Magneto issue help

JimboSoCal78

JimboSoCal78

Filing Flight Plan
Joined
Jun 9, 2019
Messages
8
Location
California
Display Name
Display name:
jimbosocal78
Hey guys/gals,

I went out to my plane yesterday to get it ready for a long cross country later this week. Oil change, check tires, overall inspection under the cowling etc.

While running the engine to get it warm to change the oil and I noticed a problem.

When selecting the L mag switch at low power the engine wants to die then eventually does die. (Slick 6314 Magneto)
Cylinders 1,3,5 egt are also much cooler according to my JPI.

However at runup check list mag check speed power @ 1700 RPM there is no issue.

Mag check is normal, EGT’s are uniform across all 6 cylinders, drop is under 75 rpm and different from right mag is ~40-50rpm.

These magnetos have about 400 hours on them. Other than the low RPM issue, the engine runs perfectly in all other types of operation.

ILL ALSO ADD THAT I REMOVED THE P-lead FROM THE LEFT MAG AND HAD NO ISSUE WITH THE KEY IN THE OFF POSITION AND ENGINE RUNNING (running on the left mag only.)

My ignition switch ACS with turn to start is old has about 1500 hours on it, could that be the issue? Bad/Worn contacts grounding out the Left mag at low rpm?

I’m pretty stumped on this one and my I/A is out of town at the moment so no help there.

According to my poh everything thing is normal for the run up.

Am I just being a sissy by being concerned about the low RPM drop?

Thanks in advance for all your help/ideas

Jim
 
Last edited:
I’ve tired it rich and leaned out, rich keeps it running slightly better/longer.
 
Sounds like the mag is getting weak. Your not getting a hot spark at low rpm. Your only a 100hrs from the inspection time, pull it and have it serviced. I'm going to bet 1,3,5 are the lower plugs on that mag.
 
unsafervguy said:
Sounds like the mag is getting weak. Your not getting a hot spark at low rpm. Your only a 100hrs from the inspection time, pull it and have it serviced. I'm going to bet 1,3,5 are the lower plugs on that mag.
Click to expand...


1,3,5 are the lower plugs leads.
 
JimboSoCal78 said:
Hey guys/gals,

I went out to my plane yesterday to get it ready for a long cross country later this week. Oil change, check tires, overall inspection under the cowling etc.

While running the engine to get it warm to change the oil and I noticed a problem.

When selecting the L mag switch at low power the engine wants to die then eventually does die. (Slick 6314 Magneto)
Cylinders 1,3,5 egt are also much cooler according to my JPI.

However at runup check list mag check speed power @ 1700 RPM there is no issue.

Mag check is normal, EGT’s are uniform across all 6 cylinders, drop is under 75 rpm and different from right mag is ~40-50rpm.

These magnetos have about 400 hours on them. Other than the low RPM issue, the engine runs perfectly in all other types of operation.

ILL ALSO ADD THAT I REMOVED THE P-lead FROM THE LEFT MAG AND HAD NO ISSUE WITH THE KEY IN THE OFF POSITION AND ENGINE RUNNING (running on the left mag only.)

My ignition switch ACS with turn to start is old has about 1500 hours on it, could that be the issue? Bad/Worn contacts grounding out the Left mag at low rpm?

I’m pretty stumped on this one and my I/A is out of town at the moment so no help there.

According to my poh everything thing is normal for the run up.

Am I just being a sissy by being concerned about the low RPM drop?

Thanks in advance for all your help/ideas

Jim
Click to expand...
So you're saying that the engine dies with the mag switch on L at idle, but runs fine with the L P-lead disconnected?

First you'd want to verify that the Left mag position is shutting off the Right mag, that the leads haven't been reversed. No use chasing the wrong mag.

Then you'd want to disconnect that Left p-lead at both ends and see if there's a short of any sort--intermittent, weak or otherwise--between the lead and the shielding or ground. Put a meter on it and wiggle the wire around some.

