Another version of how not to build a model engine

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Russel:
Even if it is pure ethanol, it will tend to draw moisture out of the air if there is any humidity. That can be a big problem with chainsaws and gasoline that has a small amount of alcohol in it.

Russ

sorveltaja:
Russel, thanks for the information. That's what I was after. Not water-based, but that ethanol absorbs water from the environment :beer:.

After installing new breaker points/cam -combo, they seem to work just fine. At first I had a doubt, if the breaker's spring was too stiff, but it doesn't affect the engine's behavior.

When testing, once the engine fired, it ran at fast speed for a short time. I noticed by the ear, that something was preventing it to run longer.
At earlier stage, I had to kill the spark to stop the revving.

But anyway, I checked the ignition system(numerous times), and it was ok. Although the compression felt quite right, there was something wrong.

I have avoided opening the cylinder head, because I've finally managed to get it airtight; But no other way to check the valves.

Most excellent chance to reveal the interior of the head also.

I couldn't get the gasket off willingly, so I'll let it be:

Above pics show the major flaw in my design; middle holes are far too close to the ignition chamber; or the cavity is too wide.
Making a gasket for that is an adventurous thing.

Cylinder head:

As this picture shows, there is a brass button to increase the compression ratio. It has something to do with earlier cylinder head sealing problems.

Valves as they are; far from being similar to each other:

Cylinder liner, made of stainless steel, having two brass parts silver soldered to it:

bogstandard:
S,

Very interesting design for a side valve.

If you don't mind me giving you a suggestion which you might benefit from.

Even a basic bit of gas flow design might help with the problems you are experiencing.

It seems that the fuel might be being held around the valve area instead of the charge being sucked down into the cylinder.

If you look at the C-o-C that I have attached, I think just cutting the corner off the brass slug, like in the two top pics, would improve the gas flow a lot to give a more efficient burn.

If you ever needed to make a new head, the bottom picture shows how it could be improved even further, by shaping the head a little more, and moving the plug a little more into the corner of the cylinder.

John

75Plus:
S, The head gasket can be made of copper foil which should contain the heat and pressure. I don't know about your location but here in the US copper foil can be found in stores that carry craft supplies.

Joe

sorveltaja:
Bogs, thanks again for the demonstration :thumbup:. The reason for the spark plug placement is, that I originally was going to add 'dieselish' compression screw(and contra piston) to cylinder head cover.

I'm not sure yet, what to do with that brass button. Maybe I'll bevel it.

In the meantime, to replace the M2 screws, I drilled cylinder head's 2mm holes to 2.5mm, and made an M3 threads to them:

My M3 threading tap has snapped, thus being so short. About 2mm too short for the head. I took an M3 screw, and ground there a bevel, so with that I got the threads finished:

Joe, I actually have 0.1mm(~0.04") copper sheet. Don't know if that is thin enough, but I'll give it a try:

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