Verifying the AeroVee Secondary Ignition Timing

[pfhoeycfi]

I did the in flight timing verification again this morning. I thought I'd give it a try in the colder air. With just the primary on, my average CHT is 7 degrees F cooler than with just the sec on. How large of a delta warrants making an adjustment to the secondary ignition? Interestingly, the average EGT was 34 deg higher with just the primary on vs with just the secondary on.

Peter

[Bryan Cotton]

Peter,
Of course they don't really give you a magnitude in the manual. I think my CHTs varied by a few degrees but I honestly don't remember how much. I'd be happy with 7 degrees, especially 1) if you are happy with your mag check and 2) the engine runs good and shows no sign of detonation or anything and 3) static or climb RPM is good on the secondary ignition.

Of course if Sonex gives other guidance I'd go with that. I set my secondary ignition with a timing light. Basically I put a mark on my flywheel when the motor was at TDC. Then I put a mark on the case which lined up when running on the primary ignition. That took me a few tries to get right. Then I swapped the inductive pickup to the secondary and checked again.


The post is here, go to the bottom of this page:
viewtopic.php?f=7&t=3232&p=48273

Edit: The NA Aerovee looks like a different animal than the turbo. Both my ignitions are set at 28 degrees.

[pfhoeycfi]

I think I will try that if I can find someone to sit in the airplane. I bought that HF timing light but haven't used it yet. One thing I do need to look at, with primary only at 35" mp (max continuous power), after about 1.5 minutes 2 of the EGTs busted the high limit. EGTs remain within limits with both or sec only. I'll pob fly this test again.
Thanks,
Peter

[Bryan Cotton]

Yeah you don't want to do that solo. One good thing is you don't need high RPM to check the timing, it is fixed.

The Aerovee Turbo secondary timing is retarded compared to the primary? That makes sense for high EGTs I think. The fuel has less time to burn in the cylinders, so more burns in the exhaust. I wonder why they are not both fixed at 28 BTDC like the vanilla Aerovee.

I realized after I've posted the same thing twice in this thread. Whoops!

[mike.smith]

Its pretty straight forward. Put a mark on the flywheel and case corresponding to 28 BTDC. The engine manual shows you how to locate this. I used a silver sharpie. I put mine around the 2 o'clock position looking in from the rear. I'll post a picture tomorrow when I pull the cowl for the oil change. Clamp the light to the battery and put it on #1 primary spark plug wire. I have done it several times in the past. I recently bought this one to do my Onex.

Once you get it working on the #1 Primary plug, shut it down and move it to the lower plug wire and try again. You should instantly see the secondary ignition mark. Anything above an idle is fine since its fixed timing. I usually go to around 1400 to not blast the person running the light. Once you get it set, you can try revving it up a bit but mine never moves.

For anyone that has done the timing light method, I have some questions.

I set the flywheel magnet to the edge of the magneto, per page 45 of the manual. But neither of those magneto wires go to the #1 cylinder; they go to the "forward" cylinders, 2 and 4. The #1 cylinder magneto wire comes from the bottom magneto. So with the timing light lead connected to the magneto wire that feeds the #1 cylinder, the magnet is at the wrong side of the flywheel to fire the spark plug and the timing light via the magneto.

When I connected the timing light to the coil (secondary) wire that feeds the #1 cylinder, the timing light never fired. I tried the wire coming from the other coil just to make sure I didn't have a bad coil, but the light never fired from that wire, either.

What am I missing?

[WesRagle]

Hi Mike,

I probably shouldn't say anything since I don't have an AeroVee. But, I will say this: Some folks (Including Scott Casler of Hummel Engines) number the cylinders according to firing order. Looking from above and behind the engine that numbering is illustrated below.

Cyl3|||||||Cyl1

Cyl4|||||||Cyl2

Perhaps Scott Todd was using that numbering scheme.

I haven't tried the "timing light method" in many years but I'm about to. I would be interested in knowing if you get a good timing light trigger by clamping to the 12 V lead (power) of the ignition coil.

Good Luck,

Wes

[Bryan Cotton]

Mike,
I typically connected to the #4 plug wire. I prefer the right side because the starter is not in the way of the marks I made, as shown in the pictures earlier in the thread. I think I preferred the front cylinders because of ease of access for the inductive timing light pickup. But because my marks are arbitrary, and just meant to synchronize the primary to the secondary, any plug would do.

It doesn't make sense that your light won't fire for the secondary - unless maybe you have shielded spark plug wires. If so can you pull an unshielded wire from your junk box and put it in place temporarily? That won't change the timing at all, but may make the difference for the light.

I would expect the primary to have less spark energy so it seems backwards, but I believe in your observation.

[mike.smith]

Hi Mike,

I probably shouldn't say anything since I don't have an AeroVee. But, I will say this: Some folks (Including Scott Casler of Hummel Engines) number the cylinders according to firing order. Looking from above and behind the engine that numbering is illustrated below.

Cyl3|||||||Cyl1

Cyl4|||||||Cyl2

Perhaps Scott Todd was using that numbering scheme.

I haven't tried the "timing light method" in many years but I'm about to. I would be interested in knowing if you get a good timing light trigger by clamping to the 12 V lead (power) of the ignition coil.

Good Luck,

Wes

Hi,
The AeroVee cylinders are #1 being the closest to the pilot, #2 forward of that, #3 closest to the passenger, and #4 forward of that.

I got a light when clamped onto the wire from the mag, but not when clamped onto the wire from the coil. But I as not seeing the timing mark when clamped to the #1 spark plug, I'm assuming because that wire is 180 degrees from where the trigger magnet is on the flywheel.

[mike.smith]

Mike,
I typically connected to the #4 plug wire. I prefer the right side because the starter is not in the way of the marks I made, as shown in the pictures earlier in the thread. I think I preferred the front cylinders because of ease of access for the inductive timing light pickup. But because my marks are arbitrary, and just meant to synchronize the primary to the secondary, any plug would do.

It doesn't make sense that your light won't fire for the secondary - unless maybe you have shielded spark plug wires. If so can you pull an unshielded wire from your junk box and put it in place temporarily? That won't change the timing at all, but may make the difference for the light.

I would expect the primary to have less spark energy so it seems backwards, but I believe in your observation.

The #4 wire would make more sense. I was going by several written instructions on the forum, indicating cylinder #1. The wires from the coils are the ones that came with the AeroVee kit. I would think any modern electrical ignition wire would be shielded?

[Bryan Cotton]

The wires from the coils are the ones that came with the AeroVee kit. I would think any modern electrical ignition wire would be shielded?

I'm not sure our wires are shielded. When I terminated the ends they didn't look shielded to me. Maybe try a different timing light. I am assuming it is not flashing, or is it flashing but just not picking up your timing mark?