AeroVee primary ignition problem

[SonexN76ET]

Disconnect your P leads and see what happens...

[mike.smith]

Disconnect your P leads and see what happens...

That's what we'll try in the morning.

Mike

[mike.smith]

We disconnected the P-leads and no change.

In fact, we did EVERYTHING you can do to the mag system. We put in new top plugs (correct gaps), re-re-gapped the mag/magnet spacing, checked the resistance and continuity of every wire in the system, checked the grounds, swapped left and right plug wires, yada, yada...

It's cylinders 2 & 4 that have EGT drops when we run the primary-only, and cylinder 2 is consistently 300-400 degrees lower than the others with #4 running about 100 deg higher than 2. The top mag runs cylinders 2 & 4.

So we're now 99% sure it's a bad top mag. It appears that it works only intermittently. We'll put in a new one and see what happens.

Mike

[radfordc]

They say experimental aviation is about "education and recreation". I think you're getting the "education" part now.

[mike.smith]

They say experimental aviation is about "education and recreation". I think you're getting the "education" part now.

Well, I SURE know my ignition system, now! :-)

As frustrating as all this is (and it has been VERY frustrating), it is very true that I know a lot more about my engine, and I'll be a lot more adept at maintenance and troubleshooting. I felt the same way about having to replace my wrist pin clips. I learned how to pull the cylinders on a hung engine, do the work, and put it back together.

So yes, it certainly is and education. But I'd still like to be flying! ;-)

Mike

[Bryan Cotton]

I never wanted to know as much about Cessna 140's as I do.

[mike.smith]

OK, gang. For anyone interested. I installed a new top mag. NO CHANGE! Keith Macht has a (running) AeroVee and helped me troubleshoot last weekend. One of the things we did was check the magnet polarity, even though Sonex thought the engine wouldn't even run with the magnet reversed. Well, I think it does, but just poorly.

Keith and I checked the polarity with a small compass per the AeroVee instruction manual. We both found that page confusing and thought we had it right. But Keith went home and did the same compass check on his engine and found it the reverse of mine.

So we are no pretty sure (?!) we need to reverse the magnet. It looks like we can leave the back plate on the engine mount, loosen the intake, disconnect some wires, and use an engine hoist to separate the engine from the back plate just enough to get access to the magnet.

Even if it was a stupid mistake on my part, I will simply be happy to take it as a learning exercise if I actually get it fixed. I'll let you all know how it goes.

Mike

[SonexN76ET]

Mike,

Before you go through all this trouble in taking the engine off, may I suggest you try one very simple test? Everything you have described sounds like it is a grounding problem.

Run an 18 gauge ground wire directly from the battery to the engine block (not the mounting plate), then run a wire from that connection on the engine block to the magnitron. Also, disconnect your P lead.

This test should only take a few minutes. If this does not work it will have ruled out a grounding problem. If it does work, it will have saved you countless hours. This follows the same logic of running a negative lead directly from the battery to the starter. Paint, surface oxidation, dissimilar metals, etc, all can cause poor ground continuity.

I agree with Sonex that it is not the magnet. If it was the magnet, the lower magnitron should not fire either. I do not know how you could do a magnet test with the engine mounted with all the other metal in the way, so I would not be that confident in the magnet test. Also, as shown in the manual, different compasses show different results. When your friend tested his magnet, did he use the same compass?

I would recommend not "over thinking" this. The magnitron system is as simple as can be. It can only be one of six things: a bad ground (to magnitron or to engine block), a p-lead being grounded unintentionally, a bad magnitron, a bad plug or plug wire, an improper gap setting between magnitron and magnet, or a bad magnet (which would not fire either magnitron).

I would also be suspect of the part you bought from Amazon.com. Even though it looks the same, it may not be to the same specs as the part supplied by Sonex.

[mike.smith]

Mike,

Before you go through all this trouble in taking the engine off, may I suggest you try one very simple test? Everything you have described sounds like it is a grounding problem.

Run an 18 gauge ground wire directly from the battery to the engine block (not the mounting plate), then run a wire from that connection on the engine block to the magnitron. Also, disconnect your P lead.

This test should only take a few minutes. If this does not work it will have ruled out a grounding problem. If it does work, it will have saved you countless hours. This follows the same logic of running a negative lead directly from the battery to the starter. Paint, surface oxidation, dissimilar metals, etc, all can cause poor ground continuity.

I agree with Sonex that it is not the magnet. If it was the magnet, the lower magnitron should not fire either. I do not know how you could do a magnet test with the engine mounted with all the other metal in the way, so I would not be that confident in the magnet test. Also, as shown in the manual, different compasses show different results. When your friend tested his magnet, did he use the same compass?

I would recommend not "over thinking" this. The magnitron system is as simple as can be. It can only be one of six things: a bad ground (to magnitron or to engine block), a p-lead being grounded unintentionally, a bad magnitron, a bad plug or plug wire, an improper gap setting between magnitron and magnet, or a bad magnet (which would not fire either magnitron).

I would also be suspect of the part you bought from Amazon.com. Even though it looks the same, it may not be to the same specs as the part supplied by Sonex.

We have done all the direct grounding, as you suggested. There is absolutely no grounding problem. Of that we are completely sure.

I don't think we were describing the symptoms properly regarding top vs bottom mags. The engine did not run fine on the bottom mag. It was the forward 2 cylinders that were reading low on the CHTs, but those are the ones in the propeller slip stream, and #2, reading lowest, is the beneficiary of more of that air than the #4, due to the direction of the prop. When we disconnected the grounds from each mag (separately) they both ran so poorly the engine would stop. So they were equally as bad. I think we fooled ourselves into thinking the bottom mag was running OK because the #1 and #3 cylinders were running higher CHTs than the other two, so we were thinking they were OK.

We have spent hours and weeks troubleshooting, with lots of input from Joe Norris at Sonex. We were all collectively completely out of ideas. This is really the ONLY thing we haven't changed. Given how strong the magnet is I think it's certainly possible that it could still be providing energy to the mags. I guess we'll see. I've been wrong before (but don't tell my wife).

The metal around the engine has zero affect on the compass when it is anywhere near the magnet. We had the compass 1/4" away from the magnet. That magnet will just about pull your fillings out, so the metal around the compass has no chance of overcoming the magnet.

Sonex buys 3rd party mags, too, and the one I installed runs the AV exactly as the one I took out. So I'm not presently concerned about the mag (other than spending $30 I probably didn't need to).

I value everyone's input, so I'll be sure to let you know what happens after the weekend.

Mike

[mike.smith]

Well, folks it WAS the magnet!! We pulled the engine off the backing plate today (a fairly simple thing, actually), flipped the magnet (we checked it before we did, and verified it WAS opposite the magnet that was working in Keith Macht's AV), reattached the engine, re-gapped the mags, hooked up everything I had disconnected, and fired it up. It ran great on both primary and secondary, with a max RPM drop of 50 between the primary and secondary.

So... yes, the AV will run with the magnet polarity reversed, but it will run like crap.

If you ever run an AV for the first time and have rough running on the primary, add the polarity check to your list of things to check. Of course, the best thing to make sure it's right while it's still on your work bench!

Thanks to Keith Macht for helping me TWO Saturdays in a row!

Mike