[GMAs]

the mag problem....

Lets see... ya it says that you should have them checked every 100 hrs at annual for points and condition... Hmmmm 1200... now thats a long time for a mag... your mechanic should have picked it up... but, how come YOU don't read your log books,maintance manual... after all you are the one.. that is responsible for your plane...right... (we have been thru this how many times...smile)

As to our recomendations...

normal asp non high flying...

We recomend that you have the mags serviced every 500 hrs... along with the alternator... smile... Now some have said .. well ya we took a look at them and they looked fine... but, my response was ... how do you know if you don't take them out of the plane/engine... which most are not.. they just look at them sitting their... no.. no.. that is not what we mean... the mags come off and go into the shop... and are opened up and and inspected and repaired... the ignition wires are tested with a meggar.. for break down.. etc...

Most of the time they ..the shop.. such as savage mag......

SAVAGE MAGNETO SERVICE PO Box 2401 Airport Station Bldg 73 Oakland Int. Airport
Oakland, CA 94614 Phn: (510) 562-2941 Fax: (510) 562-1593,

will do a tear down and inspection/overhaul... cost is minimal.. but, when done...it is then run on a mach and tested for operation and voltage... as well as crossfireing... which well get to in a min...

their are more things in the mag that can happen wrong than just it makes sparks... timing and springs get out of whack... seals and bearings get dry... so their are a bunch of reasons to have them done at that interval.... as we have found it keeps the fear factor down with the passengers...

But,....

Now for the high flyers.. them TURBO guys...

Here we recomend that you take them out and have them inspected every 250 hrs... yep.. thats not much... but, because you are up in a drier climate way up their things go bad quicker... grease which has water in it... yep it does... drys out...oil oxidies faster...etc... causing drag on the bearings... this in turn causes the impuse spring to have to work harder... etc... seals are another item that seem to dry out faster... and of course the crossfiring in the dist block seems to happen more frequently... which we will get into here in a min...

again the inspection is not just to physically look at the mag.. its to open it up and check how its doing... and replace any parts that are not within limits... or carbon tracked... (Bendix overhaul manual...TCM x42002 and "the Magneto Ignition System" by John Schwaner at Sacramento Sky Ranch... 800-433-3564... are two good books to have... and in Johns' book he has a section on High flying make sure you mention the 337Skymasters Club for the discount)

Now as to the pressurization of the mags... the reason that your mechanic is reluctant to change is becasue if the turbo has problems... and/or starts spitting oil/parts... guess where its going... right into the top of the mag... also it has been shown that the turbo air... you know the stuff that is compressed from the compresser side of the thing... is a lot hotter... yep about 250 deg F... don't believe me... start up and go for a flight.. land and then try and put your hand on the intake tube... its real hot... and its not from the engine... its called heat of compression... on turbines it gets up to about 450 deg f in cases... you can cook with that... and the hot compressor section gets up to about 600... but, that is for the turbine guys.... we are talking our little turbo compressors.. here....

Now if you have a device called a intercooler... then you take the temp of the compressed air for the intake back down to normal air temp levels... but, if not.. well... all that hot air is going inside the mag... and now while its dry air.. which has higher resistance to allowing a spark to cross (oh ya.. think spark plugs too.. and ignition wires... smile)... it does have its drawbacks... the heat.. which cooks parts like greases and seals...

So putting the pressure connection on... well just remember 250 hrs... is your max time for overhaul of the mags... I would think if you don't need them... I wouldn't put them on...

Now... a word about spark plugs and ignition wires...

As you go up... the density of the air decreases...along with mositure... so to make the spark jump the gap in the plug.. is going to require more voltage... yep it goes higher... and if you have a bad wire harness for the ignition... guess what... is going to start jumping out of the wire its in to x fire... to another one that it likes... not firing at the appointed spark plug...it should.... a lot of time it goes to another one that is on the intake side... fuel rich air takes less voltage.... and sparks that plug befor its time ... not good... as it really plays havic with the engine.. but, you don't know it because the prop and the mass motion is greater than the power generated.. but, the engine does...

So you can have a spark plug/ mag/ wire harness that appears perfict down on the ground.. but, up in the air... its a nightmare... and not doing what it should... and no the JPI/EGT doesn't seem to show it...

Ya.. Ya.. so what has this got to do with my broken motor mount... well the stress of the x firing is putting a pulse on the mount... and because it is so repitious it is causing it to flex... and like flexing a piece of bailing wire back and forth so many time... it will break eventually... not to mention what is happening inside to the crankshaft counter weights... which I would have checked too by the way... along with the crank and the prop and hub... as these will be the next things that will start cracking...up... and can actually end up breaking the crank...

so is the maintance of the mags improtant... yep ranks right up their with the fuel... and if you don't do it... well I am sure you all have heard the old saying... you can pays' me now ... or you can pays' me more later ... and here it does make a differance...

If you like we can get into the mags further... as their are several things that you and your mechanic should check for... and we came up with a neet little device to check them... both in flight as well as on the ground... because the impulse springs are another biggie... and most engines don't fire both plugs at the right time...unless you check it out... their are several AD's on the mags we use that don't seem to be complied with... you might want to check it out and make sure your is done too... again.. if their is any interest we can compile a status report that you can check against... along with the AD's and how they are supposed to be complied with... your mechanic should have access to the AD listing.. and it should be posted in the back of your log book... you remember that thing.. its what was supposed to be done to the airplane....

So in closing... this little mini siminar on mags... I suggest that who ever is replacing the motor mounts... (not the rubber stuff)... that you are being given a warning from the engine... something is not right in it... something is either not in time.. or that something was put in wrong... and yes mags can do it... along with bad ignition wires... and now bad counter weights on the crankshaft... as well as bad spark plugs... and one other thing... fuel... valves and lifters... (see that was really 3 things but... just checking...to see if you were paying attention)

checking the log book is the first order.. and using a seperate piece of paper of the computer... put the date, time and maintance or replacement item... and compair it to the current time and problem... (YOU ALL.... should be doing this with yours too... for record keeping... some of the computer gurus might want to come up with a program that others could have to keep records on the computer with.. would be nice)...

you should not be breaking motor mount frames... and if the vibration is so bad that its causing a cable to rub thru... you got a real big problem... that is ringing a really.. really ...big wake up bell... which if not answered.. could cause you to buy the farm... to keep flying it.. is not what you want... to do.. until you can fix the problem... its not normal... and should not be though of as such..... remember I said once the engine does talk to you... well... its limping around...breaking things.... think it has a problem???...

start with the simple things... and work up... but, because it has been going on... its later than you think.. and may end up costing you big bucks.. to have a safe plane... vibrations are deadly... to metal and... to you....

GMAs