Then you'd want to see if the AD on that ACS switch has been done. I've found lots of them overlooked. That AD requires a switch internal inspection and lubrication every 2000 hours, but ALSO requires a diode across the starter contactor to prevent damaging arcing inside the switch. The contact arrangement in the switch has one of the contact plates operating the mag and the starter contactor, and I think it's to shut the left mag off for start, to prevent kickback from the non-impulse mag. It's been a while since I had one apart; over the last few years we found it cheaper just to replace the switch than to try to service the thing and end up finding damage in it anyway, especially if the contactor diode was missing.

Here's the AD. It applies only to switches with the start position, by the way: http://www.airweb.faa.gov/Regulator...B8ABD56539B4684886256A3E00759DBF?OpenDocument

And the referenced ACS service bulletin: http://acsproducts.co/wp-content/uploads/2013/10/SB92-01.pdf
 
JimboSoCal78 said:
ILL ALSO ADD THAT I REMOVED THE P-lead FROM THE LEFT MAG AND HAD NO ISSUE WITH THE KEY IN THE OFF POSITION AND ENGINE RUNNING (running on the left mag only.)
Jim
Click to expand...
This indicates a mag switch is bad/dirty inside or the "P" lead has a high resistant short.

replace the "P" lead on the mag, remove the connection on the mag switch.
run the engine again in this configuration. see what it does.
 
Tom-D said:
This indicates a mag switch is bad/dirty inside or the "P" lead has a high resistant short.

replace the "P" lead on the mag, remove the connection on the mag switch.
run the engine again in this configuration. see what it does.
Click to expand...

Headed out there now will report back shortly.

Dan Thomas said:
So you're saying that the engine dies with the mag switch on L at idle, but runs fine with the L P-lead disconnected?

First you'd want to verify that the Left mag position is shutting off the Right mag, that the leads haven't been reversed. No use chasing the wrong mag.

Then you'd want to disconnect that Left p-lead at both ends and see if there's a short of any sort--intermittent, weak or otherwise--between the lead and the shielding or ground. Put a meter on it and wiggle the wire around some.

Then you'd want to see if the AD on that ACS switch has been done. I've found lots of them overlooked. That AD requires a switch internal inspection and lubrication every 2000 hours, but ALSO requires a diode across the starter contactor to prevent damaging arcing inside the switch. The contact arrangement in the switch has one of the contact plates operating the mag and the starter contactor, and I think it's to shut the left mag off for start, to prevent kickback from the non-impulse mag. It's been a while since I had one apart; over the last few years we found it cheaper just to replace the switch than to try to service the thing and end up finding damage in it anyway, especially if the contactor diode was missing.

Here's the AD. It applies only to switches with the start position, by the way: http://www.airweb.faa.gov/Regulator...B8ABD56539B4684886256A3E00759DBF?OpenDocument

And the referenced ACS service bulletin: http://acsproducts.co/wp-content/uploads/2013/10/SB92-01.pdf
Click to expand...

Thanks for the detailed reply, I don’t see anything in my logs regarding the switch or AD, but I do have the ignition service kit leftover (unopened and unused) from my airplane before this one.

I’m going to double check when I get out to the airport. Hopefully this is the issue.
 
Clean it with soap and water rinse well and reassemble it with no lubricant,
 
That switch actually looks just fine. I've seen worse. I think your problem will be found elsewhere.

The AD enforces the service bulletin, and both demand lubrication with the specified lubricant. Unlubricated contacts can weld themselves together more easily, or suffer contact burning more quickly.

Have additional capacitors been installed on the exterior of the magnetos?
 
Dan Thomas said:
That switch actually looks just fine. I've seen worse. I think your problem will be found elsewhere.

The AD enforces the service bulletin, and both demand lubrication with the specified lubricant. Unlubricated contacts can weld themselves together more easily, or suffer contact burning more quickly.

Have additional capacitors been installed on the exterior of the magnetos?
Click to expand...

No exterior capacitors on the mags. This plane is relatively new (2006) so I wouldn’t think adding capacitors would be necessary. I do have an email in to Textron and Cirrus though.

