what could have caused this?

[old man roger]

Looks like some one didn't do the clean air mod.


''If'' you have oil in your air box then you probably pumped oil from your crankcase vent tube into your cylinder.

This will cause the motor to hydro lock ..Oil doesn't compress so the connecting rod did.

Another reason could be that you blew a head gasket and filled a cylinder with coolant, coolant doesn't compress so the connecting rod did.