Oil leaking from spark plug hole [Archive] - Chevy Nova Forum

: Oil leaking from spark plug hole


texson
27th-June-2007, 10:58 AM
Can anyone give me an idea why there would be oil leaking from a spark plug hole. Looks like oil is leaking from #7 on my SBC.

DriveWFO
27th-June-2007, 11:10 AM
Are you sure it's oil? Could be carbon. Is the plug loose or missing a gasket?

texson
27th-June-2007, 11:18 AM
the spark plug is new, I put in myself finger tight then snug with my socket. It is oil and that is the only plug I see it coming from. Laying under neath the motor I wiped fresh oil off the bottom of the plug.

DriveWFO
27th-June-2007, 11:21 AM
Sounds like a bad valve seal for that cylinder.

texson
27th-June-2007, 11:36 AM
thanks...but not a good thing I guess

DriveWFO
27th-June-2007, 11:45 AM
thanks...but not a good thing I guess

How old are the heads? Have they been rebuilt recently?

texson
27th-June-2007, 12:06 PM
not sure how old they are, or when they were rebuilt last. Sounds like time for a rebuild or new heads.

ready2run
27th-June-2007, 12:10 PM
the valve seals would be my guess to. It would be a good place to start if nothin else

wskaiser
27th-June-2007, 01:54 PM
I am having a hard time understanding the logic of bad valve seals causing oil to leak from a spark plug. If I understand this correctly, the plug is installed and oil is dripping off of it. There is no way it can be bad valve stem seals and leak externally unless the spark plug is loose or has no gasket or is broken. Maybe I just don't see the whole picture here. Maybe a valve cover gasket allowing oil to drip down on the spark plug but not valve stem seals.

the FLYER
27th-June-2007, 01:55 PM
are ya sure the oil is coming from there ??? make sure surrounding area is clean/no evidence of oil... was the plug tight ??? if it's loose ya might see oil... Chevy's aren't famous for positive valve sealing... stockers use "O" rings on the valve stem... i'd think with a loose plug oil might be visable... if it was tight it'd probably have burnt off in the A/F mixture... maybe, i dunno how much oil we're talking...


i've seen lots of times it wasn't the plug but a leaky valve cover gasket...


check it out real good ;) might do a compression test also ;)

Real McCoy
27th-June-2007, 05:37 PM
I've seen a black thick residue on the seats of some plugs from time to time. I always felt it was a residue of carbon and gas leaking past the seal. Usually on taped seat plugs heads. If the motor runs well and you have a tapered seat plug I'd not get too excited if it shows a little crude. The key is how bad is this leakage? You may be able to use a copper plug index washer to seal it. Also plugs need to be torqued so they seat totally and the plug can transfer heat to the head properly. Most people including me don't torque them but if you go read any decent articles on plugs they always say to torque them. RM

64PRONOVA
27th-June-2007, 05:50 PM
Do a compression test and see if that particular cylinder is lower than the rest.

grooves12
27th-June-2007, 07:43 PM
My guess is that it is leaking from the valve cover, and just happens to be leaking directly above the #7 spark plug. Like someone else already said, if there is an internal problem there is no way it would leak past an installed spark plug, and if it was there would be something SERIOUSLY wrong, and the question wouldn't be about an oil leak, it would be about rebuilding a wounded engine.

Check around the edge of the valve covers, they ALWAYS leak. The design in that area is poor and the aftermarket hasn't really came up with any better solutions. You have to be real careful about not squezzing out the cork gaskets, and even if you do everything right they will still leak half the time.

Gloryhound
27th-June-2007, 07:47 PM
If it were me the first thing I would do is change the valve cover gasket. It is cheap and easy to do. Also if you have a nice set of those chrome made in China valve covers on throw them in the trash and go back to the origional steel ones. More oil leaks occure at the valve cover than any place else. Also body shop dust is a sure way of drying out old cork gaskets.

deuces2
27th-June-2007, 10:10 PM
could also be coming from oil pressure sending unit behind distributor and running over and down on # 7..... these are notorious for oozing or leaking out the top could be cheap fix.....takes a special socket to make it ez

texson
2nd-July-2007, 09:53 AM
when doing a compression check, what kind of numbers should I be looking for from a fairly stock 350 with mild cam and 327 power pack heads?

wskaiser
2nd-July-2007, 01:27 PM
I don't think the numbers are that important if this is still in reference to the oil dripping off the #7 plug. They should be about the same (within 10%) of each other from highest to the lowest. If one is much lower than the rest or if adjacent cylinders are low then you may have a problem. Does this plug foul out or is the oil on the outside of the plug, still trying to understand just where the oil is.

64PRONOVA
2nd-July-2007, 03:29 PM
Yeah, if you really have oil getting into just one cylinder, it can only be coming from two places. Either your valve seals aren't sealing or your rings are not sealing. A compression test will only tell you if the rings are not sealing. So if you really do have oil inside one cylinder, a compression test will show if it is coming from the rings if there is a dramatic difference between that particular cylinder and a healthy one. If the compression test doesn't show any difference between "healthy" cylinders and the oily one, then you pretty-much know it's the valve seals.

DriveWFO
2nd-July-2007, 03:35 PM
Yeah, if you really have oil getting into just one cylinder, it can only be coming from two places. Either your valve seals aren't sealing or your rings are not sealing. A compression test will only tell you if the rings are not sealing. So if you really do have oil inside one cylinder, a compression test will show if it is coming from the rings if there is a dramatic difference between that particular cylinder and a healthy one. If the compression test doesn't show any difference between "healthy" cylinders and the oily one, then you pretty-much know it's the valve seals.

He'd have to be practically missing the oil control rings for that much oil to be coming out the spark plug threads :eek: :)

64PRONOVA
2nd-July-2007, 03:51 PM
They could be cracked too. If the compression test checks-out though, you know where the oil is coming from. Personally, I'd rather have bad valve seals and/or guides than bad rings. It's easier to fix and usually costs less money.

grooves12
2nd-July-2007, 06:40 PM
when doing a compression check, what kind of numbers should I be looking for from a fairly stock 350 with mild cam and 327 power pack heads?

Did you read the rest of the replies and check the SIMPLE things first?? If I'm understanding correctly the oil is on the OUTSIDE of the spark plug. If that is the most likely cause is a valve cover gasket leak. Have you elimated that as the cause of the problem... or am I misunderstanding and you have oil on the electrode of the plug after removing it from the engine?

texson
2nd-July-2007, 07:30 PM
there is no oil on the plug when pulled from the hole. It very well could be oil coming from the valve cover gaskets which I am having replaced with rubber gaskets so no more leaks from there. The Oil I have seen is accumlating on the bottom of the plug so I am hoping it is the valve cover gaskets and not valves or rings.

wskaiser
2nd-July-2007, 07:59 PM
If it is on the outside of the plug it is not caused by the rings or the valve stem seals. It has to be an external leak to get on the outside of the plug. Relax and drive it because it is not internal.