Small Engines (Lawn Mowers, etc.): Lawnmowers, lapping compound, single mom


Question
Hello Marc,

I'm currently trying to rebuild a lawnmower motor and being the single mom that I am, I don't have a man around to guide me so maybe you can help.

What's the valve face and seat generally ground to?
What would cause a weak spark?

If you could help me on these two questions that would be great.

Thanks, Kelly

Answer
As a general rule of thumb, the valve is ground to 46° and the seat to 45° and then lapping compound is used to lap the two surfaces together for a perfect seal.

Several things can cause weak spark.  If this is a points and condensor ignition, you may need to change the points and condensor and properly gap the points.  Then you should check for the armature-to-flywheel gap being set to 0.010"-0.012" (no more than that).  A typical, healthy lawnmower igntion system should easily jump a 1/8" gap to ground.

Hope this helps.