Engine Design basic questions

[lohring]

My first engine that I designed and built in highschool is below. It was designed to compete with existing high performance 10 cc model race engines of the time (1960). I don't recommend that it be anyone's build.

Lohring Miller

 

[Dr Jo]

Sadly I think the OP has vanished.....

Jo

 

[minh-thanh]

Sadly I think the OP has vanished.....

Jo

Yes, only when there is a need, ,appears and disappears
It's a problem I've seen in almost every forum I've been to

 

[Longboy]

"Reading a bunch of golf magazines does not make one a good golfer" (author unknown).
Hello Andrew. You need to dip into a planned single cylinder bar stock model like a WEBSTER. Hands on experience without frustration a good way to get into the hobby. The engine bore determines your scale and everything that follows leads back to that, from the fasteners to the flywheel diameter. One inch bores will get you models that fit upon a phone book. Single cylinders cut your expense down till your confidence grows to invest in more expensive multi cylinder designs. Read build log posts here and on other forums for ideas and techniques. Do standard, proven designs then after such success, you can wildcat your own ideas. You got the machining know how in the 1st chapter......now get a chuck of aluminum and the end mill and have at it! ....Dave


Oh for cryin' out loud....he took a hike?

 

[ajoeiam]

Might be a case of TMI (too much information).

Ideas that upon first look seem fun can sometimes turn - - - - well - - - -not so fun when the full extent of the challenge appears.

He'll be back if he wants to do something.
This place is a pretty good resource for a lot of things to do with metal working - - - imo anyway!

Keep on keeping on!!

 

[L98fiero]

"Reading a bunch of golf magazines does not make one a good golfer" (author unknown).
Hello Andrew. You need to dip into a planned single cylinder bar stock model like a WEBSTER. Hands on experience without frustration a good way to get into the hobby. The engine bore determines your scale and everything that follows leads back to that, from the fasteners to the flywheel diameter. One inch bores will get you models that fit upon a phone book. Single cylinders cut your expense down till your confidence grows to invest in more expensive multi cylinder designs. Read build log posts here and on other forums for ideas and techniques. Do standard, proven designs then after such success, you can wildcat your own ideas. You got the machining know how in the 1st chapter......now get a chuck of aluminum and the end mill and have at it! ....Dave


Oh for cryin' out loud....he took a hike?

What's a phone book?

 

[minh-thanh]

Might be a case of TMI (too much information).

Maybe that's also the reason.
With homemade engine :
Simple
Designing an engine must be based on what the designer can do, or at least he must rely on his experience to judge that he can do the parts of the engine. which he designed.
If OP is confident in his abilities, then based on the knowledge he has... he can design and build his own engine. Simple

 

[Bentwings]

Hi All,

Being a newly minted engineer (as in Diploma not Engineer with a Degree), obviously I have a head full of knowledge and no real world experience.
I am also learning quite a lot including self learning (I have a book and I am not afraid to use it!). The current book I have is about the design of
four stroke engines, so with pen at the ready I was going to use this book to help design a basic One Cylinder petrol (ok, gas for you Americans) four
stroke engine. Nothing fancy, just something that "should" work and has all of the basic bits like cranks and valves and cam shafts etc. For those
interested, the book is "Engineering Fundamentals of the Internal Combustion Engine" by Willard W Pulkrabek. This guy is apparently a Guru and is
better known for his books about Two Stroke engines but I find it easy to read and understand.

I am at the very beginning of this journey. I am going to read the book and work everything out as I go, then draw it and try to build it. One of the
things I need to decide is how big to make it. I want it to be big enough so that it doesn't cost too much to fabricate, but not so small I need a
watchmaker's lathe to do the machining. I also thought that if it was big enough it might serve some useful purpose in the future. One idea in the
back of my mind was that it might be nice to use the base design for other more complex designs later. My thoughts on this were: a One Cylinder
engine should be easy to turn into something like a V-2 (No. NOT some fancy rocket from the 1940s), that in turn could become a V-4 then a V-8.
By now you are probably thinking that innocence and naivity is so sweet. Well - we all started somewhere.

So, some questions.

What is the smallest practical engine that can be built? I don't want to either make my own spark plugs or source ones only available to Pygmy tribes
of the mythical Himalayas of Antarctica. I want to scale it so that I DON'T have to fabricate EVERYTHING.

What is a good size engine that might be of practical use? My thoughts here were that a 5 Litre V8 is common so what about a 0.5 Litre engine?
This would make a single cylinder engine about 25cc or 1.5cu" - is 1/10th scale too small?

The little I have read so far suggests that a "square" engine, or close to it, is practical. What the book does NOT tell me is that Stroke is easy, but is Bore
the DIAMETER of the cylinder so that 25cc = 5 x 5 or is it the ACTUAL area of the cylinder (Pi x 2.5^2) x 5 = 19.63cc when working out the size? The book
has some great definitions but that particular one is ambiguous.

