i mentioned your engine issue to my mitsu guru and his response:
Very odd. I have to wonder if they did porting on the oil pressure bypass? Second I'd look at the cylinder walls and make sure a piston pin hasn't walked (uncommon but I've seen it). Another thing is the balance shaft delete. If they didn't use the oenophile 1.6 style stub shaft it can cause issues. The oem style has and oiling groove the knock offs don't have.