When you pull it apart, you will find the top ring side clearance will be over .006" What happens is the ring hits the top side of the groove hard when you go through TDC & it gradually puts a dent in it, making the clearence increase gradually. When you rev it past 4000rpm with excess side clearence, the top ring will break.

So I have gone with another engine, a 69 B20, that might get by with only honing and no new pistons.

If the side clearence is +.006" & you have no money, a new set of cheap rings & keep it under 4000rpms will last a while. You can recycle all the gaskets & just use a new head gasket.

Maybe the wrong grade of gas, but I never heard it pinging. Maybe setting the timing too advanced, but again, I never heard it pinging.

Low speed pinging is pretty harmeless, but keeping it pinging for too long can push it towards preignition which hurts parts. Preignition is most likely to happen at peak torque if you have something that is good at filling cylinders. At that speed it can be hard to hear anything other than the SU's with an open element. Webers are worse.

If your top ring is in two or three pieces, it's likely due to wear.
If your top ring is in a dozen pieces, it's likely due to preignition.



--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.