I have drilled some flywheels for bolting vee pulleys to, swarf comes off in longer pieces than common cast iron. I would say the flywheel is not like engine block cast iron but is a good quality cast iron more like what piston rings etc are made of.

when it went bang & bits flew out I felt All my luck was used up, never used a cast flywheel in comp motor since.
Been there and done it myself once or twice.


