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Excessive R Mag Drop

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scott-p(at)texas.net
Guest

Posted: Sun Aug 30, 2009 6:23 pm Post subject: Excessive R Mag Drop

Hi Guys,



My lovely M9F (okay, "Phi", but I don't have that key on this 

keyboard...<VBG>) magnetos (mounted on a Yak-55M) seem to have developed 

an issue, and I need some help toubleshooting it. The problem is an 

excessive mag drop on the right (#2) mag. Mag checks done between 60% 

and 65% yield a 2.5-2.9% drop on the Left mag (#1) and (initially) a 

9.5-9.9% drop on the Right (#2). Here is what I have done so far and the 

effect:



1) Replaced the plugs (NGK BR7HS gapped at 0.25). No effect. N.B., the 

ignition wires are US 8 mm automotive wires and are just over 18 months old.

2) Checked the point gap (and cleaned everything in the top of the mag 

with Isopropanol). Gap correct at 0.3 mm. No effect.

3) Reset the distributor rotor to full "aft" (i.e., opposite the 

direction of rotation) position. No effect.

4) Reset distributor rotor to mid-position. Decreased drop on Right mag 

to about 8.5%.

5) Reset distributor rotor to full "forward" position (i.e., in 

direction of rotation). Decreased drop on Right mag to about 7.7-7.9%.



This is the best that I can get. Obviously, this isn't good enough...



Any ideas on what the problem is and (more importantly to me), what the 

solution is? Preferably without recourse to "buy a new mag"...



I'm stumped.



Thanks,



Scott Poehlmann

Yak 55M N155YK

dsavarese0812(at)bellsout
Guest

Posted: Mon Aug 31, 2009 4:25 am Post subject: Excessive R Mag Drop

Scott,

 A couple of comments based on your post.  These comments  will most likely not change the mag drop.  But I believe are  important.

  

 - Mag checks are typically done at 70%, although the large mag  drop would most likely not change by doing the mag check at  60-65%.

 - The BR7HS plugs are a "colder" plug and I would suggest  changing to BR6HS plugs.  Gap the new plugs to .21 -.22.   We  have found the BR6HS plugs to be a much better plug for the M14 than either  the BR7's or 8's.

 - Rotating the distributor rotor just for the sake of trying  to reduce the mag drop is definitely a no-no.  You are forcing the rotor  point off the center contact of the mag cap ie: making the spark jump the  gap.  You could be damaging the mag cap.  The reason the rotor has  slots in it is to enable the mechanic to properly align the position  of the rotor to the scribed mark on the boss of the magneto (the mag cover  mating surface once the mag timing is properly set).  See  attached.  This positions the rotor point to the center of the contact  inside the magneto cap when the mag cap is installed.  I would  recommend you recheck the timing and after properly setting the timing,  reset the rotor by placing a straight edge across the center of the  rotor to the rotor point, then loosen the 3 screws and align the  center and the point of the rotor to the scribe mark on the boss of the  mag.

  

 Since you are getting a large mag drop, you can possibly  isolate the faulty cylinder (plug not firing) by running the mag on the BAD mag  to see what cylinders are not firing.   Start the engine and  immediately rotate the mag switch to the #2 mag and leave it there.  You  said #2 was giving you the large mag drop.  Now let it run for a few  minutes on the bad mag.  Shut the engine down.  Using a laser  temperature sensor which you can buy at Radio Shack, measure the temperature of  each cylinder at exactly the same point on each cylinder.  Pick a spot that  is easy to "shoot" with the laser.  Just make sure you measure the temps at  the same location on every cylinder.  You will likely find a cylinder that  is much colder than the others.  That will be the suspect wire/plug.   It could also be a small crack in the mag cap between the contact points.   Look for carbon traces in the mag cap.  Replace the cap for testing  purposes.  But be sure to align the rotor point to the scribe mark before  replacing the cap.

  

 Regarding the mag drop, since you are using the 8 mm wires,  you can measure the resistance of the wires from the spark plug end to the mag  cap.  Starting with the longest wire, (left mag #6; right mag #5) measure  the resistance of the wires using a digital ohm meter.  The shorter  the wire, the less resistance.  If you find a bad wire, (no  resistance) remove the end from the mag cap, cut off about 3/8", reinstall  and screw in the wire-piercing screw.  Then check the resistance  again.  If the wire still reads completely open (no resistance),  contact me off-list and I can order you a new wire.

  

 I hope this helps.  

  

  

 [quote]   ---

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william(at)netpros.net
Guest

Posted: Mon Aug 31, 2009 6:52 am Post subject: Excessive R Mag Drop

When I try to do my run up at 70% RPM my brakes won't hold.  Details are 400HP, MTV 3 blade prop, and Cleveland 6" wheels/brakes.



