While I had the valve springs and seals off I also polished each of the exhaust valve stems where they stick out of the valve guide with 600 emery paper to add a bit of a hone pattern to the valve stem to retain some oil and carry it past the seal. The finish is pretty fine but should help with oil retention on the stem and into the guide.
Hmmmmm, not sure that was a good idea. What's to stop that from "honing" the inside of the seal? In the same way that an abraded fork tube is the demise of most fork seals, don't you think this might destroy the sealing surface of the valve seals over time? 600 grit isn't for polishing, 2000 grit is. Yamaha already re-engineered it...why go farther?
Just my thoughts,
I understand your concern. Same thing I thought about, too.
The valve stem is chrome plated. 600 wet/dry with the light contact "honing" or polishing I did didn't really change the surface of the valve stem much. Hopefully just enough to carry a little more oil past the stem seals. If the stem seals get eaten up....well....I know how to change them without taking the motor apart, don't I?? LOL
Chrome valve stems are commonly buffed anyway at the valve manufacturer. Chrome plating valve stem has a hidden hazard of leaving chrome nodules on the surface of the valve stem. They are invisible but are as aggressive as a file in eating up valve guides. Stems are robotically buffed or honed to eliminate the possibility of chrome nodules so most chromed valve stems have a surface finish like this anyway. If the supplier thinks their chroming process is in control they may skip the honing or buffing process and "take a chance". I looked at the Yamaha valve stems under an SEM and they do not look like they were buffed. I was looking for the chrome nodules as a suspect for the tick problem but didn't find any evidence of them.
As far as the polishing I did causing a problem it is very very low risk. Creating a high spot on the surface will cause wear and tearing up a seal. Creating low spots in the surface (like the polishing with the 600) will just carry oil. Low spots are usually fine. High spots are what you want to avoid. That is why you can take a nicked fork tube and polish it with 600 (to remove the high spots) and it will still work fine.
I have a Honda CBX from 1979. Those bikes were notorious for eating up fork seals. They would only run about 8000 miles and start to leak. The cure is to take the fork tubes apart and thoroughly polish them with 600. My fork seal like went from 8000 miles to at least 30,000 as that is how many miles on the seals in the bike now with no leaks. The surface was "too smooth" to retain oil and the seals were working dry and would tear up.
As far as re-thinking Yamaha's "engineering".... Two responses. One, their engineering has proven to lead to tickers. I'll trust my own engineering at this point as I have a bit of experience in that area myself. Quite a bit in fact. Secondly, You telling me this is like the pot calling the kettle black. LOL. If Yamaha's engineering was so good why did you rip your forks out and sent them to be modified, or change tires, or change shocks, or change seats, or ???, or ???. LOL. Seriously, I suspect they missed something with the valve stem seal performance. Unusual but true. They may have gone with their conventional wisdom from other engines and ended up picking too dry of a seal or maybe the valve stem surface finish changed and they didn't realize it, or ???? Shit happens. React to it.
BTW. When I had my forks apart I took the damper rod that looks like a normal steel rod. Polished the heck out of it with 600. Looks shiny like chrome now. Should help the new damper rod seals I installed seal better and have less friction. 600 will definitely polish. Depends on what you are polishing.