Another version of how not to build a model engine

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sorveltaja:
In the meantime, I made another temporary breaker points to continue the testing.

Coil(an ex-transformer), that I used for ignition, stopped working, and made itself useless by sparking inside the coil:

After abusing(and destroying) several ones during the tests, I must admit, that transformer coils are not suitable for an IC ignition purpose. Not only because they can't produce reliable sparks, but they just can't handle repetitive strong current pulses.

Luckily I had an appropriate replacement part at hand:

What comes to breaker points, at first I tried several micro-switches:

They seem to fade quite fast.

Besides the temporary breaker points, that I made, today arrived the replacement for those also:

Next thing is to figure out, how to attach that to the engine, as the spring is too stiff for the humble power of small engine.
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Short video of the engine:

http://s323.photobucket.com/albums/nn471/sorveltaja/?action=view&current=01.flv

Carburetor needle is extremely sensitive, making the engine behave like a donkey.

Today it ran about half minute, at fast speed, then stopped due to heat expansions, I assume, as the cylinder head was too hot to touch.

bogstandard:
I found that a hall effect sensor and a rare earth magnet was much easier and more compact to use. I used the Tim 6 configuration.

Here is a link to other ignition types, the hall sensor takes the place of the contact breakers.

http://www.5bears.com/tim4.htm

Or go with Jan ridders version by using a piezo, which does away with everything, and fires the plug direct.

Here are a couple of pics of the last ic engine I made, after having a long running in session. It is still sitting in my shop in the same condition. I never wanted to, or ever will finish it off after getting it to run OK. It just knocked ic engines completely out of my system, after struggling with such terrible castings. It would have been ten times easier to have made it out of bar stock, as you have done, and how I made previous engines.

The second picture shows the mounted hall sensor and the magnet was mounted in edge of the small ali disc. Those two parts take the place of the points and condenser. No wear, and you can cover it in oil, and it still runs perfectly

Bogs

NickG:
sorveltaja,

The car points spring might feel stiff but remember they don't have to move much and it will only be a very small cam throw so it may not cause too much power loss when used in the correct manner - give it a go, I know the webster uses that method.

Jan used the piezo with some success but they sap quite a lot of power. He has also used the coil set up but with a microswitch as you show with success. http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_drukgestuurde_tweetakt/druktweetakt_frameset.htm

John,

I've never seen that one before, nice engine :thumbup: what is the coil on it? Why is there an inline switch shown on the Tim 6?

Cheers,

Nick

bogstandard:
The engine is actually the Westbury Whippet, and the castings for it are available from Hemingway. But they are so bad they are almost unusable, especially the head area ones. I had to get a friend to build up areas of the casting with ali weld, just so that I could carry on with it. They were up to 1/8" out in places.

Those coils are now not available, and were made for fitting into model aircraft with 4 stroke petrol engines. They are only about 3/4" diameter.

The inline switch is in fact where you would mount the contact breaker or in my case, the hall sensor.

John

NickG:
John,

I thought I recognised it. A friend of mine is building the Chenerey V Twin Aero Engine with castings from Hemingway but he has also had all sorts of problems with the head castings especially. Valve bushes in the wrong place, wrong angle and blow holes everywhere. I think he tried 3 that I know of but then resorted to machining from solid. It looks a much better job and he said it was far easier.

Incidentally, if anybody is interested Hemingway say they supply a similar model electric coil to John's and they supply the TIM 6 in kit form, but they'll cost you an arm and a leg! http://www.hemingwaykits.com/acatalog/Ignition.html

Oh right, I see now, they just haven't shown it in the same way as the TIM4. I don't get TIM 7 ... :scratch:

What sort of battery did you power yours from? I know Jan uses cordless drill batteries and the like.

Nick

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