Starting a new engine

[Bogstandard]

When I saw the vid of Chucks pseudo hit 'n miss I was mesmerised by it and played it over and over again, and when Chuck gave a very good explanation of the poppet valve system I then decided that I must make one. I am not going into the full build, but just like the mine engine, snippets in time during the build.
When I start an engine I always make sure, if possible, to have the major bits to hand so that I know I won't be held up during the build, a sure fire way of a project finding its way under the bench.
Here is a pic of the basic materials for this project. I have a confession to make, I have already started on it. I had a lump of old rusty steel bar and before going any further I needed to know if it would be any good for the cylinder. It didn't turn out too bad, by the time I had got rid of all the holes and cross drillings in it, there was enough left to make a cylinder for an engine of 1" bore x 2" stroke. A real silk purse out of a pigs ear.

So the other bits are a plasma cutout aluminium 1/2" thick disc that should make the base, uprights and con rod.
Some gears that by machining and ganging will give me a 6 cycle engine.
The top end of a sash weight which will give me the piston, the loop from the top won't be thrown away, there is still a bit of cast in that just begging to be made into something.
A bit of SS rod out of an old printer, and some flanged bearings that I use for everything because I have so many I will be making engines for years to come.
The last bit nearly made me cry when I got it out of my stash, a lump of bar end brass to make a couple of flywheels. I don't know why it upset me because I got a load of it from the scrapyard, but it is just the thought of using it. I just might find a bit of replacement steel so I won't have to use it.
Now lets see if we can make an engine from junk, plus a little bit.

John

 

[Bogstandard]

Right, here we go about how I go about making a new engine.
I always start with what I call a 'fag packet' sketch (in American that would translate into an empty cigarette packet being opened up and drawing on the plain paper interior), but in this case I have used a piece of paper. The drawings contain a basic prelim view of the engine with quick notes on it showing features that will be required to make the engine. Usually no dimensions are shown as this is a suck it and see (or winging it) build. So here is my sketch, not pretty to look at but it shows what I want.

This is as far as I have got at the moment, the cylinder is basically made, the piston is finished. When the piston is put into the cylinder with a bit of oil spread around, it takes nearly 30 secs for it to drop to the bottom, so I have a good enough seal to carry on to the next stage.

By the way, if this engine works as well as I hope, I will build another but using materials for running on air only, and no races.
It should make an ideal beginners project. (Shred please take note)

John

 

[Bogstandard]

Now I am starting to design and make things, but still winging it.
Marv would say, 'all this could be drawn up and everything calculated to get the angles correct, and made from those drawings'. I don't work like that, it is too slow for me and also geometry isn't my forte.
So here is where I am up to.

I want to fit roller bearings into the big and little ends, so a machined one piece crank can't be used, so I have gone for a built up one, with one of the crankpin ends left floating to allow disassembly for bearing fitting, I might put a bolt thru it or just leave it floating, it depends how the flywheel standards turn out, and if they are rigid enough to allow for a floating pin or not. That is a go back to it job as the engine progresses.
To give you some sort of scale on this engine, the conrod is about 4.5" long by 3/4" high by 1/2" thick, so this is no small engine. As you can see it has been roughed out on the bandsaw and is now ready for machining, all on the miller, no lathework on this rod at all.
The holes are in fact finished to size for fitting bearings, but treated in different ways. I always like a bit of force fit for my bearings when going into ali, so the large hole was just brought up to 1/2mm undersize then the 13mm drill was very quickly wacked thru the hole in one hit, to leave behind a very rough surface. This gives me the interference fit I am after.
The smaller 10mm hole was finished in a different way, the hole again was brought to 1/2mm undersize but then a 10mm hand reamer was fed in from either side until it only just protruded from the opposite side. This gives a slight taper going into the centre of the hole, because unlike machine reamers, hand reamers have a tapered lead in and I use that to my advantage. The further the bearing is pushed into the hole, the tighter it gets, and I am using two bearings, one inserted from each side.
Nice tight fits all round.

John

 

[cfellows]

The valve I used in the video, although functionally the same, is physically different. Hopefully you can see in the pictures below how this other, inline arrangement works. The view is from the top. The first picture is with the poppet valve closed, so the air is free to pass from the cylinder to the exhaust. The second picture is with the Poppet Valve Open, which pushes the small blue piston valve down, closing off the exhaust port, and exposing the inlet port to the cylinder.

Although this valve arrangement is more elegant, it's much harder to keep air from leaking around piston valve when "firing". So, you tend to get a lot more air noise and the engine consumes more air when running.

Chuck

 

[Bogstandard]

Chuck,
Many thanks for making the effort to explain it to me. It is a more compact unit.
I will be going with your original solution to the inlet and exhaust system, mainly because it will allow me to have a remote poppet valve, as shown in my rough sketch and allow me hopefully to have a scale looking speed control, I suppose that I will have to have a slightly different timing on the cam to allow for the connection pipe from the remote poppet to the engine.
What do you think of the bore/stroke ratio that I am planning, 1" bore, 2" stroke. My reasoning for this is to give a slower running engine, and is the same ratio as I use for my live steam engines.
Can you give me any pointers towards spring pressure on the sliding piston, it would save me a lot of time in experimentation if you could.
As I have said before, your engine totally fascinated me.
If this one is a success I am hoping to scale it down and make it a little easier to make, then present it as a build package on this site to give the beginners a chance of making a copy of your great little engine.
Again many thanks for your input.

