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View Full Version : What is wrong with this intake valve?


Jesus_Freak
12-30-2009, 10:53 PM
I am in the middle of a minivan dilemma. I am pulling my intake (moderate headache) to get to and repair my valve cover gaskets. I noticed the circled intake valve spring with some discoloration near the top. What can cause this? Should I take any action while I am in? Thank you very much for any advice.

trickskier
12-30-2009, 10:58 PM
It's very hard to tell from that pic. I would suggest doing a compression test on all of the cylinders first.

DemolitionMan
12-30-2009, 11:05 PM
I would think that at one time the engine ran hot. Or maybe hot enough to burn that spring.

JimN
12-31-2009, 12:23 AM
Is there any way you can shoot one of more springs so we can see the difference more easily?

Jesus_Freak
12-31-2009, 08:39 AM
Yes, that picture was lame, but it was the only one I had at the time. Thank you all for your consideration. The largest difference between said valve spring and the others is the carbon crust. It is hard to see in these, b/c my garage lighting smells. The spring in question is located in the bottom right of the picture below.

Jesus_Freak
12-31-2009, 08:43 AM
In the picture below, it is in the upper RH corner. It is hard to see the differentiation. It looks here as though there is a general trend from light to dark from bottom to top. The camera lighting doesnt help the situation.

Jesus_Freak
12-31-2009, 08:45 AM
One more...Here it is in the bottom LH corner and is blurry :o. Again, the main difference is the minor buildup of carbon crust that caught my attention.

trickskier
12-31-2009, 08:53 AM
Looks like it could be caused by exhaust gas coming through a bad valve seat, valve guide, or possibly a burnt or cracked valve (hopefully not). Again, a compression test on all cylinders would be the first thing that I would do.

JimN
12-31-2009, 11:56 AM
I agree about it possibly being a bad valve seal or stem. If the valve stem is slightly bent, it will wear and will eventually allow exhaust gases to blow past it and the seal. If the intake is already off, it's halfway to not being a huge pain in the butt kind of job.

x-10ron
12-31-2009, 11:56 AM
first question would be how did it run before your pulled the v/c? a burnt valve would have a slight rough idle due the valve not seating. i would look at the v/c first before you condem anything, maybe thats where the pcv port on the v/c covers is at and you will get some discoloration in the area. if it was running good and no valve train noise i would not waste my time and worry about it. how may miles on are on the van?, where is the oil fill on the v/c cover? is it on top of that area?

Jesus_Freak
12-31-2009, 02:31 PM
first question would be how did it run before your pulled the v/c? a burnt valve would have a slight rough idle due the valve not seating. i would look at the v/c first before you condem anything, maybe thats where the pcv port on the v/c covers is at and you will get some discoloration in the area. if it was running good and no valve train noise i would not waste my time and worry about it. how may miles on are on the van?, where is the oil fill on the v/c cover? is it on top of that area?

Thank you all. Let me hit multiple things here:

1. I have not done a compression test yet. Given the fact that the intake is off (no place for fuel to go), how do you suggest I do this? I guess I could pull the fuse on the fuel pump before I begin to turn it over...

2. It ran fine before disassembly. The only reason I did was a nasty burning oil smell from v/c leakage that I could no longer stand. It has about 165,000 miles and has no problems. It gets the same mileage now as it has for years.

3. There is no oil fill or PCV entry near the suspect intake valve.

4. I considered the fact that the valve is bent or not seating before I started the thread; however, the valve is clean near the head and the van runs fine. How do gases leaking passed the valve seat discolor only the top of the spring? A leak so small that I cannot detect it during idle does not seem like it would have momentum enough to shoot up and only affect the top of the spring.?.? What am I not seeing clearly?

JimN
12-31-2009, 02:49 PM
1. I have not done a compression test yet. Given the fact that the intake is off (no place for fuel to go), how do you suggest I do this? I guess I could pull the fuse on the fuel pump before I begin to turn it over...

2. It ran fine before disassembly. The only reason I did was a nasty burning oil smell from v/c leakage that I could no longer stand. It has about 165,000 miles and has no problems. It gets the same mileage now as it has for years.

3. There is no oil fill or PCV entry near the suspect intake valve.

4. I considered the fact that the valve is bent or not seating before I started the thread; however, the valve is clean near the head and the van runs fine. How do gases leaking passed the valve seat discolor only the top of the spring? A leak so small that I cannot detect it during idle does not seem like it would have momentum enough to shoot up and only affect the top of the spring.?.? What am I not seeing clearly?

1) You don't want fuel to go into the cylinders when you do a compression test- you want it dry but it should also be done at normal operating temperature, so it's kind of a moot point. The pistons will draw air into the cylinders and when the valves close, the piston will compress the air and you'll see any anomalies at that time. If the valve guide leaks, you may hear it as a hiss near the stem and spring. You could rotate the crank manually to check this, too. I'm not sure I would crank it with the starter when the VC is off but you could do the compression test with the motor on a stand, if you had to. You would only need to have the intake on if you were testing vacuum.

4) When the piston is compressing the fuel/air charge, the pressure is fairly high but when combustion occurs, it's a lot higher. If that cylinder was collecting ash on the valve seat, it will eventually reach the stem, which can collect some and wear the guide, over time. If it runs well, it may not have any problems. Also, if the oil doesn't reach that spring directly when the motor runs, it will just bake the fumes onto the parts that tend to be drier than others.

Did you see any sludge on the inside of the valve cover at that valve? If not, I'm not sure I would be worried.

Jesus_Freak
12-31-2009, 03:45 PM
1) You don't want fuel to go into the cylinders when you do a compression test- you want it dry but it should also be done at normal operating temperature, so it's kind of a moot point. The pistons will draw air into the cylinders and when the valves close, the piston will compress the air and you'll see any anomalies at that time. If the valve guide leaks, you may hear it as a hiss near the stem and spring. You could rotate the crank manually to check this, too. I'm not sure I would crank it with the starter when the VC is off but you could do the compression test with the motor on a stand, if you had to. You would only need to have the intake on if you were testing vacuum.

4) When the piston is compressing the fuel/air charge, the pressure is fairly high but when combustion occurs, it's a lot higher. If that cylinder was collecting ash on the valve seat, it will eventually reach the stem, which can collect some and wear the guide, over time. If it runs well, it may not have any problems. Also, if the oil doesn't reach that spring directly when the motor runs, it will just bake the fumes onto the parts that tend to be drier than others.

Did you see any sludge on the inside of the valve cover at that valve? If not, I'm not sure I would be worried.

1. Agreed fully! I just didnt want the fuel spraying my face and/or under the hood. That was why I was thinking about what to do with the fuel pump.

4. Yes, nearly isentropic compression during the compression stroke and then p = complex f(T) during combustion. I just didnt think a small leak (too small to noticeably affect idle) would force garbage up to the top of the intake valve spring.

Based on your suggestion, JimN, I further inspected the v/c near said spring. The PCV gases are indeed directed to that area. The PCV hose connection is not near there, but it is baffled over to there. Therefore, it is a false alarm...just PCV trash. Feel a little embarrassed.

Thank you all for help.

TEAL98
01-02-2010, 02:58 AM
Very informative thread! Elaborated on very nicely by Jim!:)