Author Topic: 4 Cylinder, 2 or 4 stroke, compressed air engine (Read 11247 times)

cfellows · « **on:** June 15, 2015, 04:50:29 PM »

I'm starting a new thread on this build since it will use my standard ball / slave exhaust valve. The unique thing about this engine will be an interchangeable valve tube so I can run it as either a 4 stroke or a 2 stroke. The valve tubes will be geared to run at 1/2 the speed of the crankshaft so the 2 stroke version will have 2 sets of holes at 180 degrees. The 4 stroke version will have one set of holes.

The milled out sides with brass air tubes added are for visual interest and could have as easily been left solid with air passages drilled all the way through.

The crank will be a modified cross plane design so the throws are all at 90 degrees to each other. It'll be interesting to see how this sounds in 4 stroke mode.

The bore and stroke will be 1/2" x 1/2". The Overall engine length will be about 3" long, 1.5" wide, and 2.5" tall when assembled. Below I've attached a PDF file with 3D, rotatable drawing.

Chuck

AussieJimG · « **Reply #1 on:** June 15, 2015, 11:02:59 PM »

Another interesting project for me to follow. There's just no stopping you is there?

Jim

b.lindsey · « **Reply #2 on:** June 16, 2015, 12:53:12 AM »

Looking forward to following along Chuck. Always something to learn from your builds!!

Bill

cfellows · « **Reply #3 on:** June 20, 2015, 02:40:06 AM »

Thanks Jim, Bill.

Started making some chips on the block today. Here I'm boring the cylinder holes using my CNC mill/Drill. It just bores out the hole with an end mill in a circular pattern as it spirals downward.

Here's the block from the top... and, yes, the thicker section between the middle two cylinders is done on purpose

And the bottom...

The aluminum blank is 1.5" x 1.5" x 3". The cylinder holes are 17/32" diameter and I will be pressing in cylinder liners cut from thin-wall brass tubing with an ID of 0.5". I'll also be doing some shaping of the outside of the block later, but want to keep the blank in it's rectangular form for now for holding purposes.

Chuck

cfellows · « **Reply #4 on:** June 20, 2015, 09:52:29 PM »

Some more work done. I pressed in the brass cylinder liners.

Then drilled the hole for the valve tube and pressed in a piece of 7/32 thin-walled brass tubing for the liner.

The valve tube itself will be made from 3/16 drill rod. It will have a long, axial hole drilled most of the way through the center, then radial holes will be drilled to feed highpressure air to the cylinders.

Chuck

fumopuc · « **Reply #5 on:** June 21, 2015, 03:57:32 AM »

Hi Chuck, I am quietly following along.

cfellows · « **Reply #6 on:** June 25, 2015, 03:27:25 AM »

Today I pretty well finished up the cylinder head. I first located and center drilled the port holes using the DRO function of my CNC milling machine.

Then I used my drill press to finish drilling the inlet and exhaust port holes. Then, back to the CNC mill to locate and center drill the mounting holes. Finally, back to drill press to finish drilling the Mounting holes. Here is a picture of the finished head from the bottom.

And from the top, showing only the mounting holes.

Chuck

cfellows · « **Reply #7 on:** June 26, 2015, 09:57:46 PM »

I had started on this crankshaft a number of months ago and finally got it pretty well finished today.

It's made from 3/4" diameter 12L14 and the journals are 3/16" drill rod. It's of assembled construction which allows me to use one piece connecting rods with no screw on rod caps required. And, it can be disassembled at will to remove the connecting rods.

The sub assemblies are Loctited using Loctite 620. The sub assemblies are held in the longer center pieces with 2, 8-32 setscrews for each journal. The crankshaft is assembled using a V-block to hold everything in aligment. You can only see 2 set screws on each of the larger pieces, but there are actually 2 more on the opposite side of each piece.

And here is the crankshaft shown in the engine block.

I have used a similar crankshaft assembly technique once before, on my 4 cylinder Boxer aircraft engine.

Chuck

cfellows · « **Reply #8 on:** July 05, 2015, 04:44:17 AM »

Managed to spend some time in the shop today. I got the connecting rods made and most of the shaping of the block finished.

The rods and all the block shaping was done with my CNC mill/drill.

