Happy New Year!
I hope I can pick your brains as I think I am missing the obvious. 10 hours after a 500hr inspection, I decided to reposition (turn a bit) the L magneto since it was a bit close to another part. Now my engine with two Slick 4301 magnetos quits on key position L. I tried to verify everything:
Mounted with cylinder 1 in TDC, pin in the L hole, P lead and ground connected. I checked for a spark, both upper and bottom sparkplug fire in cylinder 1 and 3. Then I checked for a key or cable problem, disconnected left P lead and ground cable so that the magneto would run without cable connection. Engine started, key to R runs fine, key to L and the engine stops. So I think there is no problem with the cable or key position since it wasn’t connected and the engine stopped nevertheless.
That leaves the magneto. I have the feeling that the L magneto sparkplugs don’t fire at the correct time. Could there be an internal magneto problem? But why, the magneto worked well for 10 hrs after inspection. Or could I have broken something while installing the magneto with the pin? Maybe I fiddled a bit too much and the rotor moved?
I am sure any of you will identify the obvious error that I am missing. Many thanks!
Oh, I forgot to mention that I set the timing on 25 degrees prior TDC and in sync with the R magneto.
When the timing pin was inserted in the magneto chassis, and the magneto in place on the back of the engine, was the propeller turned at all? If so, the magneto has probably been internally damaged.
If that is not a factor, when the ignition lead plate was removed from the back of the mag, did it get at all wet? Raining/damp day – outside work? It takes very little moisture in there to ground the spark inside the mag.
In my installation rotating the magneto sets the timing, and even the slightest rotation of the magneto has quite some impact on the timing. Just to have the easy things out of the way first, I assume that the timing was checked and set > after < the last movement of the magneto took place? 25 prior TDC should ignite any engine, no matter whether it’s the correct timing or not for the specific engine. Did you set the timing yourself and you do have experience with doing it? when I set the magneto timing my first time I was surprised that it is not as easy as I imagined it to be. With the correct tool no problem, but you do have to know how to set it up right that you get the correct timing information.
Pilot Dar is spot on with the possible damage if moved with pin installed.
Timing is never set on TDC of the engine, as noted, 25BTC would be correct,
IF you had the mag off, depending on the type of drive the eng/mag has on the left side, some use rubber couplings, some use std gear on the impulse coupling. IT is very easy to drop the couplings into the case. A big OOOOPS.
Also, with out a timing light, now way to actually sync to the opposite magneto.
You really need a mechanic to redo and see if the mag is damaged,
Trying to start eng, at this point you can do some big money damage if the timing is off and it happens fire. Of course , if you have unlimited funds and time. Try it! lol.
Carl
A little extra note: If you do turn the crankshaft while a timing pin is inserted it does not take much to damage the distributor block. The block can get cracked easily. I’ve seen a lot of Slick magneto distributor blocks where a tiny piece of the little tower on the inside of the distributor block is broken off, this can happen with only a very minor bit of force from the the timing pin. Mechanically this won’t make your mag malfunction, however, when resetting the internal timing at 500hrs inspection etc. the slight difference could mean there’s a possibility to skip one tooth of the gear when setting the timing, so the distributor block should be replaced regardless.
planewrench, could you please tell me how a gear could fall into the crankcase (or accessory housing)? Magneto gears are normally fixed to the mag with a nut?
