I just installed a set of brand new lifters in the 261 we built up for John's big pickup. They were flat-bottomed. Now, these were the milk can shaped solid lifters, so the same check might not apply to hydraulics. A concave-bottom lifter is definitely worn out, and there will be corresponding damage to the cam lobe it runs on. Lifters rotate because the bore they run in is very slightly off-center to the cam lobe, not necessarily because of the shape of the bottom of the lifter.

I've checked new hydraulic lifters for small block V8'a, and they do have a slight radius on the bottom. I'm not sure if that also applies to stovebolt hydraulics. If your lifters can be adjusted so they run quiet and there's no obvious loss of lift at the valve, let that sleeping dog lie!
Jerry


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