SonexBuilders.net

I am having a very serious problem with the primary ignition system that me, Sonex and everyone I know have been trying to solve, but to no avail. Everyone is stumped.

I'll use P for primary and S for secondary.

- With both the S and P turned on, it runs fine.
- When I turn off the P the S runs fine, from idle to high RPMs.
- But when I turn off the S, the P runs really rough, and will only keep running at around 2,000 RPMs or higher. Any lower and it starts to run so rough that the engine quits.

We have done the following (in fact, more than once):
- Regapped the top spark plugs
- Checked the spark plug wire connectors. They are on correctly, and fully engaged with the spark plugs
- Re-gapped the space between the mags and the magnet, with the .010 spacer provided.
- Checked the mag ground wires for continuity and a solid ground

Sonex says to turn off the S and when the EGT goes down on a cylinder(s) then that is where the problem is. However, the EGTs never change when turning off the S, so we can't narrow down the problem to one mag, or one wire, or one spark plug. The problem seems to affect every cylinder equally, and both mags equally.

I know the EGT sensors work. They do go up and down with throttle changes, and with changes in mixture settings.

We tried disconnecting the ground wire to the top mag, and then ran the engine. We turned off the S ignition and the P ran rough. Only a little rougher with one mag than with two. But the weird part is that when running with one mag, the EGTs didn't change. Shouldn't two of the cylinders drop off? Does disconnecting the mag's ground have the affect of disabling the mag or not?

We then reattached the ground wire to the top mag, and disconnected the ground from the bottom mag. We ran the engine and got the exact same result as we did when we disconnected the top mag's ground.

So the only thing we have not specifically checked are the P-leads. In not sure what to check or how. The P-lead wire runs from the mag, through firewall, and to the switch. It's a shielded wire, so I have the shield grounded. To put a multi-meter on it I would have to run a wire from the meter to the back of the instrument panel where the switch is. Is that what I need to do? And what am I looking for (electrical is NOT my strong point). I know how to check for continuity with a multi-meter. That's about it. The rest is voodoo to me.

It's not a fuel or air problem, since the engine runs fine on the S ignition.

An A&P looked at it with me, but the mags being that of a lawnmower engine, means they don't know much about how to troubleshoot it. He was just guessing.

I am VERY open to suggestions. The P is completely unusable at the moment, so I'm completely grounded (I've been trying to make my first flight) until I figure this out. Very frustrating.

Mike Smith

Have you tried disconnecting both primary p-leads on the mags at the same time and running it?
All those wires should do is cut spark off when grounded via a switch. With the leads disconnected the engine
should run fine on the primary. Just shut off engine with the mixture after testing.

I have not. But I will now :-)

Mike

.Mike,

I am no expert but I am sure that the problem is the shielded wire on the p leads. It is partially grounding the magnitrons causing the roughness.

Unlike other P leads referenced in homebuilders manuals calling for shielded wire, the P leads to the Aerovee magnitrons are not connected to the Aerovee when it is switched on (thus the upside down ignition switch called out in the manual). When you turn the switch off (which is really on , remember the upside down switch shown in the manual) it connects the p leads to the magnitron p lead and grounds the p lead, thus shutting down the magnitron. The shielded wire is likely partially grounding the magnitron causing the roughness. Again I am no expert, just trying to help. It appears the grounded shielding may be allowing the ground to "jump" to the highly charged magnitron the same way if you hold a negative wire close to the positive post on a battery. Good luck!

Your problem may be with the large triggering magnet. If the magnet retainer bracket is loose, even a bit, the magnet will flex outward under higher RPM and close the 0.010" gap between the magnet and the magnatron unit. Once they strike each other, the shock to the magnet will destabilize it. The magnet might be slightly weakened, thus causing the roughness when running only on the mags, or it might be really messed up and the engine won't hardly run at all.

