Small Engines (Lawn Mowers, etc.): Loud lawnmower engine, craftsman riding lawnmower, briggs and stratton

Question
Initial problem was loud noise and engine shut off on Craftsman riding lawnmower. I went out to mower and checked it, engine would not turn by hand. engine is a 17.5hp Briggs and Stratton model 31C707-0230-E1.
I have some experience with working on engines, so took it apart, connecting rod was broke in pieces, looked like bolts came out, sump engine damaged.
Crankshaft, gear, cam, valves all looked good.
ordered parts, replaced sump engine, seal and gasket, connecting rod. piston also looked fine and cylinder wall.
Once together put oil in and started. Started ok, but load.
Replaced head gasket, rechecked head and valves, valves seating good. put back together and reset valve to 0.1 clearance at lifter when lifter is at rest.
Still loud and seems to want to backfire through carb.
Replaced muffler and fly wheel key, and still very loud.
Lost, seems like timing issue,  
I set timing by lining up cam and crank shaft marks, been told that some are set one tooth forward?
Not sure why it is so loud. I did not mark rods or lifters, when disassembling, but seems to match up. I am going to tear apart. oil linger appeared ok. is it possible rattling around?
Starts ok, and runs, will drive around yard, No idea what I did not get right as it is so very load, head has no damage, set head up to plate glass to check for warp or any gaps, it set flat, I did replace head gasket, and cannot find anything showing clearance settings or if timing should be advanced.

Need help,neighbors probably would appreciate it to since I keep redoing and restarting.
Sounds like an old farm tractor puttering along.  

Answer
Timing marks on camshaft and crankshaft should be lined up, NONE run one tooth ahead as you asked.  

As far as the noise is concerned, you only have one outlet and that is the exhaust.  Do you have an exhaust gasket installed properly?  Is the muffler rusted out inside perhaps?  Do you have a cracked exhaust manifold?

Backfiring through the carb--- lets look closely at the valve adjustment.

The Valve clearance should be set at 003 to.005 in on the Intake and .005-.007 on the intake.

You need to adjust the valves 1/4 inch past TDC on the COMPRESSION stroke


Hope this helps you...I know how frustrating things like this can be.