OK, I'll bite, what is switching to a larger bolt for?
I was hoping it will have better clamping force for the flex plate.
MBHD
It will provide better clamping force, but as Harry said, the clamping force isn't the issue as to why they come loose. We did it because spinning 9000+RPM with a heavy flywheel and a lot of HP, the 7/16" bolts just didn't seem adequate. If you keep the engine out of the harmonic shake zone they won't come loose. Today, with better dampners it might help keep this problem better under control.
Does your crank have provisions for dowels? That helps prevent flywheel/flexplate movement also.