John

 

[cfellows]

A 1" bore x 1.5" stroke would be more in line with the ratios I typically use for a slow running engine, but a 2" stroke should work fine too, if you don't mind the amount of air it will use to run it. The engine in the video has a 7/8" bore and probably about a 1.25" stroke.

Spring pressure on the sliding piston is pretty light, something with a wire size like a retractable ballpoint pen spring. The sliding piston fit should be a loose enough fit that the spring can return it to the home position once the poppet valve closes. I'd use a 1/4" or maybe even 5/16" diameter port for the sliding piston valve.

By the way, there are two more engine videos on my website now that use this same poppet valve arrangement. The 2 cylinder horizontal engine is a "4 stroke" version, and the 1 cylinder vertical is a "2 stroke" version.

Chuck

 

[Bogstandard]

Chuck,
You've done it again and saved me hours of development time with that spring and piston info.
I think you must make engines the same as I do, make and modify as you go along. You end up with some very interesting engines doing it that way. And of course you will understand more than most how much a little bit of info like you have given me shortens the development time, plus less bits to remake over and over again trying to find the right solution.
I looked at your other engines, absolutely wonderful, and unique. I just hope mine runs as well as yours do.

Many thanks

John

 

[cfellows]

I looked at your other engines, absolutely wonderful, and unique. I just hope mine runs as well as yours do.

Thanks, John. Luckily, these engines are pretty easy to get running. Most of the twiddling is to get the right exhaust note with the least amount of air.

You have a couple of interesting feature on your drawing. For example, putting the poppet valve back by the crankshaft is something I hadn't thought of. Also, the "carburetor" speed control is a cool idea.

I generally put the poppet valve in the head, but that just because I'm trying to simulate the layout of a gasoline engine as close as possible. Can't imagine why your arrangement wouldn't work just as well.

You can also vary the speed of the engine with an inline pressure regulator. It gives a little bit different running characteristics and the exhaust note is a little softer.

The nice thing about this type of valving is that it works about the same on virtually all engine designs - singles, twins, inlines, v-engines, radials, etc. The other nice thing is that it only requires one cam lobe and push rod.

On a future model, I want to use an impact valve motion instead of the standard cam configuration. The new model will use a spring loaded push rod that will be pulled back by a spiral shaped cam. When the push rod is pulled fully back, the cam will release the push rod and spring pressure will "fire" the push rod into the valve stem, like an airgun. This will open the intake valve much more quickly, but then also will shut much more quickly. I'm hoping this action will more closely simulate the combustion of fuel in the cylinder by using a lower volume of air at a much higher pressure.

Chuck

 

[Bogstandard]

Chuck,
The reason for the remote poppet valve is that if a beginner was building the engine it would give him a chance to move it around to get it to fit as he might not be able to use the same gearset as I will be using. It won't be to 'scale', but it would solve the problem.
With reference to getting the engine sounding 'right'. I too like to have the exhaust note correct if possible.
This is a little idea that I came up with a couple of weeks ago and it does work well, plus it is very easy to experiment with to get the right sort of sound.
http://freeforums4u.com/viewtopic.php?t=536&mforum=homemodelengine

Used it to good effect on my mine engine

[ame]http://www.youtube.com/watch?v=76FAAv-PB78[/ame]

It just might work on yours, and it only takes a few seconds to try out.

John

 

[Bogstandard]

Got a little bit more done today.
So here are a couple of pics which also demonstrate a couple of tips.

This first one shows one of my tips that I used on the pipe flanges, but for a different use this time. To set up for machining a taper on the conrod.
All I did was mark up the conrod with the taper I want, and by swapping and changing different sized rods or drills in the two holes I got the line parallel with the top of the vice jaws. Used in conjunction with a back stop, once one side was machined it was just flipped over, pushed up to the backstop and tapped down onto the jaw tops and the second side was machined. Perfect symmetry on the conrod.

Here is the finished rod after a couple of hours work.
But it is the flywheel blanks in the background that are the source of the second build tip. You will notice on each of them at the centre is a small machined boss, sitting on top of the main central boss, it is only 10 thou thick but is a major contributor to less friction in these engines we build.
If the flywheel, or in fact any rotating part is against a ball race or a plain face, this boss ensures that the friction is reduced by only having a small surface area in contact. Also if used against a ball race it makes sure that only the centre part of the ball race is being turned.

You will notice that there is an item missing, the crankshaft. That has been consigned to the recycle bin. The reason being is that I am taking Chucks advice and going for a shorter stroke, 1.5" instead of 2". It will only take an hour to make a new one.
But it does go to show that asking the right questions and taking advice when it is given makes building these engines a lot easier.
By using the info Chuck has given me has most probably shortened the build by about a week.

