Rough magneto

Alain1

Alain1

New member
Hi, Have Bendix Mags on my 165 Franklin. Both running great in July but airplane was quiet for few months due to annual and gear job.
Now the left mag is rough. No valve stuck, no bad lead or static filters, switch is good and clean.
Is there something in Magnetos that can give problem because sitting for a while? Can there be corrosion on points or something?
Any suggestion?

Alain
 
Alain,
Check your sparkplugs first before worrying about the magneto. Run on the right mag only at startup for about 30 seconds then check for cold cylinder. Use a digital remote sensing thermometer.
Dan
 
Might be points but I would bet more probably a plug issue. The last time I dealt with this was two months ago on an older Cessna 172, and the right mag was running rough, and was running smoothly 2 days prior. First thing I went to were the plugs on that side and I could see nothing wrong. I then spent hours tracking down the problem, trying the points, condenser, plug leads, mag itself, etc...then when I was completely baffled I decided to pull the plugs one more time. Using a magnifying glass I found the tiniest piece of lead you can ever imagine shorting the electrodes of one of the spark plugs, lower plug. I know we all know this but most problems with these airplanes/engines hve the most mundane and simplest of answers. I would say pull and check the plugs, then clean and re-time the points.
 
Forgot to mention in my first post,
Plugs brand new, so I tought of a defective new plug, swap with a set of new C-10 I had, same thing.
Turn the prop slowly to check the fire, spark on each plug. Does not mean the spark is good quality and can be intermitent I know.
Can I pass a little file to clean the point? Is this feasable without removing the magneto?
 
Clean points carefully, set gap. Set spark plug gap .016-.019. One small drop of oil on the felt. Did you test all the leads with a lead tester? Set mag timing. Test engine as mentioned earlier.
 
Have not tested the leads, I parked it in the hangar a couple of months ago to do the gears, was working fine then. Lead ends are clean at both end. I know it could be a weak spot along the cable so does not mean because the ends are clean that full juice is going thru. But again, one day fine when parked and now, kaput. Don't know if it was parked with the left mag points open, a layer of dirt or corrosion could have taken place there. But point don't corrode do they? aren't they made of platinium?
Timing didn't moved, was working fine. I will check the plugs again but like mentionned earlier, they are new,and will try cleaning the point...
 
Alain,

Platinum? Maybe or maybe not. Many are just Tungsten. In any case the Platinum is just a thin overlay on the contact surfaces. My suggestion: rotate all of the spark plugs from one magneto to the other and see if the problem follows. Spark plugs are more fragile than they look. Drop one on the floor....then drop it in the trash!

O-ring Seals
 
All Plugs swapped and checked, other batch tried always same probem, drop of 175 r.p.m. on the left mag, lead check at Spark plug end, good contact and clean, at distributor, same thing, point cleaned, no improvment, now I am thinking of changing the harness, it's not really new, but before spending 300.00 $ on that, Could there be a deposit of carbon on the rotor to distributor contact? could tthis cause occur?
Don't feel like removing the mag and getting to do the timing again...but if I have to do it, then will do.
 
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