[AT] Testing a coil

[Mike Sloane]

Steve brings up a point that I haven't seen mentioned on this thread: 
all of the problems I have had with coils have been that they are seem 
OK cold but fail when hot. Depending on the tractor involved, and the 
location of the coil, it takes between 10 and 20 minutes for the coil to 
get hot enough to cause it to start to break down. This problem can be 
caused by someone converting from 6 to 12 volts and neglecting to put a 
ballast resistor in line with the coil/distributor. (Burned points are a 
sure sign of this situation.) Even with decent electronic test gear, I 
have never been able to test a coil - you need to be able to test it 
under load and heat. And, of course, a bad condenser will give you 
exactly the same symptoms, so I usually change out the condenser before 
spending money for a new coil.

Mike

Steve W. wrote:
> My old distributor machine has a dedicated coil tester on it. What it
> basically does is run the coil off a motorized set of points while it
> sets inside a small heater unit. The heater gradually warms the coil
> while the points cycle. It has an adjustable plug gap on it that you set
> according to the chart (basically 6 volt coils get 3/8" gap and 12 volt
> ones get 1/2") You actually start testing by putting the coil in the
> freezer overnight. Then install it and crank up the tester. You let it
> run until the temp on the coil hits 200 deg. If it sparks the entire
> time it is good.
> Don't see why one couldn't be built using an old distributor and a small
> motor.
> 
> Steve Williams
> 

-- 
Mike Sloane
Allamuchy NJ
<mikesloane at verizon.net>
Website: <www.geocities.com/mikesloane>
Images: <www.fotki.com/mikesloane>

"If they give you ruled paper, write the other way."
Juan Ramon Jimenez (1881-1958), Spanish writer


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