My 03 996 has had a major failure and I'm trying to find anyone who has seen anything like this happen before. Under very low idle and speed I heard a metallic "clang" noise from the motor and then it died and would not restart. Had it towed to the shop where they had to drop the motor and pull off the 1-3 head to find the problem. One of the intake valve seat rings on the #3 cylinder popped out and caused damage to the head and top of the piston. My mechanic, very knowledgeable and reputable, says he's never seen this happen on one of these engines. I've posted to two other forums and have yet to find anyone who has ever seen this before.

Here you can see the missing valve seat ring and the damage done to the head when it came out. I had my mechanic remove the other valve for comparison.



Different angle...


View of damaged piston..

 

Wow...sorry about the damage!

I inserted the photos for you so people wouldn't have to open another window.

bob

 

Thanks! Don't know what I did wrong but it wouldn't work for me.

 

Bummer. Valve seat came unseated. head and piston damage, maybe cylinder sleave, maybe metal fragments in the oil caused other damage?

 

Didn't happen on my P-car, but I had a similar problem on my inline 6 L series Datsun 240z motor about a year after the heads were rebuilt, though the seat never complete dislodge, it pop out half-way. Needless to say I brought it to another shop to have head rebuilt, and they guessed the previous machine shop grounded down the seats too much so it lost rigidity.. but who really not entire sure how it happened..

Good luck with your repair.

 

Thankfully there appears to be no cylinder wall damage and when they drained the oil there was no metal so I think the damage is pretty contained. My mechanic also said it didn't look like the engine had ever been apart before so no previous work caused the issue.

 

You're sure there was no mechanical over-rev just before this event?

I could see two scenerios.

1) happened just like your mechanic sated. Valve seat came loose, stuck the valve open it contacted the piston then distruction.

2) Over-rev, valve hits piston, valve comes apart and in the process takes the valve seat with it.

Luckily the cylinder walls do actually still look good from those photos.

 

No over-rev. I had just driven home from work and was pulling into the garage when this happened. My mechanic builds/rebuilds Porsche racing engines and said he's never even seen this happen to one of them.

 

Sorry to hear ...

 

Possibly a clogged coolant passage in head causing hot spot....Abnormal expansion of this area of the aluminum cylinder head causing valve seat to "fall out". if the head is salvageable,definitely have the head thoroughly inspected and carefully checked before reassembly.

 

Interesting theory Fleet Z. I will ask my mechanic about that. Thanks.

 

I have seen this on older 911's (1970's), 356's, and 914 type IV motors, some heads are more suseptible than others, and then sometimes THINGS JUST HAPPEN. Perhaps the head or seat was ever-so slightly out of tollerance when assembled; in this scenario I would think the seat would be more likely to be out of tollerance then he head, but then again, hard to actually suggest one over the other. Anyways, not a whole lot of damage, so I'm happy for you. I have seen spark plugs in other motors installed without crush-washer spacer and the tip is hit by the piston and brearks off. It's funny that even one tiny little piece of metal bouncing around in there makes it sound like a BASS DRUM Amazing.