Horn Repair/Excessive Resistance

[v8fordman]

I pulled out 5 extra horns this past week since the weather has been miserable. All of them are Spartans. After disassembling, bead blasting, cleaning, painting and doing a thorough check of all components, I have one which has me puzzled. Before final reassemble, I always check to make sure the armature runs free and quiet. On one of these I have to give it (armature) a “push start” with my finger. It will then run free and quiet UNTIL the armature gets real hot. Heat indicates excessive resistance, but where could it be coming from. I checked the field coils and they are within tolerance. Any suggestions. I guess I should stop and say 4 out of 5 isn’t bad!!

 

[Synchro909]

I beg to differ on "Heat indicates excessive resistance". If the resistance is too low, too much current will flow, possibly more than the size of the wires can handle. It is too much current that causes the heat.
That said, I have a horn that won't go when the armature stops in a certain place. It is a bad sector. If I give it a push or move it to another place, away it goes. I suspect yours is the same. Like you, I have a couple of spare horns so I haven't bothered fixing it. To rewind the armature is way more than the horn is worth.
4 out of 5 isn't bad!!

 

[Herb Concord Ca]

Clean the commutator with 400 sandpaper. May have remove the insulation between the commutator copper segments (called under cutting).