I have oil coming out of the front cylinder spark plug on my 1978 300 2WD. I would imagine that's not a good sign and no I haven't ever done a compression test on the engine yet but am looking to buy a tester soon. Agh... It's only money I guess....

 

First off, are you sure it's coming OUT of the spark plug hole? It may be a leaking valve cover gasket that's leaking down onto and around the spark plug.

But if it is, it could be a number of things.

You may simply have bad valve seals and oil is dripping from inside the valve cover/drive train into the piston. It may be bad rings. It also may be bad valve guides.

I agree a compression test will get you started in the right direction.

 

I'm sure the oil is coming from the cylinder as it's dry under the valve cover and wet with oil all around the spark plug and under it. I just ordered a OTC aka Owatonna Tool Co. tester last night (since I'm from Minnesota, yeah you bet!) and I'll post the results when I've done the test here. Let's see, to test I should: have all plugs pulled, give the engine 5-8 rotations right? With a warm engine?

 

So, I did a compression test and the sesults are 120 psi for the first and the sixth cylinder and 130 psi for the rest. Looking at the plugs tells me something is going on with that first cylinder. The plug is black, oily and has carbon buildup while the rest of the plugs have a milkfish white on the ceramic and look like they're firing. I wander if the first cylinder is firing at all? I have a in-line spark verifier that I'll hook up to see what that will tell me. I'm running Champion RF18YC plugs now so on the chart they say that they're on the hotter side.

I'm not sure if it'll help but I'm thinking on a new cap and rotor and a new coil. I've never replaced them myself in the 3 years and 5,000 miles that I've owned the trucked the coil looks prehistoric!

 

Fortunately, that's still decent compression. Only an 8% variation between them. 15% or so is when you need to be concerned.

However, something's definitely up if you have a black plug, and the rest aren't. It could be that it's not firing. Another culprit could be a bad valve, or a problem with one. Does it clack or make noise at all?
I had a black plug and it turned out that the rocker arm came off.

 

No clicking or clacking but I can get a valve cover gasket and take a look under the cover. Any ideas what I should look for while the cover is off besides the obvious? I of course can clean up the cover... But that won't help my bad cylinder...lol I suppose it's a little early to price a rebuilt head swap.

 

Before you do that, run a check to see if the spark plug is firing. One way is to put a timing light on the wire and see if it flashes. That'll let you know if it's sending spark. If it is, the cap, rotor, distributor, etc. are working.
Another is to pull the plug out, put it back in the wire, and ground it with some jumper cables to the frame. Then have someone turn it over and watch the spark plug to see if it's generating spark.
One way to keep the engine from starting while you're doing this is to just pull the wires off the other spark plugs.

If it's sparking in the bad cylinder, you know you more than likely have other issues.

 

Ok, I'll check that and get back to ya. Thanks for the help!

 

It seems to me that even if the plug is not firing, it shouldn't have oil deposits on it. The oil is coming from somewhere.

With the compression numbers you have, while some may be getting past the rings, my money is on valve guides / seals.

If it were me, I'd do a leak-down test and see what it shows. I'm betting you hear air (or if you spray soap you'll see bubbles) at the valve guides or valve seats.

That's just a guess though..

 

I think the plug is firing. I hooked my inline spark tester between the plug and the wire and it shows spark. I then unplugged the wire while the engine was idling and there was a noticeable change to the idle and then back to normal after I plugged it in again. So at least I know it is running on six cylinders supposedly. I live in the sticks but NAPA has their own machine shop 70 miles from here. I don't drive my truck in the long winters up here so maybe I'll see what a valve job would run me at NAPA.

 

While you are at it specify a 3-angle valve job with a 30* back-cut on the intake valves. The heads on these engines need all the help they can get.

 

I talked to the local small town mechanic and he said to,just drive it and not to worry about it. Speaking of help for these heads did you see the tip in the sticky about using Chevy S10 rocker arms on these heads saying you'll get more lift with them?

 

Using the 1.7 Chebby rockers trick has been around for some time and is usually used with the stock cam for a little more lift. I think a set can be had for about $50 MOL.

 

Maybe it's just me, but I have a hard time trusting a mechanic that tells you to just drive with a problem you have. There's obviously an issue.

At least for now, maybe pull the valve cover and inspect. Who knows, the issue may be straight up evident and fixable.


If I remember right, the Chevy rockers arms only work on a specific style of a head/stud setup. Can't remember which one it is, but it's worth some research before you buy them.

 

A leak down test would be the simple way to tell if there is an issue with the head, either valves, seals or guides. I'd do that before anything else.

In terms of rockers, the chevy roller rockers only work on a head that uses studs for the rockers. On my 300, the rockers bolt down.

Getting back to the original problem; oil on the plug is coming from somewhere. Obviously.

It can be up from the rings, down from the head. That's about it. A leakdown test will tell where; if it holds pressure that's good. given the symptom, I'm guessing it won't hold pressure. In that case, listen for air escaping.

Out Exhaust - bad exhaust valve or seat
Out Intake - bad intake valve or seat
Pull valve cover and look / listen at guides

If none of the above, I'd been thinking rings..

Best to test rather than jump to conclusions..