Any one building small engine

[SmithDoor]

Here is a excel work sheet for compression ratio.

Ok excel not allowed

 

[SmithDoor]

Now this Excel worksheet
It is in a zip file

Dave

 

[KenC]

The blind bore of your cylinder is not necessary, just use a separate head screwed in place like on a Cox but threaded for a plug. This way you do not have to lap a tapered blind bore. Have you built a sensible sized engine, say 1 cc to 2.5cc ? If not I guess you have a long path ahead of you. Why not build a proven design like Richard Gordon's 0.1cc Nano, plans for which are available. Far better than struggling both with the design and the manufacture for your first engine, let alone a small and challenging one.
Ken

 

[KenC]

Just checking your design. The stroke is 0.3 and the head clearance is 0.05". So even if you wrongly use the full stoke for compression, this gives a comp ratio of 6 to 1 which is very low. But bearing in mind that the exhaust will be open for a bit less than half the stroke, your effective comp ratio will be perhaps 4 to 1 at best. At such a low ratio the engine is unlikely to run and it certainly will not run without the battery attached to the plug. If you could publish the timing period for the exhaust then a proper calculation could be done for the head clearance, but it will be a lot less than 0.05" and just a bit difficult to achieve on such a small blind bore!
Ken

 

[KenC]

Now this Excel worksheet
It is in a zip file

Dave

Your calculation is incorrect. Compression ratio is not just stroke divided by head clearance. It is calculated from the amount of stroke after the exhaust port is closed. And do not forget that on such a small engine, the volume within the body of a 1/4" glow plug will be significant and must be taken into account when calculating comp ratio. This is one reason why small capacity glow plug engines do not use a conventional plug but instead they have an element within a separate head. This also allows the use of shims to set the correct ratio once the engine has been run and tested. Without knowing the position of the upper edge of the exhaust port and many other dimensions, your comp ratio cannot be calculated. I am sorry if this sounds less than encouraging, but the simplicity of your drawings and this basic error leaves me wondering how much you really understand about the complexities of the design and manufacture of our little engines. I would do some real reading before you cut any metal or you may be put off the hobby before you even get properly started.
[You can see some of my own engines on Flickr here www.flickr.com/photos/kcemb/albums/72157666328197690]

 

[SmithDoor]

I am trying to find the information on compression ratio.
My engineering books do not cover engines
So left with internet witch is so so
Any data you have would helpful.

The bind hole cut down on machine work but as point if make mistake hard to recover.
Good new I am still working on the design.

Thank you for your input.
Dave

Your calculation is incorrect. Compression ratio is not just stroke divided by head clearance. It is calculated from the amount of stroke after the exhaust port is closed. And do not forget that on such a small engine, the volume within the body of a 1/4" glow plug will be significant and must be taken into account when calculating comp ratio. This is one reason why small capacity glow plug engines do not use a conventional plug but instead they have an element within a separate head. This also allows the use of shims to set the correct ratio once the engine has been run and tested. Without knowing the position of the upper edge of the exhaust port and many other dimensions, your comp ratio cannot be calculated. I am sorry if this sounds less than encouraging, but the simplicity of your drawings and this basic error leaves me wondering how much you really understand about the complexities of the design and manufacture of our little engines. I would do some real reading before you cut any metal or you may be put off the hobby before you even get properly started.
[You can see some of my own engines on Flickr here www.flickr.com/photos/kcemb/albums/72157666328197690]

 

[el gringo]

yes,...and any gasket thickness in the vertical stack needs to be taken into account.
I've noticed this to be ignored in some designs.
Ray M

 

[SmithDoor]

yes,...and any gasket thickness in the vertical stack needs to be taken into account.
I've noticed this to be ignored in some designs.
Ray M

No gasket just Aluminum to steel

Dave

 

[el gringo]

No gasket just Aluminum to steel

Dave

Yes, using no gasket is best if conditions permit, although all is to be considered during design.

 

[SmithDoor]

Yes, using no gasket is best if conditions permit, although all is to be considered during design.

I plan to have a blind hole for the cylinder so do not need a head gasket.
The only other part need a gasket in crankcase there plan to use a o-ring.
Building this small is very different over the very large engines I have work on

Dave

 

[KenC]

I wish you all the luck in the world with your venture. If you want help send me a pm.

 

[SmithDoor]

Thank you

Dave

I wish you all the luck in the world with your venture. If you want help send me a pm.

 

[Olli-Matti]

I did just build my first one: Boll Aero 1.8. Finished it before christmas. When you get to it take a look at the great article by KenC about the piston and liner fit here: Finishing and fitting the piston and cylinder

My Boll Aero:

 

[KenC]

Olli-Matti. Pleased my article was a help to you.
KenC

 

[SmithDoor]

FYI
When finished with the engine it installed on model and fly.

Dave

hi Dave!
well, i´m not a real engine maker, but i´m learning a lot... i really love small engines, and i had build a Weaver 1cc (waiting for a new test after some work) already re-build an original Deezil 2cc with good results... at least it runs and starts easy .... Noone original did) and now i´m working with a reduced Mills 0.56cc.. a lot of fun!

 

[SmithDoor]

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