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  Magneto Switch Configuration w/o Shower of Sparks (SOS) Ignition



Here's a tip I picked up while at the Beech Talk / Continental Motors factory tour and training event in September 2012.


It involves our magneto switches as relates to Shower of Sparks (SOS) ignition systems or NOT having an SOS ignition system.


Let me see if I can paraphrase from my notes what is going on here. The SOS ignition system is set up to amplify the left magneto spark or create multiple pulses of sparks, in any event, the right mag is completely shut down during cranking via a tab in the magneto switch which grounds out the right mag. See mag switch picture and tab picture.



So, if you have long since gotten rid of your SOS ignition system and gone to dual impulse magnetos and still have these tabs in your mag switches, you're only starting your engine with one mag (the left mag)!



In my case the SOS system has long since been removed BUT the tabs were still in place on my mag switches. Once these tabs were removed my starting (both hot and cold) was noticeably quicker/better.



Check out this ugly rigged Mag Switch "tab" configuration, found in a Bonanza owner's plane after he read this narrative and checked his switch!





IMPORTANT: BOTH MY MAGS ARE IMPULSE MAGS (Slick 6310). If both your mags are NOT impulse mags, DO NOT remove the tab! If you have no clue about these details, call your A&P. This activity requires an A&P or supervision by an A&P anyway so yours should be nearby to consult.



In case you're wondering what the Shower of Sparks (SOS) ignition system looks like, here is the major component - the vibrator that creates the pulsing sparks.


Sometimes it's in the engine bay and in the case of other airframes it may be mounted in the cockpit. In one B55, the control box was mounted above the pilot's rudder pedals. A window leak resulted in a flood of the red cupped box and subsequently corroded this SOS box to death.





From Don Maxwell's narrative:


The "Shower of Sparks" system is composed of a magneto with two sets of points installed, a vibrator switch, ignition switch and the aircraft battery.


The magneto has two sets of contact points. One set is adjusted to open 25 degrees before TDC used for normal operation. The other set; the "retard points" are adjusted to open 25 degrees later at TDC for starting."




Here are some additional comments about the SOS system from Beech Talker Kent B.:


I have the Bendix Shower Of Sparks mags and system installed on my TA. I had a problem a few years back with one of my engines not wanting to start. After consulting with my engine overhaul guy (Bolduc Aviation), they sent me a fax covering all the in's and out's of the SOS system.


You and others here have covered all the basic facts concerning the SOS. But I would like to add a few things I found during my troubleshooting of the problem I had. It ended up being the SOS P-lead not contacting the tang inside the mag due to either the tang was not bent forward enough or the half moon soldered on the end of the P-lead had wore itself off.


We all know that when the mag switch is moved to the start position it:


1. Shuts off the R/H mag

2. Sends battery voltage through the Starting Vibrator to the L/H mag

3. The high tension voltage goes through a different set of points adjusted to fire the spark       plugs at or near 0 degrees TC.


The Starting Vibrator, (mounted above the L/H rudder pedals in my TA), should make an electrical sound that varies in pitch or tone when the engine is started. That's how I found the problem with one of my engines not starting. I heard a steady tone and figured the circuit was open.


It's a great system and when I go to start my Lyc 540's, it only take a few prop blades to go by and the engine starts right up!



And some nasty Kickback troubleshooting guidance from Rich H.:


With shower of sparks, the left mag should be grounded out in the START position, and the right mag should be grounded out in the advanced position, leaving only power shower of sparks (retarded) position.


In kickback instances, two possibilities to look at are that the wire for the grounded position is faulty (broken, bad connection at the mag or at the switch),




Perhaps you released the key to the RUN position and before the starter spring could disengage one (or both) of the mags fired in the advanced position, kicking back against the spring.


When my shower of sparks was giving me problems a few years ago (a new vibrator solved it all) I had unconsciously gotten into the habit of sensing when the engine might start and releasing the key.  Sometimes it worked but a couple of times I got an expensive kickback.





Here are some troubleshooting thoughts from BT'er Charles W. on the SOS system:


You don't have to get to the vibrator to test it.


You can remove the wire going to your starter and pull a plug on each cylinder.


Put your number 1 cylinder to about 10 degrees BTDC on a compression stroke.


Hold the number 1 plug wire about 1/2 inch from the engine ground and turn your starter switch to start. You should hear the vibrator working.


You should see a continuous spark at the plug wire You can rotate the engine forward and back a little to see the continuous spark.


If you have a good spark you are good, if the spark is weak or nonexistent you have a problem.


The problem could be, a bad vibrator, bad wiring or faulty retard breaker points.


If the vibrator is making noise and you don't have a spark, your condenser is probably bad.


To test it you can install a simple auto condenser in the vibrator and redo the above test.


The biggest problem is if you go to a discount auto store with a youngster working the counter whether they will know what you are talking about, when you say you want a condenser.



Happy Skies and better starting!



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