777Dave

777Dave

Well Known Member
I have an airplane equiped with 2 bendix mags and "shower of sparks" system. I also have no key switch but instead have a 4 position switch allowing me to select off, left, right and both (mags). To engage the starter I have a simple toggle switch.
Just confirming that I should be using "left" selector for start to avoid kickback.
Cheers and thanks
 
Shower of Sparks mags don't have impulse couplings.

Both should be on when starting if both have the system installed. Otherwise you only want to be starting on the mag with the shower of sparks.
 
clarify

Correct, no impulse coupling.
Its a spring loaded toggle so same as push button. Interesting because its well hidden and almost impossible to see.(thief) I have read a couple of older threads that talk about this setup so I think the builder (not me) decided to do it this way.
As I mentioned, I'm just confirming that left mag start is preferable.
Bob, SoS is only on the left...
 
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As I understand things, left mag only for starting is to let the impulse coupling do its job and only have a retarded spark.

Usually an impulse coupling is on one mag, and the other mag will fire at static timing----------so it is bypassed for start.

While Rocket Bob is correct that a shower of sparks setup is not intended for use with an impulse mag----------you never know if someone has batched up a bunch of mismatched parts, and thus my original question.

I see no reason to start on left only in your case---------as at cranking speeds the right mag is not doing much of anything in the spark department, unless it also has a SOS or impulse coupling-----just not enough electrical energy developed in the mag at cranking speed. It will not hurt to start left only if it is the only mag with the shower of sparks setup.

http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf
 
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Mike,
You may be confusing an impulse coupling - which is a spring loaded affair that both increases the magnet speed and hence the voltage, and retards the timing to near TDC - with a retard breaker, which retards the timing. You want a retard breaker mag (at least with Slicks, I'm not familiar with Bendix) to trigger the shower of sparks (called Slick start with Slicks).
I would turn any non retarded mag off during start. While true, usually they won't fire at cranking speed, it might (say, a plug gap was extra small) and this could result in a kick back and damage.
 
BobTurner said:
Mike,
You may be confusing an impulse coupling - which is a spring loaded affair that both increases the magnet speed and hence the voltage, and retards the timing to near TDC - with a retard breaker, which retards the timing.
Click to expand...

Nope, no confusion there.

The OP was not the builder of this plane, and did not initially state if the SOS was only on the left mag--------thus I was asking questions to determine what his setup was, if in fact he even knew for sure how it was setup.

When someone is asking about a plane they did not build, it is good to get all the details straight..............what actually is, may not be how we would have done it, and best to not fall into that thinking process.
 
A traditional and typical shower of sparks mag has a second set of retard breaker points that need to be switched to during cranking of the engine to start.
This is typically done using one of the "extra" terminals on the back of the traditional key switch that we don't use with impulse coupling mags.
If a toggle switch is being used to control the SOS mag, it is likely that the even if engine is being started with only the left mag. active, the engine is still being started without retarding the timing. This does have a danger of kick back.
 
Mike S said:
I see no reason to start on left only in your case---------as at cranking speeds the right mag is not doing much of anything in the spark department, unless it also has a SOS or impulse coupling-----just not enough electrical energy developed in the mag at cranking speed. It will not hurt to start left only if it is the only mag with the shower of sparks setup.
Click to expand...

Not entirely true mike.
You are correct that without the snap of an impulse coupler, the spark is weak, but it is still strong enough to cause a problem. Especially with the fast spinning starters that we typically use now a days.
This weak spark is not retarded in timing (not good).
This is why the traditional keyed start switch has a location for a grounding plate so that the right mag (if it is a non impulse mag) is disabled while cranking in the start position. If both mags are impulse, then the grounding lug is left off so that both are enabled during start.
 
yesterday

I did 4 starts yesterday, all using L mag only for start and I feel that it cranks smoother using only the left, still starts quickly.
Thanks for numerous enlightening responses. :D
Enjoy the holidays!!
 
Shower of sparks

May I ask is this a 0-360A1D out of a Mooney? If so there is a switch for this application and one of the two mags has a extra set of retarded points for starting.
 
Mooney

YES, it is an A1D out of a Mooney!
Can you elaborate on the switch? The left mag has a "shower of sparks" label on it. Not the right.
 
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777Dave said:
YES, it is an A1D out of a Mooney!
Can you elaborate on the switch? The left mag has a "shower of sparks" label on it. Not the right.
Click to expand...

