I will be installing a new hydraulic flat tappet cam very soon. My question: could I use the existing 10W-30 synthetic oil in the motor now (4 months old/weekend driving) or should I change it for some dino 30 weight?
Of course, I will change it again after the break-in period for the cam.
Just as brin stated you need a oil rich in Zinc and Phosphate. I broke my engine in last week and used Rotella T diesel along with a shot Comp Cams engine breakin lube. You can also go to you local GM parts deptartment and buy their GM engine oil supplement. Good luck! Do some research on how to break it in during the initial startup.
I just broke in an aggressive high-lift flat tappet solid lifter cam without any problems using Shell Rotella T 15W 40 "dino" oil. It's made for diesel engines and already has the extra additives you need for initial break-in.
In addition to the oil, you also need to make certain the new lifters spin freely in their bores when you install them. Do NOT slather the cam lobes and lifters with too much assembly lube. A thin film on both the lifter bottoms and the lobes is all that's necessary. Too much lube is as bad as not enough. Too slippery and the cam lobe may not get enough grip on the lifter bottom to set it in motion, spinning in their bores. No spin and you WILL lose a lobe.