well i messed with it 3 years ago. I tried to keep in in lock position, but it always rotated back after I tried pushing the other ones in. My case was pretty small too so that didnt help. I eventually got it, but I'm just saying its better to spend the extra money and get a cooler with a backplate.
I find it's easiest to do the CPU and heatsink install before mounting the motherboard. Or, just get a $10-15 cooler on sale that has a backplate and enjoy something quieter, cooler and better.
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