Cotton AeroVee 0795

[Rynoth]

Well, it shouldn't run at all. Mags could be bad in more than one fashion, they definitely owe you new ones.

[Area 51%]

My money is on one good and one bad magnatron.

Remove your temporary short-circuit wires one at a time with a test run in between. If you remove a wire and the engine smooths out, you've found the good magnatron.

[Rynoth]

My money is on one good and one bad magnatron.

Remove your temporary short-circuit wires one at a time with a test run in between. If you remove a wire and the engine smooths out, you've found the good magnatron.

Good test, I had this thought also but was it running smooth when mags switch was off in first test? Edit: Watched your earlier video again at the 3 minute mark. The roughness definitely suggests 1 mag not shutting down when grounded.

You might only have 1 bad mag, and you're firing on 2 cylinders only when both mags are grounded out. I'd still lean towards having both mags replaced though.

Edit: On further consideration, I think this is exactly what your EGT test is telling you. If you're running on 2 cylinders only, the exhaust gasses are still going to make their way through the pipes and warm the other "cold" EGT thermocouples to a lesser extent.

Sidenote: I was taught in my early flight school days to always do a mag check just prior to every engine shutdown. A quick flip of all ignition switches OFF/ON at idle before killing the engine with mixture/fuel shutoff. I'm curious if this is standard practice for others (I believe it should be.)

[Bryan Cotton]

My money is on one good and one bad magnatron.

Remove your temporary short-circuit wires one at a time with a test run in between. If you remove a wire and the engine smooths out, you've found the good magnatron.

Great idea, thanks.

[Bryan Cotton]

Randy/Area 51 for the win on this one.

With the top magnetron P lead disconnected, the bottom magnetron P lead shorted to ground, and the secondary ignition turned off, the motor ran good. This would indicate that the bottom magnetron was not turning off though its P lead was shorted to ground.
With the top magnetron P lead shorted to ground, and the bottom magnetron P lead disconnected, the engine ran terrible when the secondary was turned off. This would indicate the top magnetron P lead is able to shut off the magneto.

[Bryan Cotton]

Last night's test run. Also Adam's first time running the engine.


Also, we discovered that with the mixture all the way off, the engine still ran. I assume I just need to adjust my mixture travel, does that sound right?

[pappas]

Yeah, adjusting the mixture lever throw for full open and full close sounds like the most likely culprit. Some guys have had issues because they were not getting the fully open position correct. Sonex used to say 45 degrees on the mixture arm. Newer plans say a "minimum" of 45 degrees.

[Bryan Cotton]

Sonex is sending me a new magnetron. Too bad I didn't think to put the bad one on the top! That would have been easier.

Thanks Lou for your comment on the mixture.

[pappas]

My top mag melted itself about a year or so ago. I sent Kerry some pics and they sent me a replacement at n/c pronto. No complaints from me.

[Bryan Cotton]

We set the secondary ignition timing today. It was waaaay advanced initially.

I went and set the prop so the top magnetron was lined up for firing, like in the initial setup for setting the secondary ignition statically. Then I painted a line on the flywheel and one of the gear teeth, and drew a line to match on the case.

We ran the engine with the timing light inductive clamp hooked on a magnetron plug wire. I had to erase the line with acetone and move it so they lined up when it was running and the timing light fired. Once I had that line good for the magnetrons, then we swapped the inductive pickup to the secondary ignition plug wire. It took a lot of tries. I think we really need a good way to hold the magnet ring from moving while you loosen, tighten, and move the prop. But, we finally got the secondary timing set pretty good.

I can't shut off the mags yet, but the drop when I turned off the electronic ignition was 40 RPM. Seems like a good start.

I bought this timing light from Harbor Freight:
https://www.harborfreight.com/timing-li ... 40963.html

It has a stupid feature that lets you adjust when the light fires. I recommend duct taping it to zero, else you will bump it and wonder what in the heck is going on.