Shower of Sparks

[slowflyin]

Need some advice regarding my SOS. My 70 F model's is equipped with the

standard twist against the spring and push to start switch. What I think is different

is my SOS does not come on until I push and engage the starter. Isn't is suppose

to come on when I turn the key all the way to the right?

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[Andy95W]

Yes, the Shower of Sparks (buzzing sound) should come on when you turn the key to the right. Your internals may be staring to wear out.

There is another thread around that talks about taking the switch apart and replacing the guts with a Bendix repair kit, or simply taking a piece of scotchbrite to the contacts, and taking the mechanism to a locksmith to clean up as well.

Good luck!

[slowflyin]

Thanks for the reply. My sos comes on with starter engagement. I disconnected the starter just to check. Sure enough...buzzzzzz when I push the key in for start. I'm thinking my ignition switch is wired improperly.

[Vance Harral]

Thanks for the reply. My sos comes on with starter engagement. I disconnected the starter just to check. Sure enough...buzzzzzz when I push the key in for start. I'm thinking my ignition switch is wired improperly.

 

No.  Not all models are wired the same, our '76F is wired exactly the same as yours: SOS doesn't come on until switch is pushed in.  I do think "most" Mooneys are wired so the SOS comes on when the switch is turned against the spring.  But it's incorrect to extrapolate that to all models.

[slowflyin]

Thanks Vance. I appreciate the reply. It seems like it would be nice to hear a confirmation the sos was working. However, it's nice to know my bird is probably the way Mooney made her.

[bonal]

My ignition does not require a push to engage the starter it operates like an automotive switch. When I was having start issues (mag related) we disconnected the starter and confirmed the SOS was working properly but it only comes on during the starter operation and you can't hear it while the motor is turning over. By disconnecting the starter you can easily hear the fire works.

[carusoam]

Anybody have a starter vibrator?

I have forgotten if this may be relevant...

I do remember vibrating my starter manually a couple times...

Best regards,

-a-

[Andy95W]

No.  Not all models are wired the same, our '76F is wired exactly the same as yours: SOS doesn't come on until switch is pushed in.  I do think "most" Mooneys are wired so the SOS comes on when the switch is turned against the spring.  But it's incorrect to extrapolate that to all models.

What does your POH say? It should be fairly clear from reading the start procedures.

Finally, what does it say about hand-propping? That was the original idea between seperating the SOS and starter functions, to enable you to engage the retarded spark and SOS but not the starter, and then hand prop.

[Vance Harral]

What does your POH say? It should be fairly clear from reading the start procedures.

Finally, what does it say about hand-propping? That was the original idea between seperating the SOS and starter functions, to enable you to engage the retarded spark and SOS but not the starter, and then hand prop.

 

Can't speak to other models, but the POH for the '76F wouldn't help you with either of these questions.  The normal starting instructions just say, "turn to 'START' and push forward", which gives no clue about whether the SOS is enabled by the first or second action.  There are no procedures for hand-propping in the POH either.  In fact, it specifically says, "Hand cranking is not recommended".  The only way I know our switch is wired as designed is from a combination of the aircraft schematics, and the technical documentation for the mag switch itself.

 

I know people have hand-propped Mooneys with SOS systems, but using a switch with separate SOS vs. crank connections always seemed like a dicey proposition to me.  It doesn't take much of a slip by the person manning the switch to engage the starter while intending to engage only the SOS.  It's safer to disconnect the starter first, in which case it doesn't matter which position enables the SOS.  I'm sure somone will jump in and say you wouldn't be hand-propping if the starter could turn over the motor in the first place.  But if the battery is *completely* dead, it won't run the SOS either.  So there is no point in hand-propping unless you have at least some energy in the battery - i.e. not enough to crank, but enough to change the dynamics of hand-propping if you slip on the switch.

 

When you combine those risks with the tricycle gear configuration of the Mooney, and add in the slightly higher compression of the 200-hp engine in the later short bodies, it's not hard to understand why Mooney would remove hand-crank instructions from the POH.  My guess is the change in ignition switch wiring happened around the same time.

[N201MKTurbo]

Ok, no lectures!

It is impossible to hand prop the engine if you cannot get the shower of sparks to come on without engaging the starter.

My F was very easy to hand prop, I have never been able to do my 201.

[1964-M20E]

My SOS comes on when you twist all the way to the right then push in to start.

As for hand propping a Lyc 200HP I'll leave that to the experts like N201MKTurbo.

