black scale on interior of briggs

[38racing]

I picked up a cheap and likely abused MTD mower with the 31 series on it. It uses a bit of oil so I decided to replace the rings. I have the head and sump off. head had some carbon on it but I noticed that the face of the cam gear is covered in a black crust . Looks muck like a carbon build up on a head. First time I recall seeing that when I've pulled one apart. Likely cause?

[RoyM]

Burnt oil, that engine was HOT Are the piston and rod discolored?

[38racing]

Have not pulled them yet. I cut with it a bit last year but since it was using oil I did not want to sell it without doing rings.