicator to bump it into parallelism with the lathe ways.  Then, using a coaxial indicator, I moved the Y axis until I had minimum wiggle in the indicator.

After that, it was just a matter of standing around while the boring bar did it's work.

Note:  I made the boring bar using a humk of 1.5" 1018 bar stock.  The cutter was a short piece of 5/32" tool bit.  I drilled a hole in the bar (not quite all the way through) off center by 5/32" so the cutting edge was on the centerline of the workpiece.  An 8-32 tap size hole was drilled from the bottom of the tool bit hole through the bar and tapped 8-32.  Then, I drilled and tapped another 8-32 holes crossways for a setscrew to hold the bit in place.  The 8-32 screw into the end of the tool bit hole was for adjustment.

Since I don't have any square broaches, I drilled the tool bit hole 1/4", which was undersize and drove the tool bit in using a brass hammer.  This allowed it to self-broach at the corners.  It worked fine.   
24 September 2016:
After a couple of days off, I got some more done to the engine.

Motoring-in the mains.
While making the dip stick (the brass thingy to the rear of the crankcase) and the breather (the steel thingy at the front of the crankcase), I motored the main bearings to work out the initial tightness.  Then, I started on the connecting rod.
       Cleaning up one face of the rod.                                                          Sawing off the rod cap.                                                      MIlling the other face of the rod to dimension..

The rod ready for machining to width.
The rod is made from a solid piece of 6061 aluminum.  The big end bearing will be the aluminum rod itself.  The small end will have a bronze bushing for the wrist pin.

First, after cutting the stock to length plus some, one face was milled flat.  One side of the width was also milled flat to procide a couple of reference surfaces for laying out the rest of the rod.  Then, the big end was drilled and tapped for the rod bolts.  After that, the rod cap was cut off of the rod.

The rod and the cap mating surfaces were milled flat and the opposite surface of the cap was finished to dimension.  After bolting the cap back onto the rod, the other face was milled to dimension.  

Tomorrow, I will mill the width to dimension.  I may go ahead and bore the big end to fit the crankpin but, at that point, there will be a pause to allow the cylinder liner to arrive from
J.B. Castagnos in Louisiana.  Once it is here, I can measure it and make sure I don't have to modify the rod length to accomodate the liner if it is shorter than the design calls for.
25 September 2016:
I had a look at the CAD drawing and find that I designed the piston with enough room to move the wrist pin boss up as much as 1/8" without affecting anything else in case the liner ends up being too short.  In that case, I finished the rod.
        Boring out the big end.                                                                   Removing excess metal.

The connecting rod, such as it is.
I'm not real pleased with the way the rod turned out.  There were some unanticipated interference problems between the top of the rod and the opening for the liner so I had to remove some metal in that area.  Also, I'm not happy with the new 3/8" X 3" ball end mill I got for this job.  It's too limber and no matter how slowly I feed it, it wanders around.  That made for some sloppy looking fillets.  It will work, though.

The wrist pin bushing was Loktited in place and, using a flapper wheel, I now have a nice fit with the pin.

The crankpin diameter is 1.499" so I bored the big end to 1.500".  When I tried a test fit, it was too tight.  I dunno where that comes from but I will address it with some TimeSaver lapping compound when I have the crankshaft out for drilling the hole in the end of it for a pin to hold the timing gear.  This pin will be made of aluminum in case the rotary valves bind-up.  I don't have any more of the miter gears and don't want to ruin them.  
26 September 2016:
Today, I finished the rod by making the dipper tube and fitting it to the crankshaft.  I also drilled small holes close to the edge at the top of the rod bearing on both ends.  These holes match up with the undercut of the crankshaft and I think that the oil that is picked-up by the rod will quickly get to the undercut, go around and flow out of the holes, providing lubrication for the piston, wrist pin and main bearings.  (or so it says here in the fine print.)

All ready for the cylinder.
The trouble with the fit of the rod was that, when I was milling off the excess metal, I must have clamped it a bit too tight in the mill vise and forced the bore out of round by 0.001", just enough to make it really bind.  The fix consisted of putting the rod (with the cap bolted on) in the press and carefully squashing it in the opposite direction until it was very close to round again.  The fit was still too snug to suit me so I used TimeSaver lapping compound to get the rod to fit with about 0-.001" of oil clearance.

We now pause until the cylinder gets here.
2 October 2016:
After a pause, the cylinder arrived.  Today, I measured it up and started machining on it.  A BIG thanks to J.B. Castagnos who donated it to the cause.

I don't think the cylinder could have been closer to a fit for what I need.  I will have to modify the deck plate to accomodate the cylinder because I had so much trouble attempting to machine it.  The way it cuts, I think it is malleable iron or low carbon steel which is fine for this application.
                        The cylinder, as received.                                       Turning the reference diameter at the bottom of the cylinder.

