With valve noise we assume that the sound is concentrated around the cylinder head of the engine. The valve themselves do not make the noise, it more likely that the sound comes from the camshaft chain. The Honda service manual writes that the cam chain should be inspected for wear and damage when unusual noise comes from the engine.
The problem is that the cam chain is not a easy to access service item and needs hours of work just to check if it is damaged or has signs of wear. Of course the official Honda service manual for the Honda CBR300R is pretty vague and it's up to the mechanic to identify what is a “unusual sound” and what is not.
Two identical motorcycles next to another with different air-filter will already sound different, and most owners of the Honda CBR300R also change the stock exhaust system…
But we're very confident that the problem is the cam chain or the cam chain guides that are the source of the problem.
Of course we never hear the original problem sound, we contact about most of the mechanics of the larger Honda dealers and ask them what would be a “Excessive Noise” from the engine….
So our chef mechanic (Thai) who worked for several manufacturers around the world, including names as Ducati, Aprilla, S&S and Kawasaki, called several mechanics from the dealer list and got very inconclusive nobody of all dealers and Honda service centers was able to describe what is “Excessive Noise” from the top-end (cylinder-head) in a uniform matter….
The only mechanic who made some sense was a mechanic from Honda BigWing Bangkok who said that “excessive noise” would also be detectable by unusable vibration… Wish is again something not specified in the Honda CBR300R Service Manual … so how can Honda tell dealers and service centers to look for extensive sound when they themselves are unable to specify that sound…