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YOUR RESEARCHPurpose of Spark Plug Tubes?
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Replace just one of those o-rings you'd have
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Suggestion · Original poster
The O-ring is a wear item that would wear differently from a valve cover gasket and if you had to replace just one of those O-rings you'd have to take the entire valve cover off.
Leading evidence: 'Replace just one of those o-rings you'd have' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Replace just one of those o-rings you'd have' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Replace plugs, tubes, coils and o-rings in my 1999 c2
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Suggestion · Original poster
I'm planning on replacing the plugs, tubes, coils and O-rings in my 1999 C2.
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Suggestion · Original poster
So the coil already has a rubber sheath that seems to run the length of the hole in the head that the spark plug goes into.
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Replace just one of those o-rings you'd have
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Suggestion · Original poster
The O-ring is a wear item that would wear differently from a valve cover gasket and if you had to replace just one of those O-rings you'd have to take the entire valve cover off.
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This is mostly out of curiosity but I'm trying to figure out what the spark plug tubes do. I'm planning on replacing the plugs, tubes, coils and O-rings in my 1999 C2. It's 20 years old and I don't want to have to get in there again.
So the coil already has a rubber sheath that seems to run the length of the hole in the head that the spark plug goes into. And then for some reason there is a plastic tube with O-rings around that. It seems redundant. Are there openings that would allow oil to seep out into the hole that the spark plug is installed into?
I don't get it. Why do you need a plastic tube and a rubber tube around the spark plug?
Keep in mind, these are "hemi" engines with hemispherical shaped combustion chambers, hence, the most efficient location for the spark plug is dead center of the combustion chamber and protruding through the valve cover.. If you remember seeing Chrysler "hemi" engines of the 1960's, they also had spark plugs in the center of the combustion chamber and protruding through the valve cover. Other combustion chamber designs have the spark plugs protruding out of the head off to the side, and not through the valve cover, think Chevy 350 small block. As mentioned by the previous poster, the spark plug tubes/O-rings insulate the inside from the outside without the coil/sheath, which is a high voltage electrical component, being bathed in oil having to perform that function. Also, with regard to your last sentence, remember that only the threaded half of the spark plug is inside the engine, the porcelain half is technically outside of the engine, although covered by the coil's rubber sheath. Its actually a beauty design if you think about it.
In short: They prevent oil from escaping the engine and also keeps air from entering. The crank case is under vacuum so the o-rings need to be tight to not mess with air/fuel mixture.
OK, after reading these and then looking at a cross section, I think I get it now.
Because the best place to put the spark plug is dead center in the chamber, the spark plug/coil assembly travels through the valve cover which is basically a hollow elongated dome like any other valve cover. Inside that you have the valve & cam assembly which needs oil. Porsche could have fabricated the tubes that the spark plugs go into as part of the valve cover (that's how I was originally picturing this in my head). But that would have probably been more expensive and they still have to have some sort of seal or O-ring on the bottom of that tube where it fits into the head (the connection that 993GT mentions). The O-ring is a wear item that would wear differently from a valve cover gasket and if you had to replace just one of those O-rings you'd have to take the entire valve cover off. So, they went with the tubes and O-rings which could be easily replaced one at a time.
Fun job, not. I just did this two days ago.
You don't change one oring, you change both the inner oring and the outer oring (even if only one is leaking) for each tube. While you are at it, the solenoid plate/seal ($20) should also be changed. You won't get to this that often so � while you are looking at it � change it.
Autoatlanta has the best prices. Plan ahead, order seals and plates before you get started. Or pay through the nose at the dealer.
FWIW the spark plug tubes were eliminated in 2002-on and became part of the aluminum cylinder head/valve cover. In case any 6.2 owners are reading this and wondering.
