Bendix Mag SF-4 issue - 400 rpm drop on right mag/sparkplug.

[skyking3286]

We also replaced the condenser, which is really easy. It is accessed through the slotted button on the bottom of rear end of the mag. The single wire pokes through the compartment and attaches to the lower bolt on the right side of the points. Sort of where the obvious place would be.

New condenser, which rumor has coming from Toyota but it met MS:



Installing it on the back points:



That was easy.

[skyking3286]

Now the mag is ready to install. We replaced the carbon brush and the gaskets to the engine and the top of the case.

Timing mark on the gears is marked:



Before it started it looked like this:



The installation and the timing took the longest. We had issues running out of the adjustment to get it to time right. Finally did it.



Now, the next chapter in the story:

[skyking3286]

Nothing like having new parts in a mag that was giving you troubles. It starts strong after the annual and we taxi back to the hangar. I'm a happy camper.

Now to fly. First flight was .8 tenths of an hour. Runup is perfect as always. Nice. Upon return, we have a slight issue again with the right mag.
Shoot. Not as bad as before, but it's still there. And just like before, if I fly less than .7 of an hour it doesn't seem to be there.

Next flight is 1.1 hours. And we do a run up after we land.

First the landing, with that little A-65 sounding nice:

http://vimeo.com/80043647

and then we taxi to the run area and check that pesky right mag. Here is the issue live and for your viewing pleasure:

https://vimeo.com/80700562

Rough, doesn't want to really go smooth. With both mags you would never notice the issue at all. This is the top plugs/Right mag. Only when used for a while.

So we still have a problem. But, unrelated to that, there was a problem with my 1990 Honda Civic. It was starting fine, but after it warmed up a bit it would refuse to start. It would crank all day, but no start. And not always, just once in a while. A quick internet search revealed that the solder on the main PFM relay wasn't good. Cold solders, components that weren't really well attached to the circuit board. And as heat and vibration work on the relay, its not unusual to have it refuse to connect the fuel pump relay. I so I pulled the relay, re soldered the circuit board and now it runs just fine.

This was the lifesaver on the internet:
http://www.tegger.com/hondafaq/mainrela ... relay.html
Read that last paragraph on the page.

So that has me thinking - that the plug wires are also soldered. And that the heat and vibration also are a part of the issue. I had new plug wires on the plane in 2002 or so, less than 120 hours on them. Next step? I'm running up to the airport with my 45 watt soldering iron. The mag is pretty much finished as far what I know. The only other thing would be the distributing rotor. But that seems unlikely.

As the mag turns....

[Richard Murray]

Mark,

Can the mags be swapped? ie the right installed in the left position and the left in the right position

I can't remember if you tried this or not.

[skyking3286]

We decided against it when the switch tested OK and the plugs were swapped. It seems to be all about the right side. But I'll unhook the R spark plugs next time and try to start it and then switch to R mag just to check.

[skyking3286]

Went up to the airport with a lot of snow pellets flying and checked the spark plug ends of the plug wires. A couple of them were grey and grainy and so I'm definitely going to resolder the ends. I don't think that micro-cracking can be as much an issue compared to a 12 volt relay system, with all the voltage going across any gaps, but who knows. That's my next step.

[Paul Agaliotis]

Mark,
Have you megged the wires. If you're satisfied with the mags and plugs the only thing between them is the wires. It still has all of the indications of a bad plug.
Paul

[skyking3286]

Update:

I think we figured it out. The vertical terminals. Harry Fenton and Paul Nyenhaus up at Arlington both came up with it.

They expand with heat and there are small cracks that can open up just enough to ground the spark into the mag case. I put two new ones in the mag, cleaned the contacts on the distributor rotor and the terminals and only had a slight miss, which means there are two more I need to put in.

I also rearranged the plug wires so they couldn't cross other ones. It was a bit of a spaghetti tangle before. I think one wire might be a little marginal with the ohm meter, but I need a better meter to check it. Progress.

So if you have the problem and think you need to replace anything on the mag replace, in this order:

1. Vertical terminals
2. Condenser
3. Coil
4. Plug wires

[Richard Murray]

Big THANKS Mark and ditto's to Harry and Paul.
The learning curve has turned upward.

[Captgrumps]

If we only has an Ignition Analyzier with a Scope. But then would have to carry an extra crew member.