Fixing a Magneto on a O-470R in a C-182

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JoseCuervo

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JoseCuervo
Went to go fly on Sunday, started the 182 up, and it struggled a bit to start up, back-fired once, and then ran good out to the run up area.

Got to the mag check, set RPMs at 1700, switched to Left and RPM stayed at 1700, back to Both, stayed at 1700.

Switched to the "R" on the switch and RPM's fell to below 1000, with a backfire, before I could switch back to BOTH. Tried it again, same result.

Taxied back, put it in the hangar, and had an omelette at a local place instead of 100 miles away.

My mechanic works out of an airport 10 miles away from where I base the plane, and, as there was no urgency, didn't want to try and find someone at the airport where I hangar on a Sunday.


On Monday, went and visited with my mechanic, and he said he could drop everything (he was busy in an overhaul in an engine for a guy that is impatient) or if not important, wait until Wednesday (today).

I agreed today would be soon enough.

He asked me if they were Slicks or Bendix, and, I had to tell him I didn't know. He asked if I stuck an Ohm meter on them to verify the key switch is actually wired correctly. Again, I didn't know.

So, he agreed to meet on Wednesday.

Yesterday, I did go out and pull the cowl, and confirm the mags are Bendix, which when I relayed that information to him, he seemed relatively happy they were Bendix and not Slicks. Hopefully he was happy as they are easier for him to fix, and not happy because he was going to make more money off of me.

I did take pictures and the part number, and, it looks like from Spruce, an overhauled one is $621

95c921ca9250deeb09e33b53b3fd594f.jpg
4ca394f7a5a404a33073f5924e37965f.jpg
 
You had a bad mag drop and are already planning on mag overhaul?!? Did you look at the spark plugs? Have an engine monitor?

I had a problem like that on a 4 banger one day and using the mag switch and engine monitor knew exactly which spark plug was fouled. I taxied back to the hangar and within 15 minutes had the plug out, cleaned and reinstalled and checking to see it the problem was fixed...
 
bnt83 said:
You had a bad mag drop and are already planning on mag overhaul?!? Did you look at the spark plugs? Have an engine monitor?

I had a problem like that on a 4 banger one day and using the mag switch and engine monitor knew exactly which spark plug was fouled. I taxied back to the hangar and within 15 minutes had the plug out, cleaned and reinstalled and checking to see it the problem was fixed...
Click to expand...

Not planning on an overhaul yet, just reporting the steps I have taken.

It was far more than a fouled plug. Those are easy to avoid and to fix.

This was a "dead" mag. Might be a loose wire, might be a completely bad mag. I did no trouble shooting beyond the key switch.

Headed to meet the mechanic now.
 
JoseCuervo said:
Not planning on an overhaul yet, just reporting the steps I have taken.

It was far more than a fouled plug. Those are easy to avoid and to fix.

This was a "dead" mag. Might be a loose wire, might be a completely bad mag. I did no trouble shooting beyond the key switch.

Headed to meet the mechanic now.
Click to expand...


Did you take the mag out? That picture sure looks odd.

Yeah, I thought I could clear the plug issue that day and no matter what I tried it wouldn't so ended up pulling that spark plug.
 
No RPM loss on one mag is a indicator that it is only running on one mag, a complete loss of RPM on the other mag indicates it is not firing that mag when the other is shut off. (grounded) So this means your right mag is bad or the P lead is shorted to ground all the time no matter what position the Ignition switch is in.

So, what to do.... remove the Right hand P lead. see if it will start with the left grounded = (Ignition switch in the R position). no start= not P lead.
remove the mag, take to your mechanic. 4 screws/ 2 nuts it is off.
 
I didn't read that line well, Tom is on the right track.
 
Checkout_my_Six said:
my money is on the switch......
Click to expand...
Removing the Right P lead then if it starts I'll agree it could be the switch, simply meter it out to find the ground, it may be a simple shorted wire, they are Co-axal wires and many times they short to the ouster shield.
I wonder what the Mag drops were prior to this?
 
Checkout_my_Six said:
yes....they can fail open or shorted or intermittent short to ground.

It could also be a shorted P-lead to ground.
Click to expand...
Switches & P leads normally give a warning prior to failing entirely. A total failure isn't normal, they usually are intermittent then fail.
A broken point cam follower is instant and total failure. and pretty common. intern failure of the mag, is total and sudden.

this is why we should do the Idle mag check prior to shut down. He would have found this discrepancy at the end of the last flight had he done this.
 
bnt83 said:
Did you take the mag out? That picture sure looks odd.

Yeah, I thought I could clear the plug issue that day and no matter what I tried it wouldn't so ended up pulling that spark plug.
Click to expand...

Have not removed the magneto yet.


Definitely not fouled plug. Total loss on the switch to right.
 
Tom-D said:
No RPM loss on one mag is a indicator that it is only running on one mag, a complete loss of RPM on the other mag indicates it is not firing that mag when the other is shut off. (grounded) So this means your right mag is bad or the P lead is shorted to ground all the time no matter what position the Ignition switch is in.

