[SEL] Checking a Magneto

[Rob Skinner]

On 9/20/06 6:13 AM, "mullt at att.net" <mullt at att.net> wrote:
> I understand that replacing a magneto can be expensive, sometimes more
> than the engine itself. My question is, how can you check a mag on an
> engine that is not running to see if it is okay. Can you hook a test
> spark plug up, crank the engine and expect to see a spark?
> 
>> Hi Tom,
>> Yes, you can check a magneto by hooking up a test plug.  But that won¹t tell
>> you the whole story.  If the plug is fat and blue, that¹s a good sign.  If
>> it¹s skinny and yellow, the engine might have problems running.  Don¹t let
>> this scare you off of an otherwise good deal.  Magnetos can be fixed up just
>> like valves or piston rings.
>> 
>> Sometimes the mags are easy to fix, sometimes not.  One thing to consider,
>> never trip a mag with the high tension lead disconnected.  It can seriously
>> degrade the secondary winding.  Hooking up a plug or grounding the lead is
>> the proper way of handling the situation when you need to trip the magneto.
> 
> 
> How about engines with ignitors. How can you check them?
> 
>> There is not much to go wrong with the ignitor.  Sometimes points wear,
>> creating an intermittent condition.  Very commonly, the rotating shaft and
>> it¹s bore will wear so that good electrical contact is lost.  This will have
>> to be addressed, and it¹s not usually a huge problem.
>> 
>> If the ignitor is run by a battery and coil, you can easily replace either.
>> If the ignitor runs from a magneto, there are timing issues and the
>> electrical integrity of the magneto to consider.  It can be hard to check the
>> entire system without actually running the engine or testing the magneto on a
>> bench.
>> 
     
 
     Rob Skinner  
     1721 Brookdale Avenue  €  La Habra, CA 90631  €   562.694.2301
     rskinner at rustyiron.com   €   http://www.rustyiron.com