Now that I know you pulled the heads....

I'd 100% check timing.

If you split the case -- you could have a piston clip that didn't seat properly, and is catching on the cylinder wall.

Put a mechanical gauge and measure the oil pressure. It won't be perfect, but you can tap off the top of the heads.

You might have blocked some oil passages with sealant, it's real easy to put too much on when you are putting the valve covers back together.

check the vario-cam. Maybe air got trapped in there during sitting and its just not engaging and
you're getting some rattle in the chains/guides?

I'd check compression or do a leak down to confirm there's no bent valves, or something sticking on the valves/valves seats.

lots of possibilities -- try to narrow it down via diagnostics.

Mike

Thank you so much. Is there a procedure available for the replacement of the pressure relief valve? Or is that pretty straightforward? I see one can order a new piston, seal, and spring from Pelican. Is that all there is to it?

Gravy. Remove the bolt (watch for a litle oil, capture it in a cup), remove old, install new... snug her up. 5 minutes. :cheers:

get the 997 parts