is it only the CRF 250 with valves issues?

i've also got an 04 crf250r and havent had any valve issues at all.

all 4 strokes have valve "issues" if not properly maintained. Keep them adjusted to specs and when they finally need replacing go with a good quality set of stainless such as Kibblewhites

Stainless valves last a lot longer than titanium. I believe honda put them valves in to stop customers from coming in with broke rods. If your brothers head has been shimmed more than 3 sizes from stock, likely the piston is at its service limit also. And the rings went south some time ago. In my opinion the only thing the 250f has in common with the 125 is maintenance schedules. Hours on an engine is still hours of wear.

Follow the maintenance guidelines in the owner's manual and you shouldn't have problems. Just as was said before, pretty much and "new age" four stoke that uses shim under bucket technology and titanium valves will have "problems" if the valves are not maintained properly. You can only adjust/shim the valves for so long before they need to be replaced. Check the owner's manual for replacment guidelines. I have a 05 CRF250R and have had no "problems" with the valves. I check them about once a month and adjust as necessary. I replaced the intakes about a year ago while replacing the topend. Just a note the exhaust valves on my 05 were already stainless from the factory. If you do decide to go with Kibble White or other aftermarket stainless valves, it may be necessary to replace valve springs, retainers and valves seats as the new stainless valves will be heavier and need more spring to keep them moving as fast as the lighter titanium and the seats may take more of a pounding with the increased spring tension. I use factory stuff and just take care of it.

I have a few friends who had '04 CRF250's and the intake valves tightened over time (like after 2+ years). Just keep an eye on the clearances every 10 hours or so, and if they tighten, just drop in smaller shims. If you reshim 2-3 times, then you are usually due for new valves/springs. You'll have to check the valve clearances regularly on any 4-stroke MX'er. It's not very difficult, and only takes about 30-45 minutes to check.

I have an '06 CRF250 which I have raced for 2 years, and the valves are still in spec, never been reshimmed.