Broke an Intake valve yesterday..............but WHY?

So, I had a great weekend at US60 and decided to race at my home track yesterday.  All was well and the car was backing up numbers all day.  Was driving up for 3rd round of eliminations when the motor started to make a helluva racket so I immediately turned it off and pushed it back to the pits.  Pulled the valve covers off and the number 7 intake rocker was loose and the valve spring was stuck down.  There is no unusual wear on any of the valve train and I'm almost at a loss as to why this happened. (Thank God it didn't happen at 7,000 RPMS).  My dad believes that possibly the alky dried out the guide and the valve hung open and smacked the piston.  

Also of note: this cylinder had a couple of gouge marks from flying debris but also appears to be cracked as well.  I'm assuming the crack is collateral damage and not a previous issue.  

looks like a deal similar to a friend's MoPar a few years ago. With fresh Indy heads and a brand new set of Ferrea valves, an intake valve broke off at the stem just like yours. We couldn't find any other obvious cause. Unfortunately for my friend, his occurred at about 6800 rpm. I think he saved the intake maninfold...and not much else.

Bummer...

Your car was working really well this weekend. Did you guys find out what's wrong with your dads car?

D. Sea wrote:Bummer...

Your car was working really well this weekend.   Did you guys find out what's wrong with your dads car?

Thank you.

Broke the cam pin. He's got one head off so far and there's one bent intake valve and 4 bent exhasut........

Usually, a valve bends then on the following revolutions it breaks; (it is now side loading the stem when on the seat and even at 1,000 RPM it is opening and closing at over 8 times per second) ... sometimes they do just break due to metal fatigue.

The cracked cylinder is most probably later damage from the broken valve head.

dang that sucks! Hopefully you can save the head.

cool40 wrote: dang that sucks! Hopefully you can save the head.

Charlie's got his work cut out for him for sure

Race Ready Fabrications wrote:My dad believes that possibly the alky dried out the guide and the valve hung open and smacked the piston.  

Do what?? What kind of guides do you have?

Real sorry to hear that ..
The Mustang is just awesum, and your dad's car is just plain cool.