Chuck

dvbydt · « **Reply #9 on:** July 05, 2015, 09:47:10 AM »

Chuck, I like the way this is shaping up. Are the conrods Ali?

Ian

cfellows · « **Reply #10 on:** July 06, 2015, 04:08:02 AM »

Thanks, Ian, yes the con rods were cut from 3/16" thick aluminum.

Today I made the pistons. I still have to cut the wrist pin holes and install a set screw. One of the things I like about CNC is that I can make multiple copies of the same part, usually faster and almost always more consistent in size and shape than I would do by hand. Such is the case with the rods and the pistons.

The rods were all cut from one piece of aluminum. Using Visio, I drew up one rod, then made 3 additional copies. I exported the drawing of 4 rods, side by side, to a DXF file which I then loaded into CamBam. There, I set the cutting parameters and generated the G-Code. I mounted the piece of aluminum in the milling vise, loaded the G-Code into Mach3, and set the spindle to the x/y zero position. Then, I stood back and watched while it cut out all 4 connecting rods, one after the other.

For the pistons, I first turned them to diameter and finished them to length. Then, I mounted an ER-collet block in my milling vise and centered it on the spindle. Again, the profile of the cutout in the piston was drawn in Visio and exported to DXF. On to CamBam, then Mach3. The G-Code cut the pocket in one, continuous downward spiral. When it was finished, I removed the piston from the collet, inserted the next blank and repeated the G-Code program. Fast and simple. For those of you who haven't tried CNC, I'll bet you'd love it. Yeah, it'll cost you the better part of $1000 if you convert your mill yourself and including the cost of software. But it's just another tool and we all know, good tools aren't cheap!

Chuck

DavidF · « **Reply #11 on:** July 06, 2015, 04:21:46 AM »

Looking forward to hearing this one... I must say Im a bit perplexed, I dont recall you using cnc on you builds...Am im losing it?

cfellows · « **Reply #12 on:** July 06, 2015, 06:19:06 AM »

I converted my mill/drill to CNC a couple of years ago, but haven't really used it on any engine builds up until now. It took me a while to master the software process from design to part making.

Chuck

PStechPaul · « **Reply #13 on:** July 06, 2015, 08:14:47 AM »

Nice simple design.

I'm not sure I understand a two stroke versus a four stroke compressed air engine. I thought they were just single or double acting. Perhaps you can explain?

cfellows · « **Reply #14 on:** July 06, 2015, 03:26:41 PM »

Quote from: PStechPaul on July 06, 2015, 08:14:47 AM

Nice simple design.

I'm not sure I understand a two stroke versus a four stroke compressed air engine. I thought they were just single or double acting. Perhaps you can explain?

My compressed air engines are built to mimic internal combustion engines in look and sound, which is where the 2 or 4 stroke reference comes from. The main difference, of course, is a short blast of high pressure air is used for power instead of combustion.

Chuck

cfellows · « **Reply #15 on:** July 16, 2015, 04:32:18 AM »

Been making some progress on the engine. I got the crankshaft assembled with the pistons and rods. Everything fits in the block, and although it's all a bit tight, there's no binding. I've no doubt a little running in powered by a drill or the lathe will loosen things up.

I also finished the crankcase bottom / engine mount. The crankcase will be open on the bottom, for easy lubrication and to make things visually more appealing. The tabs on each corner will be mounted on top of 1/4" diameter posts about 5/8 inch long. I like to see moving parts moving...

I shaped the timing gear end of the block. The protrusions will cover the outer diameter of the timing gears. More for interest and a finished look than actual functionality. The two main timing gears will be connected with an intermediate idler. This lets me use smaller gears, more in proportion with the rest of the engine.

And here's a final group photo...

I expect the next job will be the timing gears, then the cam tube.

Chuck

cfellows · « **Reply #16 on:** July 18, 2015, 11:36:48 PM »

Got the timing gears and valve tube done.

Here is a back view of the valve tube. This part will be enclosed in a threaded housing to which the air line will be attached...

On to the slave valves. Getting close to having this thing ready to run...

Chuck

cfellows · « **Reply #17 on:** July 22, 2015, 04:20:52 AM »

We have a runner!

I'm not finished with it, but did get it to a point where I could test it.

