Flat tappet cams in conventional push-rod motors are lubed by sling-oil off the crankshaft. The crank must be spinning fast enough to sling that oil in volume to the cam. That is about 2,200~2,400 RPM.
There are a number of factors at work here. But one is paramount. The lifters must be hard enough to live and they must be ground right so that they spin on the lobe. The number one failure is due to lifters "skidding" and not spinning.
The old expression of a "flat cam" was not about a lobe being worn down so it would not open the valve, it was about the cam lobe taper being gone. So the cam presented a flat surface - no lifter spin.
The absolute number one thing to do is to make sure that all the push-rods are spinning. If you can't stand oil droplets in your motor bay, get clips or a cut-away valve cover. Or put old towels or blankets on the fenders/liners.
But just after firing that engine, pop the valve covers one a time and look and make sure every push rod is spinning the same. If not, shut it down and find out why ... If they are, shut it off, button it up, refire and hold a varying high idle at 2,200+ for 15 minutes.
If your motor is equipped with Crower Cam Saver or Howards Direct Lube lifters (hydraulic or EDM solids), it is less of a requirement. Those designs will lube the lobes directly so your high idle regimen is reduced to spin-check and maybe 5 minutes of 2,200+.
Do not get weird about the oil. Joe Gibbs or Brad Penn are good oils. 10W-30 is fine. But so is Chevron Delo/Supreme, Rotella T5 or any other decent modern oil with 1,200 PPM of zinc. Millions of cams have been broken in on HDEO. No off brands, house brands, etc. Valvoline VR-1 Silver Bottle is the number one hot-motor oil out there for flat tappet motors. It would be a very good choice.
Make sure you have a magnetic drain plug. Use some JB Weld to stick a magnet of the side of the oil filter. Run your new motor for 500 miles and change. Look at the drain plug. Cut open the filter. Look where that magnet was glued on. If iron/steel particles are fuzzy and stuck to either magnet, find out why?
I hope you blocked the oil by-pass's? You want all the oil going through the filter - all the time. Use an oversized filter. The larger media area will allow cool oil to pass easier on start-up.
Unless your motor has bone stock OEM every day valve springs, you need to take precautions. There have been soft cam cores and MANY imported lifters that will not live. Johnson or Delphi USA made lifters are usually very good. Crower and Howards have never had reports of soft faces. Crower is the only outfit that publishes face hardness, but Howards sources their lifters from the same MFG (Johnson).
If you do all the above, it'll run 200,000 unless extremely wild. If you don't, who knows ...
If lifter metal gets loose, it will take the whole motor. It gets embedded in piston skirts and bearings and the whole thing has to be redone ...
The motors you rebuilt in the past were from USA sourced parts - especially lifters. Today, it's a turd shoot where the parts come from ...
