Advancing vs retarding the secondary trigger

[BK9977]

I am still trying to get this Aerovee running decent. I just want to make sure about the timing on the secondary ign.

Advancing the timing would be rotating the cap clockwise, retarding would be counter clockwise, correct? (looking from the back towards the front)

What are the effects of an advanced timing? What are the effects of a retarded timing?

When I do a mag check how do I know what way to turn the cap, or is it just a crap shoot without a timing light? (I don't feel comfortable having someone doing that while I operate the controls) Lets say I turn off the secondary ign and get a rpm drop, which way do I turn the cap?

I have looked in the Aerovee manual and factory just says to follow the procedure in the manual but it doesnt really go into as much detail as I think it should about the timing as it just says turn the cap. I can't believe there isn't a more specific method to get this thing dialed in.

Thanks
Bryan

[radfordc]

Too little spark advance will cause low power, and poor performance. Too much advance will cause hard starting, pre-ignition, and high CHTs.

If you follow the manual you will be very close to correct. You check by first looking at the mag drop on the ground....should be less than 50 rpm. In the air, fly for 20 minutes at cruise power and let the CHTs stabilize. Then shut off the secondary ignition system and again fly for 15-20 minutes and let the CHTs stabilize. If the engine runs cooler with the secondary off you are slightly advanced.

I recently did this after replacing the triggers on my engine. Running on both ignitions my CHT was 350. Running with the secondary shut off my CHT was 310. I need to retard the timing about 1 degree (turn the magnet cap counter-clockwise about .15") and try again.

[MichaelFarley56]

I think you have the direction of turning wrong. When you're looking at the back of the engine facing forward, clockwise would retard the timing and counter clockwise would advance the timing.

I did pretty much the exact same thing Charlie did to set my timing. To begin the process, look at the AeroVee manual, page 45 to see how to line up the coil housing to the magnet shoe then make sure the secondary timing mark is lined up with the trigger sensor. This should get you pretty close...close enough to get a smooth running engine that you can fine tune once you're flying. Then do what Charlie described.

I've never used a timing light...trial and error has fine tuned my engine!

Is your engine not running well? Is there something else going on? If you're having issues, maybe it's a mixture issue and not an ignition issue. Fill us in!

[BK9977]

Ok, Mike, you are right, I am still not used to this engine turning "backwards" compared to other aircraft engines.

But yes, it does not seem to want to run decent. I am about right, maybe a little lean at full throttle, but way, way rich at idle (#2 needle). It is to the point where I have to pull the mixture control so far out to lean it to stay running at low rpms, (less than 1700)it starves it of fuel. I thought it may be timing, I had a difference of 120rpm at 1900 rpm, so I advanced it. However in doing so it caused my WOT rpms to drop by 150rpm and started to run worse, but the drop was in limits, around 20 rpm drop. I think maybe I advanced it too far???

In talking with a A&P buddy last night he thinks I may have an intake air leak. So I am pulling the elbows and resealing them, and replacing the plugs because they are fouled. I will play with the timing next week a bit more.

[radfordc]

Back in Nov I noted that I needed to adjust my secondary ignition by a degree or two more retarded. Today, I got around to actually doing it. The concern I had was the tiny amount of change required...I needed to move the magnet only about .020-.025". Thinking about it I realized that if I could lock the magnet in place I could move the prop and this would give me much more control since the amount of movement at the prop tip is .5-1.0". I found that I could tape the magnet puck tight enough that I wouldn't move. All I had to do then was loosen the retaining bolt and move the prop forward just a little.

[MichaelFarley56]

AWESOME idea Charlie! That's brilliant!!

[GWMotley]

That's a similar idea I posted awhile back but probably on the Aerovee forum. Instead though, I taped the magnet down, loosen the bolt, then apply tension in the direction I wanted. This prevented me from actually moving the magnet very much, just a fraction of movement was all the tape would allow.

[radfordc]

After tweaking the secondary ignition another degree or so retarded I flew again today. After takeoff I shut off the secondary ignition, climbed to 4000 feet, and cruised for 20 minutes. The temps stabilized with the temps as shown here.



I turned on the secondary ignition and the EGT's immediately dropped a few degrees and after 10 min the CHTs stabilized a few degrees higher.



Again, shutting off the secondary, the temps returned to the initial readings.

[kmwoody]

I finally (after thinking it was good enough) adjusted my timing Charlie's way, by taping the magnet and moving the prop. After advancing (yes, advancing) the magnet by moving the prop 1" - 6 inches from the tip two times, the EGT on the hottest cylinder went from 1350 and rising - 30 seconds after takeoff to staying under 1290 troughout the climb.

Now I have been experimenting diverting cooling air from the coldest cylinder #2 to the hottest #1. I duct taped a piece of aluminum to the baffel in front of #2 and it seemed to lower the temp by 6 or 7 degrees.

I have seen, on the Yahoo Groups, pictures of dams for just such a purpose. Does anyone on here have measurements or pictures of what has worked for them?

Thanks

Ken W
Sonex 959

[edtropper]

I have had a problem with #1 & #3 overheating in climb and when ther is a load on the engine. I changed the baffle seals and made sure every opening had RTV in it. Also increased the outlet openings to let more air out of the cowling. all helped a bit. Also tried air dams in front. Started playing with the timing but no luck so far. Does anyone have any other suggestions?