150R Head Problems?

First off my 150r has about 24 race hours on the engine and more than that in practice hours, I’d say at lease 50plus hours total. I replaced the piston with a new stock unit at about 20 hours everything looked good no unusual wear at all; the black coating on the skirts was still there. I checked valves about every 8 hours. Its never been run hot and oil is changed regularly. The last time I checked the valves the right side intake valve had closed up. So I reshimed it, I went from about a 175 to about 150 shim to get it back to spec. I knew the face had to be going away so I ordered new valves and also ordered anew wiseco piston. Yesterday, I tore it down to swap in all my new goodies. Installed the new piston and rings and slid the cylinder back on so far so good. Removed the valves from the head and cleaned the head up that’s when I saw a problem, the intake seats appear to be deteriorating. Just a small spot on both intake seats toward the center of the head maybe about 8mm’s wide and maybe .5 to .75 mm’s deep. Just beginning to get down where the valve face seats but not into it yet. But it’s like the seats are crumbling. Exhaust side of the head looks fine no visual problems with valves or seats. Can these seats be replaced? My service manual makes no mention of replacing the valve seats nor does the micro fiche show the seats separated from the head. Right now it looks like I need to just buy a new head. Does anybody know if this can be fixed for a reasonable price? The new head from Honda is just under 200 bucks that doesn’t seem too bad for the number of hours that’s on the bike. In the future is this something that can be prevented or should I look for this at 50 to 60 hours run time?

I checked my springs, service limit is 37.4mm I am at 37.8mm and the new ones check 38.00. Exhaust the same way down about .2 but not near limit. I called Kibblewhite about the valves they don't have them yet. Should have them in 1-2 weeks.

I got my 150R back together. New head, new valves, new springs and a wiseco piston. All Honda OEM parts. I would like to have gone with Kibblewhite valves and springs but I had to go with my small pocket book. Problem was I had already bought Honda valves and springs a few weeks back with intentions of changing them out when I was changing the piston. But then found the damage to the intake seats and had to get a head. My son will be moving up to a 250 after this season is over so I figure I will only need to put maybe 20 to 25 hours on the 150R. So it should do that easily. I will however take Rich’s advice and go with the Kibblewhite valves first thing on the 250 and maybe head off some problems.

That's a good idea. Thanks for the advise. It's a learning curve with these new high revving 4-stokes all this info helps out alot. All in all I'm very happy with way its preformed this year.

I got my 150r back together with new head and valves and springs also installed the wiseco 12.2 comp piston. My son got to race it this weekend and it performed great.
He said it had a lot more snap out of the corners than before, he really liked it. I just wonder if the piston made that much difference or it might just be that everything is new.