[Barry_R]

Agreeing with the group to an extent. I build a lot of flat tappet engines, and follow procedures religiously for break in. So far we've only had a couple go down over the past five years, and they've been traceable to secondary issues - one was not properly broken in, another filled the crankcase full of gasoline from something that got into a carb.

Are you using a double spring? If not - you should be. A single sping with those presures will kill you. I don't have a problem with the pressures shown, but they are too high for break-in. Pull the inners - a PITA - but necessary.

Like they said - look for mechanical interference - retainer to guide, retainer to valve seal, pushrod binding against guideplates or rubbing on heads, rocker binding, coil bind, etc.

I'm not the biggest fan of hydraulic rollers in 460s due to the short pushrod/angularity issues unique to this engine - but they are an effective solution to this problem on a street piece.