What are general tolerances used in engines like this? Metric please - I can cope with "thous" but I have 10 fingers not 12 so it is easier for a "youngster"
(over 50) from Australia to work it out. 1 thou = 0.0254 mm - just sitting on the edge of the accuracy of "common" machine tools.

Final question. I have been a member here for a while, mainly lurking and reading other people's posts. I did at one stage download some files from
this site but they seem to have disappeared. I know there was a way to do it but there don't seem to be many files in the downloads section, only
posts about the files. I recall downloading some Steam Engine plans some time ago. I notice I can attach file to this post so is it I just didn't dig deep
enough into the Downloads forum? What I would really like to find is a simple car style engine plan to have a good look at. It doesn't have to be a V8
just one with all of the standard bits - cylinders pistons, crank and cam shafts, valves, etc.

Thanks in advance for all of your help.

Cheers I agree with above assume ts.

If you want a challenge, something I’ve wanted to do for a long time. Two stroke or even 4 stroke Rc model engines are not too expensive. I’ve wanted a two stroke in line Rc model engine not many are available. You could get two then design a new crankshaft and crank case adaptor and connect them together . On the inter net there are a couple of conversions using mostly stock parts using weed eater engines some Rc engines like Zenoah have a stub of crank sticking out the rear . A jaw coupler with urathane spider would be a neat project . I have a pair of two cylinder double acting steam engine connected this is an assembly kit . Lots of pieces but no real machine work . This is a pretty pricey kit and it takes a lot of trickery to make it run right. But it will run on 30 psi compressed air. The hardest part is getting the eccentric on the piston valve slighted correctly the instruction page basically says “ adjust as shown in the picture. This shows the eccentric with Allen wrench sticking out of set screw ( grub screw) it’s up to you to figure out the exact position and it’s critical . I have a long document on eccentric setting piston valves that I still have not mastered . I’ve had several opposed twin Rc engines and they have run very well again the crank shaft is special on these but very durable

Andrew

 

[Steamchick]

Hi Andrew, On setting the eccentric for a steam engine, you should not go far wrong when set 15 degrees ahead of BDC for exhaust valves just opening... or inlet just opening at TDC? - I have used both as a starting point then tweaked to optimise depending on use of the engine.
Of course, a lot depends upon the geometry of inlet and exhaust opening and closing times, arrangement of eccentric linkage, etc. - Which is why there are so many different geometries of valve gear, Joy, Stephensons, Walschearts, etc...
The Steam equivalent of the piston ported "valve-less" 2-stroke IC engine would always be the Oscillating engine, - which can be made without worrying about valve timings. Just drill ports accurately according to "the book".
N.B. Joining engines in series, as suggested by our old friend Bentwings, can cause some strange effects in flexible couplings by different cylinders getting a bit ahead or behind others, and setting-up some terrible (destructive?) torsional vibrations.... When a resonance occurs they fight each other until the coupling is over-stressed and fails. Far better to have torsionally rigid couplings with "perfect" alignment.

I suggest you do as "a majority" of modellers have done.... Make a small steam engine - and make it run and power something. This will prove your skills at making things like pistons and bores that fit properly, crank-shafts that are not misaligned, valves that seal, bearings that do not rattle or seize, etc.
Then you can use the proven skills to make small IC engines. Start with a piston ported 2 stroke to prove you can make a runner with good compression.
A half-inch to 1 inch bore and stroke is a reasonable starter model - steam or 2-stroke IC - before you get too ambitious and go smaller or bigger! (I started with a 1/2" bore and 3/4" stroke V-twin steam oscillator - because the kit was cheap. Learned a lot!).
Then think about 4-stroke IC valves and valve gears! Modelling is an education in precision manufacture, so always use the best tools and materials you have or can afford.
And always ENJOY the hobby. We all make mistakes - then discuss solutions or lessons learned on this website. A good way to learn is from mistakes - hopefully others' mistakes, not your own.
K2

 

[Steamchick]

Ho Hum, just read post #22...
Bentwings and I are talking to the ether - as happens... Must be an age thing...? - Am I getting old?
K2

 

[lee webster]

I am not the OP. But I could have been. He asked the question I never thought to ask. When I drew up (I won't use the word designed, it makes it sound as though I knew what I was doing) my first engine, I didn't know anything about bore to stroke relationships etc, or that one could build their own sparkplug. With this post I know a bit more. I am sure it will help me design an engine with a good chance of working. I am "drawing up" an engine and getting to grips with Solid Edge at the same time. Not as easy as DesignSpark, but it has more going for it. My new design is a 30mm bore and stroke, open crank horizontal single, water cooled OHV with two luverly flywheels. Oooo, I do love me a flywheel.
Don't give up on this post, I need it.