John

 

[deere_x475guy]

Bogstandard, great looking engine there. I really admire you guys that can take what you have and design, build a working engine. Heck like I said I still don't have on that runs yet. I did get a good ways on the cam for the Edwards Radial 5 and will post pics of that in another thread. Keep the pics coming...))

 

[cfellows]

John, I love that connecting rod. You really do very nice work. Can't wait to see more...

Chuck

 

[rake60]

That connecting rod looks very authentic.
It looks like a highly polished cast rod.
Amazing work!

Rick

 

[Bogstandard]

Thanks for the good comments lads.
There is a reason for doing this profiling to a con rod. If you just had flat sides, in ali it is in fact a fairly weak component. By adding a curved profile to it the rod will in fact be a fair amount stronger. It is a clear case that goes against logical thinking, removing metal to make the item stronger.
There were no special jigs or angle pieces used in its making, just a couple of rods as shown in the first pic for doing the side angles, a 1/4" roundover bit, a 1/4" bullnose bit and a standard endmill. The main bits to making something like this are, the backstop, and machining the component in the correct sequence so that you can still hold it safely to carry out the next sequence.
Eventually, when I get some free time, I will do a little series on how easy these things are to make without any special jigging.
By the way Rick, if you give it a good dose of course grit blasting and painted afterwards, it would look just like a real casting.

John

 

[Bogstandard]

I would just like to add something because of a thing that Bob said.

I really admire you guys that can take what you have and design, build a working engine

MOST engines consist of a cylinder, piston, rod and crank.
The only major difference between any of them is how the power is got to the top of the piston, everything else is just basically the same.
So there are no mystical spells or alchemy to building an engine, just a few basic rules.
Once you can get these under your belt, plus a bit of machining experience to make the basic parts it is well within reach of everyone.

I would prefer rather than somebody praising me for doing something, to ask how it was done. That way you could learn how to do it as well.
Something like 'Hey John, nice conrod, can you tell me how you put the tapered profile in the side'.

John

 

[gilessim]

I was just looking at this post and wondering exactly how you did that gouged out bit on the sides John, it doesn't look like you just tilted it in the milling vice with a ball end cutter ,or did you?

 

[Bogstandard]

Giles,
That is basically the process but you need the fixed stop as a reference. Basically you start off with a slight uplift on the end you want to go deeper and wider. Lift the cutter slightly and look to see if it is anywhere near to the same taper as the outside faces, if not, just raise the end a bit more, I do it with a small wedge, bring your cutter down again into the narrow end until it just touches and take another cut. Repeat this until you have a tapered slot that matches with the outside edges. All I do then is just mark my little wedge, flip the job over, put the wedge into the mark and do your cuts to get down to depth. It really only takes minutes and gives a very good rendition of casting.

Hal,
Maybe I should have worded it slightly differently.
Your final sentence says it all.

John

 

[Bogstandard]

Cookin' with gas now.
Managed to get a pair of flywheels to the roughed out stage, just need a bit of file work to blend everything together, then a quickie polish and they will be finished, but that bit comes later, get it running first then bling it up. Why waste time on something if it won't run.
The first one took over 3 hours, but once I had got all the co-ordinates the second took less than half that.

This is a shot of the new 3/4" throw crank, it looks a bit out of wack because the top right hole is free, this will allow it to be used with ball races, the rods on the sides will be trimmed to fit once the upright plates are made.

Now the basic parts for the engine are made, so it is just a matter of getting them into the correct positions to each other, plus it must also look right. So tomorrow it will be a bit of ali platework.

This is what I was on about a few posts back. Once you have the basic engine configuration, then make it into whatever you want.
Just imagine it as either a horizontal or vertical, steam or gas engine. This basic design could be used for any of those. It is just a matter of putting the right bits on.
The difficult bits now start, because I have never made a poppet valve system so I am working in the dark, thank goodness for Chucks info.


John

 

[1Kenny]

So thats how you put the relief in the rod. My simple mind couldn't figure it out. :?

Kenny

 

[Bogstandard]

Kenny,
I think I have said this before. Machining isn't at all difficult, it is just a matter of thinking how to do it.
Now you have read the post, and everyone else who has read it as well will have no problems making these tapered recesses. By the way it doesn't work with a normal cutter (unless you do a more complicated setup), or if your depth goes deeper than half the cutter width at the wide end. If that happens, you need to go to the next size up ball end mill.
I tend to shy away from complicated machining methods and usually just stick with a few special shaped cutters to get to where I want. In fact the flywheels were made with a 3mm and a 1/4" slot drills on the RT and on the lathe just my profile tool and a special tool that I ground up specifically to make the recesses in the flywheel. I have many hundreds of tool bits that I have tried over the years, but I still come back to a basic few. So you most probably don't need a lot of the 'special' cutters that are available, just go back to basics and use the basic ones to their full potential.

Easy way out John.