Small Engines (Lawn Mowers, etc.): B&S starter gear failure, aluminum ring, gear failure

Question
The starter gear on my B&S 16hp single cylinder continues to fail after several starts.  It uses a plastic starter gear and an aluminum ring gear.  I have replace the clutch and gear assembly after less than 15 starts. I have tried to shim the starter and still no luck.  Visually inspecting it for proper alignment after installing appears to mesh correctly.  Any ideas?
Thanks

Answer
 Hello Danny:

 There is a Problem with the Valve Lash on Some Briggs Engines(and other OEM'). The Valve Lash is Loosening and Causing the Compression Release Lobe of the Cam Not to Operate Properly and Damaging Starter Gears. Check this First, Please. Check the Ignition Switch. A Bad Ignition Switch can Engage the Starter while the Mower is being Operated. You can Only See this with the Blower Cover Off and are Testing for this Problem. If you Hold the Starter Engaged Too Long After the Engine has Fired and is Running, this will Happen. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John