What puts the valves out of clearance?? (Cyber?)

[mx916]

Just curious as to what drives the valves out of proper clearance.
I recently did mine at 14,000 miles and found only 1 exaust valve slightly out of spec. (tight). I never redline my bike or abuse it in any way. Is that why my valves were so close to spec?? Do bikes ridden hard tend to go out of spec more often?? Thanks for input. (Cyber, please jump in on this!)

[Black_peter]

Re: What puts the valves out of clearance?? (Cyber?)

Do bikes ridden hard tend to go out of spec more often??

Yes.. hard driven engines live hard lives..

The valve train wears. The valves fit tighter into thier seats..
The adjusters go out of adjustment..

As the cams rub against the lifters and the lifters rub on the valves these parts are bound to wear. The key is to get the right parts to wear..
(Not the cams!!) so as these parts wear (actualy get smaller)
the cam is no longer opening the valve the same amount as when new.
Here you have "loose" valves..
So the engine is not performing at peak performance.
Valves can also sit deeper into the seats in the head..
They can naturally "snuggle in" or due to poor tuning
burn slightly and get smaller..
This in effect makes the valve longer and you get "tight" valves.
This could lead to the valve not closing all the way and leaking by..
So the engine is not performing at peak performance...
It is also important that the valve train parts remain in good relitive contact (at least when warm) sloppy parts wear faster.

[The CyberPoet]

Black_Peter hit the most basic reason right on head: metal wear from repeated abrasion/impacts. Wear on the valve guides, the springs, the tappets as well as the valve stems, cams and seats. And since all metals are not perfectly equal in metal composition (although usually very close these days), one valve's stem may wear at a faster rate than another -- ditto on all the other moving parts.

There are other lesser reasons, including:
For nut-adjuster type valves, vibration actually moving the adjuster nut slightly over time (normally only if the nut wasn't tightened properly).
Carbon or sulfated-ash build-up at the valve seat or valve lip.
Minor bends in the valve stems (ones small enough not to be visible nor problematic in general) because some carbon build-up or metal shaving got trapped between the valve and the valve seat or valve stem and the cam temporarily, so the movement acted like a hammer to bend the valve stem minorly to compensate.
wear at the cam bearings and journals, as well as the cam retainers.
thermal metal fatigue at the valve face (exposed to the heat & compression pressure of combustion continuously), so a few atoms' worth are lost each combustion event.

KNOW THIS:
OEM Valves for Katana engines are generally pretty cheap, $20 for intake and $30 for an exhaust valve. Why the price difference? Because the exhaust valves have to be made out of tougher, more thermally capable metals, since they don't get cooled by the inrushing fresh fuel-air charge, while the intake valves do...

Cheers
=-= The CyberPoet