Today I finished drilling the air feed holes in the cam tube and made the exhaust manifolds as well as the springs.

The ball valves are 3/16" diameter. I made the springs by using the threads of a 3/4" 6-32 socket head cap screw as a form. I mounted the SHCS into my 3 jaw chuck and wrapped .010" music wire tightly around the thread grooves as I spun the lathe slowly under power. when the spring was released from the form it unwound just enough to make a spring that's about .160 OD.

I have to finish mounting the engine on a base and do some tuning. I think the timing could be tweaked a bit and I also believe the exhaust springs need to be shortened by 3 or 4 windings. These changes should result in smoother running at low rpm's. I'll make a video when I get the changes made.

The engine is currently set up to run as a 4 stroke. I will have to make another cam tube with double the number of exit holes to see how it runs as a 2 stroke.

Chuck

AussieJimG · « **Reply #18 on:** July 22, 2015, 04:54:26 AM »

Congratulations Chuck, it is always nice when they come to life the first time. No doubt we will have video soon.

Jim

cfellows · « **Reply #19 on:** July 25, 2015, 08:04:45 PM »

Here's some pictures and a video of the finished engine...

<a href="https://www.youtube.com/watch?v=dYALQvq4FPA" target="_blank">http://www.youtube.com/watch?v=dYALQvq4FPA</a>

Still have to make another cam to run the engine in 2 stroke mode and see how that works...

Chuck

BillTodd · « **Reply #20 on:** July 25, 2015, 08:18:08 PM »

Great - It sounds much bigger than it is :-)

Bill

Roger B · « **Reply #21 on:** July 26, 2015, 07:07:20 AM »

Looks and sounds good, congratulations

sco · « **Reply #22 on:** July 26, 2015, 09:49:39 AM »

That's super neat Chuck - nice job, sounds just like its ready for work ;-)

Simon.

Kim · « **Reply #23 on:** July 26, 2015, 04:56:14 PM »

Pretty neat Chuck! Congratulations!
And very nice video too.
Kim

cfellows · « **Reply #24 on:** July 26, 2015, 08:22:22 PM »

Thanks for the comments, folks. Here is a second video where I've drilled a second set of holes in the cam tube. Each cylinder now has 2 holes at 180 degrees in the cam tube which is turning at 1/2 the RPM of the crank. This gives each cylinder a power pulse on each revolution, basically mimicking 2 stroke operation.

<a href="https://www.youtube.com/watch?v=jiYGQ74AO90" target="_blank">http://www.youtube.com/watch?v=jiYGQ74AO90</a>

The engine does run smoother, has more power, and is self starting. You be the judge which version sounds better...

Chuck

PStechPaul · « **Reply #25 on:** July 26, 2015, 08:30:43 PM »

I have driven a Ford 9N tractor, years ago, and I seem to remember it sounding very much like this model engine. And it seems to have a little bit of the distinctive Ford "lope" when idling.

[edit] I prefer the sound of the four stroke when idling, but I think the two stroke is smoother and sounds better at high speed.

zeeprogrammer · « **Reply #26 on:** July 27, 2015, 12:32:55 AM »

Very cool Chuck.
Sounds like an IC!

b.lindsey · « **Reply #27 on:** July 27, 2015, 12:41:56 AM »

Well done Chuck!! Both versions sound great but I think I favor the 2 stroke for smoothness. Are you still planning on shortening the springs any to see what effect it has on the lower rpm range or would that mess things up when using higher pressure? Nice design and excellent execution as always!!

Bill

dvbydt · « **Reply #28 on:** July 27, 2015, 09:23:35 AM »

Super job, novel as is usual with your engines, well done.

Ian

mnay · « **Reply #29 on:** July 28, 2015, 07:35:38 PM »

Amazing work. I love the sound as much as the way they look.
Keep em coming.
Mike

fumopuc · « **Reply #30 on:** July 28, 2015, 07:46:58 PM »

Hi Chuck, I like the two stroke version. Sounds better.

AussieJimG · « **Reply #31 on:** July 31, 2015, 07:53:25 AM »

Classical simplicity. A lovely engine.

Jim

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Author Topic: 4 Cylinder, 2 or 4 stroke, compressed air engine (Read 11247 times)