Mag trouble on my 252

[Greg252AY]

Flew our m20k 252 up to rogers ark and found the engine was running a little rough on the descent. After landing tested the mags and sure enough it would barely run on the left mag.Had a local mechanic pull the mags and drove over to quality aircraft accessories in Tulsa and the left mag tested bad. They could not rebuild that mag and I ended up purchasing a new slick mag (part number 6324). Now is where it gets weird. installed the new mag yesterday and it would barely run on the new mag. Mechanic checked timing several times and the plugs and leads and his best guess is a bad new mag. Of course we couldnt get a another mag until monday so I got the pleasure of driving back to Texas 7 hours instead of 1.5 hour flight. The local mechanic seemed like a knowledgeable guy but is there anything special about replacing a pressure mag on the 252 that he could have overlooked?

[Danb]

I would agree first off a bad mag, I wonder why they could not rebuild yours although the cost is likely similar. I just got my mags back from QAA and they said my left one was shot and scewed up but they rebuilt it for over 1amu, also had the right mag have another 500 hour inspection. Plane runs better than new, since I bought it new or four months old, starts on the first blade..good luck and report back. Those pressurized mags take a beating 

[Guest]

Flew our m20k 252 up to rogers ark and found the engine was running a little rough on the descent. After landing tested the mags and sure enough it would barely run on the left mag.Had a local mechanic pull the mags and drove over to quality aircraft accessories in Tulsa and the left mag tested bad. They could not rebuild that mag and I ended up purchasing a new slick mag (part number 6324). Now is where it gets weird. installed the new mag yesterday and it would barely run on the new mag. Mechanic checked timing several times and the plugs and leads and his best guess is a bad new mag. Of course we couldnt get a another mag until monday so I got the pleasure of driving back to Texas 7 hours instead of 1.5 hour flight. The local mechanic seemed like a knowledgeable guy but is there anything special about replacing a pressure mag on the 252 that he could have overlooked?

I would look in to a conversion to TCM/Bendix ignition system and dump the Slicks.

Clarence

[jetdriven]

+1. We often get Slick magnetos that wont run out of the box and I'd guess about half of them now wont run to 500 hours.  Plus Bendix mags are cheaper.

 

[philiplane]

Slick mags are worse than garbage. Slicks empty your wallet and cost you flight time. At least garbage can be used to make compost...

On the other hand, if the new mag does just what the old one does, the problem is probably not in the magneto. If you have Champion spark plugs produced between 2008 and 2014, dump them ASAP.

[cliffy]

Have seen two new Slicks turn out bad on an overhauled engine. The "E" gap proved to be bad internally on both. 

[Danb]

Clarence how difficult and costly is it to change from slick to Tcm/Bendix? What would we gain other than longevity which is important

[Guest]

You'd gain a boost in reliability.  

TCM/Bendix will take competitor ignition systems back as cores.  You just have to be sure there is a kit for your engine.  Most older Lycomings had Bendix mags at birth and have had Slicks installed along the way. 

Clarence

[Browncbr1]

I wish I had researched mags more before installing newly rebuilt slicks.  I had a little over 600hours on the previous set which were running perfectly fine.   I have about 10hours on these rebuilt slicks and have been worrying about them.    I've been having difficulty with fouling plugs since the install.  

Do mags either fire or not fire?  Or can they produce weak spark on one or more plugs individually?   It's always my #1 lower plugs that is giving me trouble.... But, haven't run the engine very hard. Mostly local loitering, low power LOP

[jlunseth]

Went through the same thing this summer.  Traced it to a bad spark plug wire to one of the Cyl 2 plugs.  The insulation looked ok, but the conductor had apparently deteriorated so we had contact sometimes (and everything would work fine) and then contact would fail and the engine would run rough on that mag. during runup.  In my case it was bad enough that we had some carbon in the hole for that wire in the cap.  I would check the cap, wires and timing on that mag.  Not very likely that a new or rebuilt mag. (that was bench tested before being released) would fail in the same way as the old mag.

[bradp]

Yes slicks can produce a weak spark.   This was the issue with my left mag that came back from overhaul.   Lycoming technical support had my A&P and I measure spark produced across an air gap of varying lengths for each mag from mag to the end of the spring on the lead / harness to a good ground.  There was a value below which will not fire an engine.   This was for an IO360.   

[Guest]

I wish I had researched mags more before installing newly rebuilt slicks.  I had a little over 600hours on the previous set which were running perfectly fine.   I have about 10hours on these rebuilt slicks and have been worrying about them.    I've been having difficulty with fouling plugs since the install.  

Do mags either fire or not fire?  Or can they produce weak spark on one or more plugs individually?   It's always my #1 lower plugs that is giving me trouble.... But, haven't run the engine very hard. Mostly local loitering, low power LOP

There are several modes of failure, weak coils, bad condensers, incorrect E gap or internal timing, bad points, bad cams, loose distributor fingers, worn bushings, stripped distributor gear teeth, are a few of the more common ones.  Slick seems to do many of them.

Some mags start fine and quit when hot, others just outright die.

Clarence

[Browncbr1]

Yes slicks can produce a weak spark.   This was the issue with my left mag that came back from overhaul.   Lycoming technical support had my A&P and I measure spark produced across an air gap of varying lengths for each mag from mag to the end of the spring on the lead / harness to a good ground.  There was a value below which will not fire an engine.   This was for an IO360.   

I will investigate with my a&p.   Thank you