Loose ignition switch connections - no start?

[DXB]

To make a painful story short as i can - '68 M20C with O-360-A1D just out of annual, mags had 500hr IRAN, engine runs great on local flight.  Then I flew 2 hrs to Hyannis yesterday- no problems at all. I come back this am and try to start, temps in 50s,  Starting vibrator box buzzes, battery is strong, starter turns great, but not the slightest hint of combustion going on.  I then get it preheated- still won't make any combustion. I have the mechanic come out on a Sunday - he finds no spark being made on bottom plugs.  Connections from starting vibrator to left mag are fine, harness and plugs are fine.  I suspect a left mag problem caused by the recent IRAN.  But then he checks the starter switch, finds multiple loose connections to the switch, tightens them all.   It makes spark, starts immediately.  

But I don't really get what happened here because I don't know the system well enough.  My questions- Did the p-lead ground fail to be broken because a loose connection to the starter switch? If so, would it have been possible for the mags to ground unintentionally in flight? I would think the opposite- it would leave you with a hot mag.  Anything else I should investigate here?  

For whatever it's worth, the ignition switch was replaced in the last 10 years, is made by TCM.  

[Yetti]

P Lead to ground = grounding out the magneto which means no start.   So the P lead at the switch was contacting something and completing the circuit to ground.  One of the mags is grounded out when moved to start and the SOS takes over. The other one is advanced.

[jamesm]

Based upon from what you said "... finds no spark being made on bottom plugs"  two of the bottom 4 plugs I believe there  should have been spark on 2 of the 4 bottom plugs from the Shower of Sparks. Since each magneto has 4 connections, 2 top and 2 bottom.   For  grins verify  the timing of the SOS breaker points on left mag and possibly  mag to engine timing is correct or perhaps the the mag internal timing is off.  You could do a continuity check /Buz out of  the p-leads. Just because it came out of annual doesn't mean parts don't fail or perhaps timing slip or bolts that should have been tighten were over looked and lets face it some of the bolts aren't easiest get to, to be able to torque down properly.  Side note...

years ago I had the ignition circuit break go intermittent on me it was a bugger to troubleshoot it was causing my starting problems.

Hope this helps.

James '67C

 

[carusoam]

Dev, some recent discussion that may be somewhat enlightening...

As mentioned above, there is something funny with the description that all of your bottom plugs were not firing.  Each mag is assigned to two top and two bottom plugs.  This way, if a mag quits, you don't get stuck firing on all bottom plugs.  Small lead balls have a tendency to build and fall into the bottom plugs and can interfere with the spark in individual plugs.

Did you get back home?

Good luck finding the answer,

-a-

[DXB]

11 hours ago, jamesm said:

Based upon from what you said "... finds no spark being made on bottom plugs"  two of the bottom 4 plugs I believe there  should have been spark on 2 of the 4 bottom plugs from the Shower of Sparks. Since each magneto has 4 connections, 2 top and 2 bottom.   For  grins verify  the timing of the SOS breaker points on left mag and possibly  mag to engine timing is correct or perhaps the the mag internal timing is off.  You could do a continuity check /Buz out of  the p-leads. Just because it came out of annual doesn't mean parts don't fail or perhaps timing slip or bolts that should have been tighten were over looked and lets face it some of the bolts aren't easiest get to, to be able to torque down properly.  Side note...

years ago I had the ignition circuit break go intermittent on me it was a bugger to troubleshoot it was causing my starting problems.

Hope this helps.

James '67C

 

Yup you guys are absolutely correct - On lycoming O-360 with Bendix retard breaker mags, the retard points driven by the vibrator are on the left mag, which fires the top plugs on 1&3, bottom ones on 2&4.  Mr. Maxwell also helped straighten me out, as usual: - http://www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

We were testing spark on bottom plugs with the ignition switch to start position and vibrator buzzing (but not pushed in to drive starter, obviously).  Here 2/4 should fire, and 1/3 should not, but none fired.   He couldn't find anything visibly wrong with the ignition system until he pulled the starter switch, which seemed to have multiple loose lead connections on it.  Very frustrating to have to pay a high end shop owner in Hyannis 3 hrs overtime on a Sunday to find this, so I could make it home.  I don't think the shop that did my annual messed with the starter switch though- I suspect the loose switch connections were related my major panel job a few months ago.  And since we messed with a whole bunch of connections and relays at once, I'm not even certain it was that.   I'll the annual shop double check my ignition system carefully when I take the plane back for a couple other post-annual squawks  

[Marauder]