So, what to do.... remove the Right hand P lead. see if it will start with the left grounded = (Ignition switch in the R position). no start= not P lead.
remove the mag, take to your mechanic. 4 screws/ 2 nuts it is off.
Click to expand...

I assume that is the P-Lead?
e2489bf0d9a2e02db97f9742b57e436d.jpg



Which are the 4!screws and 2 nuts?
12f6e644d2454f3c99d6bdf5fca3ac3f.jpg
 
Tom-D said:
Removing the Right P lead then if it starts I'll agree it could be the switch, simply meter it out to find the ground, it may be a simple shorted wire, they are Co-axal wires and many times they short to the ouster shield.
I wonder what the Mag drops were prior to this?
Click to expand...

Mag drops were "normal" on the last flight.
100 rpm on each side, -/+ 50. Or something like that.
 
The P-lead circuits including the white wires and the external filters look rough. Still may not be the problem tho.
 
Checkout_my_Six said:
my money is on the switch......
Click to expand...

Please send your money to help pay for the repairs. First thing we checked today was the switch with a multimeter, and the switch was good out to the mags.

Right mag was diagnosed as not working.
 
Pulled the right mag off, and it headed down the road in the mechanic's pick-up to be fixed. 5 minutes dinking with the switch to make sure that wasn't the problem, 5 minutes to remove the mag and contain the hardware, pick up tools, close the hangar.

The steps to remove:
  • Undo the white wire
  • Undo the P-lead with a 3/4" wrench
  • Remove the 4 flat-head screws that contain the sparkplug wires
  • Remove the spark plug wires and rubber boots
  • Remove the two bolts with 1/2" socket that hold the mag on to the engine

baf4c45946754023f1879d9ecab46002.jpg


977df76ad1043ed39768c2251a4c866b.jpg
 
JoseCuervo said:
Please send your money to help pay for the repairs. First thing we checked today was the switch with a multimeter, and the switch was good out to the mags.

Right mag was diagnosed as not working.
Click to expand...
here ya go.... ;-)

US_One_Cent_Obv.png
 
Let us hope the coupling does not fall into the accessory case. there is nothing holding it in place. picture #1.
 
Checkout_my_Six said:
they fall down....into the sump. :confused:
Click to expand...
REALLY<<< do you want to pull the sump just because some clod did not remove them properly. Do you realize there is a bunch of gears in the way of them falling all the way to the sump? 10 seconds worth of work with a pair of needle nosed plyers could save an engine tear down.

Some people just don't get it.
 
I've fished them out....even ran a cam down the back of the accessory case and into the sump. I'm well aware of what's there. Most times they just drop into the oil sump. Thanks Tom. ;)
 
It's so much easier to simply remove them as the mag comes off.
 
JoseCuervo said:
Went to go fly on Sunday, started the 182 up, and it struggled a bit to start up, back-fired once, and then ran good out to the run up area.

Got to the mag check, set RPMs at 1700, switched to Left and RPM stayed at 1700, back to Both, stayed at 1700.

Switched to the "R" on the switch and RPM's fell to below 1000, with a backfire, before I could switch back to BOTH. Tried it again, same result.

Taxied back, put it in the hangar, and had an omelette at a local place instead of 100 miles away.

My mechanic works out of an airport 10 miles away from where I base the plane, and, as there was no urgency, didn't want to try and find someone at the airport where I hangar on a Sunday.


On Monday, went and visited with my mechanic, and he said he could drop everything (he was busy in an overhaul in an engine for a guy that is impatient) or if not important, wait until Wednesday (today).

I agreed today would be soon enough.

He asked me if they were Slicks or Bendix, and, I had to tell him I didn't know. He asked if I stuck an Ohm meter on them to verify the key switch is actually wired correctly. Again, I didn't know.

So, he agreed to meet on Wednesday.

Yesterday, I did go out and pull the cowl, and confirm the mags are Bendix, which when I relayed that information to him, he seemed relatively happy they were Bendix and not Slicks. Hopefully he was happy as they are easier for him to fix, and not happy because he was going to make more money off of me.

I did take pictures and the part number, and, it looks like from Spruce, an overhauled one is $621

95c921ca9250deeb09e33b53b3fd594f.jpg
4ca394f7a5a404a33073f5924e37965f.jpg
Click to expand...
 
My money is on the coil being the problem. I had exactly the same symptoms as you.
 
I always bet on the cam or brush wearing out first... But I was really surprised that the one I just removed and inspected had basically zero wear after a couple hundred hours of use. I guess the silly $1.32 capsule of contact assy lube (that holds maybe 2 drops of grease) actually did its job!
 
Just to close the loop on this....


"Removed R/H magneto, disassembled, replaced broken impulse coupling spring, points, and oil seal. Re-assembled, installed, and timed to engine."


Costs:
Labor $150 (includes 2 round trips of 20 miles to travel to my hangar).
Breaker Points $57.81
Impulse Coupling Spring - $10.00
Oil Seal $17.45

Total: $235.26

Runs like a top now....
 
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