On my EVO I discovered the source of a mysterious oil leak and thought I'd pass on what I found!
My EVO is a true daily driver and has more than 140k miles on the clock. trying to find the source of an oil leak on the oil pump side led to this discovery as the source. (initial diagnosis was a pump going bad)
The oil pump timing belt gear had a groove wore in it where the oil pump shaft seal rides. This was a real B!tch to diagnose as you can't really see down into the back of the gear. I found it by dragging one of my small seal picks across the face and felt the groove, I then used a small inspection mirror to verify! Sure enough there is a significant groove that was worn into the sealing surface of the gear!
I've rebuilt lots of 4g63 engines and almost routinely just re-used the same timing belt gear! I will definitely check them going forward.