10 hours ago, jamesm said: Based upon from what you said "... finds no spark being made on bottom plugs"  two of the bottom 4 plugs I believe there  should have been spark on 2 of the 4 bottom plugs from the Shower of Sparks. Since each magneto has 4 connections, 2 top and 2 bottom.   For  grins verify  the timing of the SOS breaker points on left mag and possibly  mag to engine timing is correct or perhaps the the mag internal timing is off.  You could do a continuity check /Buz out of  the p-leads. Just because it came out of annual doesn't mean parts don't fail or perhaps timing slip or bolts that should have been tighten were over looked and lets face it some of the bolts aren't easiest get to, to be able to torque down properly.  Side note...

years ago I had the ignition circuit break go intermittent on me it was a bugger to troubleshoot it was causing my starting problems.

Hope this helps.

James '67C

 

Yup you guys are absolutely correct - On lycoming O-360 with Bendix retard breaker mags, the retard points driven by the vibrator are on the left mag, which fires the top plugs on 1&3, bottom ones on 2&4.  Mr. Maxwell also helped straighten me out, as usual: - http://www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

We were testing spark on bottom plugs with the ignition switch to start position and vibrator buzzing (but not pushed in to drive starter, obviously).  Here 2/4 should fire, and 1/3 should not, but none fired.   He couldn't find anything visibly wrong with the ignition system until he pulled the starter switch, which seemed to have multiple loose lead connection on it.  Very frustrating to have to pay a high end shop owner in Hyannis 3 hrs overtime on a Sunday to find this, so I could make it home.  I don't think the shop that did my annual messed with the starter switch though- I suspect the loose switch connections were related my major panel job a few months ago.  And since we messed with a whole bunch of connections and relays at once, I'm not even certain it was that.   I'll the annual shop double check my ignition system carefully when I take the plane back for a couple other post-annual squawks  

Dev -- I had a list of things to fix after my avionics upgrade as well including removing loose metal shards from their drilling.

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[DXB]

Now I get a call from the mechanic that helped me with my plane in Hyannis yesterday-  he found an extra crush washer and thinks  he forgot to  put one on when he reinstalled my bottom plugs   Could I please check before I fly again - Heck yes I will!  At least he called- I imagine he was relieved when I picked up the phone.

 

I also noticed when he pulled the plugs yesterday that my annual shop had rotated some of my 4 massive plugs to the bottom- meaning they moved some of my 4 fine wires to the top.  This makes no sense.

 

Am I experiencing what is known among aircraft owners as a "frustrating maintenance experience" ?

[Marauder]

Now I get a call from the mechanic that helped me with my plane in Hyannis yesterday-  he found an extra crush washer and thinks  he forgot to  put one on when he reinstalled my bottom plugs   Could I please check before I fly again - Heck yes I will!  At least he called- I imagine he was relieved when I picked up the phone.

 

I also noticed when he pulled the plugs yesterday that my annual shop had rotated some of my 4 massive plugs to the bottom- meaning they moved some of my 4 fine wires to the top.  This makes no sense.

 

Am I experiencing what is known among aircraft owners as a "frustrating maintenance experience" ?

Yep... In the 24 years I have owned my plane, I had a lot of mechanics wrench on my plane. I have seen the quality vary with the people swinging the wrenches. I think it probably isn't much different than other professions.

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[Oldguy]

1 hour ago, DXB said:

...I also noticed when he pulled the plugs yesterday that my annual shop had rotated some of my 4 massive plugs to the bottom- meaning they moved some of my 4 fine wires to the top.  This makes no sense.

 

Am I experiencing what is known among aircraft owners as a "frustrating maintenance experience" ?

It would have made more sense to me if he rotated all bottom to top, but just some of them is a bit puzzling. And rotating plugs when they are not all of the same type makes no sense to me, but I am just a PP.

[jamesm]

Hope this is okay to repost.... more information on magnetos.

http://themooneyflyer.com/FLIP-JAN/index.html#p=17

James '67C

 

[Alan Fox]

The reason it didn't start is because the ground for the shower of sparks feeds back through the main p lead , in other words the vibrator feeds pulsed power through the retard lead , and grounds through the P-Lead...... It is the dumbest circuit I have ever seen , until you really study it , you will never be able to troubleshoot it , A lot of mechanics will actually replace with impulse , because they cant fix it ,   The shower of sparks , kicks ass when it is working properly...

[Browncbr1]

I remember reading it somewhere and glanced over this thread again, but can anyone remind me what is wrong when the engine doesn't fire until you release from cranking on the ignition switch?

