What are these markings in the cylinders?

[elliottw]

I'm rebuilding an LB7 with 288k miles on it. He said it had a knock and it went away when he cut out cylinder number 2. All the rod and main bearings looked good for an engine with close to 300k on it. So we pulled the heads off and it has these black markings, they look uniform and they are in all the cylinders. Is it spray pattern from the injectors? We're thinking it has a knock from the injectors, he got new tips on them last year, I'm sure at one point the whole injectors were replaced as it has a lot of miles. Can you guys give me any input on these markings though? Thanks

[KB3MMX]

Originally Posted by elliottw

I'm rebuilding an LB7 with 288k miles on it. He said it had a knock and it went away when he cut out cylinder number 2. All the rod and main bearings looked good for an engine with close to 300k on it. So we pulled the heads off and it has these black markings, they look uniform and they are in all the cylinders. Is it spray pattern from the injectors? We're thinking it has a knock from the injectors, he got new tips on them last year, I'm sure at one point the whole injectors were replaced as it has a lot of miles. Can you guys give me any input on these markings though? Thanks

HAHA, nobody answered this yet ?????? !!!



Anyway, it's called Duramax "Leopard Spots".. It's a GOOD thing.

In the manufacture of the Duramax engine, a electronic inductive heating process is used to harden the upper portion of the cylinders...making them VERY strong.

[elliottw]

Awesome dude! Thanks, we were scratching our heads as to what they were lol

[Bluemm]

I am in the middle of changing my headgaskets and noticed these same marks. Now I know what they are.