Starting problem

[M20F-1968]

I'm posting this hoping to get some assistance in troubleshooting a starting problem.   I  have independent  Bendix magneto's and the shower of sparks.   I sent out my magneto's for 500 hour service to Aircraft Accessories of Oklahoma.  This is a shop I have used for over ten years without any event.  This time was different.  The work performed was a 500 hour inspection/repair.   I expected the Mags to be overhauled.   That is of no consequence if they worked, but that is not the case.  The part number of the Mags are BL-600614-2 and BL-600644-1.  

When the mage were installed after completion of the work, the plane would only start if the key was returned to the Both position, after cranking in the start position.   My mechanic called Aircraft Accessories and a technician there walked him through the task of taking the left Mag apart and cleaning the points.  Once put back together and reinstalled, the engine started correctly three times on different dates.  Then, the problem returned.  It now starts, or tries to start, twice as it did before, only after the key is allowed to return to the "Both" position after cranking in the "Start"position. 

The retard and primary points appear to be opening, the ignition switch was checked and found to be in order.  I installed a new Shower of Sparks which did not correct the problem.  My guess is that this is a Magneto problem seeing that if occurred after Aircraft Accessories worked on the Mags, and more specifically a point problem.  My next step seems to be to remove the left Magneto and send it to another shop to be checked.  Any other ideas?

John Breda

[M20F-1968]

Who are to go to shops for magneto repair these days?

John Breda

[PT20J]

16 minutes ago, M20F-1968 said:

Who are to go to shops for magneto repair these days?

John Breda

Aircraft Magneto Service. But I think Cliff stopped doing dual mags if you need that.

[David Lloyd]

Remove the left mag p-lead at the mag.  If it won't start, mag.  If it will start, p-lead or switch.  

[M20F-1968]

4 hours ago, David Lloyd said:

Remove the left mag p-lead at the mag.  If it won't start, mag.  If it will start, p-lead or switch.  

But this is a Bendix BL-600614-2 Magneto, with no impulse coupling and with a shower of sparks.

John Breda

[Andy95W]

Check the retard breaker points p-lead.  It sounds like it’s grounding on something (maybe even the knurled nut itself).  After that, I would suspect the switch itself.  What you’re describing is a fairly common mode of failure of the switch.

When moving the switch to the “start” position, the switch grounds the left primary and right magneto circuits, activates the shower of sparks, and sends it to the retard breaker points which should open at 0° BTDC, thus enabling the engine to start at TDC.  Since the problem started with magneto removal/installation, and the magneto appears to be sound, the next most likely culprit would be that the retard breaker lead finally broke down enough that it’s grounding on its own.

What happens when you release the switch to “both” is that the engine has enough rotation speed to energize the primary circuits of the magnetos and enough inertia to start at 25° BTDC.

[carusoam]

Andy covered way better than I could… but I wrote it and pushed send to see his post get there before mine…   

 

1) This is a well known symptom for the Mag responsible for starting… L mag(?)

2) after that my memory won’t fill in all the details… 
 

3) The typical reason for the engine to start when the switch is returned to B…

Is related to the mag timing used for starting… it changes from 20°BTDC to 0°….  Making starting a breeze…

4) I forgot the detail Why it starts when the switch goes to B…

5) But…. If the mags got OH’d as expected… they didn’t get wired properly, or L & R got swapped some way or another…

 

6) Should be an easy thing to identify… by your local mechanic prior to sending one back…

PP thoughts only….

Best regards,

-a-

[M20F-1968]

8 hours ago, Andy95W said:

Check the retard breaker points p-lead.  It sounds like it’s grounding on something (maybe even the knurled nut itself).  After that, I would suspect the switch itself.  What you’re describing is a fairly common mode of failure of the switch.

When moving the switch to the “start” position, the switch grounds the left primary and right magneto circuits, activates the shower of sparks, and sends it to the retard breaker points which should open at 0° BTDC, thus enabling the engine to start at TDC.  Since the problem started with magneto removal/installation, and the magneto appears to be sound, the next most likely culprit would be that the retard breaker lead finally broke down enough that it’s grounding on its own.

What happens when you release the switch to “both” is that the engine has enough rotation speed to energize the primary circuits of the magnetos and enough inertia to start at 25° BTDC.