I would remove the magnet and retainer cover and inspect it for scuff marks or scratches, check to see how strong the magnetic force is (it should be "gorilla strong"!), and if there's any doubt replace it. Also check the magnatron units for signs of impact. They can take some abuse, but the heat of friction from a rubbing magnet cover will eventually break them down internally.

When you reassemble the magnet and cover, make sure that the screws are tight, and have locktite to really hold them in place.

Jeff Shultz

mike.smith wrote:So the only thing we have not specifically checked are the P-leads. In not sure what to check or how. The P-lead wire runs from the mag, through firewall, and to the switch.

Are you saying that you have one P lead wire going to a switch that controls both mags? If so that is a problem.

Each mag must have a separate P lead wire going to its own separate switch. Actually you can use a DPST switch...which is just two separate switches in one case.

radfordc wrote:

mike.smith wrote:So the only thing we have not specifically checked are the P-leads. In not sure what to check or how. The P-lead wire runs from the mag, through firewall, and to the switch.

Are you saying that you have one P lead wire going to a switch that controls both mags? If so that is a problem.

Each mag must have a separate P lead wire going to its own separate switch. Actually you can use a DPST switch...which is just two separate switches in one case.

No, I'm just saying the TWO P-lead wires go from each mag to the individual poles of a DPST switch. I was just short-handing the response.

Mike

sonex1374 wrote:Your problem may be with the large triggering magnet. If the magnet retainer bracket is loose, even a bit, the magnet will flex outward under higher RPM and close the 0.010" gap between the magnet and the magnatron unit. Once they strike each other, the shock to the magnet will destabilize it. The magnet might be slightly weakened, thus causing the roughness when running only on the mags, or it might be really messed up and the engine won't hardly run at all.

I would remove the magnet and retainer cover and inspect it for scuff marks or scratches, check to see how strong the magnetic force is (it should be "gorilla strong"!), and if there's any doubt replace it. Also check the magnatron units for signs of impact. They can take some abuse, but the heat of friction from a rubbing magnet cover will eventually break them down internally.

When you reassemble the magnet and cover, make sure that the screws are tight, and have locktite to really hold them in place.

Jeff Shultz

Sonex tells me they don't believe a magnet can be de-magnetized like that. That said, one mag leg was making very light contact with the magnet while rotating through. We reset the gap so nothing is touching. And yes, when we regapped the mags the magnets were very strong. Impossible to move by hand.

I've got another set of AeroVee eyes coming tomorrow. I would be tickled pink if we simply found that I had wired something wrong. If not, then we're still rather lost. We'll keep looking.

Mike

SonexN76ET wrote:.Mike,

I am no expert but I am sure that the problem is the shielded wire on the p leads. It is partially grounding the magnitrons causing the roughness.

Unlike other P leads referenced in homebuilders manuals calling for shielded wire, the P leads to the Aerovee magnitrons are not connected to the Aerovee when it is switched on (thus the upside down ignition switch called out in the manual). When you turn the switch off (which is really on , remember the upside down switch shown in the manual) it connects the p leads to the magnitron p lead and grounds the p lead, thus shutting down the magnitron. The shielded wire is likely partially grounding the magnitron causing the roughness. Again I am no expert, just trying to help. It appears the grounded shielding may be allowing the ground to "jump" to the highly charged magnitron the same way if you hold a negative wire close to the positive post on a battery. Good luck!

Hmm... If the shield was grounding the mags then the mags wouldn't work at all, would they?
Mike

mike.smith wrote:

radfordc wrote:

mike.smith wrote:So the only thing we have not specifically checked are the P-leads. In not sure what to check or how. The P-lead wire runs from the mag, through firewall, and to the switch.

Are you saying that you have one P lead wire going to a switch that controls both mags? If so that is a problem.

Each mag must have a separate P lead wire going to its own separate switch. Actually you can use a DPST switch...which is just two separate switches in one case.

No, I'm just saying the TWO P-lead wires go from each mag to the individual poles of a DPST switch. I was just short-handing the response.

Mike

OK. When I bought my Sonex the two mags were wired together on one switch...didn't run worth a darn.