5.5 brigs and straton lawn mower wont run?

Have a 4.5 B&S that had a similar problem. Took it to a mower shop and found out the Flywheel Under the pull rope had shifted on the shaft. Basically the machine is junk! The only way to repair is to pull off the flywheel from the shaft and get a new alignment pin installed. The reason this occurred is hitting something with the blade that is solid enough to stop the engine. This can cause two different types of damage, the one you've got or bending the shaft on the bottom of the engine. If you get lucky, the engine will still run (although the blade will not cut level).

Well it's also possible that the emergency cut off cable has stretched. It happened to mine but only after about 15 yrs. I figured out it was stretched when it started pulling hard & since the brake is on the same kill lever that should have been a tip off. Instead of buying a new cable I just drilled a hole about a 1/4" further away. Works like a charm for a 15 yr old mower anyway.

The emergency cut off or cut off cable really because you don't just use it for emergencies grounds the ignition system when you release it. It's like the old fashioned kill levers that used to be right next to the plug on mowers & mini bikes to kill it.

Only two reasons why a small engine wont run. No gas No spark.