Compressed Air V8 Cirrus

[cfellows]

Thanks, Don, Chuck, Brian.

Here is a picture of the first piston. I decided to make them from brass since it's easier to machine than steel.

Chuck

 

[rhitee93]

Well now, that gives me a whole new appreciation for the scale of this engine

 

[cfellows]

I got the pistons all made today. Still need to drill the wrist pin holes, but other than that, they are finished. I decided to make them out of steel rather than brass, mostly cause I hate using my brass, but also I figured the steel would wear better. Turns out they weren't all that hard to machine.
I first cut 8 blanks from 3/8" OD drill rod. The blanks are are about 7/16" long which is 1/16" oversize. The first lathe operation after skimming the end is to drill a 1/8" center hole that is 5/16" deep. This will leave a 1/16" thick top on the finished piston.

Next I used a 5/16" end mill to bore out the bottom 1/16" deep, forming the skirt.

Here's 7 of the pistons after drilling the bottoms...

Unfortunately I didn't take any pictures of the slot milling operation. All I did was chuck each of the pistons in an ER20 collet chuck that allowed me to hold the piston vertically in my milling vise. Then I made multiple passes with a 1/8" end mill to form the slot. After milling all the slots, I then trimmed off the tops of the pistons in my lathe to bring the finished length down to 3/8".

Here's the finished pistons along with all the other parts I have todate.

Next I'll be figuring out the details of the valve and air supply assembly. This could take a few days...

Chuck

 

[Don1966]

Looking good Chuck, I am partial to the brass pistons. Never realized how small they were till you had it on your finger.

Don

 

[cfellows]

Thanks, Don

A bit of an aside today. Actually, building fixtures and improving the work area, all related to building this engine.

For the air delivery system, I'm using 3/32" brass tubing. Because of the engine design, I'll be needing a 90 degree bend in each tube that will have to be pretty tight. I have a nice tube bending set, but it won't achieve the radius I need. So I set out to make a special jig.

I needed to turn a 3/32" wide groove with a radiused bottom 3/64" deep. So, I ground a semicirular (more or less) tip on a 3/32" cutoff blade.

Then I chucked a 3/8" diameter length of drill rod in the lathe and cut the groove. Well, I actually cut two grooves because I originally planned to make a two-piece bending jig. I later decided it didn't need to be that complex.

Next I milled an axial notch on the center line of the rod and silver soldered a rectangular piece of cold rolled steel into it.

Finally, I drilled a 3/32" hole though the cold rolled steel, positioning the drill bit in the groove in the rod.

To make the bend, I insert the tubing into the hole...

Clamp the jig into my bench vice and make the bend using my thumb

Chuck

 

[cfellows]

I'm getting into what is arguably the most tedious part of the project. I've more or less settled on the air valve and delivery system. This part is hard because I want to keep the engine looking as much as possible like an IC engine which means keeping the air plumbing as inconspicuous as possible.

Here's a picture of where I am so far...

First I drilled the 7/32" axial hole along the top of the block. The brass tube with the air connection on the end will be Loctited into place later. The rotary valve will be a 3/16" length of drill rod with a 3/32" hole drilled lengthwise most of the way (but not all the way) through from the back. A flange will be soldered onto the back of the tube. This tube will then be inserted into the brass tube from the back of the engine. The flange will fit inside the air connector and will ride on a shoulder inside. This is the stop that will keep the valve tube from just sliding out the front of the engine when air pressure is applied to the back. The secondary cam gear will be mounted on the front side of the air tube and turn it at 1/2 the crankshaft speed.

Radial holes will be drilled through the side of the brass tube and the valve rod. These holes, which can barely be seen just below the ridge of the crankcase will then supply air through 3/32" brass tubes to the top of the cylinders.

The hex pieces are made from 3/16 hex brass. They will be threaded, cone side up, into the holes along the ridge of the crankcase. A 1/16 axial hole will be drilled through the center of each one. The brass tubes will have a flange and threaded caps to hold them onto the brass hex pieces.

OK, so is everyone thoroughly confused now?

Chuck

 

[Don1966]

Sure Chuck the brass tube will supply air to the engine right. Nothing confusing about that. Just how it gets to each cylinder is confusing.