Andy, for one of

Thanks for your reply.   It seems that you may be able to help me think through this problem.   You are saying  something very similar to my  excellent but out-of-state mechanic.   He suggested that I  make a jump or lead consisting of a 3/16 ring terminal with two 18 or 20 gauge wires  coming from it,  one short and one long.   The  other end of  the long wire  will terminate  in a spade terminal  and attached to the black  connector on the shower of sparks.  The short  wire will terminate in a 3/16 ring terminal  and connect to the primary post P lead on the magneto itself.   This jumper  is intended to bypass the ignition switch to determine if the problem lies in the ignition switch (or its related wiring)  or with the magneto itself.  

Neither  one of us has been able to reconcile why this problem happened after the left magneto was worked on.  Further,  the problem went away when the magneto was removed and the points cleaned.   After three good starts,  the problem returned.  From  that history it sounds like the problem is inherent to left magneto.   Are  the points in the magneto finicky enough that  contamination or some other unrecognized abnormality of the points could cause this problem?

 Your further input is appreciated.

Thanks,

John Breda

[M20F-1968]

8 hours ago, Andy95W said:

Check the retard breaker points p-lead.  It sounds like it’s grounding on something (maybe even the knurled nut itself).  After that, I would suspect the switch itself.  What you’re describing is a fairly common mode of failure of the switch.

When moving the switch to the “start” position, the switch grounds the left primary and right magneto circuits, activates the shower of sparks, and sends it to the retard breaker points which should open at 0° BTDC, thus enabling the engine to start at TDC.  Since the problem started with magneto removal/installation, and the magneto appears to be sound, the next most likely culprit would be that the retard breaker lead finally broke down enough that it’s grounding on its own.

What happens when you release the switch to “both” is that the engine has enough rotation speed to energize the primary circuits of the magnetos and enough inertia to start at 25° BTDC.

Andy, 

Thanks for your reply.   It seems that you may be able to help me think through this problem.   You are saying  something very similar to my  excellent but out-of-state mechanic.   He suggested that I  make a jump or lead consisting of a 3/16 ring terminal with two 18 or 20 gauge wires  coming from it,  one short and one long.   The  other end of  the long wire  will terminate  in a spade terminal  and attached to the black  connector on the shower of sparks.  The short  wire will terminate in a 3/16 ring terminal  and connect to the primary post P lead on the magneto itself.   This jumper  is intended to bypass the ignition switch to determine if the problem lies in the ignition switch (or its related wiring)  or with the magneto itself.  

Neither  one of us has been able to reconcile why this problem happened after the left magneto was worked on.  Further,  the problem went away when the magneto was removed and the points cleaned.   After three good starts,  the problem returned.  From  that history it sounds like the problem is inherent to left magneto.   Are  the points in the magneto finicky enough that  contamination or some other unrecognized abnormality of the points could cause this problem?

 Your further input is appreciated.

Thanks,

John Breda

[Andy95W]

14 hours ago, M20F-1968 said:

 

 Are  the points in the magneto finicky enough that  contamination or some other unrecognized abnormality of the points could cause this problem?

 

Hello John,

The magneto points generally aren’t a problem once they’re set, although the assumption of contamination getting on the retard breaker points is one possible cause of your problem.  More often, I’ve seen breaker point hold down screws that weren’t torqued properly or the retard breaker point wire getting pinched between the magneto case halves (there’s a lot crowded into a small space on that left magneto.)

I had to look at the switch wiring schematic to understand what your mechanic was talking about with that wire jumper- but I think he’s really onto something there, and it seems like it should work to isolate the magneto from a potential switch problem.  I think he knows his stuff.

The reason I still lean toward a possible bad wire is that those things lead pretty hard lives.  Vibrating on one side, anchored on the other, and hot as blazes most of the time.  If the wire was starting to break down, it could have been helped by the magneto removal, and then over a few starts shorted again.  If nothing else, it’s pretty easy to check once you have the top cowling off.

If you do send the left mag back out, Aircraft Magneto Service in Montana gets very good reviews and seem very trustworthy  

Good luck, please keep us posted.

[M20F-1968]

I thought I'd post more details about my starting problem saga.   I made the jump or lead as described in an earlier post by disconnecting the output from the shower of sparks and connecting in its place a lead that goes to the retard points on the  left magneto and a further connection to the P lead terminal.    An attempt to  start the engine in this configuration, which takes the ignition switch out of the picture, showed a continuation of the same problem; namely a failure to start  the engine in the start position.  The engine started only when the key was released and allowed to return to the both position in when the engine started on the right magneto alone.   This confirmed that there is a problem in the left magneto.  