 Anybody else have that problem?  I would think the 440 HP engine makes it even worse ...



 Thanks!



 William Halverson

 YAK55 



 



 At 05:24 AM 8/31/2009, A. Dennis Savarese wrote:

 [quote]Scott,

 A couple of comments based on your post.  These comments will most likely not change the mag drop.  But I believe are important.

  

 - Mag checks are typically done at 70%, although the large mag drop would most likely not change by doing the mag check at 60-65%.[b]

dsavarese0812(at)bellsout
Guest

Posted: Mon Aug 31, 2009 7:10 am Post subject: Excessive R Mag Drop

Good point William.  Thanks for sharing that because it  is important.

 Dennis

 [quote]   ---

dougsappllc(at)gmail.com
Guest

Posted: Mon Aug 31, 2009 8:12 am Post subject: Excessive R Mag Drop

Bill,When we run the big 30 inch tires and the borer super prop on the cubs we have a similar problem.  We solved it by using a oil squirt can full of what ever type of brake fluid your fond of, this is the type of oil can with the "squeeze it" handle, squirts across the shop with each pull.  (tape a lazer pointer to it and it's wonderful for killing wasps and yellow jackets--messy though)  Use a piece of clear plastic tubing big enough to fit tightly over the nozzle, the other end should be just big enough to slip over the bleeder valve on the brake housing,(which should be on the upper side of the housing.)  Pump the hose full of fluid to remove the possibilities of any bubbles, slightly loosen the bleeder valve, you should see a slight bit of fluid appear, quickly skip the tube over the bleeder valve taking care not to trap any bubbles in the line.  Pump the lever on the oil can until you see the pucks in the brake housing start to move outward.  Stop pumping just before the pucks contact the surface of the disc on your Clevelands, pause a moment keeping the clear plastic tube vertical and any air bubbles rise up in the line, next close the bleeder valve, disconnect the hose and your done.  It is best to do this when the aircraft is jacked up enough to spin the tires to check for a dragging brake.  This is the theory:  The brake pucks force the pads out against the disc when the brake is applied, then they retreat to the "at rest" position when the brakes are released.  Any wear in the pads or on the disk will require more fluid being needed to make the puck extend and firmly grip the disk than it did when these parts were new, "back pressuring" the brakes replaces this fluid.  Note that this will make your brakes "touchy" if you pump them up to much.  Give it a try, it just might solve your problem.

 



Best,

Doug



On Mon, Aug 31, 2009 at 7:48 AM, William Halverson <william(at)netpros.net (william(at)netpros.net)> wrote:

  	  Quote: 	
		    



 When I try to do my run up at 70% RPM my brakes won't hold.  Details are 400HP, MTV 3 blade prop, and Cleveland 6" wheels/brakes.



 Anybody else have that problem?  I would think the 440 HP engine makes it even worse ...



 Thanks!



 William Halverson

 YAK55 



 



 At 05:24 AM 8/31/2009, A. Dennis Savarese wrote:

  	  Quote: 	
		  Scott,

 A couple of comments based on your post.  These comments will most likely not change the mag drop.  But I believe are important.

  

 - Mag checks are typically done at 70%, although the large mag drop would most likely not change by doing the mag check at 60-65%.



et="_blank">http://www.matronics.com/Navigator?Yak-List

tp://forums.matronics.com

===========

_blank">http://www.matronics.com/contribution



	


	


-- 

  You cannot legislate the poor into prosperity by legislating the wealthy out of prosperity. What one person receives without working for, another person must work for without receiving. The government cannot give to anybody anything that the government does not first take from somebody else.  When half of the people get the idea that they do not have to work because the other half is going to take care of them, and when the other half gets the idea that it does no good to work because somebody else is going to get what they work for, that my dear friend, is the beginning of the end of any nation. You cannot multiply wealth by dividing it."*

 

Always Yakin,

Doug Sapp

Phone 509-826-4610

Fax 509-826-3644

 

  [quote][b]

scott-p(at)texas.net
Guest

Posted: Mon Aug 31, 2009 7:13 pm Post subject: Excessive R Mag Drop

Hi Dennis,



Thanks for the usual thorough and thoughtful info. I will do all of your 

suggestions. I was under the misapprehension that the slots in the rotor 

were to allow for synchronization between the two mags, which led me to 

the idea of checking a variety of positions. Hopefully I have not 

damaged the caps, although I have only run the engine for a total of 

perhaps 15 minutes since varying the rotor position. I will reset it to 

the boss mark (which I hopefully can find...) as specified in your 

e-mail. Please confirm that it is the CENTER LINE of the rotor (which 

has two contacts on it, one in front of the other, separated by perhaps 

0.5 cm; thus the center line is between the two contacts...) which is to 

be aligned with the scribe mark.



