I pulled my head this week to do a new big bore kit and found one intake valve that didnt look healthy. All the valves, including the bad one, were in spec and had never needed to be shimmed since new. I cant seem to figure out what would kill just one valve. One would think that atleast 2 would be damaged and there would be cylinder damage but that is not the case.....curious to what you guys might think. The machine shop, Mongoose, has no idea eithe




valve shown with other intake valve



backside of valves

my only guess was an issue with the manufacturing of that one valve.. or there is an issue with the seat that's causing the valve destruction. How ever for the most part the valves do not rotate atleast not to that degree of destruction that I'm aware of..

I think you might be right. I'm very doubtful it was a foreign object that caused the damage. The machine shop said the seats had normal wear but nothing unusual. I'm not very experienced with mx motors but would there be blueing on these little valves from heat damage?

If you look closely at the bad valve on the last picture you can see there is a chunk on the edge that is almost ready to fall out.....good thing I pulled this head. Could have been worse.

I have never seen that happen.

Just taken the head off my 08 and seen exaclty the same damage on one of my intake valves!! the valve clearence on this valve has suddenly closed up, so i expect the valve seat is nakard  ... does anyone know what could have caused this type of wear??

Looks like a metallurgical or manufacturing defect in the valve. From what I can see in the pictures, they look like clean breaks, not from an outside force. Strange alright.

chipped valve = dirt in engine and or exccesive carbon deposits.

seen this a few times on cars that done get air filters changed.