Welll this is new...

Well iv been doing this car thing since 1997... But this?! This is ... Umm... "New".

Anyone seen this before?

10 points if you have.

That IS weird, I've never seen it before, and no idea what may have caused it.

Anyone?

My hypothesis is the ring thickness on this engine is incorrect causing a flutter of some kind.

I looked it up and found out it is refered as « Leopard Spots », and these are a result of the GM Duramax induction hardening process. There is a GM bulletin that says it is normal. Here’s the link : https://static.nhtsa.gov/odi/tsbs/2014/MC-10138697-9999.pdf

Explanation at the end of page 2, and picture on page 5.

I also found out that other manufacturers uses induction hardening and these marks were visible too.

Edit : Looks like it could be laser honing as well?

https://www.gehring-group.com/sites/default/files/text/laserhone_en-en-ww.pdf

But I’m not sure how the honing process could create these marks. Maybe they were heat treated and then laser honed after.

Thank you for sharing this!

It's often said that engine builders only have two responses to issues: "I've never seen this before" or "they all do that". This discussion just went from one to the other, and I found that amusing!

Hahaha I’ve never thought about this but that is so true!!!

it's pretty cool, I have never seen it before but I want it hahaha where do I buy it from and will it be available from my local machine shop soon.

What's the engine ? does anything measure different, as above I would think it is a heat treatment of some sort but I would like to know more about why it is done this way

Ah leopard spotting. Thanks now i know also.

This was 1998 4m40T in the Pajero @200 000km ODO. it has low compression and overheating and uses water we pulled the head and saw water jacket on cyl 2 breached. Anyway i digress.

And i agree with Mr Ferguson.

Im just overlooking the other aspects of the engine also making sure it is all as it should be. Figured it is better to suspect a problem and confirmbthat its nothing than suspect it is nothing to justbbe suprised at the problem. Prevention is better than repair.

Thanks to everyone for the input. It is really appreciated