Burnt Valve?

[mdazb]

Hello, Per the dealer, I have a burnt valve in my #2 cylinder of my 2000 4runner 2.7. Did a compression check myself, all cylinders are good but the #2 only shows 90 compared to 150 in the other 3. My motor has 130,000 miles. Anything else I can do before I yank the head. A friend was telling to check the valve/cam shims?
Any help would be great.
Thanks

[Brian R.]

Do a blow-down test where you put some comrpessed air into the spark plug hole and see where it comes out. They should have done that to determine it was a burned exhaust valve, but you never know.

[mdazb]

Thanks for the reply,

Okay I did do the test with the compressed air this afternoon. Made sure all four lifters were up. When I applied the air, the cams turned to the point where the intake valves were now open. I'm thinking the valves are fine maybe just the lash adjusted with shims. Can't get a feeler gauge under any of theme for that cylinder. What are your thoughts?

[Brian R.]

There is a weak point in the compression and you have to make sure you've found it. Redo the blow down with keeping the crank from turning with all the valves closed and not so high a pressure. Make sure you have determined where the gas is going.

[mdazb]

Okay I'll try that tomorrow. Thanks for the help.

[mdazb]

Question, If the valve WAS burnt enough to cause the low compression and the engine light to come on, wouldn't the air escape regardless of the pressure applied?

[Brian R.]

I was suggesting the lower pressure just to make holding the crank easier. The higher the pressure, the easier it would be to detect the point of leakage.

[mdazb]

Did the test again with not as much pressure. I hear it somewhere, can't pin point it. Sounds like its coming from the timing chain galley. Again if i give a little more pressure to it, it wants to turn the cams. I'm assuming if the valves are okay, the cylinder would fill with air and hold?

[Brian R.]

Originally Posted by mdazb

I'm assuming if the valves are okay, the cylinder would fill with air and hold?

Only if the rings and cylinder walls are ok. If the air doesn't come out the exhaust or the throttle body, it is coming past the rings. To detect the air leaking past the rings, listen to the oil filler cap hole.

Repeat the standard compression test with the engine at operating temperature, then add a squirt of oil through the #2 spark plug hole and repeat. If it's a ring or cylinder wall problem, the compression should increase.

From your description, the blow down test indicates a cylinder sealing problem, not a valve. It's not conclusive unless you listened to the exhaust and throttle body to eliminate them.

[mdazb]

did a wet compression test in cyl.#2 no change. Still 90. Ended up pulling the head. Found 1 exhaust valve bad.

Thanks for all your help bro...

[Brian R.]

You're welcome. I guess a bad valve was the cheapest of the possble problems you could have found.