Oil leaking into spark plug holes

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Oil is leaking into my spark plug holes!
or,
My spark plugs have oil on them, but I'm not burning oil!
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Oil is leaking into your spark plug holes from the valve chamber. It's not a good idea to leave the oil in the spark plug holes, as it can pool high enough to damage the rubber boots of your spark plug wires, will make the plug hole really messy, and it may eventually become a fire hazard. Below is how to fix it.

Honda's preferred spark plug location means that the plugs (and their wires) must pass through deep recesses in the top of the valve covers to get to the combustion chamber. This gives better plug placement in the combustion chamber, and more zoom for your Honda. It creates a small problem though: Under the valve cover, all around the spark plug recesses, is an open space that is constantly being showered with oil, and that oil will get into the spark plug recesses unless something is done to keep it out. Honda does this by sealing any joins between parts with little rubber donuts (AKA "grommets").

The rubber donuts eventually get old and stop sealing, letting oil seep into the spark plug holes and puddle there. The cure is replacement of all four (or six), along with the valve cover gasket itself (themselves) at the same time. It's an easy project for anyone who's done more than just oil changes.

However, there's a fly in the ointment here: Certain Honda engines, specifically the 4-valve-per-cylinder, single-overhead-cam ones (such as the D15B that's used in many Civics), have an additional rubber seal under the one I just mentioned! This one also gets old and starts leaking, but these are a LOT harder to replace! Not a job for a beginner!

NOTE: The rubber parts under discussion here are not actually red and orange, they're black, I just used colors to make it clearer which was what.

Here's a typical D15B head assembly. It's complete except the valve cover has been removed.

The red lines show the locations of the rubber gasket and donuts that will be exposed once you remove the valve cover. These should be replaced every few years to forestall the possibility of leaks. The spark plugs pass through the donut holes on their way to the combustion chamber.

These are easy to replace.

Just don't overtorque the valve cover nuts!! 7 ft lbs, no more!!

Here's an exploded view of the D15B. I've simplified this schematic so as to leave only what's necessary to understand where these rubber thingies are. (The view is from the left-hand door of the vehicle, looking forwards, opposite of the schematic above. The timing belt pulley would be to the left if it were in this graphic.)

The rocker arm assembly consists of many, many parts, all held loosely together by many long bolts (two are shown in position at left). The camshaft is in the middle, under the rocker shafts. The three shafts form an upside-down triangle, with the point facing downwards. On each rocker shaft are the valve lifters, fanning outwards from the cam in order to reach the valve tops. In this manner, Honda achieves 4 valves per cylinder, but avoids the expense of two camshafts.

The red circles show the position of the rubber donuts that you install at the same time as the valve cover gasket. The orange circles, (called "O-rings" in this diagram) on the other hand, require that you unbolt the entire rocker arm assembly and lift it off. Once the rocker arm assembly is off, you can then pick out the O-rings and replace with new and your leak will stop.

Apparently the rocker assembly can be stuck in place fairly well, and may require some jostling and gentle tapping with a nylon hammer before it will let go.

Three serious opportunities will arise here for messing things up royally if you don't know what you're doing:

The rocker arm bolts must be loosened in reverse order of tightening (consult your manual), and very gradually so as to release the tension of the valve springs upon the camshaft. Releasing too much tension in one place at once can distort the camshaft and damage it.
The bolts that hold the rocker assembly together should under NO circumstances be removed completely! Unscrew them only enough to let go of the head, then LEAVE THEM IN PLACE, lifting them off together with the assembly. If you remove them, the assembly will fall apart and it will take you quite a while to get it all back together again!
Do NOT tip the assembly upside down or sideways. The bolts could fall out, causing the same problem as removing them in #2.

The O-rings are under the parts that bolt the rocker arms and camshaft in position. Those parts are called "cam holders", even though they do somewhat more than just that.

Honda asked this assembly to do a lot of things. The cam holders also hold the rocker shafts, and have the spark plug holes in them.

Again, you can see the red donuts, and at the bottom of the cam holders is the orange of the O-rings.

If you're still up to it, the preceding information ought to be enough to help you fix your oily spark plugs. Just remember to loosen and tighten the bolts in the correct order (consult your manual), and a bit at a time, so as to unload and reload the camshaft evenly.

As a contrast, here's a B18A1, one of Honda's double-overhead-cam engines.

Because Honda has gone through the trouble of putting two camshafts, one on either side of the head, the spark plugs can pass directly to the combustion chamber without having to go through removable cam holders, so no additional fancy sealing is needed. Other than the upper donuts, there is no possibility of oil leakage into the spark plug holes in this engine.

There are no rocker shafts either, you'll notice. The cams rest directly over the valves, with just the lifters (rockers) between the two.

And in case you're wondering, that's my '91 Integra's engine.

One last note: Of late, Honda has revised their head and valve cover design to eliminate the rubber seals, and thus the leakage problem. These engines are easily recognizable with the valve cover off, as they have tall metal tubes rising out of the head. It appears that, generally speaking, if your engine is a VTEC, it's got the tubes. Somebody told me Honda went to the tubes across-the-board in 1996.

Some examples of the intubated engines:
(I wish I had more Accord info, but I don't. Anybody...?)

D15Z	F20C engine	K20A engine