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Magneto timing light defective?

alcladrv

Well Known Member
I got to the point in my condition inspection when it was time to check the timing on my magneto though the engine had been running well without any issues. I pulled my Magneto Synchronizer TP-105 aka "buzz box" off the shelf after it sat unused since my last condition inspection when it worked fine. The prop was set to TDC for cylinder #1. I hooked up the unit to the "P" lead on my magneto using the Left lead and, of course, the black lead to ground. I powered up the left magneto through my ACS keyswitch and the Right light on the unit glowed steadily with a steady tone. Rotating the prop slightly back and forth made no difference.

I swapped leads, connecting the Right lead to the "P" lead and got the same result. Then I completely disconnected the unit from the magneto and turned it on and it did the same thing. So, it seems like the unit is broken? If so, is there a way to easily fix it, say with a new battery or internal reset?
 
Does your left mag have an impulse coupling? You need to remove a spark plug from each cylinder first to prevent an engine kick, then being up #1 to TDC, then continue pulling half a blade more until the impulse clicks. Next turn the mags to “hot”, Then back the prop up and sneak up on 25 degrees Brfore TDC, and tell me what happens.
 
My synchronizer, which I believe is the same as the one you mentioned, has a 9 V battery inside. You might open it up and check for a battery and verify condition. I have changed it several times over the years.
 
The prop was set to TDC for cylinder #1. I hooked up the unit to the "P" lead on my magneto using the Left lead and, of course, the black lead to ground.

?

On the right mag (and left after you’ve tripped the impulse coupling) the buzz box should be quiet at 30 deg BTDC, start buzzing as you turn the prop to 25 deg BTDC.
 
All of the plugs were out and the impulse couple snapped before I connected the sychronizer. I have a Slick 4371 for the left (bottom) plugs and a Lightspeed Ignition for the right (top) plugs. Whenever the unit was turned on, whether or not it was connected to the magneto, the right light stayed on and tone was steady regardless of how far I rotated the prop.

Thanks
 
All of the plugs were out and the impulse couple snapped before I connected the sychronizer. I have a Slick 4371 for the left (bottom) plugs and a Lightspeed Ignition for the right (top) plugs. Whenever the unit was turned on, whether or not it was connected to the magneto, the right light stayed on and tone was steady regardless of how far I rotated the prop.

Thanks

Your original post says that you are setting cyl #1 at TDC, then moving the prop a bit. The point that subsequent posters have gently made, is that you need to set the cyl at 25 degrees BTC in order to test the mags properly. They don't fire at TDC.

Might that be the issue?

Also, the mag switch needs to be in Both.
 
I should have clarified that the 25 BTDC was aligned with the little hole on the front of the starter. The prop happened to vertically straight up and down. Also, the mag switch was tried in Both, L and R, separately, all with the same result. Doesn't having the light on indicate that the points are closed? In my case, the light is on all of the time regardless of prop position and even when the unit is not connected to the mag.

I'm going to try changing the battery.
 
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