[N601RX]

The shower of sparks or the left mag isn't working if it cranks when releasing the key.  It's also possible to get a very expensive kick back if it doesn't crank.  Retard contacts in the left mag in conjunction with the sos will fire the plug at TDC.  If it cranks on either mag when the switch is released it is firing the plugs at 25 degrees before TDC.  It the starter and prop doesn't have enough momentum to continue in the direction of cranking it is possible for the piston to be shoved back down in the opposite direction of rotation.  This can be pretty harsh.

[Browncbr1]

Thanks for enlightening me!

[triple8s]

I know a fellow who had an E model one time, was the first Mooney I ever rode in, anyhow, his would hit only when the key was released and one time it kicked back and the result was the whole end of his fancy SkyTec starter was broken off ! 

Another very important thing to remember if you have the SOS sytem, the engine can fire once the SOS begins to buzz. If there is a problem with the starter, solenoid, starter wire or ignition switch so that the starter isn't energizing when the SOS vibrates, the front of the engine is an EXTREMLY dangerous place to be. If a person decides to see if the SOS is sparking and a lead is removed from a SOS spark plug and the 3 other leads are left on that is another dangerous situation. Theoretically an engine with a vibrating system could start by just initiating the spark if the crank was positioned exactly right. Point I am trying to make is if the crank is positioned properly and there is any combustible vapor in a cylinder which has a lead connected to the SOS mag then once the vibrator makes the first sparks the prop could very likely kill anyone in its path. 

[triple8s]

http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf

 

 

[Andy95W]

 

To make a painful story short as i can - '68 M20C with O-360-A1D just out of annual, mags had 500hr IRAN, engine runs great on local flight.  Then I flew 2 hrs to Hyannis yesterday- no problems at all. I come back this am and try to start, temps in 50s,  Starting vibrator box buzzes, battery is strong, starter turns great, but not the slightest hint of combustion going on.  I then get it preheated- still won't make any combustion. I have the mechanic come out on a Sunday - he finds no spark being made on bottom plugs.  Connections from starting vibrator to left mag are fine, harness and plugs are fine.  I suspect a left mag problem caused by the recent IRAN.  But then he checks the starter switch, finds multiple loose connections to the switch, tightens them all.   It makes spark, starts immediately.  

But I don't really get what happened here because I don't know the system well enough.  My questions- Did the p-lead ground fail to be broken because a loose connection to the starter switch? If so, would it have been possible for the mags to ground unintentionally in flight? I would think the opposite- it would leave you with a hot mag.  Anything else I should investigate here?  

For whatever it's worth, the ignition switch was replaced in the last 10 years, is made by TCM.  

Most likely cause would appear to be the Shower of Parks connection at your starter switch.

The SoS sends high voltage electricity through the ignition switch to the Left magneto retard points.  If either of those connections were loose, no high energy current would make it to your left mag spark plugs and why the engine wouldn't start.

This would also be why the mechanic couldn't get spark on any of the lower plugs- 1&3 because the right magneto is grounded during start, 2&4 because the high energy voltage wasn't getting through the ignition switch due to the loose connection.

I disagree with Alan who said, "it is the dumbest circuit I have ever seen."  I have always thought it was a rather ingenious and elegant solution, using only one switch, to control 6 separate functions, some of them simultaneously.  And it is surprisingly reliable and maintenance free over thousands of hours of operation.

But yeah, it definitely looks confusing at first glance.

[DXB]

 

Most likely cause would appear to be the Shower of Parks connection at your starter switch.

The SoS sends high voltage electricity through the ignition switch to the Left magneto retard points.  If either of those connections were loose, no high energy current would make it to your left mag spark plugs and why the engine wouldn't start.

This would also be why the mechanic couldn't get spark on any of the lower plugs- 1&3 because the right magneto is grounded during start, 2&4 because the high energy voltage wasn't getting through the ignition switch due to the loose connection.

I disagree with Alan who said, "it is the dumbest circuit I have ever seen."  I have always thought it was a rather ingenious and elegant solution, using only one switch, to control 6 separate functions, some of them simultaneously.  And it is surprisingly reliable and maintenance free over thousands of hours of operation.

But yeah, it definitely looks confusing at first glance.

Thank you! Exactly the answer I was seeking- convinced I fully understand what happened now, and that the problem has been adequately addressed.  I hadn't appreciated that the SOS sends current back through the switch.  Folks who did my panel job must have been sloppy in redoing the connections to my switch. Trivial thing with painful consequences.  

[Yetti]

Good workmanship is not trivial.  Sadly good workmanship is hard to find.