As I mentioned in post 11, if the shower of sparks mag is a retard breaker magneto (I think they all are but can't say for certain), it requires the use of a traditional keyed ignition switch for the timing to be retarded during start.
The retard breaker points are a second set of points inside the mag that is positioned so they open later in rotation which retards the firing of the magneto while cranking for start.
The keyed ign. switch is wired in a way that switches between the two sets of breaker points depending on whether it is in the start (cranking position) or the both position.
A retard breaker mag should have two P lead connections on it.
I suspect that your starting vibrator is being switched on by your start toggle switch, but if the left mag is only controlled by a single toggle, it is likely that it is not being switch into retarded timing mode while cranking... danger of kick back.

A quick google search found THIS explanation by John in the Sacramento Sky Ranch manual (see page 45).
 
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I think I will have to look closer at the switch wiring. Thanks for the great link.


This is what my mag selector switch looks like.

magswitch-1.jpg


magswitch-1.jpg.html


Anyone recognize its origins?
 
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0-360A1D shower of sparks

This system has a vibrator box on the firewall,One of the two mags will have two leads coming off the back,this is the one containing the retarded points for starting,you can find these switches on ebay from time to time.The good thing about this engine is its an easy conversion to Pmags as you have two good drive gears and mounting studs are the right length,something to think about at rebuild time.
 
777Dave said:
I think I will have to look closer at the switch wiring. Thanks for the great link.


This is what my mag selector switch looks like.

magswitch-1.jpg.html


Anyone recognize its origins?
Click to expand...

I don't recognize it... looks very old and not likely compatible with a SOS mag.

The simplest process for you to evaluate your system at this point is to just look at the mag that says shower of sparks. Does it have a P-lead wire connected to each of the two terminals on the mag.? If not, then you are for sure starting without the mag timing being retarded (regardless of what procedure you use) and are at a high risk for kick back. If there is a wire connected to each of the two terminals, then you need to do further investigating to determine what means (if any) is being used to switch between the two sets of breaker points when cranking or in normal run mode.
 
That magneto selector switch looks very similar to what is in my Yak-52. It has a shower of sparks on the left magneto. Starting technique on the Yak is to hold the starter button in with the magnetos on '0', then after the engine kicks, flick the Maggies to both, then release the starter button. The shower of sparks is engaged by holding the starter button in. Perhaps you have a similar setup?
 
update

Got a chance to look behind the panel today.
My mag selector switch is very simple with a shielded lead running from each of the 2 terminals to each mag.
There is a shower of sparks vibrator on the firewall with power supplied from the toggle start switch via the starter solenoid. Repeated attempts to make it vibrate were unsuccessful. Power verified to the unit but no noise or vibration.
The left mag has 2 P leads and the right has one.

I'm thinking the vibrator is toast.... for the moment undecided as to replace ($450 new) or go Pmag which of course is more.......
 
another option

Hi Dave,
I had the same setup on my RV with the same problem. I replaced the one bendix mag with an impulse coupled mag and eliminated the shower of sparks.
 
impulse

rvator51 said:
Hi Dave,
I had the same setup on my RV with the same problem. I replaced the one bendix mag with an impulse coupled mag and eliminated the shower of sparks.
Click to expand...

That's another possibility for sure Tom. The SOS mag (left) that I am running is S4LS-200 BL600614-1 Any idea of the impulse coupled model I would replace it with? Looking at a rebuilt Bendix.
 
The shaft length may be different,you will need to change the studs to long on the left side,acquire the impulse gear and housing. Makes more sense to go one p mag on the left side,you will use the same gear and studs,eliminate the shower of sparks stuff and have the benefits of EI for the same cost as repairing/rebuilding what you have.In time you can acquire a second P Mag.
 
further SOS troubleshooting

So I've had a chance now to do a bit of further investigation and testing of my Shower of sparks system.
Spoke to a magneto repair shop and was advised to check the vibrator by grounding the "BO" terminal on the vibrator and activating the start switch. Did so and the vibrator activated! So it seems to work fine.
Then checked the shielded lead that leads from the BO terminal on the vibrator to the retard terminal on the left mag... good continuity. The magneto was removed and serviced and all normal, points included.
Now advised to remove #1 plug lead, select Left mag and pull prop through TDC to see if there is a strong spark but if the vibrator won't activate, how can the SOS system provide spark at TDC like it is supposed to during starting?

I have decided to try to sort this system out without changing major components...

Thanks
 
We had a similar problem on our Yak (with a similar switch/mag setup to you). Turned out to be a bad HT lead from the starting coil to the left magneto. From memory, the lead tested ok with a meter, so was not found initially. When replaced spark was fine. Not saying this is your problem, but sometimes the cheap things (HT leads) are easier to swap than expensive (mag, coil etc).
 
Can you clarify what you mean by "coil". My system only has the SOS vibrator leading to the Magneto....
 
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