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I think youre thinking too much. Theyre not hard on these bikes. For reference i run a HC piston and aftermarket cams with stainless steel valves in both of my bikes with no reliability issues or concerns. Theres many other examples of this without issues. Cams, HC piston, and an ecu tune is considered a mild build.

We installed an RHC cam and spring kit , 13.8 or 14.1 JE Piston , .05 Cometic copper base gasket in my sons 13 Crf250r . I installed at 50 hours from new if my memory serves me correct. I was a little concerned about valve life at this point . However , we then proceeded to put another 50 hours on the motor package . Those hours were very hard race / practice hours . Son was a fast Nov/ Inter In SoCal Moto /Off road etc. When I pulled the motor apart it was in excellent shape and...

twisted proven pc c4mx xpr all make great stuff, if it was me id talk to frenchie at c4mx, hes huge on making insanely fast easy to ride setups

New valve seat and guide material is the key to long lasting performance, along with a properly built crank. Id go with a new rod, have Crankworks assemble, true and balance(to OEM spec). Stock valves are more than fine once you have valve seat and guide material that doesn't beat them to death (iron seats on titanium = valve death) Pro1 racing in tempe(down the road from crankworks) can install new seats and guides made of MOLDSTAR90, which not only makes your valves live longer, but has better heat transfer and seal than an iron seat. Once the crank and...

Take the head to Jaime at TD if you’re have the vortex done. He did a great job on my KTM, decked the head, cut the seats and CNC port.

Head mods can definitely make a bike "feel" different. Typical head mods involve modifying and reshaping the intake and exhaust ports (and/or valve seats) to change and improve the airflow through the head. If you just want to make more horsepower, you can usually grind and reshape the ports so that they are bigger and flow more air at higher rpm's. The downside to this is that it doesn't flow air as efficiently at the lower rpm's, which leads to a "lazy" feeling at lower rpm's and when rolling on the throttle, but as rpm's increase, the power ramps up...

The valves are probably bent. Similar thing happened to a buddies yzf250, except they put the piston in backwards. Valves hit the piston for a few seconds, they tore it back down and turned the piston around. Bike ran great for 2 entire months of riding every weekend, then it seized right up. The valves had actually broken in half and dropped into the cylinder. It was a 18 yzf and the reverse engine had confused them. They had no idea the valves bent after the initial run

Bent valves allow an excessive amount of oil to leak past the valve guides. All the oil from your cam area is leaking into the cylinder. You should be able to confirm this with a leak down test. Did you check the cylinder diameters and ring gap or did you slap the top end together without inspecting it?