I just go by the 3 rules for a motor to work correctly.
1 Spark / 2 Fuel / 3 mechanical condition of all motor parts .
If the motor won't turn over when starting and it's not the coil rubbing on the flywheel and the motor is not seized then it would be a compression issue,this type of motor you can rule out fuel leaking into the cylinder but if the guides or rings are not within the correct specification then oil can leak into the cylinder causing it to hydraulic lock when starting but if that was the case on start up the engine will blow smoke for a several seconds.
These motors have a Automatic Compression Release mechanism on the camshaft that holds the valve open on starting if this is malfunctioning compression is not released causing the engine to lock up when starting.