For completeness, my next step is to confirm that there is in fact 12 V going to the starter vibrator  while cranking the engine.   I do not expect there to be any discrepancy here but will check anyway.  If there is not a drop in voltage,  the left magneto  will be taken off and sent to be serviced.   

A year ago  Aircraft Accessories of Oklahoma  didn't want to hear that there may have been a problem with their repair of the Left magneto.  The diagnostic work recently performed confirmed (assuming proper voltage to the starter vibrator) that the L magneto is not  functioning as it should.   This may have to be  subject of a second thread.

John Breda

[Shadrach]

1 hour ago, M20F-1968 said:

I thought I'd post more details about my starting problem saga.   I made the jump or lead as described in an earlier post by disconnecting the output from the shower of sparks and connecting in its place a lead that goes to the retard points on the  left magneto and a further connection to the P lead terminal.    An attempt to  start the engine in this configuration, which takes the ignition switch out of the picture, showed a continuation of the same problem; namely a failure to start  the engine in the start position.  The engine started only when the key was released and allowed to return to the both position in when the engine started on the right magneto alone.   This confirmed that there is a problem in the left magneto.  

For completeness, my next step is to confirm that there is in fact 12 V going to the starter vibrator  while cranking the engine.   I do not expect there to be any discrepancy here but will check anyway.  If there is not a drop in voltage,  the left magneto  will be taken off and sent to be serviced.   

A year ago  Aircraft Accessories of Oklahoma  didn't want to hear that there may have been a problem with their repair of the Left magneto.  The diagnostic work recently performed confirmed (assuming proper voltage to the starter vibrator) that the L magneto is not  functioning as it should.   This may have to be  subject of a second thread.

John Breda

You should be able to hear the SOS starter vibrator with the key in the start position but not pushed in. 

To your earlier statement with regard to overhaul vs IRAN. Are you sure they were overhauled at 500hr intervals. It may have been the case but seems unnecessary.

[Guest]

I’d verify that the P leads are oriented correctly, L is left and R is right, and SOS is correct at the magnetos.  Remove all of the plug wires and one plug from cylinder 1.  Turn the prop until cylinder 1 is at TDC on the compression stroke.  Disconnect the starter solenoid control wire to disable the starter motor.  Follow the plug wires from the left mag to cylinder 1.  Have an assistant turn on the master switch, and turn the ignition switch to the start position.  Hold the plug wire from the left mag with a pair of pliers about 1/2” from a rocker box screw.  A shower of sparks should jump from the wire to the screw.  Turning the prop back and forth will open and close the points, turning off the sparks.

Clarence

[tony]

I've sent my mags to these guys.  Very knowledgeable and they run the mag at altitude before they send it back.  A little pricey but they do go work.

 

https://www.aircraftmagnetoservice.net/

 

 

 

[Yetti]

On 9/1/2021 at 9:10 PM, M20F-1968 said:

I thought I'd post more details about my starting problem saga.   I made the jump or lead as described in an earlier post by disconnecting the output from the shower of sparks and connecting in its place a lead that goes to the retard points on the  left magneto and a further connection to the P lead terminal.    An attempt to  start the engine in this configuration, which takes the ignition switch out of the picture, showed a continuation of the same problem; namely a failure to start  the engine in the start position.  The engine started only when the key was released and allowed to return to the both position in when the engine started on the right magneto alone.   This confirmed that there is a problem in the left magneto.  

For completeness, my next step is to confirm that there is in fact 12 V going to the starter vibrator  while cranking the engine.   I do not expect there to be any discrepancy here but will check anyway.  If there is not a drop in voltage,  the left magneto  will be taken off and sent to be serviced.   

A year ago  Aircraft Accessories of Oklahoma  didn't want to hear that there may have been a problem with their repair of the Left magneto.  The diagnostic work recently performed confirmed (assuming proper voltage to the starter vibrator) that the L magneto is not  functioning as it should.   This may have to be  subject of a second thread.

John Breda

remember there are safeties in the mag that the P lead turns off.   If the P lead is out the mag will be grounded.

