Size standards for homemade engines !!?

[minh-thanh]

Size standards for homemade engines !!?
Hi All !
Currently, I have several types of engines with different cylinder diameters
I'm thinking about a standard size - or rather, cylinder bore - for the engines I'll be building
With a cylinder diameter of 16 mm, 2 and 4 engines may be fine but it cannot be used for a diesel engine (injector).
With a diameter of 20 mm it seems fine for 2, 4 stroke, diesel and flame eater engines
If I follow the existing design, I have engines with different sizes
And if I chose my standard cylinder size, I would have to design all the engines for myself

Do you choose a standard cylinder size for your engine ?

 

[GreenTwin]

I was in the process of standardizing on a 2" bore, and a 10" diameter flywheel, for steam engines.

Then the Ball Hopper Monitor and the Prusa XL came along, and so now we have 12" flywheels and a 2.125" bore.
The bore uses the scale factor to go from a full sized 28" diameter 4hp Ball Hopper Monitor flywheel to a 12" scaled flywheel.

The 12" flywheel is the largest I can machine myself, and a bit on the big side for me to be honest.
I want to hold the 2.125" bore because the piston rings are easier to make, and the smallest parts are not too small for me to easily see and machine.

I have various magnification levels of reading glasses, but it becomes very cumbersome to use the higher magnification ones.

It seems like with small/tiny parts, about the time you get it made, you drop it on the floor, and it rolls back into the Twilight Zone, never to be seen by humans again.

I have been asked "Why not just build a Ball Hopper Monitor with 9" flywheels ?".
I think the 9" flywheels are too small in my opinion, for me anyway.
I admire the smaller models, but my preference is to build what I consider more towards the grand scale for model engines.

A ball hopper monitor with 12" diameter flywheels would be the only one in the world, and I think would display well.
Yes it will be a bit on the heavy side.

So 2" bore with 10" flywheels for steam engines, and something near or at 2" bore for gas engines, with whatever sized flywheel the scale factor makes it.

.
Edit:
The full sized 3hp Frisco Standard has a 4.75" bore, and a 26" diameter flywheel, so if we scale down to a 2" bore, the flywheel will be 10.9" diameter, which is sort of in the 10" range (close enough).

I am designing the Ball Hopper Monitor around purchased gears, and so that also locks in a lot of dimensions.

For the Frisco Standard, I will be casting a set of helical gears from the 3D models that JasonB sent me, using the lost-PLA method with resin-bound sand, so I can 3D print those gears at any scale, and don't have to adhere to purchased gears (you can't purchase 2:1 ratio helical gears of the same diameter anyway).

.

 

[Jasonb]

16mm cylinder sounds small for a 4-stroke. You will have to use very small valves and spark plugs.

I have done twelve engines either my own design or scaled from other old designs and used 24mm bore on all of those which works quite well, this for steam, 2 & 4 Stroke, Hot air and flame licker.

The other thing governing size if making a scale model is being able to machine the largest part which is often the flywheel so that may well dictate the bore and mean 20mm or 16mm may be used if the flywheel of the original is quite large.

 

[TonyM]

I wouldn't base my engines on a standard piston size. With only a small lathe to work on the maximum flywheel size I can do is 8.5 - 9 inch. So I decide what scale I am using depending upon flywheel size. Piston size is developed from that scale(approximately).

 

[xander janssen]

I go for 25 mm bore since I can easily buy 25 mm honed hydraulic cylinder tube and this is then ~1:8 to ~1:12 scale if I build replicas of old stationary and marine engines.

 

[minh-thanh]

Thanks for the comments !
Personally, I quite like the 20mm diameter
Regarding the flywheel, I think if we can't make the diameter large, we can make the outer rim of the flywheel thicker.
I'm looking to limit too many diameter , which will help with purchasing materials, tools, etc. becomes easier.
Another advantage is that some engine parts... can be shared, which makes machining a bit simpler.

 

[Steamchick]

My Father standardised on 1inch bore... for small steam engines, stroke from 1" to 2". The fixings at 6BA were as small as he could easily handle (BIG fingers!) - and see.
I can make stuff using 8BA fixings, but I baulk if I need more than a few fixings at 10BA! - And "non-scale but looking good" is my moto for fixings. (4 x 6BA may work, but 6 x 8BA look better?). I have made in 1/2" bore to 1 1/4" bore (Steam) But would not really want to go below 3/4"/20mm bore in future.
A watch and clockmaker I know makes internal combustion engines (up to a double 9-cylinder radial engine) at 1/2" bore.... because whether single cylinder or multi-cylinder, he has made jigs and fixtures for making pistons, valves, etc, and makes his own spark plugs too - because of the small size. Even uses piano-wire push-rods! But his eyes suit small things... not distances.
So check on a comfortable size for your fingers and eyes for the small bits, like fixings, etc. before you determine "Bores", etc.
Enjoy!
K2

 

[stang86efi]

Here is my project . It will have a 1.500" bore, with 12" flywheels that are patterned after a Heavy Electric design. Machined they weigh in at 23 lbs each. I agree with others in this forum about the smaller scales and their hardware. I work much better with at least 9" flywheels.
Kudos to you guys that build the smaller ones!

 

[Steamchick]

My lathe isn't big enough for those flywheels...

 

[minh-thanh]

So check on a comfortable size for your fingers and eyes for the small bits, like fixings, etc. before you determine "Bores", etc.
Enjoy!
K2

The way I do the engine is the opposite of your opinion.
I usually choose - always - cylinder. If I am capable of making cylinders, other parts will follow

My lathe isn't big enough for those flywheels...

That's also a reason,
Too much engine size will be a problem

 

[olympic]

It seems like with small/tiny parts, about the time you get it made, you drop it on the floor, and it rolls back into the Twilight Zone, never to be seen by humans again.

Couldn't agree more.
And not just parts. I once lost a 000-120 tap ( don't even think of asking what I was up to); it broke (again, don't even think of asking how). Though I found the shank, the threaded part, which I had hoped to perhaps salvage in some undefined way, had vanished into an alternate universe, and I had to buy an expensive new one to tap the one hole that needed threading....

 

[werowance]

last couple 4 strokes i did were 7/8 bore and 3/4 bore. one thing i was glad about is the largest collet i had was 7/8 and i prefer holding the piston in a collet if i can to do all the underneath the piston work. yeah, couldve used a vise or vise/vblock etc but the collet is so much easier and holds better in my opinion when im doing stuff like that

 

[josodl1953]

I find 20 mm a handy dimension for cylinder bores, I used it for my Edwards radial 5 and now for my boxer twin. You could use the same fixtures etc. if you use the same bore everytime. 20 mm gives you just enough space in the cylinder head for valves and 1/4" 32 TPI thread for glow and mini spark plugs.

Jos

 

[minh-thanh]

I find 20 mm a handy dimension for cylinder bores, I used it for my Edwards radial 5 and now for my boxer twin. You could use the same fixtures etc. if you use the same bore everytime. 20 mm gives you just enough space in the cylinder head for valves and 1/4" 32 TPI thread for glow and mini spark plugs.

Jos

I quite agree with you, 20mm diameter seems to be the best for me, Only with stirling engines it seems like that diameter , engine will be quite large