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Key start switch/magneto problem

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psiegel(at)fuse.net
Guest

Posted: Mon Apr 16, 2007 11:46 pm Post subject: Key start switch/magneto problem

I have an intermittent problem with which I could use some help.



I have a left/right/both/ start switch activated by a key.  On the left circuit is a Lightspeed electronic ignition and on the right circuit is a traditional magneto.



I went to fly the other day, and after start up, I had no RPM information on the Grand Rapids engine instruments display.  I tried a run-up test, and when going from "both" to "right", the engine stopped running, but would come back to life when either "both" or "left" was selected.

The next day I tried it again and everything worked normally?



Any advice on where to begin troubleshooting?  Keyed mag/starter switch?  Magneto?



Thanks in advance for any advice!

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nuckollsr(at)cox.net
Guest

Posted: Tue Apr 17, 2007 5:29 pm Post subject: Key start switch/magneto problem

At 03:42 AM 4/17/2007 -0400, you wrote:



 	  Quote: 	
		  



I have an intermittent problem with which I could use some help.



I have a left/right/both/ start switch activated by a key.  On the left 

circuit is a Lightspeed electronic ignition and on the right circuit is a 

traditional magneto.



I went to fly the other day, and after start up, I had no RPM information 

on the Grand Rapids engine instruments display.  I tried a run-up test, 

and when going from "both" to "right", the engine stopped running, but 

would come back to life when either "both" or "left" was selected.

The next day I tried it again and everything worked normally?



Any advice on where to begin troubleshooting?  Keyed mag/starter 

switch?  Magneto?



Thanks in advance for any advice!


	


    Don't know what advice to give.  The transient event

    is essentially impossible to troubleshoot when it

    won't hold still long enough to diagnosed. Which

    system drives the RPM display. Which system is designated

    the "right" system. If the right system is the source

    for tachometer info, then the symptoms you cite point

    to a transient failure of that system. Until it

    happens again and stays broke, the best you can

    do is wiggle all the joints and see if you can find

    anything loose.



    Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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ceengland(at)bellsouth.ne
Guest

Posted: Tue Apr 17, 2007 5:59 pm Post subject: Key start switch/magneto problem

psiegel(at)fuse.net wrote:

 	  Quote: 	
		   

 

 I have an intermittent problem with which I could use some help.

 

 I have a left/right/both/ start switch activated by a key.  On the left circuit is a Lightspeed electronic ignition and on the right circuit is a traditional magneto.

 

 I went to fly the other day, and after start up, I had no RPM information on the Grand Rapids engine instruments display.  I tried a run-up test, and when going from "both" to "right", the engine stopped running, but would come back to life when either "both" or "left" was selected.

 

 

 The next day I tried it again and everything worked normally?

 

 Any advice on where to begin troubleshooting?  Keyed mag/starter switch?  Magneto?

 

 Thanks in advance for any advice!

Does the mag p-lead drive the GR tach? If so, it sounds like the mag's 
	


p-lead is still grounded even when you select it with the switch.



I'd lift the p-lead from the switch & see if it will run on the mag. If 

not, then I'd break the connection between the p-lead & the GR tach. 

(might be a problem in the tach keeping the p-lead grounded)



Oops, just read the line about it being back to normal. Intermittent 

sounds a lot like the switch, if you don't have any wires chafing 

against the airframe anywhere.



Charlie

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hooverra(at)verizon.net
Guest

Posted: Wed Apr 18, 2007 3:25 am Post subject: Key start switch/magneto problem

Several avenues exist to isolate this problem.

1.  Is the Grand Rapids Tach pick off isolated with a resistor ?  If so 

will grounding the Grand Rapids end kill the Mag. If not you can 

eliminate the Grand Rapids as the root cause. If it is not isolated 

check with Grand Rapids for recommendations.

2. With the tach pick off eliminated disconnect the P lead from the Mag 

and connect an Ohm meter. On the lowest scale the switch should show a 

short when in the off or left positions. with the switch in both it 

should be open. Now do the wiggle test. If you do not see a short appear 

don't quit!!

3. Have you used shielded wire for the switch connection? Visually 

verify the points where the shield is terminated. Neatness is the key 

here. Are there any whiskers of the shield loose. Has the center 

conductor been nicked?

4. Check the length of the wire for damage. If it is pinched or chaffed 

then you could develop a short.

5. The least likely would be foreign material floating around inside the 

Mag switch but if nothing else is found I would visually inspect the switch.

6. The last unlikely thing would be a bad Capacitor, Coil or foreign 

material in the Mag.

7. If the Grand Rapids was not isolated and you isolate it then an 

intermittent on the GR side may still allow the tach function to fail 

without killing the mag. If this occurs a similar look at wiring to the 

GR is in order.

The school of thought that it must be in the failure mode to find it is 

partially true but I suggest that in such a simple installation that the 

root cause of the problem will be obvious if you look close enough.

Remember It's only magic until you understand.



-- 

Ralph C. Hoover

RV7A 

hooverra at verizon dot net

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