? What causes a damaged TURBO exhaust valve?

[Craig 930 RS]

Appears that the #3 exhaust valve has major leakage through the exhaust valve



What typically can cause this? Valves were adjusted properly.
Ideas.......?

[javadog]

Well, it would be helpful to actually examine the valve but usually they either get too hot or hit something.

The overheated condition can come from inadequate heat transfer to the seat because something held it off of the seat (carbon, lack of proper clearance); or the guide is worn enough that heat can't flow from the stem to the guide; or perhaps the mixture was a little too lean in that cylinder and it ran a little (or a lot) hotter.

The impact damage scenario would involve Mr. Piston. Either we revved it too high, a bad valve spring was involved or the clearance was insufficient when the motor was built.

You shall see, when it comes out. 'Tis a real bummer.

JR

[david.avery]

Craig, is it possibly stuck on some carbon? My old 84 930 had bad leak down figures once until an italian tune-up.

[greglepore]

Well, it could be any of the above. It could be carbon, but on a highly mod'd 930 with serious track usage, I'd suspect anything from a lean condition in that cyl that burned the valve or a mechanical overrev on a downshift that just barely nicked the valve due to float. I'm discounting the carbon b/c the way your car is driven its not particularly likely.No real way to tell until you determine why the valve isn't sealing, then work backwards from there. Good argument for a cht gauge, if you don't have one already.

[ruf-porsche]

try a borescope to take a peek