Cylinder with mounting step machined, shown  with bore plug and chatter marks.
All day, I was plagued with chatter.  I tried every feed and speed on the lathe along with many different tools, grinds and configurations.  Nothing helped.  When finishing the O.D., I think I will see if I can use the steady rest on the bore plug, which will be temporarily pressed into the top of the bore.  It's obvious that using the center does not make it rigid enough.  With my little lathe, stiffness in the carriage and compound are troublesome but that's what I have so I will have to try to make do.

Preparation to machine the cylinder consisted of chucking the "top" end in the 4-jaw and getting it centered as well as possible.  Then the bottom end, which was hanging out about seven inches, was tapped until the bore indicated true.  After indicating both ends once more, the end was faced clean, the bore plug was tapped into place, and the O.D. was turned to clean it up.  Then the step was machined for aligning the bore with the deck plate.  Since this cylinder is a lot thicker than the one I originally planned to use, I will drill a couple of 10-32 clearance holes in the deck plate, then drill the cylinder and tap it 10-32.  These bolts don't have to be very strong because all they do is hold the cylinder in place while the head is off.  The studs do the major holding-down.

I hope I won't have to bore the I.D. of the cylinder because I'm sure chatter will be worse using a long boring bar.  When I measured the bore, it was 3.004" at one end (the top) and 3.008" at the bottom.  The bore is more or less clean with the exception of a couple of slightly "fat" spots below the ring travel area. 
They shouldn't be a problem.  Right now, it looks like there is about 0.002" of taper where the rings run.  

Tomorrow, I will chuck the cylinder on the turned area of the O.D. and will indicate it true.  With the plug in place and held there with the live center, the steady rest will be moved into place and will run on the large O.D. of the plug.  I sure hope my dinky lathe likes that because I really hate to listen to the chattering, stresses the machine and the marks it leaves are ugly.
3 October 2016:
It took all day but I got the cylinder faced to length, the O.D. turned and started on the honing.
Turning the O.D.                                                                           The finished O.D.
I finally figured out how to get a nice finish on the cylinder.  I did the rough cuts to get the scale off and get it nearly cleaned-up by using a pretty agressive carbide insert, low spindle speed and slow feed, taking about 0.005" at a time.  When I got it almost done, I changed the tool to an insert with an 0.015" radius tip, taking only a couple of thousandths off per pass.  And that's why it took the whole day to do the job.  

I still have to reverse it in the chuck and make sure the mounting surface is square to and centered with the bore.  When I turned the small section of the O.D. at the top of the bore, I indicated the rough O.D. of that end and need to go back to the bottom and make sure it's on the money now that I have a well centered O.D. and I.D. at the top.
4 October 2016:
The cylinder bore is finished.  It ended-up closer than I thought it would be.  The bore at the top is 3.005" X 3.0045" (measured 90 degrees apart).  At the end of the ring travel area, it is about 0.0005" bigger in both directions.  At the bottom of the bore, the diameter is 3.008".  These dimensions are just fine.
    The top end of the cylinder.                                                         The bottom end of the cylinder.
Then, I set-up and drilled the mounting holes (4" 6 bolt circle) and tapped them 10-32 at both ends.

My cooling idea evolved over time and I decided to make it a porcupine-type system.  The reason for this was twofold.  One, I don't have any 1/8" steel plate to make the fins and it would be a P.I.T.A. to make them anyway.  Two, I do have a bunch of 1/4-20 all thread lying around so I will make the cooling pins out of that.  There were some early engines that used this system of air cooling as well as at least one car, the Knox.  In the left-hand photo below, you can see one of the pieces of all thread screwed-in as a test fit.  The holes are all tapped two turns using a bottoming tap so the pins can be jammed in place.
Drilling the holes in the second row of pins.                                                        Tapping the holes.
I decided to use the rotary table to drill and tap the holes for the cooling pins.  The pins are spaced 20 degrees apart, making each row have 18 pins.  The rows are spaced 0.5" vertically and each row is staggered 10 degrees from the next.  I'm not sure how many rows of pins there will be but I hope to be able to cover a little more than the stroke, maybe four rows.  We'll see how the all thread holds out and how bored I get with the whole process.  I've already screwed up one hole by only rotating the table 5 degrees.  Oh, well - it will give youall something to razz me about when you see the engine.
6 October 2016:
Well, THAT was fun!  I just finished drilling and tapping the 90 holes.  Then I made 90 (count 'em) pins out of the 1/4-20 all thread.  I made an installation tool to screw them and bottom them out as shown in the left-hand photo below.
                       Installing the pins.                                                          Painted and mounted on the deck plate.

