R1_Pilot

There is like carbon buildup between the valve and the valve seat and it does not close all the way ... it will not seal. You just have to reseat them.
It usually happens on the exhaust valves.

J

crank

ahhh, very cool! time for a lapping lol ?

drhess06259

If it is a burnt valve is there a way to fit it without pulling the head? I don't belive in the bottle of cleaners type stuff but that is all I can think of off the top of my head to clean valves

R1_Pilot

If its a burnt valve you pretty much have to remove the head.

J

RedY2KS2k

Almost exclusively on exhaust valves:

When an intake valve opens air at near ambient temperature (and fuel droplets that will evaporate and cool the valve further if you have port injection rather than direct injection) flow across the back of the valve head, and cool it.

When the exhaust valve opens, extremely hot combustion gasses flow over the valve seat and across the back of the valve head. That valve head needs to transfer heat to its seat in the head, and hence to the head's water jacket then to the radiator.

And this process can be self-destructive. If the valve or seat burns enough that it doesn't seal, then hot exhaust gasses flow over the back side of the valve before it opens. Now it has more heat to transfer, but imperfect contact surfaces so it transfers the heat inefficiently. It gets worse until the valve head burns so badly that a piece falls off. Then it really gets your attention. #3 exhaust killed more air-cooled VW engines (the oil cooler blocked some of the cooling air to the head at #3) than all other causes combined.

R1_Pilot is correct: if the valve and/or its seat is burned, the head has to go to the machine shop.

And with 30k miles on a boosted engine, I still vote burned valve.