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Magneto timing help

Robin8er

Well Known Member
I'm timing the magneto on my engine. Lycoming O-360. I have one lightpeed ignition and one magneto. The lightspeed is timed correctly and was easy to do.

I'm having trouble with the magneto. I'm using a timing pin and timing light (buzz box). The engine is currently at 25 degrees BTDC. The magneto buzz box lights up with a green (OPEN) light like it is supposed to, however I can rotate the magneto several degrees and it stays green, probably about 20 degrees that is in the "green/open" position. is this normal? how do I know exactly where to clamp down the magneto?
 
Did you snap the mag before you put in the pin? Since it's installed and the pin is out, turn the prop till the coupling snaps, then back up to beyond your timing marks, and see if that helps. You may have to pull the mag and start over if that doesn't help.
 
Rh or lh

Look at mag dataplate see what direction it is RH or LH, make sure pin is in correct hole.
 
If pin was inserted and the mag or engine was moved, remove the mag and inspect for damage immediately. Pin is only for initial orientation. Points should just open at 25 degrees (or whatever your data plate says). Disregard what the light does after initial opening. I?d suggest going over the procedure with your A&P.
 
My mag does the same, there is a window for the circuit to stay "open". for correct timing, I was told to clamp down the mag at the first sign of "open" (light went on or beeping sounded) when rotating prop clockwise (viewed from cockpit). I timed mine this way without issues.
 
The spark fires when the points open. All you care about is getting them to open at 25btd. As a previous poster mentioned, if you rotated the engine with the timing pin in, you could have damaged the magneto. That is just for rough setting during installation.
Look up detailed timing instructions or a you-tube video on-line.
 
As others have stated, this is normal. The ignition/timing point is when the light first goes on, while turning the normal engine rotation direction. The opening point while going backwards / the closing point going forward is not relevant, except for getting a judge of point wear or rubbing block wear. With a mag, you normally cover that by properly setting the e gap.

Larry
 
Last edited:
I think I got it timed correctly, thank you to everyone that helped :)

It makes sense that you only care about the moment that it opens. The way i have it now the light comes on right at 25 degrees BTDC.
 
Suggestion

The OP posted incomplete information. As a result some of the suggestions were all over the map.
Suggestion Example:
I have an RVxx with Lycoming 0 360A4A. Lightspeed ignition on right side and Slick impulse mag on left.
Now we have a good starting point and can post some pertinent suggestions instead of stumbling around in the dark.
The OP discussed the timing pin which tells us it is a Slick mag. But it could be impulse, non impulse or shower of sparks.
 
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