We did lubricate the new contacts as called out in the SB with Exxon Mobile aviation lubricant 33.

I think it is the mag beginning to fail. As it
Turned out in had the wrong p lead disconnected when I was troubleshooting this wasn’t even thinking about it but had the right mag p lead disconnected lol. Upon reconnecting that and disconnecting the mag with the issues (left) the engine did exhibit the same problem in the off position as it did with the p lead connected and in the L position.

I’ve ordered a set of Kelly OH mags from spruce (gonna replace both) at a cost of ~$1500 for the pair. Should be here by Wednesday, installed Wednesday night or Thursday AM.
 
Bad ignition points will also cause a mag to become intermittent at very low speeds.

From 60 years ago I remember the first MN cold spell would identify automotive point problems from slow cranking speeds. The points didn't break cleanly, causing much of the spark energy to be dissipated at the points rather than in the high tension circuit. Same thing can happen in magneto systems.
 
As will a bad distributor block.....it's worse with low RPMs. That's why I recommend a low mag check.
 
Tom-D said:
Clean it with soap and water rinse well and reassemble it with no lubricant,
Click to expand...
Dan Thomas said:
That switch actually looks just fine. I've seen worse. I think your problem will be found elsewhere.

The AD enforces the service bulletin, and both demand lubrication with the specified lubricant. Unlubricated contacts can weld themselves together more easily, or suffer contact burning more quickly.

Have additional capacitors been installed on the exterior of the magnetos?
Click to expand...
Hmmmm
 
nrpetersen said:
Bad ignition points will also cause a mag to become intermittent at very low speeds.

From 60 years ago I remember the first MN cold spell would identify automotive point problems from slow cranking speeds. The points didn't break cleanly, causing much of the spark energy to be dissipated at the points rather than in the high tension circuit. Same thing can happen in magneto systems.
Click to expand...

In magnetos, erosion of the points will advance the magneto's internal timing as well as the mag-to-engine timing. Wear of the points cam or points rubbing block will retard the timings. Either way, the magneto's E-gap changes, weakening the spark even if the points are making good contact and breaking properly. E-gap is the rotational difference between the full-register position of the magnet with the armature and the position where the points open, which comes shortly after full register. It represents the largest fall in flux when the points open, and therefore the strength of the pulse from the secondary winding that powers the sparkplug.
 
99 times out of a hundred the cam follower will wear faster than the points will erode, causing the points to open late and close early causing the dwell time in the coil to produce low voltage.

Point opening late, retards timing.
 
Slick magnetos supposedly are designed so the cam follower and the points wear at the same rate, cancelling out any timing drift. Whether that actually works in the real world I don't know.
 
Dana said:
Slick magnetos supposedly are designed so the cam follower and the points wear at the same rate, cancelling out any timing drift. Whether that actually works in the real world I don't know.
Click to expand...
That would actually depend upon the effectiveness of the condenser in any mag.
 
Tom-D said:
99 times out of a hundred the cam follower will wear faster than the points will erode, causing the points to open late and close early causing the dwell time in the coil to produce low voltage.

Point opening late, retards timing.
Click to expand...
Old lesson learned in shop class back when cars still had points . Dwell changes timing , timing doesn't change dwell .
 
Donny Hughes said:
Old lesson learned in shop class back when cars still had points . Dwell changes timing , timing doesn't change dwell .
Click to expand...
Changing dwell must change timing because the points open and close at different times, point opening is the timing.
Changing timing does not change how long the points will stay closed, that is dwell.
 
JAWS said:
LOL! ;)
Click to expand...
It's a fond memory . Picture this my shop teacher J.W. Moody standing in front of a hand full of kids smoking his non filtered cig. White shirt with tie tucked in behind the buttons of his shirt making the profound statement . Dwell changes timing, timing doesn't dwell. That's just deep ! I remember it like it was yesterday . He became a good friend of mine and we remained friends until his death .
 
You must log in or register to reply here.
Back
Top