I am going to try the BR6 plugs and see if that fixes the problem, and 

will also see if I can identify a "cold" cylinder. Failing that I'll 

measure the resistances of the plug wires.



As to doing the run-up at 65%, I was taught this (I think by Nik...) 

when I first transitioned into an Su-29 about 7 years ago and frankly 

have never given it any thought since then.



Thanks again.



Scott



A. Dennis Savarese wrote:

[quote] Scott,

 A couple of comments based on your post.  These comments will most 

 likely not change the mag drop.  But I believe are important.

  

 - Mag checks are typically done at 70%, although the large mag drop 

 would most likely not change by doing the mag check at 60-65%.

 - The BR7HS plugs are a "colder" plug and I would suggest changing to 

 BR6HS plugs.  Gap the new plugs to .21 -.22.   We have found the BR6HS 

 plugs to be a much better plug for the M14 than either the BR7's or 8's.

 - Rotating the distributor rotor just for the sake of trying to reduce 

 the mag drop is definitely a no-no.  You are forcing the rotor point 

 off the center contact of the mag cap ie: making the spark jump the 

 gap.  You could be damaging the mag cap.  The reason the rotor has 

 slots in it is to enable the mechanic to properly align the position 

 of the rotor to the scribed mark on the boss of the magneto (the mag 

 cover mating surface once the mag timing is properly set).  See 

 attached.  This positions the rotor point to the center of the contact 

 inside the magneto cap when the mag cap is installed.  I would 

 recommend you recheck the timing and after properly setting the 

 timing, reset the rotor by placing a straight edge across the center 

 of the rotor to the rotor point, then loosen the 3 screws and 

 align the center and the point of the rotor to the scribe mark on the 

 boss of the mag.

  

 Since you are getting a large mag drop, you can possibly isolate the 

 faulty cylinder (plug not firing) by running the mag on the BAD mag to 

 see what cylinders are not firing.   Start the engine and immediately 

 rotate the mag switch to the #2 mag and leave it there.  You said #2 

 was giving you the large mag drop.  Now let it run for a few minutes 

 on the bad mag.  Shut the engine down.  Using a laser temperature 

 sensor which you can buy at Radio Shack, measure the temperature of 

 each cylinder at exactly the same point on each cylinder.  Pick a spot 

 that is easy to "shoot" with the laser.  Just make sure you measure 

 the temps at the same location on every cylinder.  You will likely 

 find a cylinder that is much colder than the others.  That will be the 

 suspect wire/plug.  It could also be a small crack in the mag cap 

 between the contact points.  Look for carbon traces in the mag cap.  

 Replace the cap for testing purposes.  But be sure to align the rotor 

 point to the scribe mark before replacing the cap.

  

 Regarding the mag drop, since you are using the 8 mm wires, you can 

 measure the resistance of the wires from the spark plug end to the mag 

 cap.  Starting with the longest wire, (left mag #6; right mag #5) 

 measure the resistance of the wires using a digital ohm meter.  The 

 shorter the wire, the less resistance.  If you find a bad wire, (no 

 resistance) remove the end from the mag cap, cut off about 3/8", 

 reinstall and screw in the wire-piercing screw.  Then check the 

 resistance again.  If the wire still reads completely open (no 

 resistance), contact me off-list and I can order you a new wire.

  

 I hope this helps. 

  

  



     ---

jan.mevis(at)informavia.b
Guest

Posted: Mon Aug 31, 2009 10:25 pm Post subject: Excessive R Mag Drop

I had the same problem with my Yak50, MTV prop, M14R with 450 HP. Now with new brake pads, problem is solved. It should be possible to adjust the brake settings though.  

   

Jan  

       

From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of A. Dennis Savarese

 Sent: maandag 31 augustus 2009 17:06

 To: yak-list(at)matronics.com

 Subject: Re: Excessive R Mag Drop  

  

  

     

Good point William.  Thanks for sharing that because it is important.  

    

Dennis  

   	  Quote: 	
		      

----- Original Message -----   

    

From: William Halverson (william(at)netpros.net)   

    

To: yak-list(at)matronics.com (yak-list(at)matronics.com)   

    

Sent: Monday, August 31, 2009 9:48 AM  

    

Subject: Re: Yak-List: Excessive R Mag Drop  

    

   

  



 

 When I try to do my run up at 70% RPM my brakes won't hold.  Details are 400HP, MTV 3 blade prop, and Cleveland 6" wheels/brakes.

