Orange Pistons

[Signature620]

I've got the head off of a cm871 because it has a leaking #4 injector sleeve. It's done 900,000km. Spent most of it's life deleted but has had a variety of cals through it. The last 1.5 years it's had a 600hp cal with safe timing and a Holset HX60 fitted. Everything has been fine until the fuel/coolant cross contamination.

Upon removing the head, I notice the rear 3 pistons are orange when wiped and the front 3 are just covered in a light carbon. It runs rough intermittently at idle but fine at any other speed.

Timing actuator perhaps???