Small Engines (Lawn Mowers, etc.): Spark Plugs, mtd riding mower, compression stroke

Question
My manual recommends to replace the spark plug in my MTD riding mower B&S engine every year.  Is this really necessary?  The electrode is not rounded off and the plug looks fine when cleaned and the gap checked etc.

Thanks.

Answer
Engines can run a very long time on a spark plug.  However, every time the plug fires under the compression stroke there is some very slight wear on the plug.  After many years of use this wear is visible.

For a less than a couple of bucks you can replace the plug.  It it cheap insurance to ensure the engine performs it's best.  So, yes, I would replace the spark plug.

Eric