Life Span of Valves

SO, coupla weeks ago, had some problems at the track.  Gave away another race due to breakage.
According to the tell tale on the tach, it never saw 6300 rpm.  
I've been running these A-heads for about 8 yrs, is there an "end of life" expectancy for valves ?  OR just this one  ?

No they don't last forever......

Sounds like about 8 years................ Sorry couldn't help myself, it's I've been around the Coug to long.

An intake valve broke so I would be really looking at the valvetrain especially the springs.  What do the keepers on the other valves look like?  Are they all polished up from "fretting"? Sometimes too a valve can be very slightly bent then each time it closes the spring forces it against the seat and it flexes it back and forth. Over time the fatigue breaks the stem.

This is one thing I would like to understand. The possible causes of valve failure other than piston to valve contact. Could a weak or broken valve spring caused it?

jones wrote:This is one thing I would like to understand. The possible causes of valve failure other than piston to valve contact. Could a weak or broken valve spring caused it?

absolutely ! A weak spring allows the valve to bounce on the seat which is far worse than high spring psi. Not saying this is the case here .........

Far too many guys rely on "buzz words" . There is quality stainless material and then there is stainless material. Some guys only hear "stainless" and feel good about it. Just like the word forged. Some builders cycle them out by hours , others by laps or miles , and others by "seasons". Most stainless valves are made in Brazil or China , but some are still made here. Manley and Ferrea offer some excellent valves.

Thankx for the comments and suggestions. The valves were the ones originally supplied with the heads. Ya, they've been thru a valve job, or two.
I really shouldn't bitch, and i'm not, it's just racing.
The springs were new at the beginning of the season, i'd havta check the log book to see how many runs actually.
When the covers were pulled, all the stems were in place, no broken springs. Just .250+" of lash on #7 Intake.
Like Blake says, this one was only good for 8 years. Must be kinda like rear gears, mine are only good for 2 years. Another hard lesson !