It’s very rare for an intake valve to “just break”....... without some sort of help.
Look everything over carefully when you pull it apart.
The last broken intake valve I can think of was in a 452 head.
That motor was running an aggressive SFT cam with 1.6 rockers.
The actual failure that resulted in the broken valve was the tangs got sheered off the locks from the valve hammering shut repeatedly.
The locks had actually worked there way towards the top of the valve, and the roller wheel from the rocker had pounded a trough into the top of the locks.
When the tangs finally let go, the valve slid down the guide, the piston whacked it, and then the head of the valve snapped off.
The cause of the valve hammering shut and pounding the locks into oblivion was that the spring had died.
Only that one spring was dead........ down like 30-40lbs.
The other 15 tested within a few pounds of new.
Why that one spring died was the unanswered question on that failure.
The valve stem is still attached and the keeper still holding retainer. With the spring pulled tight. The head is off and there is a hole in the piston luckily it didn't scar up the cylinder. The head of the valve is wedged in the port and the guide is cracked, the exhaust valve looks to be bent also. The chamber and seat is scarred up.
