I recently noticed a tapping noise coming from my OM617 at certain RPMs and tracked it down to the valve rockers. You make a loud metallic tap when wiggling the rocker between the cap nut and the cam lobe - specifically on the exhaust valves. I double checked the clearance and they are spot on at 0.35mm (just talking exhaust since intake clearance is too small to make this noise). Is it normal for the rockers to make this noise with the factory suggested clearance? Does anyone else hear that noice when their engine is at certain RPMs?
Here's a video demonstrating what I'm talking about. I'm curious to know your thoughts and suggestions.
https://www.youtube.com/watch?v=dD8kRzXzjVs