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Engine won’t run on the right mag after installing tach pickup, troubleshooting help needed.

K

Kooshball

Well Known Member
I am looking for suggestions on an ignition issue that just showed up after replacing the tach pickup that is installed in the inboard vent hole of my slick 4370 mag. The mag was overhauled ~15 hours ago and the last time I flew before annual, it worked fine. This mag is on the right, and I have a lightspeed ignition on the left.

We had to take the mag free of the engine to rotate it enough to access the vent plug area to replace the tach pickup sensor. For reinstall, the tack pin was inserted in the L hole as indicated on the mag name plate, prop set to 25deg BTDC, and the mag reinstalled. The wire harness on the back of the mag was marked and reinstalled in the same place it was removed from.

Timing was set using the light, the tach pickup was wired and then we did a runup. The rpm indication was correct but during mag check, the engine stopped running when I turned off the left ignition.

We rechecked timing which was still correct, removed the mag wire harness to make sure the springs and insulators were in their sockets and they were correct. If timing is checked with the mag switch off, the lights on the tester stay on as you would expect, but then indicate correctly when the mag is turned on which leads me to my first question:

Is it possible for the timing light to show the points opening and closing as they should but still have no spark?

What else should I check before assuming that the mag is now somehow bad?

Thx!
 
Did you confirm that you were on number 1 cylinder compression stroke? Sound like it may be 180 degrees out of time. Pull the plug out of cyl 1 put you finger in the spark plug hole and verify you timed it correctly
 
Bill.Peyton said:
Did you confirm that you were on number 1 cylinder compression stroke? Sound like it may be 180 degrees out of time. Pull the plug out of cyl 1 put you finger in the spark plug hole and verify you timed it correctly
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I will confirm today but my A&P and I were pretty careful about that and getting the pin in the back of the mag right.
 
Kooshball said:
I will confirm today but my A&P and I were pretty careful about that and getting the pin in the back of the mag right.
Click to expand...
I did the same thing. I thought I had it timed perfectly. I took the mag back off and pinned it again. It is easy to have that pin in the wrong place. I used duct tape to hold the pin in place until I had the mag back on. On the runup it worked great.
 
Kooshball said:
I will confirm today but my A&P and I were pretty careful about that and getting the pin in the back of the mag right.
Click to expand...
I think post 2 is describing a likely cause.
If you find timing correct, then I would remove the grounding wire from the mag to rule out external problems like a faulty starter lock.
4370 is a no impulse magneto and it would be normal for this mag to be grounded when the starter key is in the START position.
Be careful when the mag is not grounded. Don´t turn the prop by hand.

Good luck
 
I also support 180 deg out of phase, also you may have to add more resistance to the pickup circuit as it may be less than the coil impedance
Try another 10 k .
 
I confirmed timing is set to the compression stroke of cyl 1, and I confirmed that the pin was located at the correct spot. I slowly turned the prop and I can only get it to drop into the hole when number one cylinder is 25° before top dead center on the compression stroke. I also re-made the ring terminal crimp connection at the P lead and unfortunately, I still have the same problem where the timing light shows a. operable magneto, but the aircraft will not run on just the right magneto.
 
Have you confirmed that your ignition switch is not grounded when in "R" position? If you are using a key type switch this type failure is not uncommon.

Have you tried post #5?
 
Mel said:
Have you confirmed that your ignition switch is not grounded when in "R" position? If you are using a key type switch this type failure is not uncommon.

Have you tried post #5?
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Nothing is grounded that I can see. When the R switch is on, the timing light comes on and off as it should, when the switch is off, the light stays on. If I set the the prop to 25 deg so the light goes out, then toggle the R switch on and off the timing light goes on and off.

I even removed the tach pickup, reinstalled the vent plug and ran the engine but it still won’t run on R.

At this point I have returned the setup to how it was the last time it ran properly and still can’t figure it out. Should I pull the mag at this point and send it out?
 
Just some more info on my troubleshooting and setup since several folks have pointed me toward the start switch.

The builder setup the starting circuit different than a keyed switch. I have lightspeed ignition on the left, which is were I start the engine. The starter is a push button which has circuitry to prevent the starter from engaging if the right mag is on since it does not have an impulse coupler. Because of this, there is only one wire going to the mag for the p-lead and the right mag is not disrupted anyway when you start since you can’t start if the right mag is switched on.
 
Kooshball said:
Just some more info on my troubleshooting and setup since several folks have pointed me toward the start switch.

The builder setup the starting circuit different than a keyed switch. I have lightspeed ignition on the left, which is were I start the engine. The starter is a push button which has circuitry to prevent the starter from engaging if the right mag is on since it does not have an impulse coupler. Because of this, there is only one wire going to the mag for the p-lead and the right mag is not disrupted anyway when you start since you can’t start if the right mag is switched on.
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I would remove the P-lead from the 4370 mag. Then try to start the engine.
Don't turn the prop by hand.
If the engine runs ok you have a problem in the start circuit.
If the engine won't run without the P-lead connected then I would send in the mag for inspection.

Good luck
 
Avanza said:
I would remove the P-lead from the 4370 mag. Then try to start the engine.
Don't turn the prop by hand.
If the engine runs ok you have a problem in the start circuit.
If the engine won't run without the P-lead connected then I would send in the mag for inspection.

Good luck
Click to expand...
If I start the engine with the p-lead removed from a mag without an impulse coupler, will there be risk to the engine since the spark will not be retarded?
 
Kooshball said:
If I start the engine with the p-lead removed from a mag without an impulse coupler, will there be risk to the engine since the spark will not be retarded?
Click to expand...
Yes, you are correct I just realised that.
you need to start the engine on the electronic ignition and then remove the P-lead from the 4370 mag and then try to run on the mag only

Good luck
 
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