How to Test a Small Engine for Spark
If your small engine isn't starting, you'll need to diagnose many issues including the spark plug. This video walks you through the steps of how to test for a spark using a spark tester.
Disconnect power. Put mower on its side and removed hex nut, spacer. blade insulator,blade,fan,and blade spacer, so that armature shaft can be pulled through embedded bearing in mower bottom.
Put mower back upright on its wheels. Use Torx driver to remove motor cover. Clean all debris from equipment.
Make a drawing to identify placement of wiring terminals to enable correct reassemble. Note that the bridge rectifier has one beveled corner to help identify terminal placement. Label brush holder assemblies to prevent mixup during reassembly. Remove brush holder assemblies from motor. Place brushes back in holders and use wire ties to hold brushes in place, then wire tie assemblies to mower handle so that they will be out of harm\'s way during the repairs. Mark the upper side of the motor shell so it doesn't get put back in upside down.
Use the three-eights nut driver to remove the two hex nuts holding the motor end plate, then remove the end plate containing the bearing. Note: you may check the wear on the old bearing by placing the end plate over your new armature, and check for excess play.
Carefully extract the armature from the motor housing.The outside shell of the motor contains no wire bundles, but is a very powerful magnet. You may elect to have an assistant hold the magnet down as you pull the armature straight up,out of the bearing at the other(bottom) end of the motor well.The magnetic resistance is significant.The magnetic shell will want to come out along with the armature, but the two must be separated at some point. Do not panic if the magnetic shell comes out along with the armature.It can be easily reset into the mower. Note the tab and slot on one end of the magnetic shell that will help you reestablish the correct position for installation.
Once the armature is out, be sure to check the status of the bearing in the motor well. Its mounting should be secure, but the inside should turn freely, and, because it is sealed, requires no lubrication.
IMPORTANT: There are eight small holes in the outer circle of the motor well that are probably plugged with grass debris. Clean them out with a wire or other small object as they help the motor pass air over the armature windings. They give the air somewhere to go.
Now, with the new armature, you may reassemble the motor, just by reversing the steps above. Happy mowing.