OK, now I remember I did see the weight. But, have you read the drinking thread? Yes, I now remember, you have! Old age, or wot? I want to touch it. Carresss it. Fonddle it. No, serious now. Need to see it close up to be really happy to analyse failure mode! ps. Can I speel or knot?
what are drilling it with and are you using cut and tap spray or Trefolex cutting paste if you keep the speed of the drill down and use cut and tap spray or Trefolex cutting paste you should be ok with a sharp drill
It is a problem with the bolts, either not torqued correctly, or interference under heads. The flywheel is not designed in that area to transmit torque using the bolts as dowels, hence it cracked there. Its pretty much that simple. Ive seen similar failures on other stuff, and read approx 1000 pdf files(seriously) on failure analysis in this type of mechanical joining. Ive learned one thing over the years, NEVER think stuff will fit or be ok out of the box, ever.
Is there a chance revs are playing a part? This was an unlightened flywheel spinning to 8k rpm at what I believe were factory torque settings.
No, I believe they are designed and tested well above that by may factors, say for example you were to go from 5th into 2nd(hard, but doable) 2000 times, the limiter wont save you there and the flywheels speed will be excessive. Since torsional Impact loads lessen the farther you rev after max torque it rules out the whole Impact torsion also the faster you spin it. Ive a lot of info on this but its heavy stuff and you cant really just jump in at the middle of it and make sense of it without starting at the beginning if you get me.