Keep the best magneto

Today Warren and I have compared the two magneto’s to find the one with the best spark. This is the one I am going to keep as an original magneto; running independently.

The other magneto, will undergo a bit of a rebuild:

  • I will still use the distributor.
  • I will still use the contactor.

But that’s where it finishes for generating the sparks. What I am doing is using a modern car ignition coil, that feeds into the magneto where the old coil used to feed into the distributor. The contactor will still be used but now it will switch the external ignition coil, using the battery as a power source.


What this means is I will have nice big sparks, see photo on the right of at least 10mm, even at the lowest engine speed, that’s while cranking the engine.
This ignition system relies on a battery though, but I have a battery already, so no extra weight.

The second real magneto is still there, generating nice sparks when running, so that’s my safety net.

As an interesting extra thing, Warren is going to try to make an alternator of the magneto I am rebuilding, so basically rewinding that coil you see just above, to generate a supply for the charging the 12V battery. It won’t be much, but I might as well use it. The same alternator signal can be used to produce my tachometer signal, using some electronics circuitry…



OK, I tried starting the engine last weekend, but no luck.

The main problem is the ignition system really. When the engine is hand cranked, there is no spark. This was last weekend.

In the last few days, with the help of Warren, we decided that the capacitor inside the coil is failing. After taking that out, by disconnecting it and wiring a modern one across the contacts, the spark improved a lot.

I can now create sparks about 5 or 6 mm long. BUT that’s when spinning at a nice speed. At crank speed it’s still hopeless.


Have been talking with a guy in the states about rewinding the coil. But with the new capacitor, I have the feeling that the spark isn’t going to improve a lot.

So I have made a decision to start using a modern car ignition coil.


Is it going to run

To get you out of your suspense, I can tell you that the engine didn’t run today 🙁 🙁

The sparks generated by the 2 magneto’s are just not there when I hand start the engine by swinging the propeller. Yesterday it definitely sparked, but that’s at a faster spinning rate.

So going to find someone here in NZ who apparently has done lots of them. Chad told me to ring a guy he has worked with/for who will know the man I am looking for.


Earlier today, my fuel tank, and the mixture control:




Nicki on the controls, in case it goes,  🙁 it didn’t.



I started to do some work on the magneto’s. Have a look here.


Ignition leads

Today was going to be the day to start the engine, but no luck yet 🙁

First I had to make 10 brass screws with a sharp points to install the ignition leads into the magneto’s. Made them by putting the screw with nuts in the electric drill machine, and an angle grinder to make the point.

After that I, checked all 10 ignition lead connections with a spark plug, see right photo.




The axle going into the magneto has a clever way of setting the ignition timing. The 3 nuts you see here, lock a disk that is connected to the axle. By loosening up these nuts, you can change the timing of the magneto so it fires the spark plug at the right time.


After setting the timing of the magneto’s, connecting all 10 ignition leads, connecting the oil tank, and the fuel tank (will show you that one tomorrow), it was time to try and start the engine.

With the ignition switched off, the throttle closed, the primer control open, I spined the prop a few times to suck fuel into the carburetor. Then with the ignition on the throttle a bit open I tried starting but no luck so far.

I think I need to get more fuel into the engine. After I primed the engine, I didn’t open the mixture control, assuming that there would be enough petrol in there to do at least something, but I was wrong. I will also check if the spark plugs work. I know they do, but check that to see if the work at this crank speed.

Been doing some more reading on the mixture control, and it shows that I didn’t have a clue, did I !!!!

You need the mixture control fully open, to create a rich mixture. Then once its running you start leaning it for maximum RPM, for the current throttle setting. That throttle setting was the only thing I could find in my Velie manual. The say have it at 1/8 open.

So looking forward to tomorrow !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Ignition timing

Picked up 10 spark plugs today. They are a Champion D16.

I also started working on the magneto’s. In the past it just all looked complicated, with timing, and so many cog wheels etc. But now I understand it all, it looks pretty straight forward.

The engine needs to be timed to fire at 30 deg ahead of centre. So to do that, the engine is turned in the direction of rotation until the #1 piston is coming up on compression and is 30 deg ahead of top dead centre. So that is where I want ignition.

Now I need to set the magneto right. This magneto has a rotor with the magnet and a small gear. The distributor has a large gear that is driven by the small rotor gear.

On the same rotor, is a cog that drives the contacter. So first I position the rotor so the contacter is about to open. Then I mount the distributor with its large gear in the position where the #1 ignition lead is “in contact” with the high voltage coil. There are two marks on this distributor that show me exactly where that is, so that’s easy. And yes when the distributor blocks are in place I can now see that the distributor is exactly in the right place.

That’s the magneto timing set really. Now turning in the direction of rotation, the contacter opens when the distributor is exactly over the #1 contact.

So that’s done, all I need to do now is mount the magneto’s on the engine. There I can “disconnect” the magneto from the engine with 3 nuts, so I can move the magneto so it’s firing exactly at 30deg ahead of centre , but I will do that in the next few day’s.

Spark plugs

Got an email from Chad:


These low compression engines will tolerate any number of different plugs.

If you must have noise canceling then you should go shielded but since the mags are not set up for shielding you’ll have to ground the woven exterior of the standard modern aviation mag wire. Of course there may be some automotive wire that will do the same thing but I don’t know. You must however stay away from carbon core automotive wire – they must be wire core.

This is not to say that non shielded installations will in fact cause radio interference. You might experiment first before investing. My experience is that some do – some don’t!

So yes that’s what I wanted to hear so that’s good. This means I am going to find some local available spark plugs, and wire them to the magneto’s