Re: Cotton AeroVee 0795
Posted: Sun Aug 15, 2021 3:28 pm
by Rynoth
Well, it shouldn’t run at all. Mags could be bad in more than one fashion, they definitely owe you new ones.
Re: Cotton AeroVee 0795
Posted: Sun Aug 15, 2021 3:56 pm
by 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.
Re: Cotton AeroVee 0795
Posted: Sun Aug 15, 2021 4:03 pm
by Rynoth
Area 51% wrote: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.)
Re: Cotton AeroVee 0795
Posted: Sun Aug 15, 2021 6:44 pm
by Bryan Cotton
Area 51% wrote: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.
Re: Cotton AeroVee 0795
Posted: Sun Aug 15, 2021 10:10 pm
by 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.
Re: Cotton AeroVee 0795
Posted: Mon Aug 16, 2021 9:27 am
by 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?
Re: Cotton AeroVee 0795
Posted: Mon Aug 16, 2021 11:09 am
by 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.
Re: Cotton AeroVee 0795
Posted: Mon Aug 16, 2021 11:50 am
by 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.
Re: Cotton AeroVee 0795
Posted: Mon Aug 16, 2021 4:43 pm
by 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.
Re: Cotton AeroVee 0795
Posted: Mon Aug 16, 2021 11:12 pm
by 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.
Re: Cotton AeroVee 0795
Posted: Tue Aug 17, 2021 2:30 pm
by Bryan Cotton
Rynoth wrote: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.
I would expect the dead cylinder would be pumping cold air past the EGT in its exhaust pipe. How is the other cylinder going to pump hot air backwards through the pipe and into the engine?
Re: Cotton AeroVee 0795
Posted: Thu Aug 19, 2021 7:47 am
by Area 51%
Bryan Cotton wrote:
Rynoth wrote: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.
I would expect the dead cylinder would be pumping cold air past the EGT in its exhaust pipe. How is the other cylinder going to pump hot air backwards through the pipe and into the engine?
It would be interesting to have an EGT on the exit pipe of my air compressor. No combustion there either, but the pipe is too hot to keep your hand on.
Re: Cotton AeroVee 0795
Posted: Thu Aug 19, 2021 7:51 am
by Bryan Cotton
Area 51% wrote:It would be interesting to have an EGT on the exit pipe of my air compressor. No combustion there either, but the pipe is too hot to keep your hand on.
Interesting point. I would suspect the heat of compression is much less than the heat of combustion.
Re: Cotton AeroVee 0795
Posted: Thu Aug 19, 2021 8:32 am
by GraemeSmith
Rynoth wrote: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.)
A rare flight school. Most don’t want you doing this. If you don’t get it JUST right and get a fuel air charge pass through the cylinder and exhaust valve into the muffler - as the mags go hot again and the engine runs - the next exhaust cycle will ignite the charge in the muffler with a “pop” and you can blow the muffler off. Even if it’s new and takes the hit - it stresses it and shortens the life.
Rookie students rarely have the finesse to do it right. So it’s banned.
–
But it’s a very legitimate test if you can do it right and just “blip” it a fraction to check the mags are grounding.
Like I did just after flying on Tuesday and lo and behold - I have a hot mag…
If it’s not one thing… 
Re: Cotton AeroVee 0795
Posted: Thu Aug 19, 2021 1:32 pm
by Bryan Cotton
I was taught to check for a hot mag. I do it occasionally. Never blew up a muffler. Not much worry on a Sonex.
As a teenager, I was stuck behind a large truck on a large hill once in my '71 Olds Cutlass. Finally got a pass zone after cresting the hill. Went wide open, and passed the truck. Took my foot off the gas and it got stuck wide open. My first thought as I passed 90 MPH was to turn off the ignition. Then did some troubleshooting and discovered the floor mat had jammed the pedal. Ignition back on. That muffler blew in a spectacular fashion.
If it’s not one thing…
Here’s hoping for you that it’s the top mag!
Re: Cotton AeroVee 0795
Posted: Thu Aug 19, 2021 8:01 pm
by Rynoth
GraemeSmith wrote:
Rynoth wrote: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.)
A rare flight school. Most don’t want you doing this. If you don’t get it JUST right and get a fuel air charge pass through the cylinder and exhaust valve into the muffler - as the mags go hot again and the engine runs - the next exhaust cycle will ignite the charge in the muffler with a “pop” and you can blow the muffler off. Even if it’s new and takes the hit - it stresses it and shortens the life.
Rookie students rarely have the finesse to do it right. So it’s banned.
–
But it’s a very legitimate test if you can do it right and just “blip” it a fraction to check the mags are grounding.
Like I did just after flying on Tuesday and lo and behold - I have a hot mag…
If it’s not one thing…
Indeed, throttle should be fully idle (as closed as possible) and the “blip” should be as short as possible. I’ve never experienced a backfire in all my years though (granted I also have never flown an aircraft with a muffler.)
FWIW the flight school was Embry-Riddle Aeronautical University, not a small operation by any means.
The real trick in many aircraft is not letting the key get jammed when you go to “off” on the mags, since that’s also typically the key removal position.
