Scott, I am not sure what radial depth is or how to measure it. I'm just a small time hobbyist. This motor was a zero deck with flat tops and 58cc chambers so it was running around 12 to 1 compression. I did run it on pump 93 in the street with the timing backed off a couple of times. Otherwise it always got at least a 50 50 mix of race gas. This was probably why I started to get oil leaks and had to wire the dipstick in even though I had a breather on one valve cover and a PCV on the other valve cover. I have to say the motor still felt strong but its a good thing I pulled it apart when I did. Jim
Sorry Jim...missed this. Like Jay said, radial depth is how deep the groove is in the piston vs the width of the ring. Think of it as the "ID" of the ring when compressed. Jay pretty much covered how to check it.
If there was enough detonation to break the second ring, you'd see evidence of it on the top ring.
I'm going to answer my own question and say it looks like you have gapless second rings. I, personally, would advise against that. I'm not a fan of gapless rings in general, but the second ring is no place for them. It can cause pressure to build up between the top ring and second ring lifting the top ring off it's land. The top ring seals in two places...not just against the cylinder wall, but also against the ring land in the piston. If the ring loses contact with the bottom of the land it can lose cylinder pressure and cause a loss of power. Race engine builders started seeing benefits in thinner and thinner rings and those that liked the gapless rings still wanted that technology but because rings, especially top rings, were getting thinner and thinner, they didn't have the material that could take the heat and still build a gapless top ring so they moved the gapless ring to the second ring where it sees far less heat. Now days we have real good top ring technology and the gapless second is a thing of the past. I guess what I'm getting at is, since you;re going to have to replace the rings, I would not recommend a gapless second. The second ring is not a compression ring and really shouldn't be treated as one. It's an oil scraper and trends these days are to open up the second ring gap even more than the top ring. This allows any pressure ethat gets by the top ring...and there will always be some...a place to escape and not build pressure between the two. Not sure how that plays into what you had happen there, but I just thought I'd throw that out there.