Thanks, Chuck. Thanks, Brian.
Here's the process of building the rotary valve tube.
The rotary valve tube actually starts out as a 3/16" length of drill rod. The first step is to press a small flange onto the back end.
I made the flange from 5/16" drill rod and drilled the center hole with a #2 drill bit which is about .002" smaller than the 3/16" diameter of the valve tube. I deliberately made the flange over-sized on both the diameter and length so I could turn it to finish dimensions after it was fixed on the valve tube (which is still a solid rod at this point). Here's how the valve tube will fit in the engine once finished.
Next I had to drill a 3.5" deep center hole in the rod. The only bit I had which was long enough was 1/8" so that's what I used. I had to back out of the hole, clear the chips, and add oil about every 1/8" to keep the drill on center and to keep the chips from piling up and seizing the bit.
Once the center hole was drilled, I inserted the valve tube into the crankcase from the back. Here's a picture of the valve tube fully inserted after I had drilled the center hole.
I then attached the larger timing gear to the front part of the valve tube where it extended out of the crankcase. Notice that the center hole does not go all the way through the valve tube. Here's what it looks like with the valve tube installed and the two timing gears attached to the valve tube and crankshaft, respectively. The crankshaft and the valve tube are now geared together and the valve tube will rotate at 1/2 the rate of the crankshaft giving the engine 4 stroke operation.
Here I've turned the crankshaft so that the first cylinder in the firing sequence is at top dead center (far right cylinder).
Next I attached a disk which has 4 lines scribed 90 degrees apart to the crankshaft. These lines are used to measure exactly 1/4 turn of the crankshaft.
Here I'm ready to start drilling the holes in the valve tube. I've already center drilled the holes in the flare fittings so it's just a matter of running the drill bit down until it hits the valve tube and drilling through to the center hole.
After drilling the first hole, I rotate the crankshaft 1/4 turn and proceed to the next cylinder in the firing sequence where I again drill a 1/16" hole through the side of the valve tube into the center hole using the cylinders flare fitting as a guide. This operation is repeated until holes have been drilled for all 8 cylinders. This results in 8 individual holes in the correct position for each cylinder. Note, however, that after I finish drilling all the holes, I have to retard the valve tube timing. As drilled, the holes are fully open when the piston would be at top dead center and in fact you want the piston to be half way through it's stroke before it's valve hole is fully open.
I hope this is a little clearer than mud. Let me know if you have any questions. I expect to have this engine running by the end of the day. Or perhaps I should, ready to run by the end of the day. Whether it actually runs remains to be seen!
Chuck
They are pretty big but I didn't particularly want to make smaller gears and have to use an idler in between. I'm going drill holes or make spokes in the larger gear so it will be less bulky looking.
