Ignition Timing of a Noname HT Bicycle Engine

multipaul · May 27, 2012

I've read most of the threads about ignitions and timing. A lot of people seem to possess timing lights. But there was nowhere to read how the timing advances or retards as a function of rpm.

Now I did it, and here are the results:

The woodruff key has a little bit play in my crankshaft. We should keep in mind that 0,1mm play corresponds to 1,4° change in the ignition timing. I fixed the piston and turned the magneto to the left. Then I screwed down the nut.

I mentioned that measurement is my third hobby.
Has anybody got other values? Has anybody got any values?

Multipaul

multipaul · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

Be careful with the good feelings people have. Much more powerful, faster, smoother, better in every way..
Even don't believe foreign diagrams and charts! My motto: Measure and find hard facts.

http://www.youtube.com/watch?v=8sKg6h9pDmw

Multipaul

multipaul · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

...The magnets are weak. Typical China scrap?
Not mine. So I am a lucky man.

The left part of the picture shows a 60x60x5mm N52 magnet. Nominal force 110kg.
14 M8x1 nuts for the super magnet and 11 for the HT rotor. Not a bad result.

Working on prejudice, sometimes it must be done.
But my engine has other, really big mistakes. We probably sit in the same boat more or less.

Multipaul

rustycase · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

Thanks MP!

Good info to have!

I wonder how different cdi's vary...
rc

biknut · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

First of all, nice work mp. I appreciate your effort, and willingness to share your results.

How sure are you of your measurement? I'm suprised to find out the stock ignition has any advance at all. I was guessing that the initial timing setting was all you get. After that the timing stayed the same throughout the entire rpm range. Something like 12 degree BTDC

multipaul · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

Dear Biknut,

this is the first analog CDI I measured, that really advances remarkable.
And that won't be by chance.

The degree wheel and pointer I made myself.
If there is interrest, I can try a pdf to share it.

The pointer is made of a small bronze sheet 0,25mm thick and soldered at the edges. It is very light (less than 5 grams) but very stiff. This is necessary because of the high centrifugal forces at higher rpm.

Depending on the woodruff key the graph may be a few degrees higher or lower. But the shape of the curve is determined (at least for this HT engine).

I don't know, whether it is possible to print this picture. Perhaps it must be repixeled some times.
It is best to cut out the pointer and stick it with double sided adhesive tape on the bronze sheet. The sheet can be bougt in every model shop. The pointer has blue lines and green lines. The blue ones must be bended 90° up and the green lines 90° down.

The pointer. One is made of paper, the first tray.
One pointer cut and bended and the pointer nearest to the camera is the one you saw in the video. It is one part and soldered in every corner.

Klick to enlarge.

The degree wheel is stuck on just a piece of cardboard. Then it can be screwed to the motor.

At last TDC must be found and the inner piece of paper with the degree marks from 0° to 45° must be fixed with the Zero mark on TDC.
(Sorry, for me it's easier to explain that in German.)

Developing is fun.

- Multipaul

2door · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

Multipaul,
I applaud your research and thank you for sharing your findings.

I am curious however how many different Chinese 2 stroke engines you have experimented with. In my experience, playing with a variety of engines and using an automotive cam degree wheel I've found appreciable inconsistancies in magnet index verses piston position. Some as much as five degrees difference when compared between engine to engine. Would this not have an impact on your findings?

Tom

Goat Herder · May 28, 2012

Re: Ignition Timing of a Noname HT Engine

Nice set up. A lot of folks will love to get that PDF.

multipaul · May 29, 2012

Re: Ignition Timing of a Noname HT Engine

Hi Tom,

I know 5 degrees more ore less that's a world in most cases.
Up to now I have one engine. At the moment it is completly apart. I have no experience with other HTs. I ordered one 66cc directly from China 7 weeks ago. Just out of interest. But it is still on it's way. Actual US-Ebay No. 170793410820.

Back to the ignition timing. How much the timing advances should be a question of the magnet strength and the form of the rotor and the distance to the coil (wich can't be varied in this case). Mounting the rotor as far as possible clockwise will push the ignition curve completely about 5 degrees up. In my video I simulated a mount counter clockwise. You can imagine that there is a crankshaft dummy inside the engine.
All in all I am careful, when pre ignition exceeds 30 degrees. Especially at high compression ratios. But I'm learning every day...

Often when there are new ignitions to measure, the members in the German forum send me the parts. For a private person I have a fine equipment and hopefully a lot of ideas.

Multipaul

multipaul · May 29, 2012

Re: Ignition Timing of a Noname HT Engine

Hallo,

down here there is my upload of the PDF. The original paper format is DIN A4, which is 297 x 210 mm. I hope it can be printed correctly.

When you test the timing of your engine, be careful. The pointer must turn freely over the ignition coil and shouldn't tuch any other parts.

I am very excited which values you will find out.

Multipaul

multipaul · May 29, 2012

Re: Ignition Timing of a Noname HT Engine

I just made a photo that shows all parts being involved in the ignition timing.

Multipaul

biknut · May 29, 2012

Re: Ignition Timing of a Noname HT Engine

I could be wrong, but that CDI box looks like it's taller than the ones I have.

multipaul · May 29, 2012

Re: Ignition Timing of a Noname HT Engine

The play between the magnet and the crankshaft can be measured easily and rather precise:

http://www.youtube.com/watch?v=FhvaNvT5NN4&feature=youtu.be

Multipaul

biknut · May 29, 2012