Magneto timing for 4A084

[Duane Scarborough]

"Someone" from Canada was having magneto timing issues a little while back.

Since then, I had computer problems myself. That seems to be resolved, and the new computer is working GREAT.

But, in the process, I've lost the contact info. I tried a couple of times to find it again, with no luck.

I "tried" to explain how the impulse coupling and the magneto worked together. But wondered if I said it right.

I thought about it again today, and thought I'd throw this out there.

http://groups.yahoo.com/group/A084Ex...s/message/3098

Here's a cut and paste from that: (just in case you're not a member of that yahoo group)

The accepted way of timing a magneto is to turn the prop forward past the impulse release, back it up to about five degrees before the timing mark. Put a piece of cellophane off a pack of cigarettes between the points and move the prop forward slowly to take the hysteresis out of the gears until it reaches the timing mark. Loosen the nuts on the adjustment slots in the magneto, advance it until the points open and release the cellophane. Then slowly back it up until it just "grabs" it. Back the prop up about 5° and then move it forward slowly to verify that the points open and release the cellophane at the timing mark.
Several companies make an electronic tester that uses both a light and an aural sound. For the home mechanic, the cellophane does just as well and saves the cost of a special tool.

More info:

http://groups.yahoo.com/group/A084Ex...s/message/3096

Another cut and paste:
OK Class, it's time for Magnetos 101

......
The impulse is a mechanism that stops the magneto from turning and holds it there until the magneto has turned to where it will be much nearer TDC before it fires. This is caused by a spring-loaded pawl that catches on a pin in the body of the magneto. The gear continues to turn but against a spring connected to the shaft in the magneto which is being held. As the engine reaches a point much closer to TDC, a cam in the impulse will release the pawl and the internal spring will snap (the noise you hear) the magneto forward causing the points to open and a spark being sent to the plug.
As the speed of the engine comes up, a weight in the impulse unit swings our by centrifugal force which pulls the pawl back to where it no longer comes against the stop and the magneto turns at the same speed as the engine.
An additional function of the impulse is to hold the rotation of the magneto so it snaps the permanent magnet past the coil faster, causing a much higher spike peak at the time of discharge.
Now that I've told you how to make a watch, sit down at the bench with a magneto and you will see and understand how it works.

Jim Foreman




Duane

[Papee]

Hmmm, I suppose that would get you close. Doing it with the magneto mounted would be just a guess as per my experience a few weeks ago. You could not feel the magnet holding. When timing the mag you find number one and turn the mag by hand until the number one sparks. Then turn it back until you feel the magnet hold the armature.

I took all the plugs out and put a plastic rod in the number one cyl and turned the prop until the cyl was up then went back and looked on the cam gear to see if the mark was up. I then installed the mag and put a continuity meter on the P terminal to check to see that it was closed. With the number one cyl at full compression stroke, the mag sitting on the impulse magnet would be when it fires. That should get you real close. I had to twist the mag a bit to get the points to close. Well, that's what did it for me when i finally got it licked. It started for me first try but needed advanced a bit.

[Duane Scarborough]

Papee,

I'd not thought much about how tough it'd be to get the ignition timing right, after removing the flywheel and bell housing, with it's timing marks, until after I'd already removed all that.

Fortunately, I started out with a fresh, out of the crate engine, and it seems to run fine. It's magneto has not been touched since it was built.

So I guess now that I need to figure out how to re-establish that reference point, so that others (or I) can do the same going forward.

I'll work on it. There's GOT to be an easy way.

Duane

[Papee]

All the reference marks you need are on the cam gear and mag gear. The is a 0 on the cam gear and . on the mag gear. Mine are painted with yellow paint.

As far as the impulse clank, that is used at startup to move the impulse faster across the magnet. It has a built in lag for easy startup. After it is started it is not used, the advance or supposed advance is just the normal timing. There is not really an advance but a lag at startup. This is what I take of it any way. I've been wrong before.

[Duane Scarborough]

Papee,

It may just be that easy. I sure hope so, but I don't really know.

Duane