I snaped 3 chains apart in two years.
One was a factoy 2007 YZ450F
Second was a factoy 2008 YZ450F
Third was a RK with about 8 race's on it.
I'm using a DID now i think.
And looking at others
Good info here.
The stock chains are junk. Consider yourself lucky that it didn't break the engine case.
My favorite chain is still the Primary Drive brand. I have the Regina ORN's on now, but to be honest..... I've had to adjust them twice and they only have 40 hours on them. I've had PD's that never needed an initial adjustment. If the Regina's make it 100 hours, I'll be surprised.