Early busas had very weak valve springs. With the updated Yosh profile, you could have been getting "bounce" which will hammer the valve faces.
Put some
good valves in it, and some
good valve springs and you should be good to go.
Jay's right -
If you run higher lift cams, rev it too high (for the cam and springs) and the springs are not strong enough, the peak (nose) of the cam will launch the valve further than the lift of the cam.
Then, the cam still rotates, the valve begins to close, but it never quite catches up to the cam profile.
The springs do close the valve, but when the valve hits the valve seat, it bounces a bit and ends up hitting the valve seat many times before it stays closed.
When that happens, the valve face gets peened (hammer tap) in and and the valve "face" depresses - letting the valve sink deeper int the valve seat - and - reducing your cam/valve clearance.
Your mechanic can catch that by noticing that your valve clearance gets less every time he checks it.
Another way to catch valve float is to inspect the bottoms of the valve spring, where they go into the head -
If you are close to valve float and valve seat "pounding", but not quite there (maybe 100 - 200 rpm shy of float), you'll see the face of the spring getting smooth and polished. That's a warning that your springs are right at the bad edge of valve control.
In racing setups, we would spend a couple hours matching and hand prepping each set of 16 - 20 springs.
Titanium valves are pretty soft and prone to pretty quick damage if they "float". "Stellite" faced steel valves are heavier but def. tougher.
Your Yosh cams, with some Yosh springs and new valves and valve guide seals should be just fine.
I only use Japanese "kit" springs in the Japanese bikes - They usually weigh a bit more, but, you rarely have to worry about them breaking, even in race use.
Word to the wise - don't skimp on valve springs - don't buy the cheapest brand. From the Road to Enlightenment... buy the Yosh springs..... :-)
As far as the stronger spring rate of the race springs, yes - there is more tappet / camshaft pressure, but the I've had a fair number of Suzuki's with Yosh or Megacycle cams and springs running around for years without trouble.
Higher spring pressure does not increase valve seat wear. We used to run even .020"/.5mm wide full width valve seats and full radius valve jobs with just a "line' for a seat and the valves and seats stayed fine - as long as we didn't get valve float.
So - it's not the seat pressure that hurts seats and valves - it's the valves bouncing.
On the other hand, I've had a gsxr1100 with some cheap valve springs come in with 8 broken valve springs after 2 years.
I think that "valve head thickness" that he was talking about is called the valve "margin".
Best regards,
Marc