That piston has a broken ring landing. I had the exact same problem on one of my 502’s and it looked the exact same. I would replace the piston and fix the head. Mine scratched the cylinder wall also. I have to look I might have a spare piston with the metric ring pack. I ended up buying new pistons for the other engine.

If I can get to it, I'll have the piston out this evening.

Wouldn't a broken ring land affect running condition and compression/leakage? Compression was done last spring and the leak down was done last night. We're probably splitting hairs here because obviously the piston is fubar. It was late last night when I discovered this so I didn't look too closely at the bore on that side, though I ran my nail across the area and felt nothing out of the ordinary. I'll look more closely tonight.

At this point I'm leaning toward a refresh on both since they're out and I have the time.

You are right, cant believe I missed that That is where they like to burn through too.

I have seen several 502 pistons burned at that exact spot. JE makes a replacement that is a couple thousandths bigger. Pretty much a hone and go. I would go ahead and bite the bullet and freshen them up

That is exactly what I did on one engine. And the replacement piston uses a normal ring pack. I ran mine lean and that is what caused my problem! Good luck.

I think you should go with your gut here Tom. It’s always nice to have peace of mind on the water without wondering when the thing you didn’t do will bite you. You have the engines on the stands now, this is the ideal time to make them “Tom Z” worthy.

I have extra Mahle rings if you needed them. 6 sets 4.466

If you have to hone the cylinder I would take all 8 out and hone/ring them all. No way to be clean enough doing only one IMO

Thanks guys. I really appreciate all the feedback and advice.

This evening was spent undressing everything and getting it on the stand. Tomorrow afternoon I’ll get the pan off and the piston and rod removed.

Looking at the bore, there is some discoloration at the top where it looks like there has been an issue. The rest of the bore looks good and I think I can get by with honing everything. That will really be for the machine shop to give a final on. The game plan now is to get this one torn down to inspect the hard parts then send to the machine shop for analysis and cleanup, etc. While this one is at the shop, the other will go on the stand to be undressed and will be rotated out once the other one comes back.

If the bores are good I’ll stay at 502. If they need to be bored, then I’ll probably just bite the bullet and step up to bigger cranks and make them 540s. I’ll know a direction I’m guessing sometime next week.

I’ll post up what I find regarding the piston and rod tomorrow. Pics included.

Yes those nice rectangular dents in piston say broken ring to me. Almost looks like piece is still imbedded in piston. Take a magnet across the dents and see where it sticks. I've seen this before haha. I'd also peer under the valves of that cylinder and see if the pieces beat up the valve seats at all on their way out.