Proposal to design a "First Build" engine

[bearcar1]

A very cool looking engine that is something other than a wobbler. (those engines just get kind of boring after a bit) This one however seems to fit the requirements of a first time builder and the materials can be commonly found. Carry on... :bow:

BC1
Jim

 

[black85vette]

Here is my starting point for a spool valve. Not sure it is right. It is a little longer than it needs to be due to the fact that I kept the port to the head and mounting screws on the frame the same as the original valve and just worked around it. I think that functionally it is close.

Any comments / thoughts?

 

[Deanofid]

It looks basically what it should look like, Vette. The distance between the two "spool" diameters will be dictated by the throw of the eccentric. You might want to figure that out first, then decide where to position the spools, and you may have to reposition the intake port slightly so it's within the the outer limit of the spool travel.

Also, you can decide the eccentric throw by how long the spool has to travel. That's a little bit backwards, but will work just the same, as long as the spool doesn't end up having to travel to far.

Nice work on the trial parts, Quick and Vette.

Dean

 

[black85vette]

I got the spool valve to work. But I decided the engine needed more piston so I turned a 3/8" piston out of brass and re-bored the cylinder. That was much better.

Now a question for you real engine designers. How do you get better low RPM performance? Mid to high RPM runs well and I would like it to run slow and smooth. My first thought is; more flywheel. I have tried changing the timing in both directions by small increments without much difference.

Any suggestions?

 

[Deanofid]

Your first thought is on the right track, Vette. Also, it may just need to be run in for an hour or two.

It's still a fairy small piston, too. That, and if it has a pretty short stroke will make it want to run at the higher speeds. A longer stroke will often slow it down. Still, more mass in the flywheel is usually a sure bet.

Is the bearing surface for the crankshaft just drilled, or has it been reamed? A close running fit here will make for a better runner. If it wobbles in the crankshaft bore even the slightest, it will eat power and won't want to run slow.

Check for anything that binds. Should spin freely if you give the flywheel a flick. If you spin it gently a number of times and it stops at or near the same place each time, it's binding on something. Crank pin or valve pin are the first place to look.

Dean

 

[black85vette]

Thanks Dean. I think I can get a little more stroke with the room I have to work with. I also have some space on the flywheel side. It will require moving the valve outboard just a bit. But the nice thing is that they are really easy to make. Then I can go with a thicker flywheel.

The bearing surface was done with a chucking reamer. I may go back and put a brass bushing in it anyway.

I have gone through the binding exercise and got everything sorted out and it is running pretty free and loose. I think I will run down today and get some thicker material for the flywheel and try that first.

 

[rleete]

Long throw, long stroke and large flywheel for slower performance. Like an old mill engine. Also, double acting helps to smooth it out, but that increases complexity for the newbie. Look at this one for comparison:

http://www.pmresearchinc.com/store/product.php?productid=3083&cat=4&page=1


Note that the smaller the engine, the harder to get to run at slow speeds. A tiny oscillator will only keep running at a blur, but make one quite large (like a 1" bore, 2" stroke) and it will putt along much slower, but with a more "lopey" sound.

 

[black85vette]

rleete; thanks for the info. I have some changes to make. Next I am going to lengthen the cylinder body by .5 inch adding .25 on each end. This will make it less likely to drill through the head end and add .25 inch of room to increase the stroke.

I have moved the valve to the outside to allow for a 3" flywheel 5/16" thick.

Dean; you made me think about wobble in the crankshaft so I am planning on adding a brass bushing .438 inch wide for the shaft. That should give it a lot more horizontal stability.

I made the changes to the drawing and welcome any comments and suggestions. I think this is pretty close.

 

[Deanofid]

Dean; you made me think about wobble in the crankshaft so I am planning on adding a brass bushing .438 inch wide for the shaft. That should give it a lot more horizontal stability.

That will make a difference. I would fill up all the space available between the flywheel and crank disc with bushing.

If you make the engine to use a simple eccentric for the valve it looks like you would actually have enough room for a simple bearing block outboard from where the eccentric would lie. No bearing problems that way for sure.
The eccentric consists of a simple aluminum disc with one hole in it, off center 1/2 the distance of the valve travel. Would require a rod to run the valve. Could be simply a piece of flat stock with a hole in each end.