Example of my mag shutdown check at 14:13 in my First Flight video:
https://youtu.be/D8Z_OK6SFh8?t=849
Re: Cotton AeroVee 0795
Posted: Sat Aug 28, 2021 1:17 pm
by Bryan Cotton
New magnatron installed, P lead works now. Issue closed.
A better idea than the blip: just let it shut off and air out.
Re: Cotton AeroVee 0795
Posted: Thu Apr 28, 2022 10:18 pm
by flyingbear
Why cant you shut off the mags>>? Defective? Mine were but Sonex knew it and made me pay for new ones.
Re: Cotton AeroVee 0795
Posted: Fri Apr 29, 2022 10:01 am
by Bryan Cotton
flyingbear wrote:Why cant you shut off the mags>>? Defective? Mine were but Sonex knew it and made me pay for new ones.
I had one defective mag. I am the original buyer and mine was replaced for free after I provided enough evidence that the mag was bad.
Re: Cotton AeroVee 0795
Posted: Sat Jul 02, 2022 3:44 pm
by Bryan Cotton
I’ve redone my sump. I got acorn nuts and drilled them for safety wire.
Re: Cotton AeroVee 0795
Posted: Sat Jul 02, 2022 3:50 pm
by Area 51%
If you drilled through the nut, you just guaranteed yourself an oil leak. The whole idea of the acorn nut is to stop any oil that gets past the sump threads. Enter the copper gaskets under (or on top of) the acorn nuts.
Re: Cotton AeroVee 0795
Posted: Sat Jul 02, 2022 5:24 pm
by Bryan Cotton
Area 51% wrote:If you drilled through the nut, you just guaranteed yourself an oil leak. The whole idea of the acorn nut is to stop any oil that gets past the sump threads. Enter the copper gaskets under (or on top of) the acorn nuts.
I drilled through the corner, not through the threaded hole in the middle.
Edit: had I drilled through the center, how could I have gotten the safety wire through?
Re: Cotton AeroVee 0795
Posted: Sat Jul 02, 2022 7:03 pm
by Area 51%
Presumably, the stud doesn’t go all the way to the bottom of the nut. If it does, the sump plate will leak due to lack of tension.
Good job with the corner engineering.
Re: Cotton AeroVee 0795
Posted: Sat Jul 02, 2022 8:30 pm
by Bryan Cotton
Area 51% wrote:Presumably, the stud doesn’t go all the way to the bottom of the nut. If it does, the sump plate will leak due to lack of tension.
I don’t think it does. The copper is squished a little bit not destroyed from following torque specs like last time. I used a nutdriver and did it by feel.
Re: Cotton AeroVee 0795
Posted: Wed Jul 06, 2022 3:47 pm
by Bryan Cotton
Update - no more oil puddle under the engine. Looks like success!
Re: Cotton AeroVee 0795
Posted: Thu Aug 04, 2022 2:17 pm
by Bryan Cotton
I’d edit that last post, but that would be dishonest. There is plenty of oil on the ground. Not from static sitting, but from when I run it. Those updates go in the “quest for the elusive dry aerovee” thread.
I think I might be running lean. I have high EGTs and little difference when I go lean and rich on the mixture. Unfortunately my nifty reversing linkages are in the way, so I have to pull my aerocarb out to make the adjustment. The manual says 1/8 to 1/2 turn. I’m thinking of shooting for 1/4 turn but would like to hear opinions from those with experience.
Re: Cotton AeroVee 0795
Posted: Thu Aug 04, 2022 6:09 pm
by Area 51%
You’ve just entered one of the most frustrating aspects of phase 1 testing. A little can go a long way…or make no difference at all. If you don’t yet have to lean to get full throttle, I’d start with 1/4 turn richer. It’s not likely you’re going to hit it right on the first try anyway, so go for an overshoot, then come back.
The frustration comes from turning the needle carrier 1/4 turn, only to have the setscrew muck-up your adjustment leaving you with a random setting.
If you don’t have one already, put a 3/16 ball bearing between the carrier and setscrew. It keeps the setscrew from turning the carrier.
You have my sympathy.
Re: Cotton AeroVee 0795
Posted: Sun Aug 07, 2022 10:35 pm
by Bryan Cotton
I finally understand the ball bearing thing. I’ll try that - someday. I did my 1/4 turn richer and it seems to run great, and the EGTs are now reasonable.
I think for now I’m not going to mess with it.
Re: Cotton AeroVee 0795
Posted: Sat Jun 29, 2024 8:48 pm
by Bryan Cotton
Re: Cotton AeroVee 0795
Posted: Sun Jun 30, 2024 10:53 am
by Bryan Cotton
We have had a few findings and I’ll try and get some pictures later. Here is a short list though:
- One of the pushrod ends fell out when I removed it from the engine. The end of the tube looked beat up - there was a big burr on it.
- Our thrust shimming was bad. Looked like about 0.020" of clearance. Besides a lot of play, the crank web has polished into the case web a little.
- I think I posted pics in the other thread, but the #3 exhaust valve looked deformed where it contacts the seat. And, the #3 intake seat fell out of the head.