Oil on spark plug threads
Oil on spark plug threads I have L92 heads and 3 of my spark plugs have a lot of oil on the threads (not on the tip). All of the other spark plug threads are perfect with zero oil. I have changed all 8 plugs a few times and it is still an issue. I am running a catch can set up and there is no oil being recirculated back into the intake. What do you think it is?
The plug pictured was the first one I pulled after running the fresh motor with no tune. All 8 tips looked black and awful. After running it for 200 miles with a better tune all 8 plugs have clean tips. However there is still the same quantity of oil on the threads of 3 plugs.
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Oil on the plugs has been a common theme for hot rods ive owned and they never burned any oil. I think its an assembly left over. It doesn't make any sense to me that the oil would be all over the threads and nut, if it was coming from the combustion chamber. Any oil in the combustion chamber would be burned, IF the plug wasn't fouled and missing. My engines with oil on the plugs like the OPs all ran very strong with no miss or skip.
Just been my observation over the years. OP, unless you start consuming oil or pick up a miss, I wouldn't worry about it.
Just been my observation over the years. OP, unless you start consuming oil or pick up a miss, I wouldn't worry about it.
It is not melted anti seize or oil from the build because I have changed the plugs at least 4 times during tuning and wiped out everything in the head I could with my finger. All the other plugs have 0 oil. The motor isn't burning an abnormal amount of oil and it runs strong. I am just scared to start shooting nitrous at it with 3 of the plugs looking like this.
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Joined: Dec 2012
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First I'd want to be sure there is no oil in the intake. If you've actually checked the effectiveness of your catch can then we can move past this step.
Second I'd look inside the combustion chamber with some type of borescope, rotating the engine so that the valves are open and perhaps you can see behind them... theory being that if oil is leaking down the valve guide you might be able to see it on the backside of the valve head. Don't know if this will be possible, but do know there are some small USB cameras out there that will fit in a spark plug hole, perhaps some with illumination on them as well.
At the very least pull the valve springs and closely examine the valve stem seals for damage.
Otherwise it's a pull the heads and have a look-see situation. Some LS7 guys have had oil-on-the-threads issue but later found good guides/seals, so the theory was it is in some cases coming in thru the PCV system into the combustion chamber and wicking up the threads.
Second I'd look inside the combustion chamber with some type of borescope, rotating the engine so that the valves are open and perhaps you can see behind them... theory being that if oil is leaking down the valve guide you might be able to see it on the backside of the valve head. Don't know if this will be possible, but do know there are some small USB cameras out there that will fit in a spark plug hole, perhaps some with illumination on them as well.
At the very least pull the valve springs and closely examine the valve stem seals for damage.
Otherwise it's a pull the heads and have a look-see situation. Some LS7 guys have had oil-on-the-threads issue but later found good guides/seals, so the theory was it is in some cases coming in thru the PCV system into the combustion chamber and wicking up the threads.
Sorry i havent updated this thread, i didnt have a chance to really work on the car until this week. My pcv system is removed. I have both valve covers hooked up to a remote catch can with a breather on top. It is effective and no oil gets in the intake. Even if oil did find its way into the intake, all of the plugs would have oil on them, not just three. I think we can eliminate that theory.
Logical explanation seems to be bad valve seals. I just performed a leak down test earlier and a cylinder with oil on spark plug had the same results as a good cylinder with no oil on spark plugs. I performed the test quickly on a cold motor, using 50 psi, and as close as I could get to TDC. I will try to perform the test again tomorrow more thoroughly but both cylinders being the same makes me believe the seals are ok.
Also, in my first post I said the oil is only on the threads but the tune is pretty clean now and there is still oil on 3 tips. So it's not just the threads.
Any one have any ideas? Also any tips on performing the leak down test? How to ensure TDC? Should I use 90-100 psi?
Logical explanation seems to be bad valve seals. I just performed a leak down test earlier and a cylinder with oil on spark plug had the same results as a good cylinder with no oil on spark plugs. I performed the test quickly on a cold motor, using 50 psi, and as close as I could get to TDC. I will try to perform the test again tomorrow more thoroughly but both cylinders being the same makes me believe the seals are ok.
Also, in my first post I said the oil is only on the threads but the tune is pretty clean now and there is still oil on 3 tips. So it's not just the threads.
Any one have any ideas? Also any tips on performing the leak down test? How to ensure TDC? Should I use 90-100 psi?
I just did the leak down test again with the engine warm using 82 psi (all the compressor would do). I tested #6 (oil on spark plug) and two good cylinders #4 and #2. All three cylinders were 82-71. I don't know what conclusion to draw from it.