 

[smwash02]

This has nothing to do with Mooney. It's a Bendix switch and the specs are published.

 

I made this picture when diagnosing mine.

 

 

I made it from the switch spec sheet.

[Vance Harral]

This has nothing to do with Mooney.

 

Respectfually disagree.  The question was whether the SOS engages with twist only vs. twist-and-push.  To answer this, you need the Mooney schematics for your airframe, to determine how the switch is supposed to connect the starter vibrator.  In later models like mine, the BO enable pin of the vibrator connects to the BO terminal of the switch.  In older models where the SOS engages with twist only, it's connected to the S terminal of the switch.  There no way to know this without the Mooney schematics, the switch spec alone is not enough.

 

Things are complicated by the fact that the spec sheet you linked to covers multiple models of switch, as well as the fact that many Bendix parts have been superceded by later TCM switches.  In particular, the PUSH TO PRIME rows in your table apply to a flavor of switch that's different from the PUSH TO START flavor installed in the C/E/F models.

[carusoam]

So the buzz people may be hearing could be...

1) SOS

-or-

2) starter vibrator

The switch has something to do with Mooneys. But, it is built by Bendix, a TCM company.

Fortunately, we don't have to be perfect English writers to participate at MS.

???,

-a-

[Vance Harral]

So the buzz people may be hearing could be...

1) SOS

-or-

2) starter vibrator

 

Not sure what is meant by this, as there can be no shower of sparks if the vibrator is not enabled (other than aftermarket mods like Slick Start).  Even with the vibrator enabled, there isn't any actual sparking at the plugs until you crank the engine, such that the LR points in the mag open and close.

 

For those interested in how the SOS system works, here are a couple of good links:

http://www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

http://www.aeroelectric.com/Mfgr_Data/Magnetos/Continental_Motors/IGN-52_Shower-of-Sparks_TM.pdf

[carusoam]

Vance,

Bonal pointed out in thread #6, that he could hear the fireworks...

I was wondering if the SOS is on at the same time as the starter vibrator. Which could be heard?

As far as hand propping, there isn't a better way to become one with the machine!!!

Best regards,

-a-

[Andy95W]

I was wondering if the SOS is on at the same time as the starter vibrator.

-a-

They're the same thing. "Shower of Sparks" is the trade name of the system; the vibrator is the actual buzzer that quickly makes/breaks the connection through its own coil to make the shower of sparks at the spark plug.

[bonal]

Bingo! Correctamundo

[isaacpr7]

I had a few ignition issues on my 68C not long ago and one of them was the SOS. After installing newly overhauled mags I was still not able to start the engine. My plugs were also new so I ruled that out as well. After talking to the mag shop I was advised to disconnect the starter and listen for the vibrator sound while crancking. I was able to hear the buzz, but when I measured the amperage on the vibrator it did not read as specified on the service manual. After replacing the SOS I finally got combustion.

[N201MKTurbo]

The secret to starting a Mooney with a bad SOS is to crank it till the engine is spinning good. Then instantly take your hand off the key. This will connect the normal points while the engine is spinning fast and will make enough spark to start. Do this when the prop is at the 12 o'clock position.

This is an emergency procedure to get you home.

[Mooneymite]

The shower of sparks box is a simple device. If it's buzzing, but not producing sparks, it is probably burned points, the capacitor, or both. These simple parts are pretty cheap (try Aviall) and easy to install.

[Andy95W]

The shower of sparks box is a simple device. If it's buzzing, but not producing sparks, it is probably burned points, the capacitor, or both. These simple parts are pretty cheap (try Aviall) and easy to install.

+1

And it's also a safety device, since it's nearly impossible for the engine to start if you have a hot mag and move the prop by hand- unlike impulse couplings which can.

[DrBill]

My Shower of sparks was not producing sparks after an annual and the plane would only start when I released the key. Turned out the points were maladjusted (too close). We set the points properly and the plane started right up. 

BILL

[slowflyin]

Thanks for all the advice.

I'm going to disconnect the starter and troubleshoot the switch.  Sometimes she cranks on the third blade.  Otherwise she cranks and cranks until I let off the switch and then she fires up.   Intermittent.  I suspect the switch may need a little cleaning.

thanks again,

 

joe

[Mooneymite]

Joe, if you have an old point file left over from when you did points and condenser in your cars, use it to clean the points in the SOS box. Your intermittent condition might get better. If so, the fix is clear.