 

[ajoeiam]

I am not the OP. But I could have been. He asked the question I never thought to ask. When I drew up (I won't use the word designed, it makes it sound as though I knew what I was doing) my first engine, I didn't know anything about bore to stroke relationships etc, or that one could build their own sparkplug. With this post I know a bit more. I am sure it will help me design an engine with a good chance of working. I am "drawing up" an engine and getting to grips with Solid Edge at the same time. Not as easy as DesignSpark, but it has more going for it. My new design is a 30mm bore and stroke, open crank horizontal single, water cooled OHV with two luverly flywheels. Oooo, I do love me a flywheel.
Don't give up on this post, I need it.

Hmmmm - - - - 'getting to grips with Solid Egde' - - - how did you manage to get a copy?

TIA

 

[Steamchick]

A bloke at the local Club brought in a new (Chinese) horizontal single - a bit smaller than that - with twin flywheels. Delivered earlier this week he could not get it going. He spent more than a day sweating and trying "all he knew" to get it going.
Problem was "no fuel". The tiny needle jet carb had a tiny air-lock underneath it, so fuel could not overcome the surface tension of the fuel at the tiny hole to allow it to be sucked into the engine past the needle.
Cure.
A finger closed the carb mouth, while another finger held the auto inlet open. Engine rotated to suck fuel into the cylinder, breaking the air-lock at the carb jet. With excess fuel it then started easily and we had fun running it and taking photos. Lovely hit and miss!
There's always a way to make things work, that are not mentioned in the Instructions! - or on the Utube videos...
But here is one that I found, so you can see the engine I am describing.

Enjoy!
K2

 

[lee webster]

ajoeiam. Are youconfusing the programme I use, Solidedge, with a programme called Solidworks? Solidedge has a community edition of their programme that is free to use with a few limitations. Type "Solidedge community edition" into a browser and it should take you to their website. As for Solidworks, I did have a free student edition, the licence lasted a year. I decided not to renew the licence because the right to use it could have been withdrawn at any time. It was a fantastic programme though.
Steamchick. That is a very nice engine! Personally I would paint it. Probably maroon.

 

[Steamchick]

Not mine to paint. But the guy (the club chairman) who just bought it does things like painting.... he likes RED - has a big pot of a proper RED. All his models are painted RED - fills a table at the open day shows. I like models in original industrial colours, Dark Green, dark Blue, mid-grey, Maroon, etc. as per original decade when they were built, and I have paint pots of Black, mid-grey, and an un-used tin of White.... for my models. I used all the dark Green. Growing-up in the 1950s there was a lot of ex-military grey available... so a lot of my memories are of the grey 1950s. Then in the mid-1960s they invented Colour. Not just televisions, but paint, fabrics, etc. and even the grass turned green... the sky was blue, sun came out and we were happy... Men stopped wearing white shirts and grey ties, but had coloured shirts, etc. Cars changed from Black to shades of greenish or blueish grey, RED, etc. - and we had the first Yellow painted house in the street. And a Red mini (car). No wonder they had to invent colour television for all that happened then.
So why have we just had 5 or 6 years when Grey has been so popular? Cars, interior decoration, etc... It started before COVID, so we can't blame that!
Maybe Grey, black and white are cheap?
K2

 

[lee webster]

Whilst I agree with your choice of colours, I think I would paint my first engine maroon, or maybe dark blue. Should an exposed con-rod be painted? I have been to hundreds of vintage car shows over the years, and seen hundreds of stationary engines running. From rusty just as found to painted and pin striped. They all have their charm. But I can't recall seeing a painted con-rod. It seems right to me though.

 

[Steamchick]

Hi Lee, Maroon with yellow pin-stripes looks good on Showman's engines. K2

 

[Steamchick]

Navy blue with white pin-stripes?
K2

 

[ajoeiam]

ajoeiam. Are youconfusing the programme I use, Solidedge, with a programme called Solidworks? Solidedge has a community edition of their programme that is free to use with a few limitations. Type "Solidedge community edition" into a browser and it should take you to their website. As for Solidworks, I did have a free student edition, the licence lasted a year. I decided not to renew the licence because the right to use it could have been withdrawn at any time. It was a fantastic programme though.
Steamchick. That is a very nice engine! Personally I would paint it. Probably maroon.

Ahhhh - - yes. I am looking - - - - except I don't do M$ stuff here.
AIUI solidedge and solidworks used to be direct competitors.

I too have found 'student editions' to be really not worth using.
Los of garbage attached to make it at least somewhat 'non-usable' imo.

Thanks

 

[timo_gross]

one thing you didn't ask about is what size machinery is required to make a model engine. I have a 200-lb bench top lathe, and a similar bench top mill, but the mill is not really stiff/rigid enough so I have a 1500-lb(?) bridgeport clone in the garage which is overkill but it was used/worn-out and practically free, and I still use the indoor bench top mill for some drilling + tapping and very light milling.

Nah!.... Bridgeport clone is not overkill. More easy to overshoot with budget or space requirements than reaching "overkill territory".
In doubt you can easier make small parts on a bigger machine than the other way round.