Small Engines (Lawn Mowers, etc.): lawnmower engine, engine model type, john deere la100

Question
i have a john deere la100 18.5 briggs, what causes the key to shear when trying to start,engine backfires & key shears

Answer
Valves?  Might need to lap the crankshaft and flywheel surface...this has fixed a couple of these problems.

Is there a washer under the flywheel nut?  If the flywheel nut torqued?

When was the first time it sheared a flywheel key?

What is the engine model, type and code number?

Eric