Dean

 

[black85vette]

If you make the engine to use a simple eccentric for the valve it looks like you would actually have enough room for a simple bearing block outboard from where the eccentric would lie. No bearing problems that way for sure.
The eccentric consists of a simple aluminum disc with one hole in it, off center 1/2 the distance of the valve travel. Would require a rod to run the valve. Could be simply a piece of flat stock with a hole in each end. Dean

That is something I kicked around early on in my head. My issue was some of the constraints we placed on this for new builders. What I like about that arrangement is that you can put the flywheel outboard and you have very little restriction on the size of it. Maybe we do another project as the "Second Build" engine and introduce the 4 jaw chuck and eccentrics.

Tonight I made another cylinder for a longer stroke and it helped the low RPM a lot. Now I am trying to carve out enough room for a 3/8" flywheel. I was thinking 5/16" but found that it is hard to find material in that thickness.

I want to do the bushing first since I think that will get some results.

Anyway it is running fairly well at about 7 or 8 lbs as it is with the new cylinder. Excuse the C clamp but I just wanted to try the cylinder and have not drilled the mounting holes yet.


[ame]http://www.youtube.com/watch?v=vvWlz9XTUBE[/ame]

 

[Deanofid]

It looks like it runs quite well Vette.
I'll bet that after you let it run for about an hour, then clean all the gray oil out of it that it will run down around 3psi.

For the eccentric I mentioned, you don't need a four jaw. Just drill one hole in a disc off center. Can be done with a drill press, or even with a hand drill, and ream it afterward.

Dean

 

[va4ngo]

I think a first time builder would also be interested in how you arrived at the build by show ing that video clamps and all

Well done I think its a great first project

Cheers
Phil

 

[zeeprogrammer]

If all you need is a lathe and minimum tools to make that then I think you have a great candidate for a beginner's engine. It's an interesting engine and looks more like what a beginner might think of as an engine. My first engine was a simple wobbler but I have to admit it wasn't what I thought an engine would look like. It seemed odd to me to have the mass of a cylinder oscillating like that.

How long would you say it would take for a beginner to make? Someone who hadn't touched a lathe yet.

 

[black85vette]

How long would you say it would take for a beginner to make? Someone who hadn't touched a lathe yet.

Not sure Zee. Lathe turned parts are the piston, valve and flywheel. Piston and valve are pretty simple turning exercises and with some guidance a few hours on those. The flywheel is not complicated but it also depends on which way they go. Flat stock or round stock? Also how much sawing they need to do and if that is with a hand powered hacksaw. That could eat up some time. The frame, cylinder, valve body and other bits are easy pieces and mostly layout / drill. Just a guess but maybe a weekend and the following week to finish? Based on my test parts I think someone with experience would do this in a day.

Brian could do in a morning if he didn't eat lunch till after 1pm :big: Then he would have the modified drawings and animation done in the afternoon. :bow:

Zee, I also ran by Metal Supermarket today to pick up some materials and talked with the guy about cutting materials. Specifically I asked about 3" round aluminum stock. He said they just charge $2 per cut. So, if someone did not have the means to part off, a band saw to cut it or the desire to start with flat stock and make a it round in the lathe, they could just order a 5/8ths inch piece of 3" round aluminum and pay the $2 cutting fee. My experience is that their cuts are pretty accurate, smooth and square. Sounded like more options to me. How does that sit with you?

 

[zeeprogrammer]

Now I'm trying to remember why I asked how long to build.... ;D

It would give some measure of difficulty and how soon the beginner would experience success. (I had mentioned earlier that, at least for me, an running engine is the primary goal.)

But that reminds me...we give each other 'That a boy', 'Great job', etc...It's important. I remember when I was in college in a microprocessor lab...the instructor said "If you build something...and it works...get up on the table and shout it out". I've done similar at work when a program finally works...stand-up...arms in the air..'yipppeeee!'. (Of course I quickly hide under the desk when everyone stops and looks at me with expressions...'what the?'.)

My point being...when it comes to instructions...remind them that they did good!

As for the flywheel...it does sound like an option..."How to get a round flywheel"...yeah...having 2 or 3 or so ways to get the raw stock ready is good.

Again...great idea here.

