Small Engines (Lawn Mowers, etc.): 18hp Briggs Intek OHV, intek, connecting rod

Question
I just rebuilt this engine and it wont run. It backfires through the carb. We have taken the motor apart 3 times to make sure the timing marks are lined up. We have set and reset the valves 3 times. It keeps shearing the flywheel key. We installed a steel flywheel key and it backfired and shattered the flywheel. Valves are set at .005 and we are at a loss. Any help would be greatly appreciated.

Answer
Why did you have to rebuild the engine?  Blown connecting rod, bad camshaft?  Do you have the service manual?  Is the engine a Vangard model?

Was there a dot or mark on the camshaft for timing?  Was there a spring on the carb shaft?

Let me know.

Eric