[Yourpilotincommand]

On 9/2/2021 at 5:43 AM, M20Doc said:

I’d verify that the P leads are oriented correctly, L is left and R is right, and SOS is correct at the magnetos.  Remove all of the plug wires and one plug from cylinder 1.  Turn the prop until cylinder 1 is at TDC on the compression stroke.  Disconnect the starter solenoid control wire to disable the starter motor.  Follow the plug wires from the left mag to cylinder 1.  Have an assistant turn on the master switch, and turn the ignition switch to the start position.  Hold the plug wire from the left mag with a pair of pliers about 1/2” from a rocker box screw.  A shower of sparks should jump from the wire to the screw.  Turning the prop back and forth will open and close the points, turning off the sparks.

Clarence

I did exactly this and found I wasn’t firing at 0 deg TDC. I had the same exact issue Andy had.. the retard  p lead was worn at the knurled screw at the mag. I cleaned up / repaired the connection… and starts right up. If trying to start at 25 deg BTDC ugly things start to happen like kick back where the engine tries to start backwards, and… you can smell your starter motor beginning to fry… that scary electrical smell. I have since replaced my starter.

[M20F-1968]

I sent my L mag out to be checked.  They found that the terminal for the retard points was not torqued properly, was loose and likely not making good contact with the ring terminal attached under the screw head inside the case.   Hopefully this solves the problem, however when we tested the input voltage to the shower of sparks with the starter turning to crank the engine (under load) the voltage dropped from 12 volts to seven volts.  The magic number it reportedly needs to be above is 9 volts.  So, I may be on a hunt to find a reason for the voltage drop.  

Also, there is 12 volts at the red terminal (volts in) at the shower of sparks before the key is turned to start.  Does anyone know if this is normal with a Bendix ignition switch?  It seems more logical that the voltage would not be on to the shower of sparks until the key is turned to start.  I will check this again when I am at the hangar.

John Breda

 

[EricJ]

1 hour ago, M20F-1968 said:

I sent my L mag out to be checked.  They found that the terminal for the retard points was not torqued properly, was loose and likely not making good contact with the ring terminal attached under the screw head inside the case.   Hopefully this solves the problem, however when we tested the input voltage to the shower of sparks with the starter turning to crank the engine (under load) the voltage dropped from 12 volts to seven volts.  The magic number it reportedly needs to be above is 9 volts.  So, I may be on a hunt to find a reason for the voltage drop.  

Also, there is 12 volts at the red terminal (volts in) at the shower of sparks before the key is turned to start.  Does anyone know if this is normal with a Bendix ignition switch?  It seems more logical that the voltage would not be on to the shower of sparks until the key is turned to start.  I will check this again when I am at the hangar.

John Breda

 

A big voltage drop on activation of the starter may mean dirty/corroded terminals at the starter or battery.   Check any/all of the high-current terminals (the big, fat ones) around the battery and the starter and in between.

[carusoam]

I recall there is an SOS manual around here someplace…. Classic 60s style of not very informative…. But may have everything you need to know…

Fuzzy memory at best…

Best regards,

-a-

[Ragsf15e]

11 hours ago, M20F-1968 said:

I sent my L mag out to be checked.  They found that the terminal for the retard points was not torqued properly, was loose and likely not making good contact with the ring terminal attached under the screw head inside the case.   Hopefully this solves the problem, however when we tested the input voltage to the shower of sparks with the starter turning to crank the engine (under load) the voltage dropped from 12 volts to seven volts.  The magic number it reportedly needs to be above is 9 volts.  So, I may be on a hunt to find a reason for the voltage drop.  

Also, there is 12 volts at the red terminal (volts in) at the shower of sparks before the key is turned to start.  Does anyone know if this is normal with a Bendix ignition switch?  It seems more logical that the voltage would not be on to the shower of sparks until the key is turned to start.  I will check this again when I am at the hangar.

John Breda

 

Two things… v = i x r (voltage equals current x resistance) means under no/low current, you may see 12 volts even if you have a significant source of resistance.  When you put a lot of current through there (cranking the starter), the voltage will then drop precipitously at the point of resistance.  So yeah, you’ll need to see why that’s dropping so far.  Maybe as easy as an old battery?  But could easily be corroded connections.

Second, some items will have a voltage source all the time, but not a ground to complete the circuit.  A good example is the master solenoid.  It’s got positive connection to the battery all the time (even when off).  The master switch supplies ground to complete the circuit. I don’t know if the sos is like that, but it’s definitely possible.