I didn't strip any threads, break a tap or otherwise dork it up except for the one misplaced pin which will be sort of hidden behind the vertical shaft.  I'm not sure how well it will cool and I will probably have to add a cooling fan once I get it running.
7 October 2016:
It took the whole day but I got the piston started.
11 am.                                                                       2 pm.
Removing most of a large hunk of even aluminum takes time when you have dinky equipment.  The piston is made from a 3" diameter hunk of 6061 aluminum.  Note the copper strip to protect the aluminum from the jaws of the chuck.  After turning the O.D. and drilling a center, the piston end was sawed-off of the blank.  It was then put back in the lathe with the "top" against the chuck so the inside of the piston could be hogged-out.

I discovered something today.  When you buy a piece of 3" diameter aluminum, it is 3", warts and all.  Once I got the O.D. cleaned-up the diameter was down to 2.996" and just almost nearly semi clean, making skirt clearance 0.009", which I think is a bit on the loose side but should work fine.  After I finish the inside of the piston, I will take it out of the lathe and put it in the mill with the bottom facing up so I can mill out clearance for the little end of the rod.

Then, I will re-mount the piston in the mill and drill and ream the wrist pin hole.

After that, it goes back into the lathe, chucked to the inside of the skirt (so as to not mar the O.D.) and the diameter in the ring area will be turned about 0.010" smaller than the skirt.  Next, the ring grooves will be cut.

Just in time, the rings arrived from Dave Reed ([email protected]).  They are 0.010" over 3" and 1/8" thick.  The gap is now 0.011" so I may have to file a little off to open the gap a bit.

The wrist pin locks will most likely be discs of 0.0625" thick PTFE Teflon.  I hope to have the piston finished and hung on the rod, rings gapped and on the piston and the whole works in the engine so I can start motoring some of the tightness out of the parts.
8 October 2016:
The piston's done,  After emailing back and forth with Dave Reed, I decided to turn the skirt for 0.010" clearance and the ring area for 0.020" clearance.  The piston was taken out of the lathe and mounted in the mill and the wrist pin bore was finished.  I made it about 0.001" undersize.
Boring for the wrist pin.                                                           Turning the ring grooves.
Then it was out of the mill and back to the lathe to do the ring grooves.  I allowed for about 0.001" side clearance and filed the ring gaps to 0.013" to make sure they wouldn't bind.

I moved the piston back to the mill and using an end mill, removed a bunch of unneccessary material from the inside.  This removed some weight and had the added benefit of giving more room for the little end of the rod to move.

When I went to press the wrist pin into the piston, I found that 0.001" press fit on a 0.625" diameter pin was a bit tight but went ahead and pressed it in.  I don't think it's going anywhere!
     The piston hung on the rod.                                                       Motoring it to work out stiffness.
Note that I decided to use Teflon buttons to protect the bore in case the wrist pin eventually goes walkabout.  

For some reason, when I got the piston in and the rod cap on and torqued, when motoring, there was a very slight knock.  When I looked carefully, I saw a little lost motion between the rod and the journal.  The cause, it turned out was about 0.002 slack in the rod.  I carefully fitted the rod when I made it but, for some reason it was just loose enough to make a slight knocking.  I took the easy way out by sticking the cap in the mill and removing 0.002".  When put back in, I couldn't detect any lost motion in the journal and it ran quiet.  Before putting on the side plate and filling the crankcase with oil, I ran it for about five minutes and detected no heat in the rod so it is not too tight.  After running the engine for a while, I'll have to get inside and check it out.  If I can remember, I will get some Plastigage (if they still make it) and make sure it has about 0.001" oil clearance.

9 October 2016:
I may have to revise the oil level.  After running it for about a half hour on the motor, there was oil standing on top of the piston.  I suppose when the head is on and it has compression, it won't be as much of a problem.  I can experiment with oil levels and maybe put a Plexiglas window on one of the side covers to make sure it's splashing enough oil to be happy.

Now comes one of the more fun parts.  The head.  

Dimensions for the head.
This part is going to be another challenge for my shop.  It's a rather large chunk of iron to be able to turn the O.D. and to face to height.  I may have to drill and tap some holes on the faces so I can mount it to the faceplate.  Some more thinkin' is going to have to be done.  
10 October 2016:
Well, after thinking on the above drawing overnight, I have decided to make a slight modification.  It only makes the head taller by about 0.100" and changes the two opposing 1/4-20 holes to 3/8-24.  These holes will be drilled all the way through and will be used, in addition to guiding the top plate (which holds down the rotary valves, to attach the head to the face plate on the lathe so I can face it to height, turn the O.D. and do some other lathe operations on it.  Most of the head work will be in the mill.

After taking the new drawing out to the shop, I chickened-out and decided to study it some more to make sure I hadn't made any blunders.  Instead, I used the afternoon to make a window into the crankcase so I could see how well it oiled.
The window, showing the oil moving around.
It's dark in there but I think I could probably reduce the oil level to about half what it is now and it will be fine. 
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The Rotary Valve Engine II

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