Confused Don

 

[cfellows]

Sure Chuck the brass tube will supply air to the engine right. Nothing confusing about that. Just how it gets to each cylinder is confusing.

Confused Don

Thanks, Don, maybe this will start to clear things up...

I think I've got the details of hooking up the air tubes worked out. I made a prototype today. It's fiddly work and the prototype doesn't look very professional, but maybe I can do better on the rest.

I think the pictures will tell the story...

The end that threads into the crankcase is a 5-40. The other end is an 8-32. The through hole is 1/16" and the OD of the brass tube is 3/32", ID is 1/16". I'll take a picture of the fixture I made to flare the end of the brass tube.

I'll probably be tearing my hair out by the time I get these air tubes all done. Gonna be a challenge!

Chuck

 

[rhitee93]

Holy smokes! The next thing you will tell us is that you will be making double flares.

Very impresive scale :bow:

 

[dreeves]

Chuck what a great looking engine you have going on there. Im always impressed with the detail you have in your engines. Thm:

Dave

 

[Don1966]

Very nice Chuck, I am wondering where the end of those tube are going to go...

Don

 

[cfellows]

Very nice Chuck, I am wondering where the end of those tube are going to go...

Don

Here's drawing of what the engine will look like with all the air plumbing done.

 

[Don1966]

Awesome Chuck, I like it already. A rotory air valve and ball check, I like.....A Karma from me.

 

[cfellows]

Awesome Chuck, I like it already. A rotory air valve and ball check, I like.....A Karma from me.

Thanks, Don.

I finished up the flared tubing connectors this morning.

The female caps and the male part has an 8-40 thread on the flare end and a 5-40 thread on the smaller end which will screw into the crankcase. There is a 1/16" center hole drilled all the way through

Both the female and male parts are made from 3/16" brass hex rod. Chucking this small stuff in even a 3" 3-jaw chuck is troublesome and can come loose when trying to cut threads. So, after noodling on it for awhile, I rummaged through my socket drawer and found a nice 3/16" socket with a depth that was suitable for my work pieces.

I used this to hold the male part for both threading operations and for drilling the 1/16" center hole.

I also used the socket to hold the female caps for chamfering the top end and cutting the bottom end to uniform length.

Chuck

 

[rhitee93]

K point for the socket idea. This solves a problem I have that I was about to buy a hex collet for.

Thanks

 

[Ogaryd]

Hi Chuck,
Just wanted to drop in and let you know how much I appreciate the the time you take to share your builds with us. You better be careful, as much as your wife liked that crankshaft, she's liable to take that hole engine.
Regards Gary

 

[cfellows]

K point for the socket idea. This solves a problem I have that I was about to buy a hex collet for.

Thanks

Thanks Brian, glad you found something you can use!

Hi Chuck,
Just wanted to drop in and let you know how much I appreciate the the time you take to share your builds with us. You better be careful, as much as your wife liked that crankshaft, she's liable to take that hole engine.
Regards Gary

Thanks, Gary, for showing your appreciation! I'll make sure the engine has some oil smeared on it which will totally turn her off!

Chuck

 

[cfellows]

I thought I'd post some pictures of the new jig I made for bending the 3/32 brass tubing...
I started with this... it's turned from 3/8" drill rod and has a 3/32" wide, 3/64" deep radiused groove turned in it. It's screwed to the aluminum block with a 10-24 SHCS.

This is clamped in my vise, about 5/16" down from the top of the jaws.

Next I place the brass tube into the groove in the bushing

... and hold it there while I slide a stop block between the bushing and the vise jaw. The stop block has a 3/32" radiused groove in it so the brass tubing won't kink.

Then I take a second block, also with a 3/32" radiused groove in it and use my thumbs pushing on it to force the tubing around the bushing.

As the Brits would say, it works a treat!
Chuck

 

[SilverSanJuan]

Clever stuff Chuck. Thanks for sharing your methods with us.

Todd

 

[Don1966]

Very nice Chuck, I like that. You coming right along with your engine. I want to see the rotary valve when you make it.

Don