 

 Anybody else have that problem?  I would think the 440 HP engine makes it even worse ...

 

 Thanks!

 

 William Halverson

 YAK55 

 

 

 

 At 05:24 AM 8/31/2009, A. Dennis Savarese wrote:

 

   

Scott,

 A couple of comments based on your post.  These comments will most likely not change the mag drop.  But I believe are important.

  

 - Mag checks are typically done at 70%, although the large mag drop would most likely not change by doing the mag check at 60-65%.   	  Quote: 	
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       [quote][b]

dsavarese0812(at)bellsout
Guest

Posted: Tue Sep 01, 2009 3:40 am Post subject: Excessive R Mag Drop

Hi Scott,

 There are 3 points to line up with the rotor.  1- the  center of the rotor; 2- the contact point on the rotor; 3- the scribe mark on  the boss of the mag.  First set the point gap to .25 to .35 mm or  .010-.014.  Then check the timing using your timing box or "buzz box",  which should be between 14.5 and 16.5 degrees BTDC.  Once the timing is  set, NOW check the rotor position to make sure the 3 points line  up.  The leading (rotating counter clockwise) point on the rotor is  the one that is used during normal operation.  This point should  be lined up with the scribe mark when the timing is set.  The trailing  point is for the starting coil.   Finally, when synchronizing the  mags, use what I call the "fine" timing adjustment eccentric which I pointed out  in the diagram.  This eccentric is on the opposite side of the  points.  Using your timing box connected to both mags, you can tweak one  mag to the other using this fine timing adjustment.

  

 I doubt the BR6's will solve the problem.  But the engine  will run much more efficiently with them.

  

 I believe someone made an excellent post yesterday about doing  the run-up at 60-65% on the Yak 55 because the brakes would not hold at  70%.  Makes perfect sense to me.

  

 Let me know how you make out.

 Dennis

  

  

 [quote]   ---

scott-p(at)texas.net
Guest

Posted: Tue Sep 01, 2009 7:21 pm Post subject: Excessive R Mag Drop

Hi Dennis,



Actually, my brakes do hold at 70% (Matco's)... But that didn't fix the 

problem. I don't think that the brakes on the Su29 did hold at 70%, so I 

suspect that is ultimately the reason for the 60-65%.



I completely reset the mags back to spec as per your description and the 

installation task card, and... (drum roll...) drop on the L mag went to 

about 1.9% and on the R mag to 8.5%, which is certainly better than 

almost 10% but still not quite right. I didn't have the ability to 

synchronize between them (no timing box--but I have access to one), but 

will try that. I have a temp sensor on the way, and will shoot the 

cylinders to make sure all are firing on the R mag, but since the engine 

runs smoothly (albeit at a lower rpm) I _doubt_ that I have a bad plug 

wire. If synchronizing them doesn't fix the problem, and there aren't 

any cold cylinders (and the resistances on the wires all check) then I 

am out of ideas and guess I'll need to find a replacement mag.



Thanks for being patient with me...<VBG>



Scott



A. Dennis Savarese wrote:

[quote] Hi Scott,

 There are 3 points to line up with the rotor.  1- the center of the 

 rotor; 2- the contact point on the rotor; 3- the scribe mark on the 

 boss of the mag.  First set the point gap to .25 to .35 mm or 

 .010-.014.  Then check the timing using your timing box or "buzz box", 

 which should be between 14.5 and 16.5 degrees BTDC.  Once the timing 

 is set, NOW check the rotor position to make sure the 3 points line 

 up.  The leading (rotating counter clockwise) point on the rotor is 

 the one that is used during normal operation.  This point should be 

 lined up with the scribe mark when the timing is set.  The trailing 

 point is for the starting coil.   Finally, when synchronizing the 

 mags, use what I call the "fine" timing adjustment eccentric which I 

 pointed out in the diagram.  This eccentric is on the opposite side of 

 the points.  Using your timing box connected to both mags, you can 

 tweak one mag to the other using this fine timing adjustment.

  

 I doubt the BR6's will solve the problem.  But the engine will run 

 much more efficiently with them.

  

 I believe someone made an excellent post yesterday about doing the 

 run-up at 60-65% on the Yak 55 because the brakes would not hold at 

 70%.  Makes perfect sense to me.

  

 Let me know how you make out.

 Dennis

  

  



     ---

dsavarese0812(at)bellsout
Guest

Posted: Wed Sep 02, 2009 3:17 am Post subject: Excessive R Mag Drop

Hi Scott,

 Once you get your hands on the timing box and properly set the  timing, then we'll see what the mag drop is.  If you have any questions on  how to set the timing, contact me off-list or call me and I will try to  help.

 Dennis

  

 [quote]   ---

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