Small Engines (Lawn Mowers, etc.): Craftsman Mower Sounds Like Sledge Hammer, mtd yardman, husqvarna usa

Question
I have a Craftsman 6HP push mower that ran fine till last week.  When I went to start it it sounded like the blade was hitting the metal shroud.  I was not.  Every revolution was a slap/slap noise.  It is almost impossible to pull start now, and it backfires.  Prior to this single event it ran perfect, starting on the first pull.  When I looked under the mower I noticed that the blade mount was cracked and would spin without the engine moving.  I replaced the part but the problem remains.  I did not hit a rock with the blade prior to the failure. What can I do.  The model # is 143.016000

Answer
Adam
Sounds like the following problems

Problem: Engine knocks.
Possible causes:

Magneto is not timed properly.
Carburetor is set too lean.
Engine has overheated.
Carbon buildup in combustion chamber.
Flywheel is loose.
Connecting rod is loose or worn.
Cylinder is excessively worn.

In your case I think the connecting rod broke and as you are trying to start this engine the rod hits the case or the piston,Now depending on the age of the mower you can get it rebuilt or junk it.

Many common problems can be remedied without going into the deep dark recesses of the engine. However, some will require either a partial or total overhaul. Eliminate all other possibilities from consideration before considering an overhaul - it will not be a fun afternoon (or weekend, or week, or month,....).
The following are indications that at least a partial overhaul may be needed:


Mechanical damage - broken, damaged, or bent parts resulting in inability to start or even turn the crankshaft for starting or excessive vibration while running. In most cases, this will be obvious - the mower died very suddenly - possibly with a loud clunk or p-ting and now the crankshaft hits something really really solid inside when attempting to pull the starter.
If it is on a Murray, Noma, AMF, Dynamark, Ultra, Sears, MTD, YardMan, White, Husqvarna (USA built by Murray/Noma), or other discount store brand, go buy a new machine. The cost of a new unit is not much more than the cost of the engine repairs, and then you won't have a worn out piece of discount store equipment to break down again in three weeks when something else goes bad...