 

[black85vette]

woohoo1

I think we have a winner! Rebuilt almost the entire engine tonight. Drew up some changes during the day. Stretched the frame 1.5 inches to make the connecting rods a little longer and thus reduce some of the angle to the valve and piston. That also let me make some room at the end of the flywheel so it would clear the valve. That should allow for a thicker flywheel if the builder wants it. However, the 3" x 3/16ths brass flywheel that I have on it is working just fine. The other big change was a .5 inch piston with .75 inch stroke. That made a world of difference. Low speed is now great and it will run down to under 3 lbs steady and smooth. That is just what I wanted. Easy to build and a good solid runner.

Now back to the drawings. I made most of the changes today but found a couple of small tweaks as I was building tonight.

Thanks to all for the great advice and ideas on how to make it run properly. Your help paid off big time. :bow:

Then on to the next phase. Document a build and put together some instructions. I would appreciate everyone joining in and adding tips, techniques and info that a new builder might need to know.

It is later than I usually stay up. I was so close to getting it running that I just kept going. I will pay for it tomorrow. No pics or video tonight. I will shoot some tomorrow when I get home.

 

[rake60]

The grin here is probably as big as your own Vette.

Nothing beats that first runner coming to life! Thm:

Rick

 

[black85vette]

Here is the tools, materials and operations for this build:

Tool list:

Lathe
3 jaw chuck
parting tool
live center optional but useful

Hacksaw or Bandsaw

Center Drill Set - cheap and useful

Tap / 4-40 taper tap

Drills
#43 .089 for the 4-40 tap
1/8th inch
7/32 to predrill for 1/4 inch reamer
15/32 to predrill for 1/2 inch reamer
1/4 inch reamer
1/2 inch reamer

Drill press - preferred

You can eliminate the the drills and reamers if you drill to size, hone the cylinder smooth and then
fit the piston / valve to the hole. Fit is not critical and a little loose is OK.


Materials list:


1/4" x 2" aluminum flat bar / 11" long
3/4" square aluminum bar / 4" long
1/2" diameter brass rod / 4" long
1/4" diameter rod in mild steel / 5" long
1/4" x 1/16" flat brass
4-40 screws 1" long 15 pieces

Not all the 4-40 screws need to be this length. You can order shorter ones or just cut the 1" down to the size you want.


Operations:

Lathe
face
turn to diameter / length
cut to length

Metal saw
cut to length / about 6 cuts
no cut part is critcal or mated to another part so no milling required

Drill
center punch
center drill
drill pilot hole
drill to size
ream
drill to depth (cylinder)

Layout
measure and mark holes for drilling

Tap
tap through and blind holes

File
file a flat spot on the piston / valve stems for connecting rod (a mill can be used)
file cut ends smooth


I think this has stayed close to the original specs and objectives. I did learn that trying to go too small is just as hard as going too big. There is a sweet spot where things are easy to work on but still not take too much material.

 

[zeeprogrammer]

Good stuff there.

Just a few thoughts...reminders...or things to ignore...

I'm working on the assumption that by 'beginner' we mean someone new to machining in general...not just model engineering...

When listing the tool list...details are helpful. For example, the hacksaw...size? blade type? number of teeth?

The material list...360 brass? 60161 T6 aluminum...kind of steel.

You might already be thinking this and just wanted to show the list of items...so I hope you forgive me.

Maybe this is over the top...would a beginner know what a center drill is? Or even what reaming is?

Again, this may depend on what you mean by 'beginner'. Would a glossary be useful? Something that gives the definitions and/or uses of the various terms?

I'm sure I'm going too far...it's all about balance. But just want to provide what help I can.

 

[black85vette]

Zee; Good input. I think as we get into the documentation phase we gather the types of things you are suggesting and include it in a "Manual" with the prints, instructions and any useful information people will contribute. I think the first step will be simply to document a build and do some photos and comments on how to build it. Then start adding tutorial type sections as they are contributed.

Tonight I finished up some loose ends. Got the bushing installed and made some new connecting rods to fit the new stretched frame and longer distances. The great part is that it ran so well that the air gauge was not even moving off the pin. So I took the tube and blew into it and was able to get it to run! My wife shot a short clip of it running.

[ame]http://www.youtube.com/watch?v=h0sbeH-Zv5Y[/ame]

Here are some still shots of it in its "final" form. Excuse a couple of extra holes and a plug where the air tube was. I made changes to it rather than start all over (again).