The root cause is from hot starts! By not following a proper procedure to start a hot engine will cause the ceramic to weaken and crack.
As a flight instructor flying many different aircraft from many different locations, this issue is a common one from starting the engine the same whether its hot or cold.
When you dump cold fuel in a hot cylinder expansion/contraction happens.
This is my procedure to determine if a hot start is required and how to do it.
1. Determine if the engine oil (always available inside the cockpit) is hotter than outside air temp, if it is move to step #2. Fuel injected engines are always harder to start when hot.
2. Mixture out, throttle cracked 1/8"-1/2", and fuel pump on. Crank engine and as soon as it start igniting advance mixture in, then hand right back on the throttle.
Generally you only get one shot at this, so if you don't do it the first time you then need to prime engine, which is what your trying to avoid because priming engine puts COLD fuel right into the combustion/spark plug. And its this that's causes abnormal wear.
