Edelbrock Victor small block head……

dusterbing the peace said
Couple more thoughts:

Since it happened on the same cylinder, maybe too much preload on the adjusters? Or not enough?

Or, have you checked retainer to valve guide clearance? Or the shim packs under these springs, may be binding the coils if something is set up different on #5.

Not being a jerk, have you floated the valves?

Also, did you have the heads checked out by a machine shop? I had some guides that were tight, although this may burn the valve first.

Just throwing more stuff out.

I had a machine shop look at the heads and even replace all the valves too because the 318 I had them on before broke a valve and had bent most of the others too(poor clearance in the bore). Like I mentioned before, the engine was still on its break-in period so high revving was off the table, at that point there's no way I could've floated the valves. It could've been a preload issue but I did cylinder 5 with the same preload as all the rest, why would this one let loose?