Rotor Button

What would cause a rotor button on a JD 4420 to just crumble in your hand when removing, Tractor had been running very badly and had just starting trouble shooting when I found this problem...

Cannot say I have seen one that bad but I have seen more then one where when you went to pull it off it would come out in 2 or more pieces due to old age

This one was only about 3 months old..

Ah but where as in was it a TSC part and made in China??

I have seen that happen but mostly in much older tractors. Ones I saw had hairline cracks or carbon traces the heat and sparking from which can damage the plastic portion. On other rotor failures, I've observed what appeared to be high voltage breakdown between the top of rotor down to the top of the steel distributor shaft which shorts out the spark and can destroy the rotor.

Those components must have a very high voltage withstand (tens of thousands) rating, but if you start doing things like running extreme wide plug gaps orrrrrrrrrrrr if theres some other sort of dist cap or plug or wire problem (any huge gap the spark must jump) which causes voltage to rise significantly (perhaps instead of 10,000 volts rise to 30,000 or so) that's when high voltage breakdown and surface arcing can take place that can damage caps or rotors and/or develop carbon traces EVEN IF THE ROTOR IS A HIGH OR LOW QUALITY COMPONENT.

If it continues to destroy rotors Id look for a dist cap problem (cracks or carbon traces) or a bad plug or wire in which the spark is jumping to far or way too wide plug gaps. A new set of plugs and plug wires and a cap and rotor may be a cure, but its hard to say over the internet without an inspection, so NO WARRANTY

John T