HI Guys, currently working on a gsxr 750 and have found an odd problem on the engine, upon looking down the intakes i noticed what looked like notching on a valve and decided to instigate, i found 6 of 8 intake valves are scored around the valve, looks to me like someone turned it in a drill against a file. two valves are unharmed and they oddly both share a port with a damaged valve so im unsure of the cause,

The head will be replaced anyhow but id like to find out what caused this issue, i have attached an image for anyone who thinks they may have an idea. i would have assumed guides but its too low on the stem.

any help appreciated